Animals for Research and Experimentation - 678 Words

Currently it is estimated that more than 100 million animals are used for research and experimentation on around the world every year. Apart from all the benefits of animal testing there are many good reasons which support banning the experimentations on animals such as: animal cruelty, selfishness, and danger of using the experiments result. Therefore animal experimentation should be banned. These days, animal testing has brought a lot of issues in the society. The first and foremost argument that is presented against animal testing deals with the issue of animal cruelty. The pain which is caused to the lab animals and the condition in which they are held captive for experimentation are not healthy at all. During the research process animals are killed and harmed, isnt killing an animal the same thing as murder? Were now living in the 21st century, and subjecting animals to long and painful experiments is no longer needed to advance as a society. Banning animal testing will in no way hurt any advancement in the future. 9 out of 10 times, the testing is found inaccurate in the end anyways. We now have alternatives such as bio-engineering and computer modelling that can provide us better, more accurate results than animal testing. Its also a much faster and cheaper method. Would you allow testing products, etc. on human babies or those mentally disabled because they have l ower IQ than the average adult human? Obviously not because its not ethical. Then how is it thatShow MoreRelatedResearch Paper Animal Experimentation2167 Words   |  9 PagesAnimal Experimentation i Should Animal Experimentation Be Abandon? Veronica Liang ESL 408C Marcia Rauch November 18, 2011 Animal Experimentation ii Research Paper Outline Title: Should Animal Experimentation be Abandon? I Introduction Thesis Statement: Animal testing is a debatable issue in modern society. Some people argue that animal testing should be kept due to medical benefits and research study conveniences. However, I think animal experimentation should be banned by refutingRead MoreEssay on Animal Experimentation and Research2491 Words   |  10 PagesAnimal Experimentation and Research In the basement of the psychology department here, a poster hangs on the wall; on it is a picture of two white lab rats and a caption that reads, ?They?ve saved more lives than 911.? This poster hangs on the wall of the room where I performed brain surgery on a rat. Many people would be morally opposed to this and any other form of animal research and experimentation and feel that it should be banned. This heated debate has been going on for centuries withRead MoreAnimal Experimentation For Scientific Research2520 Words   |  11 PagesAnimal Experimentation for scientific research is a contentious issues and the subject of much debate. On one hand it is considered morally wrong to use animal solely for human benefit. On the other hand, removing animals, completely from the lab would impede any understanding of health, disease and consequently affect the development of new and vital treatments. Two essential questions needed to be asked is does it work and is it ethical? The first is easy : yes it works. However some would sayRead MoreAnimal Experimentation Is Necessary For Medical Research1484 Words   |  6 Pagesthink if an animal tested product is being bought or not? Innumerable people fail to consider how these products came to be or if there was animal experimentation was involved. Many people are oblivious to the appalling occurrences that take place in laboratories involving animal cruelty on a daily basis. Government officials and scientists believe that testing on animals is essential for medical research, but many of the results prove to be irrelevant and the reality is that most animals that are experimentedRead MoreAnimal Experimentation Should Be Used For Research1600 Words   |  7 Pageswhether the practice of animals research should be used. Many people believe animals are needed for research, while others think it is not fair for animals to be sacrificed and treated poorly during research. Animals used for research has bettered m any human lives by new discoveries and advantages. Many people such as doctors, scientists, hospitals, research institutes use animal research to view how the human body works and to advance in scientific understanding. The first animal experiment started inRead MoreAnimal Experimentation Is The Only Option For Research978 Words   |  4 Pagesthe flu? If your answer is yes, then you can thank animal research because â€Å"Without animal research, medicine as we know it today wouldn’t exist† says Kristen Cook from pro-test.org. So, although animal experimentation can be labeled animal cruelty, sometimes using animals to experiment on is the only option for research. Animal experimentation research has brought many lifesaving medical benefits to the world. The California Biomedical Research Association states that nearly every medical breakthroughRead MoreEssay about Using Animals in Research and Experimentation623 Words   |  3 PagesAnimals should be used for research and Experimentation because if the animals get sick or show any signs of acting abnormal then the scientists know it isn’t safe for humans to use. Animal research has played a big role in nearly every medical breakthrough over the last decade. Animals have the same organ system that perform the same task, which helps determine if what is being tested is safe for humans to use. Most of the medicines animals use the same medicine as humans like antibiotics, painRead More Needless Animal Research, Testing, and Experimentation is Wrong939 Words   |  4 PagesNeedless Animal Experimentation is Wrong    If penicillin had been tested on guinea pigs, it might never have reached the public. It is lethal to guinea pigs, deactivates the blood system of rabbits and is deadly to cats (Bio-Medical Research). Scientists are pushing for more experiments regardless of the cost to the animals life. One expense is the involvement of killing animals in the pursuit of a pine-scented air freshener(Vergoth,p21). Animals suffering in experimentation labs areRead More The Cruelty of Animal Research, Testing, and Experimentation1381 Words   |  6 PagesThe Cruelty of Animal Testing and the Need for Alternative Methods In his book Inhumane Society: The American Way of Exploiting Animals, Dr. Michael W. Fox estimates that twenty-five to thirty-five million animals are used in the United States each year for laboratory testing and research (58). Research involving tests done on animals is unnecessary and cruel. More humane methods of research need to be employed. Fox states that animal tests on cosmetics and household products are nothingRead More Horrors of Animal Research, Testing, and Experimentation Essay1648 Words   |  7 PagesThe Horrors of Animal Testing    The torture and murder of millions of animals annually has been occurring for centuries now. Every year we ignore it, and every year the numbers grow. The act of vivisection or the practice of experimenting on animals began because of religious prohibitions against dissection of human corpses. After religious leaders lifted these prohibitions, it was too late. Vivisection had become a major part of medical and educational research. As well as major part of product

Career Counseling Over the Lifespan Essay - 3622 Words

Abstract Career counseling over the lifespan has more than an occupational focus, it deals with the person’s entire being with a vision that includes one’s lifespan. Career counseling takes into consideration character development, character skills, life roles, individual life and work history, goals, and obstacles. A career counselor not only assists a client with a career plan, but also with a life plan. This paper focuses on two categories of career counseling. The first focus is the history of career counseling as a field of study with the emphasis on when and why career counseling began (1800s as a study of how the shape of one’s head relates to vocational choice), who and what influenced it (Sizer, Parsons, and Davis), and how†¦show more content†¦This has progressed to an approach that deals with career development throughout a lifespan (Pope, 2000). Theories and assessments have developed that look at the many variables of work, personality, interest s, and needs (Whiston, 2003). The study has broadened with the use of technology and has been challenged by the many considerations of multiculturalism (Lewis Coursol, 2007; Whiston, 2003). A creative God who modeled work and rest created man and his relationship with work. Career counseling provides an opportunity to cultivate the relationship of God and man, assists with the discovery of one’s callings and talents, and enables one to fulfill God’s plans for his or her life. The History and Development of Career Counseling Pope (2000) describes how social reform, economic change, and federal legislation were significant factors in the evolution of career counseling. The development of career counseling began as a social movement linked to economic changes. In the early 1900s, young people were leaving the family farms and moving to cities to find employment. With this new growth and few regulations of labor, laborers were exploited and misused. In the first decade of the twentieth century, one-half million children from 10-13 years of age were employed in factories (Pope, 2000). The end of World War I and the Depression influenced the beginning of educational guidance in the public school system.Show MoreRelatedDonald Super s Life Span Theory1495 Words   |  6 PagesFor many people, finding a career that is both fulfilling and practical is a strenuous task. Fortunately, there is a plethora of different interventions, techniques, assessments, and inventories designed to aid those individuals in m aking the wisest career choices possible. But are any of those routes inherently better than the others? Or are all the differing options separate but equally effective? Donald Super’s Life Span Theory and John Holland’s Theory of Vocational Choice are just two of theRead MoreThe Macrosystem: From Child to Adult Essay1384 Words   |  6 Pagesmental health counseling. The foundational areas are the development across the lifespan, ecological theory, mental health, and mental health promotion. These together form a unique base from which mental health and community counselors practice. This is referred to as,† The comprehensive mental health counseling model, a comprehensive model.† The model places the dimensions of mental illness and mental health/wellness with and ecological context. Mental health and community counseling assess for personalRead MoreCareer Development : A Lifelong Journey3040 Words   |  13 PagesPreamble Career development is a lifelong journey combining an individual’s personality and interests with their world of work. When it comes to educating and counseling about careers in an elementary, middle, and high school it will look different, since there is an array of topics to focus on for each level of education. The focus of this Career Curriculum is for 7th Grade Students and has been based on theories appropriate to this level and created with Piaget’s Cognitive Development Theory andRead MoreA Master s Degree Of Counseling Psychology2229 Words   |  9 Pagesmaster’s degree in counseling psychology to increase their acceptance to a Ph.D, or Phs.D program. (Capella University) Other students may choose to enter the workforce with a master’s in Counseling Psychology. The licensing process varies from state to state, but most graduates will expect to prove how they have met educational requirements, ability to practice, completion of fieldwork, and exam ination. (Capella University) Capella University has a master’s degree in counseling psychology that isRead MorePursuing A Master s Degree Of Mental Health Counseling With Nova Southeastern University For The Fall 2016 Program980 Words   |  4 PagesI am writing to inform you of my strong interest in pursuing a Master’s Degree in Mental Health Counseling with Nova Southeastern University for the Fall 2016 program. I earned my Bachelor’s of Science Degree with a double major in Psychology and Research from The University of North Florida in 2013. For the past three years I have worked for Gateway Community Services as an Adolescent Outpatient Counselor. I am looking forward to continuing my education with Nova Southeastern University. I comeRead MoreA Critical Issue Of Counseling And Psychotherapy1519 Words   |  7 PagesAs we are beginning to learn, the way we approach counseling and our clients derives from our own perspectives and experiences. As it says in our text, â€Å"A critical issue in counseling and psychotherapy is that the same comment may have different effects on individuals who have different personal life experiences and multicultural backgrounds, because everyone has a unique history with a unique pattern of communication.† This proves to be true as fundamental principals of the social animal, everyRead MoreCareer Counseling, And Super s Development Theory1840 Words   |  8 PagesCareer counseling theories are as diverse as the counselors who practice them and the clients who experience them. Understanding and applying the appropriate theory for each unique client is imperative. Many career counselors use a variety of theories and techniques when working with students through their exp loration and career commitment process. Career theories I will describe in this piece include, Social Cognitive Career Theory, Solution-Focused Career Counseling, and Super’s Development TheoryRead MoreEducational Preparedness956 Words   |  4 Pages2014). In order to education the client or patient population, a nurse must be educated themself. A baccalaureate prepared nurse â€Å"uses evidence based practices to guide health teaching, health counseling, screening, outreach, disease and outbreak investigation, referral, and follow-up throughout the lifespan†(Oct., 2008). According to the AACN, Evidenced Based Practice is a core topic of the baccalaureate curriculum. Although this may be included in some associate- degree programs, there is no documentationRead MoreLifespan Reflection Paper865 Words   |  4 PagesDuring this course, we discuss human develop through the lifespan perspective and analyze the five major theories Psychoanalytic, Behaviorist, Cognitive, Humanistic and Evolutionary. Psychoanalytic is a theory of human development that holds that irrational, unconscious drives and motives, often originating in childhood, underlie human behavior. I will be analyzing my development through the psychoanalytic theory. Everyone is born with the knowledge to breathe, but not everyone knows how to breatheRead MoreNurse Midwife : A Health Care Provider For Women1579 Words   |  7 Pagesyou’re a female then you should contact a midwife. A midwife is a primary health care provider for women throughout their lifespan. This means that midwives preform physical exams, prescribe medications including contraceptive methods, order laboratory tests as needed, provide prenatal care, gynecological care, labor and birth care, as well as health education and counseling to women of all ages (American College of Nurse-Midwives). CNM-attended births account for 10% of all spontaneous vaginal births

Night Creature Hunter’s Moon Chapter 24 Free Essays

Though Jessie’s belief in me helped, I still had doubts about my sanity. Maybe I always would. But until I was sitting in the corner talking to myself again, I had a job to do. We will write a custom essay sample on Night Creature: Hunter’s Moon Chapter 24 or any similar topic only for you Order Now â€Å"Where are these dead wolves?† I asked. â€Å"Close. You ready?† I nodded. I was tired. I’d been up all night. But time was growing short. Less than a week until the hunter’s moon, and the tally of dead wolves was growing. There was no way to know how many the power eater had already killed and consumed. We could be fighting a losing battle. Hell, we probably were. But I couldn’t give up. I doubted Jessie could, either. Giving up wasn’t in either one of us. I followed her down the steps, Will at my heels. There was no sign of Damien anywhere. I glanced toward his cabin, but the curtains were drawn. â€Å"Sorry I kicked you,† Jessie said. â€Å"I shouldn’t have scratched.† â€Å"I pulled your hair.† â€Å"The biting was uncalled-for.† â€Å"Stop,† Will said. â€Å"I’m getting excited again.† Jessie and I rolled our eyes; then we laughed and she slapped me on the back. All was forgiven. â€Å"Women,† Will muttered. The three of us headed into the woods. Cadotte lagged behind. â€Å"Don’t worry about him,† Jessie said. â€Å"He’s in the zone. Trying to figure this out.† â€Å"Won’t he get lost?† â€Å"Nah. He’s not that easy to get rid of.† â€Å"I heard that!† Will called. Jessie grinned. I wanted what they had so badly, I could taste the longing at the back of my tongue – an unpleasant flavor like ashes mixed with lemon juice. â€Å"You know what you’re doing?† she asked. â€Å"Following you.† â€Å"I meant with Fitzgerald.† â€Å"Not a clue,† I admitted. â€Å"Sex is one thing, Leigh, but†¦Ã¢â‚¬  â€Å"But what?† â€Å"Attachments.† She shrugged. â€Å"You can’t have them if you’re going to be a Jager-Sucher† I flipped her off, but I knew she was right. â€Å"He could be anyone, Leigh. Anything.† â€Å"It’s just sex,† I assured her. â€Å"Any good?† â€Å"Oh, yeah.† â€Å"I figured. He looks like he knows what he’s doing.† I glanced behind us. Will had stopped a hundred feet back and was staring up at the sky. â€Å"Cadotte doesn’t seem like any slouch in that department.† Although right now he appeared to be a prime candidate for Forrest Gump of the year. Jessie’s smile became secret. â€Å"He’s not. He also isn’t a werewolf.† â€Å"Neither is Damien. Ring, remember?† â€Å"Super-duper shape-shifter, remember? For all we know, silver don’t mean shit anymore.† I stopped dead on the path. Jessie did the same. â€Å"Hadn’t thought of that, had you?† I hadn’t. Damn. â€Å"Come on.† Jessie tugged on my arm. I followed obediently. â€Å"I called the tavern owner again.† â€Å"And?† â€Å"The bartender who worked there before Fitzgerald, Abel Smith, lived in the cabin. He took off one night and never came back.† â€Å"There seems to be a lot of that going around.† â€Å"I’ll say. I ran Abel’s name. Got nothing. Mandenauer never heard of him, either.† â€Å"What does that mean?† â€Å"I have no idea. Abel could have left the gun – or anyone before him. Who knows? Your good pal Damien might even be lying.† She was right. We were no further along than we’d been before. The two of us walked in silence for a minute; then Jessie cast a quick sidelong worried glance my way. â€Å"When I fell in love with Will I wasn’t sure who or what he was.† â€Å"How could you do that?† â€Å"You’ve seen him. I was a goner the first time he said my name.† â€Å"What if he’d turned out to be a werewolf? Would you have killed him?† She hesitated, then shook her head. â€Å"I’d have protected him. I’d have done whatever I had to do to find a cure.† â€Å"Cure?† I snorted. â€Å"Right. That’s been going well so far.† I thought of all the years there’d been werewolves – too many to count. I thought of the genetically engineered ones, as well as the Weendigos, cursed by the great mystery. Those were just the werewolves we’d encountered. Who knew what lived out there in the night? There were plenty of legends and beasts but no cures. Elise Hanover had devoted her life to the project, and as far as I knew she’d gotten nowhere fast. â€Å"I loved him,† Jessie said quietly. â€Å"I’d never loved anyone before.† â€Å"I have. And a werewolf killed him. I can’t forget that.† â€Å"No?† â€Å"Should I?† â€Å"Maybe. I don’t know.† â€Å"Maybe? The answer is no. Hector murdered my father, my mother, my sister, my brother, and my fiance. You know why? Because I slept with him and that made me his. I tried to break it off, but he only wanted me more.† I’d never told anyone that. I held my breath, waited for the recriminations. Instead, Jessie shrugged. â€Å"Some guys are like that.† â€Å"He was a monster. He was going to turn me into a werewolf, too. So we could be together forever.† I shuddered as the memory slid through my mind. Hector’s voice on the phone, calling me at odd hours, telling me everything he’d planned for me. I think. â€Å"What happened?† Jessie asked. â€Å"Why didn’t he bite you?† â€Å"Edward came. Hector knew Edward would kill me if I was bitten. So he – â€Å" I broke off. No reason for Jessie to know how Hector had marked me or why. â€Å"He’s been waiting for the perfect time to come back and finish what he started.† â€Å"I wondered why you became a Jdger-Sucher.† â€Å"And you think you know?† â€Å"What better way to protect yourself than by becoming a hunter of the thing that’s hunting you?† I’d become a hunter for vengeance. But no matter how many of them I killed, it would never be enough. I was going to have to kill him. The thought sent a shaft of panic through my chest so painful I found it hard to breathe. Will caught up with us. â€Å"I was thinking – â€Å" â€Å"Gee, that’s new,† Jessie drawled. He continued to speak as if she hadn’t. â€Å"Leigh, your family was killed by the white wolf on the night of the blood moon?† Jessie had been blabby, but I couldn’t fault her for it. We had to work together, as much as I’d rather work alone. â€Å"Yes,† I answered. â€Å"Why that night, I wonder? Is there something special about it?† I shrugged. â€Å"You’re the paranormal expert.† â€Å"Not really. But I know someone who is.† â€Å"One of those elders you mentioned?† â€Å"I talked to them. No one’s ever heard of the power eater. But they knew a woman of great rank in the Midewiwin.† â€Å"English, please,† Jessie instructed. â€Å"The Grand Medicine Society. Once it was a secret religious fellowship devoted to healing through knowledge of the spirits. According to the elders, Cora Kopway has spent her life studying old texts and meeting with the spirits in her visions.† â€Å"Wouldn’t being a scholar preclude being a visionary?† Will smiled. â€Å"Not to an Ojibwe. Everything relates to everything else. Life is a circle – â€Å" â€Å"Yeah, whatever,† Jessie interrupted. â€Å"When can we see this chick?† â€Å"We?† â€Å"That’s right. I’m not letting you out of my sight until this is over.† He frowned. Opened his mouth as if to argue, then shut it again. â€Å"She likes you,† I said. â€Å"I can tell.† A voice hailed Jessie. We turned in that direction. A heavyset elderly man waved to us through a gap in the trees. He was a big guy, but his skin was so wrinkled and his shoulders so stooped he gave the appearance of shrinking. The three of us entered a clearing. Three dead wolves littered the earth. I could tell without getting any closer that none of them had been eaten. What was up with that? Jessie introduced me to her deputy as being from the DNR. Elwood shook my hand with more enthusiasm than anyone else ever had. I was half-afraid he’d dislodge the hearing aids tucked into both ears. â€Å"You know what’s going on here?† he asked. â€Å"Rabies,† I answered. â€Å"New strain.† â€Å"Never seen wolves kill their own like this.† He shook his head as he stared at the bodies. â€Å"Kind of sad.† It could get a whole lot sadder, but I kept my opinion to myself. â€Å"Tell us what you know,† Jessie instructed. â€Å"I received a call from Joe Elders. His dog took off, and he found the mutt gnawing on that one.† Elwood pointed to the gray and white wolf nearest to me. â€Å"Dog was up on his shots, so we’re kosher there.† I nodded. If we were dealing with rabies, I’d be happy, as it was, didn’t care. â€Å"What about the others?† â€Å"When Joe looked around a bit, he found ’em nearby.† â€Å"They weren’t together like this?† â€Å"No. I pulled them over myself. Sorry. I shouldn’t have done that?† I shrugged. Hard to make a fuss about the crime scene in this case. How would I explain what the crime was? â€Å"The first one was here. One there.† He pointed to the east. â€Å"About ten feet. Other one that way.† He switched his arm to the north. â€Å"About twenty feet. Almost like the wolf was waiting around to pick ’em off one at a time.† He frowned. â€Å"But wolves don’t do that, either. I ain’t never seen such a thing.† â€Å"Thanks, Elwood,† Jessie said. â€Å"We’ll take it from here.† He started to move away. â€Å"Wait.† Jessie pulled the picture of Hector out of her back pocket. â€Å"You seen this guy in town?† The old man took the photo, frowned, squinted. I held my breath. Did I want him to have seen Hector, or didn’t I? Finally he shook his head. â€Å"Can’t say that I have.† â€Å"Positive?† Jessie asked. â€Å"I’m good with faces. Fellow like that would stand out.† I let out the breath I’d been holding. Now what? â€Å"Why don’t you ask around?† Jessie said. â€Å"Sure.† Elwood put the photo into his pocket. â€Å"Whad he do?† â€Å"Nothing. Yet.† The old man shrugged and left. Jessie turned to me. â€Å"He’s got more contacts than I do. He’ll check with the owners of the cabins in the woods and on the lakes. If Hector’s anywhere near here, Elwood will hear about it.† I didn’t like leaving the search to someone I didn’t know, but if Jessie trusted the man, I discovered that I did, too. All three of us knelt next to the dead wolves. They’d been killed, violently. Throats torn out, bite marks on the bodies. But they hadn’t been eaten. Had the man and his pet disturbed the Weendigo before he could accomplish his mission? I had a hard time believing a being that didn’t flinch at cannibalism in both human and werewolf form would mind killing an intruder and his puppy dog. So what had happened here? â€Å"You said the brown werewolf killed another one,† Will murmured. â€Å"He didn’t eat him.† â€Å"Not while I was there.† â€Å"So maybe one is killing, the other is eating.† â€Å"We thought about that,† I said. â€Å"But I don’t recall two wolves in the power eater legend.† â€Å"If the white wolf is the most powerful, and getting stronger with every bit of power he eats, he could already be controlling the others.† â€Å"But does it work if one wolf kills and a second eats? Doesn’t one have to kill, then eat, to capture the power?† â€Å"I’ll have to read my notes,† Will said, â€Å"but I don’t remember anything that specific. Using the locals to help him would make sense. He needs to reach a hundred.† â€Å"If he’s powerful enough to control the others, if he’s the ultimate werewolf, how are we going to stop him?† Jessie asked. â€Å"What if silver doesn’t work on the power eater the way it works on everyone else?† Will scowled. â€Å"That would suck.† I had to agree. How to cite Night Creature: Hunter’s Moon Chapter 24, Essay examples

Pir Sensor Faraway Sensor and Actuator Techniques

Question: Discuss about thePir Sensor for Faraway Sensor and Actuator Techniques. Answer: Introduction Description The rapid increase of far off interchanges and inserted MEMS advances has made faraway sensor and actuator techniques conceivable. A WSAN is a conveyed framework comprising of sensor and actuator hubs interconnected by way of far off connections. Using detected knowledge from sensor hubs, actuators can participate in routine in like method. The alternative of lighting manage can also be made in view of the daylight drive detected by way of gentle sensors. In the actuators characterized a few client specifications and rate capacities. Their purpose used to be to conformed lights to cut back the aggregate price. In the end, the final result used to be related to stimulation and media construction frameworks (Song, B (2008)). The actuators related the utility capacities which recollect customers' field and lights inclinations to conform enlightenments in an effort to augment the aggregate utilities. Notwithstanding, it did not bear in mind the best way that participants need distinguished lighting underneath more than a few workout routines (Author index. (1981), Jin, X.(2012)). Implementation Problem abstraction The increasing population and the increasing rate of utilization of the natural resources arises the problem of power. If the power consumption continuous then in future there will be scarcity of the power and thus to avoid such problems the actuators with the LED lights are being used so that they can save unnecessary power consumption. Division of Tasks The project was broken down into smaller tasks to better facilitate project management and concurrent activity. Sensor selection, Signal conditioning circuit design, PIR sensor technology Measurement Coverage area Write the report. Problems Faced The main problem faced was determination of accuracy. Here precise fining is the best option and if there is minute error also then result will be bad. Following coverage diagram shows this (Bergveld, P. (1989)) [https://learn.adafruit.com/assets/512] Sensor Selection Identification of the Sensor Type Here we have chosen PIR325 sensor because of its features and popularities.The PIR325 sensor contains two detecting components associated in a voltage kicking setup. This course of action scratchs off signs brought on by vibration, variations in temperature and daylight. A body going before the sensor will actuate initial one and afterward the other component as appeared in figure 1 though different sources will influence both components at the same time and be crossed out. The radiation source must go over the sensor in a flat heading when sensor pins 1 and 2 are on an even plane so that the components are successively presented to the Infra-Red source. [https://learn.adafruit.com/assets/511] Performance Test of the Sensor Figure 2 demonstrates the PIR325 electrical details and design in its TO5 bundle. It would be ideal if you take note of that the separation from the front of the detecting components to the front of the channel window is 0.045 inch. Figures 3 depict a Fresnel lens intended to be utilized with the PIR325 sensor [https://learn.adafruit.com/assets/513] [https://learn.adafruit.com/assets/514] The sensor has an implicit FET speaker for low yield impedance. It is in a TO5 bundle and will work at up to 10 volts. The FL25 has shape of round and diameter is of 0.75 inch measurement with a 0.5 inch dynamic region, a 0.25 inch central length and a 26 degree field of perspective. The FL40 lens has shape of round and 1 inch in breadth with a 0.9 inch dynamic area, a 0.34 inch central length and a 14.99 degree field of perspective. The FL65 lens is 1.499 crawl square with a 0.99 inch dynamic zone, a 0.65 inch central length and a 10 degree field of perspective (Middelhoek, S. (1981), Conference Announcements. (1988)). Measurement System Implementation Hardware Configuration Associating PIR sensors to a microcontroller is truly basic. The PIR goes about as an advanced yield so you should simply observe for the pin for high flip (recognized) or low (not distinguished). Its conceivable that you'll need reriggering, so make sure to keep the jumper position at H. PIR 5V Power and associate ground to ground. At that point interface the yield to a computerized pin. In this illustration we'll use pin 2 (Office, A. (2015).). [https://www.instructables.com/file/FXYEQAUFYIZHAJN/] [https://www.sparkfun.com/products/12772] Software Configuration The code is extremely straightforward, and is fundamentally just monitors whether the contribution to stick 2 is high or low. It likewise tracks the condition of the pin, with the goal that it prints out a message when movement has begun and ceased (Sensors and actuators A. (2002). Working This movement locator circuit utilizes an ease LM324 quad operational enhancer as both a two phase intensifier and a window comparator. Intensifiers IC1A and IC1B have an increase of 100 each for a sum of around 10,000. IC1C and IC1D structure a window comparator that reacts to signals around 200 millivolts above and 200 millivolts beneath Vcc/2. The setting of the window by the low current potential drops crosswise over D1 and D2. Comparator yields bolster over D3 and D4 that pass just the positive moves into CMOS (CD4538) IC2 single shot which sustains into Q1 that drives transfer RY1. The R10 and C6 time steady decide to what extent the hand-off remains stimulated after movement is distinguished. All parts can work on 5 to 12 volts. This sort of circuit is frequently used to turn a light on outside of a house when movement is distinguished (Takahashi, K. (1988), Tesar, D. (2012).). [https://www.glolab.com/pirparts/images/appckt.jpg] Conclusion It can be concluded that this sensor is the best sensor available for current scenario and hence can detect motion very precisely. The principle commitments of this work are twofold. To start with, our model is meant for "point-like" gentle sources, for illustration, LEDs, that are extra vitality productive than usual light sources and are relied upon to be the general of lights advances later on. We reveal to exploit its mild engendering property to direct mild manage. In future due to continuously increasing power supply demand the actuator (light LEDs) will be playing a major role as they saves consumes less power and thus saves the power. References Song, B., Choi, H. and Lee, H.S., 2008, January. Surveillance tracking system using passive infrared motion sensors in wireless sensor network. InInformation Networking, 2008. ICOIN 2008. International Conference on(pp. 1-5). IEEE. Jin, X., Sarkar, S., Ray, A., Gupta, S. and Damarla, T., 2012. Target detection and classification using seismic and PIR sensors.Sensors Journal, IEEE,12(6), pp.1709-1718. Bergveld, P. (1989). Sensors and actuators, Twente. Sensors And Actuators, 17(1-2), 3-26. https://dx.doi.org/10.1016/0250-6874(89)80061-7 Conference announcements. (1987). Sensors And Actuators, 11(2), 207-208. https://dx.doi.org/10.1016/0250-6874(87)80017-3 Conference Announcements. (1988). Sensors And Actuators, 13(1), 87. https://dx.doi.org/10.1016/0250-6874(88)85032-7 Middelhoek, S. (1981). Preface. Sensors And Actuators, 2, 1. https://dx.doi.org/10.1016/0250-6874(81)80023-6 Middelhoek, S. (1981). Preface. Sensors And Actuators, 2, 1. https://dx.doi.org/10.1016/0250-6874(81)80023-6 Office, A. (2015). Acknowledgement to Reviewers of Actuators in 2014. Actuators, 4(1), 1-1. https://dx.doi.org/10.3390/act4010001 Sensors and actuators A. (2002). Sensors And Actuators B: Chemical, 85(3), II. https://dx.doi.org/10.1016/s0925-4005(02)00235-6 Takahashi, K. (1988). Preface. Sensors And Actuators, 13(1), 1. https://dx.doi.org/10.1016/0250-6874(88)85023-6 Tesar, D. (2012). Overview of the Long Term Objectives of the Journal Actuators. Actuators, 1(1), 1-11. https://dx.doi.org/10.3390/act1010001

Personal Statement Tips for International Legal Professionals

If you are applying to law school as an international candidate already working in your country as a lawyer, the best way to win over your reader in the opening of your essay is to be clear not just about your goals but also about your overseas academic background. This can often require a two-part introduction in your law school personal statement. Below are some personal statement tips to help get you started.The first paragraph of your introduction can address your goals, ideally in three sentences. With your goal statement, three sentences is the best approach. Open with a statement of your long-term goal in the law, ideally referring to a specific organization, especially if you are being sponsored by that organization. The second sentence can flesh out the first with specifics of the targeted role(s) and responsibilities. Your third sentence could offer the qualities and characteristics that you bring to the program. This would be just one approach. But most candidates forget t hat your reader wants above all to know (1) where (in what country) you eventually intend to practice law and (2) what kind of academic program you are coming from as an international candidate.This is why, if you are an international candidate, it can be worth your while to develop a separate three- or four-sentence paragraph describing your overseas academic credentials and current role as a legal professional. Remember that your reader in the United States may not know about the legal education system in your country or about what an undergraduate degree (or graduate degree, for that matter) qualifies a lawyer for in your country. It is important as a courtesy to provide this information to your reader, in clear and concise form. The absence of this information is the biggest problem that I encounter as an editor of international candidates’ law school personal statements.The other thing to remember, if you are an international candidate and especially if you are being spo nsored by the organization for which you work, is that playing to your role in an organization can be even better for you as an international candidate than offering your own personal achievements and goals in the law.This is because of the tendency that candidates have in law school personal statements to talk about â€Å"changing the world† (or words to that effect). But this is a clichà ©, isn’t it? It becomes much less of a clichà © if you can say something like this:I want to change the world, especially in the area of [say what you want to change], and I can see this happening right now at [Company/Law Firm Name, as a result of their work in†¦]. I am pursuing the [JD, LLM] in the hope of contributing to [projects, etc.]. With the degree from [School Name], I’ll be able to achieve these goals of mine with [Company Name].Suddenly, your hopes to â€Å"change the world† have become much less nebulous and generic and appear far more grounded in th e actual work that you do for a firm and that you want to do. Now you actually have a plan to change the world. This focus on a firm’s work and mission – and how it has affected yours – can also telegraph the qualities of loyalty and humility. These are two of the most valued qualities in candidates.Of course, it is fine if you do not want to identify a specific organization in terms of your short-term or long-term goals.But coming back to what I said above: Don’t forget that if you are applying as an international candidate, the first question in the mind of your reader (even before reading your law school personal statement) is this: In what country are you eventually intending to practice law? The sooner you answer this question in your essay, the sooner the reader can get on with your content – because if your reader is not sure of the answer to this question, the reader will be distracted throughout the essay. So as a courtesy to your reader, be clear about this.

Policy Development Evaluation

Policy Development Evaluation Understanding of the Brief The commissioner for the GWS Housing Group is in a mission to recruit qualified consultants on an interim basis to evaluate its tenant focused ‘housing services program’. The consultant will be in a position to show the approach of selecting the most appropriate processes and techniques for evaluation.Advertising We will write a custom essay sample on Policy Development Evaluation specifically for you for only $16.05 $11/page Learn More The commissioner is also looking for the consultants who understand the background and context to the tenant focused housing services. Apparently, the tenant focused housing services involve its tenants in three key priority areas, which include the production of information for the ‘choice based lettings process’, which is online based, and the appointment of contractors for the repairs of their estate; they also benchmark between the locations. The service also has three key objectives, which include the provision of opportunities for the tenants to control the quality, type and cost of the housing services and enabling the priority of tenants to be reflected in the GWS business plan. Another objective is the development of an approach to housing services, which stands out as the best practice all through the south east of England. With these objectives in mind, the consultants’ mission will be to focus on the choice based lettings process in the production of information and the appointment of contractors for the repairs on their estate. In addition the commissioner expects the consultants to be able to develop an interim evaluation report, which is based on the understanding of the policy, range of techniques, concluding remarks and the appropriate references. The Policy Context/Good Practice Background For the effective delivery of housing services by any organization, the tenants must be involved in one way or the other. The main reasons why tenants are involved are to improve the service delivery, to enhance accountability, encouraging community participation and developing a social capital.Advertising Looking for essay on project management? Let's see if we can help you! Get your first paper with 15% OFF Learn More Moreover, involving the residents has a direct benefit to them, businesses and the wider community. The decision by the ‘Tenant Focused Housing Services’ to ensure that tenants participate in its programs will result in the enhancement of its performance, good delivery of services and improved accountability. If for instance, the service decides to involve the tenants in refurbishment and clean up exercises, then tenancy turnover gaps can be hugely reduced, which will also benefit the tenants themselves. On the part of the tenants, such kind of involvement will help improve their community participation at the local level besides building their capacities. Based on these reasons, the service must consider involving tenants as an integral component in their objectives. This, however, requires a soberly informed approach and strategic decision making, which can only be achieved through putting down a comprehensive tenant participation strategy (Hunston 2010, p. 56). Such a strategy must aim at addressing two things. To begin with, it must be built upon the improvement of the quality and efficiency of the housing service of the ‘Tenant Focused Housing Services’. It must also aim at putting the tenants at the core of managing the housing units within their areas of aboard, in accordance with the laws of the land. In this connection, therefore, the different legislations and policies concerning housing in the United Kingdom, particularly England, must be understood and appreciated. Apparently, the country has several legislations and policies that are geared toward improving the quality of housing in the UK. Some of them include The Ge neral Housing Consents 2012-Section 32 of the Housing Act 1985, The New Homes Bonus Scheme Grant Determination 2012-13: 31/1981, Change to Ground Rent Notice and Part X Land Held by Public Bodies: Schedule 16 Bodies Covered by Part X Approach to the Interim Evaluation For the efficient accomplishment of the objectives of the Tenant Focused Housing Services, a careful approach must be used in the evaluation process. This is because individual evaluation processes have distinct ways of solving problems in their own rights.Advertising We will write a custom essay sample on Policy Development Evaluation specifically for you for only $16.05 $11/page Learn More For the purposes of attaining the goals and objectives of the Tenant Focused Housing Services, the implementation of three evaluation approaches to the program is necessary. These approaches include the outcome based evaluation, the process and impact evaluation, and the participatory evaluation. The outc ome based evaluation is where data is gathered and analyzed with an aim of establishing the effectiveness of a program in its mission to accomplish its objectives. Upon commencing the project, the consultant with the Tenant Focused Housing Services will have an obligation of gathering the relevant information time after time to consistently ascertain if the stated objectives are really being met. Various adjustments and interventions will then be induced in accordance with the outcome of the data analysis and the information collected (Bozarth 2008, p. 220). In the process of impact evaluation, measurements will be made on the well being of the operations of the project; they will be based on whether or not the project is able to attain the requirements of the target population. This implies the impacts of the project and the manner in which it is satisfying its goals must be considered. In this project, a continuous study will take place to ensure that the tenants of the GSW Housin g Group are really living up to the expected standards and according to the original plan. In participatory evaluation, all the stakeholders are given opportunities to have their hands on experience in the process of monitoring and evaluation of the project activities. Practical involvements of the owners of the project are guaranteed through the use of a variety and specific tools and equipments. This ensures that cases of isolation and marginalization do not occur. In this case, the tenants are not only the clients for the project, but also a big force to reckon with in terms of stake holding. In fact, they are the most important stakeholders to the whole project. They must, therefore, be involved in every process and in various parts of the project (Weiss 2008, p. 162).Advertising Looking for essay on project management? Let's see if we can help you! Get your first paper with 15% OFF Learn More The Tenant Focused Housing Services apparently has a project team, which comprises of five GWS staff, out of which three are tenants drawn from each of the estates. This is a good start toward ensuring that effective participatory evaluation approach is attained by the service. It is important to note that evaluation involves the use of activities, which are usually very good structured but complex. Moreover, different evaluation approaches are designed to meet different goals and objectives, which are also multi faced. It is against this standard that the process of evaluation should be assumed as an activity that brings together the efforts of various stakeholders involved. Therefore, a unifying modeled approach should be adopted for the same. Techniques/Methods Used to Undertake the Evaluation Process Based on the nature and requirements of the objectives of the projects of Tenant Focused Housing Services, the program is going to use a variety of techniques and methods in its eva luation. Of utmost importance, however, is the selection of the most appropriate tool for the evaluation process. Some of the tools that are widely used for evaluation include interviews, observations, questionnaires and focus groups. For the purposes evaluation of this study, all the tools will be used in their appropriate places. Depending on the cultural context of the tenants, there will be a careful selection of the tools to be used. The evaluation process is a specific procedure of gathering information. Therefore, the types of the information to be collected from the respondents will matter a lot in the selection of the right tool. In this case, the design of the tenants’ aboard will also offer a good consideration to make the process more specific. From the information provided under the basic information column, it is evident that different locations within the Tenant Focused Housing Services have different characteristics and the number of homes and people. This imp lies that each will tentatively receive a specific evaluation tool. In locations such as the LB Southwark for instance, which has two thousand occupants, it will not be possible to interview each and every tenant. This makes the questionnaire the most effective tool for gathering information and evaluating the activities of the location. Through the administration of questionnaires, specifically designed questions will be asked to the tenants concerning the achievement of the GWS Housing Group’s objectives and the process involved. Questionnaires will not only be used in obtaining data on whether the project goals were met or not, but also on the manner in which the activities took place and suggestions on the key areas of improvement (Saris Gallhofer 2007, p. 249). This, however, will require the administration of the open ended questions in the questionnaire. In addition, this tool will be used to find out whether the activities of the Tenant Focused Housing Services have had any bearing to the tenants and the surrounding communities. In order to ascertain the appropriateness of the evaluation tool to be used for the process, it is important to first carry out a baseline study on the population size and the modalities of the study area. This can provide a hint on the exact components of study that are required. Location LB can also use the focus groups to gather information from the many people who comprise its population. In this case, small groups comprising of between six to twelve people will take part in a discussion on specific issues of the subject in a bid of reveal self disclosure among the tenants. This is an effective way of involving the stakeholders in making decisions concerning issues that affect their welfare. Incidentally, both the questionnaire and the focus groups will be used as the evaluation techniques for obtaining information for the online choice based letting process and the appointment of contractors for repairs on their es tate. Indeed, these are the key priority areas in which the involvement of the tenants is required (Russ-Eft Preskill 2009, p. 428). In order to effectively analyze the stakeholders’ response, it could have been prudent if the GWS Housing Group provided more information about the details of the tenants under the basic information column. Of particular importance is the age groups and distribution amongst the locations. However, having demonstrated an in depth analysis on the requirements, the processes of the evaluation and the crucial aspect of involving the tenants in decision making; my final submission is that the objectives of the program will definitely be accomplished. References Bozarth, J 2008, From analysis to evaluation, with cd-rom: tools, tips, and techniques for trainers, John Wiley Sons San Francisco. Hunston, S 2010, Corpus approaches to evaluation: phraseology and evaluative language, Taylor Francis, Kansas. Russ-Eft, D, Preskill, H 2009, Evaluation in or ganizations: a systematic approach to enhancing learning, performance, and change, Basic Books, New York. Saris, WE, Gallhofer, IN 2007, Design, evaluation, and analysis of questionnaires for survey research, Wiley-Interscience, Hoboken. Weiss, JW 2008, Business ethics: a stakeholder and issues management approach, Cengage Learning, Mason.

Role of international Institutions in Mexico's Fiscal Development Case Study

Role of international Institutions in Mexico's Fiscal Development - Case Study Example The main authority on bringing economic change, therefore, lies with the indigenous political government. In the case of Mexico, the national government in the late 1980s was significantly concerned with the economic growth of the country but as the years slipped away, the commitment of the government declined so did the local living standard. Based on the above argument, it can be established that there is no need to change or develop new international trade institutional laws. But, the government is needed to get more attached to the notion of economic development. Still, the power to sponsor economic development of Mexico lies with local government. The attitude of the government is something that is needed to change and there is minimal requirement to modify rules and regulations of the trade associations. Furthermore, international institutions have nothing to do with hindrance or facilitation of growth but the locals are primarily accountable for the prevalent situation.  Ã‚  

A Non-intrusive Three-way Catalyst Diagnostics Monitor Based on Assignment

A Non-intrusive Three-way Catalyst Diagnostics Monitor Based on Support Vector Machines - Assignment Example One such situation is the engineering production process. For example, the Ford Mustang GT uses the engineered sensor to determine catalyst output (Backey 3). The sensor and catalyst ensures motor vehicle exhaust fumes adhere to the government’s environmental standards (Backey 3). Furthermore, Dr. Backey explained the current monitoring process contributes to the control of polluting exhaust fume contents. Ford Company’s ODB monitor motor vehicle maintenance device enhances the monitoring and control of the exhaust contents. The easily developed new device implements a non-intrusive maintenance process (Backey 4), not interfering with the current control strategy. The easy development and the non-interference concept effectively contribute to better control and diagnostic procedures (Backey 4). Moreover, the Ford entity implements the clustering strategy. The company prefers the FCM cluster technology. Under the technology, the entity takes into account the FCM cluster strategy. Different cluster technologies are taken into consideration. One clustering strategy is the K-means statistical tool approach. The MATLAB statistical tool is another good alternative (Backey 11). The company strategy is a continuing research and development plan, continually developing data that will enhance the Ford Company’s motor vehicle operations. In addition, the Ford entity must implement the above bucket style diagnostic strategy. The strategy is a compulsory American government requirement. Failure to comply with the requirement, the company cannot sell its motor vehicles within the United States environment (Backey 5). The sensor must be tailored to fit the different motor vehicle models. Further, the current strategy incorporates physics principles (Backey 6). The physics equations contributed to the strategy’s success. The equations were combined

Citizens view on police conduct Essay Example | Topics and Well Written Essays - 1500 words

Citizens view on police conduct - Essay Example An effective civilian oversight ensures that the police work force utilise their power in respect to the law, and the constitutional rights and freedoms of the citizens. Walker explains that there is a review board responsible for the oversight units in law enforcement agencies. The review board consists of professionals who monitor the law enforcement operations (Walker, 2005). The areas that the oversight agencies focus on include the use of force, personnel issues, and lawsuits against the police departments, policies used in police departments. The special counsel and review commission acts as mediators between the public and the police departments. Citizen oversight agencies process public complains. The internal affairs unit investigates the complaints. The counsel reviews the internal affairs investigations if they find the public complaints are justified the counsel makes recommendations that are incorporated into the policies of law enforcement agencies. According to walker and Andreaz, the recommendations are essential in the transformation of policies in police units. Citizen oversight encourages law enforcement agencies to foster a culture of openness and responsiveness. The special counsel and review commission responsible for citizen oversight publish reports that allows member of the public and media access to information regarding public complaints and the effort made by law enforcement agencies to improve the situation (Walker, 2005). Walker (2005) explains that citizen oversight have time and again failed to achieve their goals. This failure stems from factors such as poor planning, lack of political and financial support. According to walker, the resistance from police departments is a key obstacle in the successful implementation of the citizen oversight goals. Walker argues that citizen oversight agencies desire to have a working relationship with law enforcement agencies and at the same time, they value their independence and objectivity. The success of citizen oversight agencies requires finding solutions for financial constraints and resistance from police departments. It is important for police administrators to come up with ways to foster a working relationship with citizen oversight agencies. This move will facilitate the establishment of a valuable accountability system. Law enforcement units that support the role of citizen oversight agencies benefit by gaining the public’s confidence (Walker, 2005). The problems that citizen oversight agencies encounter while implementing their goals include financial constraints, unrealistic expectation set by oversight agencies, the poor planning makes it hard for oversight agencies to accomplish their goals. A lack of cooperation between oversight agencies and police departments contributes to an increased deterioration of the public’s trust in their police force. Citizen oversight agencies adopt an impartial work attitude where they focus in gathering of neu tral facts. It is due to these reasons that agency investigators fail to embrace the outrage and perspective of citizen complaints (Livingston, 2004). Walker describes that citizen oversight agencies focus on delivering the expectations of the members of the public and at the same time, assist police departments fight the issue of misconduct. However, citizen oversight agencies are encouraged to avoid offering a judgement on the allegations. On the other hand, there are police

Immune Privilege of Tissue Engineered Articular Cartilage

Immune Privilege of Tissue Engineered Articular Cartilage The immune privilege of tissue engineered articular cartilage derived from mouse adult mesenchymal stem cells and the potential of tissue engineered cartilage as a gene delivery method Chapter 1 Stem cell biology 1.1 Categorization of stem cells Stem cells are generally defined as cells possessing the following 3 characteristics: (1) self-renewal, (2) the ability to produce all cell types made in that tissue, and (3) the ability to do so for a significant portion of the life of the host (Alberts et al., 1989; Reya et al., 2001), while progenitor cells are capable only of multi-lineage differentiation without self-renewal (Weissman, 2000). Stem cells can be classified by their ability to differentiate. The most primitive, totipotent stem cells have the ability to divide and produce all the differentiated cells in an organism, including both the embryonic and extraembryonic tissues of an organism. Totipotent stem cells include the fertilized egg and the cells produced by the initial divisions of it. In mammals, these cell divisions result in an implant in the uterus called the blastocyst. The blastocyst contains an outer sphere of trophoblast cells. Trophoblast cells are capable of implanting into the uterus and helping the form of placenta which provides nutrients to the embryo. Within the blastocyst are 10 to 20 pluripotent cells called the inner cell mass. In mammalian uterus, these inner mass cells will participate in the production of all tissues and organs of the developing embryo, then fetus, then born organism. Such pluripotent cells can produce any differentiated cells in the body, but are usually unable to for m the trophoblast cells. The best-known pluripotent stem cell is the embryonic stem (ES) cell, which are obtained from the inner cell mass of the blastocyst and exist for only a brief stage of embryonic development. The last major class of stem cells, multipotent stem cells, gives rise to a limited number of cell types which are responsible for organ growth and renewal such as neural stem cells, skin stem cells and haematopoietic stem cells (HSCs) (Cheshier et al., 2009). 1.2 Selected milestones of stem cell research In 1981, Martin isolated a pluripotent stem cell line from early mouse embryos (Martin, 1981). Wilmut in 1996 first cloned a mammal, a lamb named Dolly by transferring nuclear from the adult mammary gland cell to an enucleated unfertilized egg (Wilmut et al., 1997). In 1998, Thomson obtained the first human embryonic stem cell line from human blastocysts (Thomson et al., 1998). In 2001, President Bush banned scientists from using federal funds to study stem cells from sources other than those that had already been grown because of the ethical concerns. To avoid ethical dispute over the use of human embryonic cells for research purposes, many efforts have been taken on obtaining pluripotent stem cells from differentiated donor cells. In 2006, Yamanaka find a way to obtain pluripotent cells by reprogramming the nucleus of adult mice skin cells (Takahashi and Yamanaka, 2006). Such cells are now known as induced pluripotent stem (iPS) cells. 1.3 A brief introduction of several types of multipotent stem cell The best known multipotent stem cells are haematopoietic stem cells (HSCs), that give rise to all the blood cell types including myeloid (monocytes and macrophages, neutrophils, basophils, eosinophils, erythrocytes, megakaryocytes/platelets, dendritic cells), and lymphoid lineages (T-cells, B-cells, NK-cells). HSCs are vital elements in bone-marrow transplantation, which has already been used extensively in therapeutic settings (Reya et al., 2001). In the long-term culture systems, human and rodent Central Neural System (CNS) cells maintain the capacity to produce the three main mature cell classes of the CNS: neurons, astrocytes, and oligodendrocytes, which suggest stem cells and/or progenitors exist and can survive in the culture medium (Weiss et al., 1996; Carpenter et al., 1999). In 2000, Human CNS stem cells (hCNS-SCs) have been successfully isolated by FACs (Uchida et al., 2000). Cancer stem cell hypothesis was proposed by Reya 2001 (Reya et al., 2001). This hypothesis consists of 2 components. The first component postulates that normal tissue stem cells are the target for transforming mutations and successive mutations result in the formation of a tumor. The second component is that within every cancer a specific subset of cancer stem cells continuously gives rise to all the other cancer cells and only these cells within a tumor possess the ability to self-renew, continuously proliferate. Conflicting to the first component of the hypothesis, evidences indicate cancer stem cells can also arise from mutated progenitor cells rather than stem cells (Cheshier et al., 2009). In addition, mature cells such as Lymphocytes can lead to mouse T cell leukemia independently from HSCs (Yuan et al., 2006). For the latter component of cancer stem cell hypothesis, it is likely that the cancer stem cell hypothesis is applicable to some tumors but not to others. In hematopoiet ic and some solid malignancies, only 1 in 100 to 1 in 10 000 primary tumor cells are capable of reproducing the tumor in vivo, such as human breast cancer, human neuroepithelial tumors, head and neck squamous cell carcinomas, and colon cancer. But in melanoma, nearly 1 in 4 cells possessed the ability of proliferation and developing into cancer (Cheshier et al., 2009). Cancer stem cells and CNS stem cells were reviewed by Cheshier et al. (Cheshier et al., 2009). 1.4 Mesenchymal stem cells (MSCs) and their differentiation potential Bone marrow is composed of two main systems of cell, hematopoietic cells and the supporting stromal cells (Bianco et al., 2001). MSCs reside within the marrow, maintain a level of self-renewal, and give rise to progenitor cells that can differentiate into various lineages of tissue, including chondrocytes, osteoblasts, adipocytes, fibroblasts, marrow stroma, and other tissues of mesenchymal origin. The traditional opinion about the multipotent differentiation potential of MSCs was challenged by further studies. Interestingly, MSCs reside in a diverse host of tissues throughout the adult organism and possess the ability to ‘regenerate cell types specific for local tissues e.g. adipose, periosteum, synovial membrane, muscle, dermis, pericytes, blood, bone marrow, and most recently trabecular bone, reviewed by Tuan et al. (Tuan et al., 2003). Furthermore, in 2002, Jiang et al. reported a rare cell within human bone marrow mesenchymal stem cell cultures that can be expanded extensi vely without obvious senescence. This cell population can differentiate, not only into mesenchymal cells, but also cells with visceral mesoderm, neuroectoderm and endoderm characteristics in vitro. Most somatic cell types could be derived after this population of cells was injected into an early blastocyst (Jiang et al., 2002). These studies suggest mesenchymal stem cells maintained pluripotent properties. Chapter 2 Features of Articular Cartilage 2.1 Introduction Joint cartilage formed highly sophisticated structure during the evolutionary development. There have been considerable research interests related to the cartilage cells, chondrocytes. In the last decades these studies made cartilage the first and very successful tissue engineering treatment (Brittberg et al. 1994). 2.2 Categorization of cartilage tissues Cartilage tissue is categorised in three major types by different biochemical compositions and structures of their extracellular matrix (ECM). Elastic cartilage has a small concentration of proteoglycans (PGs), and a relatively high proportion of elastin fibres. It exists in the epiglottis, small laryngeal, the external ear, auditory tube, and the small bronchi, where it is generally required to resist bending forces. Fibrocartilage also possesses a small concentration of PGs, but far less elastins. The meniscus in the knee joint is made of fibrocartilage. Hyaline is the most widespread cartilage in the human body. It is resistant to compressive or tensile forces due to its special type II collagen fibril mesh filled with a high concentration of PGs. Hyaline cartilage can be found in the nose, trachea, bronchi, and synovial joints. In the latter case, it is termed as articular cartilage (Schulz and Bader, 2007). 2.3 Compositions of articular cartilage Chondrocytes contribute to only 1%- 5% of the tissue volume; the remaining 95%-99% being extracellular matrix (ECM). Chondrocytes sense and synthesize all necessary ECM components (Mollenhauer, 2008; Schulz and Bader, 2007). The ECM of articular cartilage consists of about 60-85% water and dissolved electrolytes. The solid framework is composed of collagens (10-20%), PGs (3-10%), noncollagenous proteins and glycoproteins. In articular cartilage, 95% of collagen in the ECM is type II collagen fibrils. The rest other types are collagen type IX and XI and a small fraction of types III, VI, XII and XIV. Normal articular cartilage does not present type I collagen, which is concerned with fibrous tissue. Unlike Type I and Type III collagens which form thick fibres and thin  ¬Ã‚ bres respectively, Type II collagen present in hyaline and elastic cartilages does not form  ¬Ã‚ bres. It forms very thin  ¬Ã‚ brils which are disposed as a loose mesh that strongly interacts with the groun d substance. Type II collagen provides tensile stiffness and strength to articular cartilage and constrains the swelling capacity generated by highly negatively charged glycosaminoglycans (GAGs) of the proteoglycans (PGs). The majority (50-85%) of the PG content in articular cartilage were presented by large molecule aggrecan. It consists of a protein backbone, the core protein, to which unbranched GAGs side chains of chondroitin sulphate (CS) and keratan sulfate (KS) are covalently attached (Figure 1.1). The composition of articular cartilage was extensively reviewed by Schulz and Bader (Schulz and Bader, 2007). Figure 1. Illustration of the extracellular matrix (ECM) organization of articular cartilage (Left) and the schematic sketches (Right) of the most relevant polysaccharides of proteoglycans (PGs) in articular cartilage. The PGs consist of a strand of hyaluronic acid (HA), to which a core protein is non-covalently attached. On the core protein, glycosaminoglycans (GAGs) such as keratan sulphate (KS) and chondroitin sulfate (CS) are covalently bound in a bottle brush fashion (Modified from Schulz and Bader, 2007 and Mow and Wang, 1999). 2.4 Low capacity of self-repair in articular cartilage The aneural and avascular nature of articular cartilage, coupled with its low cellularity, contribute to both the limited rate and incomplete nature of the repair process following damage (Heywood et al., 2004). The low mitotic potential of chondrocytes in vivo also contributes to its poor ability to undergo self-repair (Kuroda et al., 2007). Some researchers believe that cartilage lesions less than 3mm in diameter self-repair with normal hyaline-like cartilage (Revell and Athanasiou, 2009; Schulz and Bader, 2007). In animal studies, full thickness cartilage defects, extending into the subchondral bone, have been reported to heal with the formation of fibrous tissue, which contains relatively low amount of type II collagen and aggrecan, but a relatively high concentration of type I collagen which is not present in normal adult articular cartilage and accordingly exhibits impaired mechanical properties (Hjertquist et al., 1971). 2.5 Metabolism of articular cartilage Joint cartilage is supplied with nutrients and oxygen by the synovial fluid diffusion facilitated by compressive cyclic loading during joint movements which acts as a pumping function (Mollenhauer, 2008). Within synovial joints, oxygen supply to articular chondrocytes is very limited, from 7.5% at the superficial zone down to 1% oxygen tension at the deep zone. It is supposed to be even further decreased under pathological conditions, such as osteoarthritis (OA) or rheumatoid arthritis (RA). The metabolism of chondrocytes is largely glycolytic. Oxygen-dependent energy generated by oxidative phosphorylation is just a minor contributor to the overall energy in chondrocytes. Nevertheless, changes in O2 tension have profound effects on cell metabolism, phenotype, gene expression, and morphology, as well as response to, and production of, cytokines (Pfander and Gelse, 2007; Gibson et al., 2008). The most important component of this hypoxic response is mediated by transcription factor hypo xia-inducible factor-1 (HIF-1), which is present in most hypoxia inducible genes (Pfander and Gelse, 2007; Gibson et al., 2008). Moreover, the matrix turnover in articular cartilage is extremely slow. Proteoglycan turnover is up to 25 years. Collagen half-life is estimated to range from several decades up to 400 years (Mollenhauer, 2008). Chapter 3 Osteoarthritis (OA) 3.1 Prevalence Osteoarthritis (OA) is the most common form of arthritis. More than 40 million US American citizens (approximately 15% of the overall population of the USA) suffer from arthritis (Schulz and Bader, 2007). OA can occur in any joint but is most common in certain joints of the hand, knee, foot and hip. OA is the most common reason for total hip- and knee-joint replacement (Wieland et al., 2005). Among US adults 30 years of age or older, symptomatic disease in the knee occurs in approximately 6% and symptomatic hip osteoarthritis in roughly 3% (Felson and Zhang, 1998). 3.2 The symptoms and diagnosis The symptoms of OA include pain, stiffness and loss of function. OA can be monitored by radiography, magnetic resonance imaging (MRI), and arthroscopy, but radiographs are still considered the gold standard (Wieland et al., 2005). 3.3 The pathology of OA The pathologic characteristics of OA are the slowly developing degenerative breakdown of cartilage; the pathological changes in the bone, including osteophyte formation and thickening of the subchondral plate; the changes in the synovium such as inflammatory infiltrates; ligaments, which are often lax; and bridging muscle, which becomes weak. Many people with pathologic and radiographic evidence of osteoarthritis have no symptoms (Martel-Pelletier, 1999; Felson et al., 2000). A protease family of matrix metalloproteases (MMP) is responsible for the initial occurrence of cartilage matrix digestion. Of this family, collagenases, the stromelysins and the gelatinases are identified as being elevated in OA. Another group of MMP is localized at the cell membrane surface and is thus named membrane type MMP (MT-MMP) (Martel-Pelletier, 1999). Proinflamatory cytokines such as interleukin (IL)-1ÃŽ ², Tumor necrosis factor (TNF)-ÃŽ ±, IL-6, leukemic inhibitor factor (LIF) and IL-17 are first produced by the synovial membrane and then diffuse into the cartilage through the synovial fluid, where they activate the chondrocytes to produce proinflammatory cytokines. These proinflamatory cytokines are considered responsible for the catabolic pathological process (Martel-Pelletier, 1999). In OA cartilage, an increased level of an inducible form of nitric oxide synthase (iNOS) leads to a large amount of nitric oxide (NO) production (Pelletier et al., 2001). NO can inhibit the synthesis of cartilage matrix macromolecules such as aggrecans and can enhance MMP activity (Taskiran et al., 1994; Murrell et al., 1995). It is well stablished that proinflammatory cytokines such as IL-1ÃŽ ² act as the key mediators of cartilage breakdown and stimulate the release of inflammatory products (NO) and prostaglandin (PG)E2, via induction of iNOS and cyclo-oxygenase (COX)-2 enzymes (Chowdhury et al., 2008). 3.4 Risk factors Osteoarthritis is considered to be a systemic disease although severe joint injury may be sufficient to cause osteoarthritis. There are several systemic risk factors related to OA. (1) Age: Osteoarthritis increases with ages, the incidence and prevalence of disease increased 2- to 10-fold from 30 to 65 years of age and increased further thereafter in a community-based survey (Oliveria et al., 1995). (2) Hormonal status and bone density: women taking estrogen have a decreased prevalence of radiographic osteoarthritis (Nevitt et al., 1996). Before 50 years of age, the prevalence of osteoarthritis in most joints is higher in men than in women. After about age 50 years, women are more often affected with hand, foot, and knee osteoarthritis than men. In most studies, hip osteoarthritis is more frequent in men (van Saase et al., 1989). Evidence suggests an inverse relationship between osteoarthritis and osteoporosis (Felson et al., 2000). (3) Nutritional factors: evidence indicates that co ntinuous exposure to oxidants contributes to the development of many common age-related diseases, including osteoarthritis. McAlindon et al. reported a threefold reduction in risk for progressive radiographic osteoarthritis was observed in persons in the middle and highest tertile of vitamin C intake compared with those whose intake was in the lowest tertile (McAlindon et al., 1996a). Vitamin D intake was observed associated with the progression of OA although not associated with risk for new-onset radiographic osteoarthritis (McAlindon et al., 1996b; Lane et al., 1999). (4) Genetics: genetic factors account for at least 50% of cases of osteoarthritis in the hands and hips and a smaller percentage in the knees (Spector et al., 1996). Candidate genes for common forms of osteoarthritis include the vitamin D receptor gene, insulin-like growth factor I genes, cartilage oligomeric protein genes, and the HLA region (Felson et al., 2000). Local mechanical factors include the body weight and the pathological alterations of the mechanical environment of the joint. Persons who are overweight have a high prevalence of knee osteoarthritis (Felson et al., 1997). OA is also considered to be related to alterations in joint mechanical environments such as knee laxity, the displacement or rotation of the tibia with respect to the femur; proprioception, the conscious and unconscious perception of joint position and movement; knee alignment , knee position in reference to the hip and ankle (Felson et al., 2000). In addition, joint dysplasias, fractures of articular surfaces, and tears of menisci and ligaments that increase joint instability precede the development of osteoarthritis in a high percentage of affected joints. Risk factors for posttraumatic osteoarthritis include high body mass, high level of activity, residual joint instability or malalignment, and persistent articular surface incongruity (Buckwalter et al., 1997; Honkonen 1995). 3.5 Treatments The medicine treatment of OA was dominated by COX2 inhibitors (Flower 2003). The other medicines include glucosamine, chondroitin (McAlindon et al., 2000), and hyaluronic acid (Lo et al., 2003). In addition, both aerobic walking and muscle strengthening exercise reduce pain and disability from osteoarthritis (Roddy et al., 2005). Articular cartilage lesions, both of traumatic or pathological origin, do not heal spontaneously and often undergo progressive degeneration towards osteoarthritis (OA). The most frequently used treatments include the artificial joint replacement, mosaicplasty, marrow stimulation, and autologous condrocyte implantation (ACI) (Steinwachs et al., 2008). Total joint replacement is most commonly performed in people over 60 years of age. (NHS 2006; Brittberg et al., 1994) Mosaicplasty is an autologous osteochondral transplantation method through which cylindrical periosteum grafts are taken from periphery of the patellofemoral area which bears less weight, and transplanted to defective areas. This transplantation can be done with various diameters of grafts (Haklar et al., 2008; NHS, 2006). Marrow stimulation methods include arthroscopic surgery to smooth the surface of the damaged cartilage area; microfracture, drilling, abrasion. All marrow stimulation methods base on the penetration of the subchondral bone plate at the bottom of the cartilage defect. The outflowing bone marrow blood contains the mesenchymal stem cells which are stabilised by the clot formation in the defect. These pluripotent stem cells which are able to differentiate into fibrochondrocytes, result in fibrocartilage repair with varying amounts of type I, II and III collagen (Steinwachs et al., 2008). The ACI tissue engineering treatment will be discussed in the next chapter. Chapter 4 Tissue engineering and autologous chondrocyte implantation (ACI) 4.1 Overview of tissue engineering technologies Tissue engineering is defined as ‘‘the application of the principles and methods of engineering and the life sciences toward the fundamental understanding of structure-function relationships in normal and pathological mammalian tissues and the development of biological substitutes to restore, maintain, or improve tissue function† (Langer and Vacanti, 1993). Three factors are considered as the principles of tissue engineering, including the utilization of biocompatible and mechanically suitable scaffolds, an appropriate cell source, and bioactive molecules to promote the differentiation and maturation of the cell type of interest (Song et al., 2004). Potential applications of tissue engineering are involved in the following fields: skin, cartilage, bone, cardiovascular diseases, organs (e.g. liver, pancreas, bladder, trachea and breast), central nervous system (e.g. spinal cord), and miscellaneous (e.g. soft tissue, ligaments). Although research is being carried out in all these fields, only few products have already entered the market. The most successful products up to now are: tissue engineered skin which is mainly used for wound cover, autologous chondrocyte implantation (ACI), and artificial bone graft (Hà ¼sing et al., 2003). 4.2 Autologous chondrocyte implantation (ACI) In 1984, a study in rabbits reported successful treatment of focal patellar defects with the use of ACI. One year after transplantation, newly formed cartilage-like tissue typically covered about 70 percent of the defect (Grande et al. 1989). In 1987, Brittberg firstly performed ACI in 23 people with deep cartilage defects in the knee. ACI is described as the following procedure: cartilage cells are taken from a minor load-bearing area on the upper medial femoral condyle of the damaged knee via an arthroscopic procedure, cultivated for four to six weeks in a laboratory and then, in open surgery, introduced back into the damaged area as a liquid or mesh-like transplant; at last, a periosteal flap sutured in place to secure the transplant (Figure 2; Brittberg et al., 1994). Genzyme Biosurgery with its product Carticel ® was the first company which introduced ACI into market and is the market leader in USA. Carticel ® is a classic ACI procedure using the periosteal cover (Hà ¼sing et al., 2008). Today the periosteum is often replaced by an artificial resorbable cover such as collagen I/III and hyaluronan membrane, such as ChondroGide or Restore (De Puy, Warzaw, Indiana) (Gooding et al., 2006; Jones and Peterson, 2006). Another new method uses chondrocytes cultured on a tri-dimensional (3D), biodegradable scaffold. This kind of scaffold, cut to the required size, is fixed into the lesion by anchoring stitches or its sticky nature. The 3D cell seeded scaffold eliminates the using of cover, thus simplifies the surgery procedure, saves the surgery time, and opens up the possibility of an arthroscopic surgery instead of the open surgery which causes more tissue damage. HYALOGRAFT from Italy is one of the European market leaders. It is a cartilage substit ute made of autologous chondrocytes delivered on a biocompatible 3D matrix, entirely composed of a derivative of hyaluronic acid (Marcacci et al. 2005). 4.3 Clinical results of ACI Brittberg studied the long-term durability of ACI-treated patients, 61 patients were followed for at least five years up to 11 years post-surgery (mean 7.4 years). After two years, 50 out of 61 patients were graded good-excellent. At the five to 11 years follow-up, 51 of the 61 were graded good-excellent (Brittberg et al., 2003). Since 1997 the year FDA approved ACI, this method has been widely performed in more than 20,000 patients all over the world. It has been reported to be effective in relieving clinical symptoms, such as pain and function (Wakitani et al., 2008). In a randomised controlled study, Knutsen et al. studied 80 patients who needed local cartilage repair with lesions on the femoral condyles of 2-10 cm2. There were no signi ¬Ã‚ cant differences in clinical results at 5 years follow-up (Knutsen et al., 2007). In another randomised controlled study that compared mosaicplasty with ACI, there was no significant difference in the number of patients who had an excellent or good clinical outcome at 1 year (69% [29/42] and 88% [51/58], respectively). In the subgroup of patients who had repairs to lesions of the medial femoral condyle, significantly more patients who had ACI had an excellent or good outcome (88% [21/24]) compared with those who had mosaicplasty (72% [21/29]) (p Clinical results of ACI were reviewed by Gikas 2009 (Gikas et al., 2009). Generally speaking, the outcomes of ACI treatment have been encouraging. However, most randomised controlled studies showed no significant difference between ACI and traditional treatments. 4.4 Limitations of ACI Microfracture is a very simple and low-cost procedure whereas ACI costs about $10 000 per patient. If ACI is not found to be more effective for improving articular cartilage repair than microfracture, the procedure will not be continued (Wakitani et al., 2008). There are several possible reasons to be blamed for the limitations of the traditional ACI procedure. The cell source in ACI is the cartilage tissue derived via an arthroscopic procedure from the low load-bearing area on the upper medial femoral condyle of the damaged knee. However, Wiseman et al. found the chondrocytes isolated from the low loaded area of the knee joint respond to mechanical stimulations in a distinct manner with the chondrocytes from the high loaded area, which suggests the traditional cell source of ACI may not provide enough mechanical response and may further lead to the insufficient mechanical properties of the repaired tissue (Wiseman et al. 2003). As cultured in monolayer, chondrocytes undergo a process of dedifferentiation and adopt a more  ¬Ã‚ broblast-like morphology, which is accompanied by an increase in proliferation and an altered phenotype. Type II collagen, the major protein produced by chondrocytes in articular cartilage, are down-regulated in the culture, while collagen types I and III are increased (Glowacki et al., 1983; Stocks et al., 2002; Benya et al., 1978). The agregating proteoglycan aggrecan of articular cartilage, is down-regulated during dedifferentiation and replaced by proteoglycans not speci ¬Ã‚ c to cartilage, such as versican (Glowacki et al., 1983; Stocks et al., 2002). Therefore, monolayer cultured chondrocytes do not express the origninal phenotype, and their ability to regenerate damaged cartilage tissue is impaired. Upon implantation, dedifferentiated cells may form a  ¬Ã‚ brous tissue expressing collagen type I that does not have appropriate mechanical properties, which may lead to deg radation and failure of the repair tissue (Brodkin et al., 2004). Chondrocytes grown in conditions that support their round shape, such as plating in high-density monolayer (Watt, 1988) and seeding in 3D structure (Benya and Shaffer, 1982) can maintain their differentiated phenotype much longer compared to cells spread in monolayer cultures. Although ACI can still be considered to be one of commonly form of repair of cartilage defects, it does have a number of scientific limitations. Some of those can be resolved using more comprehensive tissue engineered strategies which incorporates cells, scaffold materials and potentially biochemical, biomechanical and/or physical stimulation in a controlled bioreactor environment. 4.5 Tissue engineering strategies for ACI Chondrocytes derived from the low load bearing area of the knee joint respond in a distinct manner with the chondrocytes from the high loaded area. Chondrocytes cultured in monolayer have a dedifferentiation phenomenon as described above. In addition, the limitation of the transplant volume is always a major problem in autograft to be overcome (Kitaoka et al., 2001; Vinatier et. al, 2009). Accordingly, potential cell sources are widely studied for the future improvement of ACI approach, which will be discussed in Chapter 4. Seeding in 3D structures (Benya and Shaffer, 1982) can maintain chondrocytes differentiated phenotype. Ideally, cell scaffolds for tissue engineering should meet several design criteria: (1) The surface should permit cell adhension and growth, (2) neither the polymer nor its degradation products should provoke inflammation or toxicity when implanted in vivo, (3) the material should be reproducibly processable into three dimensional structures, (4) the porosity should be at least 90% in order to provide a high surface area for cell-polymer interactions, sufficient space of extracellular matrix regeneration, and minimal diffusional constraints during in vitro culture, (5) the scaffold should resorb once it has served its purpose of providing a template for the regenerating tissue, since foreign materials carry a permanent risk of inflammation, and (6) the scaffold degradation rate should be adjustable to match the rate of tissue regeneration by the cell type of interest (Freed et al., 1994). Synthetic materials such as poly (glycolic acid) (PGA), poly (lactic acid) (PLA), and poly (lactic-co-glycolic acid) (PLGA) have been investigated for use as cartilage tissue engineering scaffolds (Cima et al., 1991; Vacanti et al., 1991). Both, in vitro and in vivo studies have demonstrated these scaffold maintained the chondrocyte phenotype and the production of cartilage extracellular matrix (ECM) (Barnewitz et al., 2006; Kaps et al., 2006). Moreover, PLGA is used as a scaffold material for matrix-based autologous chondrocyte transplantation clinically (Ossendorf et al., 2007). Natural materials have also been investigated in the application of tissue engineering scaffolds in ACI. Collagen-based biomaterials are widely used in todays clinical practice (for example, haemostasis and cosmetic surgery). Collagen is also be commonly used as main components in tissue engineered skin products. Several commercial ACI products have used collagenous membraneas as the replacement for the periosteum to close the defect, such as ChondroGide or Restore (De Puy, Warzaw, Indiana) (Cicuttini et al., 1996; Jones and Peterson, 2006). The combination of type I collagen with GAG in scaffolds had a positive effect on chondrocyte phenotype (van Susante et al., 2001). Hyaluronic acid is a non-sulphated GAG that makes up a large proportion of cartilage extracellular matrix (Schulz and Bader, 2007). Matrices composed of hyaluronan have been frequently used as carriers for chondrocytes. Facchini et al. con ¬Ã‚ rms the hyaluronan derivative scaffold Hyaff  ®11 as a suitable scaff old both for chondrocytes and mesenchymal stem cells for the treatment of articular cartilage defects in their study (Facchini et al., 2006). Sugar-based natural polymers such as chitosan, alginate and agarose can be formulated as hydrogels and in some cases sponges or pads. Although these materials are extensively used in in vitro research, their role in in vivo cartilage reconstruction is still limited (Stoop, 2008). Growth factors are proved to be able to promote the formation of new cartilage tissue in both explants and engineered constructs. Insulin-like growth factor-I (IGF-I), transforming growth factor-ÃŽ ²1 (TGF-ÃŽ ²1) increases, basic fibroblast growth factor (bFGF) can stimulate cell proliferation and/or biosynthesis in chondrocytes which were Immune Privilege of Tissue Engineered Articular Cartilage Immune Privilege of Tissue Engineered Articular Cartilage The immune privilege of tissue engineered articular cartilage derived from mouse adult mesenchymal stem cells and the potential of tissue engineered cartilage as a gene delivery method Chapter 1 Stem cell biology 1.1 Categorization of stem cells Stem cells are generally defined as cells possessing the following 3 characteristics: (1) self-renewal, (2) the ability to produce all cell types made in that tissue, and (3) the ability to do so for a significant portion of the life of the host (Alberts et al., 1989; Reya et al., 2001), while progenitor cells are capable only of multi-lineage differentiation without self-renewal (Weissman, 2000). Stem cells can be classified by their ability to differentiate. The most primitive, totipotent stem cells have the ability to divide and produce all the differentiated cells in an organism, including both the embryonic and extraembryonic tissues of an organism. Totipotent stem cells include the fertilized egg and the cells produced by the initial divisions of it. In mammals, these cell divisions result in an implant in the uterus called the blastocyst. The blastocyst contains an outer sphere of trophoblast cells. Trophoblast cells are capable of implanting into the uterus and helping the form of placenta which provides nutrients to the embryo. Within the blastocyst are 10 to 20 pluripotent cells called the inner cell mass. In mammalian uterus, these inner mass cells will participate in the production of all tissues and organs of the developing embryo, then fetus, then born organism. Such pluripotent cells can produce any differentiated cells in the body, but are usually unable to for m the trophoblast cells. The best-known pluripotent stem cell is the embryonic stem (ES) cell, which are obtained from the inner cell mass of the blastocyst and exist for only a brief stage of embryonic development. The last major class of stem cells, multipotent stem cells, gives rise to a limited number of cell types which are responsible for organ growth and renewal such as neural stem cells, skin stem cells and haematopoietic stem cells (HSCs) (Cheshier et al., 2009). 1.2 Selected milestones of stem cell research In 1981, Martin isolated a pluripotent stem cell line from early mouse embryos (Martin, 1981). Wilmut in 1996 first cloned a mammal, a lamb named Dolly by transferring nuclear from the adult mammary gland cell to an enucleated unfertilized egg (Wilmut et al., 1997). In 1998, Thomson obtained the first human embryonic stem cell line from human blastocysts (Thomson et al., 1998). In 2001, President Bush banned scientists from using federal funds to study stem cells from sources other than those that had already been grown because of the ethical concerns. To avoid ethical dispute over the use of human embryonic cells for research purposes, many efforts have been taken on obtaining pluripotent stem cells from differentiated donor cells. In 2006, Yamanaka find a way to obtain pluripotent cells by reprogramming the nucleus of adult mice skin cells (Takahashi and Yamanaka, 2006). Such cells are now known as induced pluripotent stem (iPS) cells. 1.3 A brief introduction of several types of multipotent stem cell The best known multipotent stem cells are haematopoietic stem cells (HSCs), that give rise to all the blood cell types including myeloid (monocytes and macrophages, neutrophils, basophils, eosinophils, erythrocytes, megakaryocytes/platelets, dendritic cells), and lymphoid lineages (T-cells, B-cells, NK-cells). HSCs are vital elements in bone-marrow transplantation, which has already been used extensively in therapeutic settings (Reya et al., 2001). In the long-term culture systems, human and rodent Central Neural System (CNS) cells maintain the capacity to produce the three main mature cell classes of the CNS: neurons, astrocytes, and oligodendrocytes, which suggest stem cells and/or progenitors exist and can survive in the culture medium (Weiss et al., 1996; Carpenter et al., 1999). In 2000, Human CNS stem cells (hCNS-SCs) have been successfully isolated by FACs (Uchida et al., 2000). Cancer stem cell hypothesis was proposed by Reya 2001 (Reya et al., 2001). This hypothesis consists of 2 components. The first component postulates that normal tissue stem cells are the target for transforming mutations and successive mutations result in the formation of a tumor. The second component is that within every cancer a specific subset of cancer stem cells continuously gives rise to all the other cancer cells and only these cells within a tumor possess the ability to self-renew, continuously proliferate. Conflicting to the first component of the hypothesis, evidences indicate cancer stem cells can also arise from mutated progenitor cells rather than stem cells (Cheshier et al., 2009). In addition, mature cells such as Lymphocytes can lead to mouse T cell leukemia independently from HSCs (Yuan et al., 2006). For the latter component of cancer stem cell hypothesis, it is likely that the cancer stem cell hypothesis is applicable to some tumors but not to others. In hematopoiet ic and some solid malignancies, only 1 in 100 to 1 in 10 000 primary tumor cells are capable of reproducing the tumor in vivo, such as human breast cancer, human neuroepithelial tumors, head and neck squamous cell carcinomas, and colon cancer. But in melanoma, nearly 1 in 4 cells possessed the ability of proliferation and developing into cancer (Cheshier et al., 2009). Cancer stem cells and CNS stem cells were reviewed by Cheshier et al. (Cheshier et al., 2009). 1.4 Mesenchymal stem cells (MSCs) and their differentiation potential Bone marrow is composed of two main systems of cell, hematopoietic cells and the supporting stromal cells (Bianco et al., 2001). MSCs reside within the marrow, maintain a level of self-renewal, and give rise to progenitor cells that can differentiate into various lineages of tissue, including chondrocytes, osteoblasts, adipocytes, fibroblasts, marrow stroma, and other tissues of mesenchymal origin. The traditional opinion about the multipotent differentiation potential of MSCs was challenged by further studies. Interestingly, MSCs reside in a diverse host of tissues throughout the adult organism and possess the ability to ‘regenerate cell types specific for local tissues e.g. adipose, periosteum, synovial membrane, muscle, dermis, pericytes, blood, bone marrow, and most recently trabecular bone, reviewed by Tuan et al. (Tuan et al., 2003). Furthermore, in 2002, Jiang et al. reported a rare cell within human bone marrow mesenchymal stem cell cultures that can be expanded extensi vely without obvious senescence. This cell population can differentiate, not only into mesenchymal cells, but also cells with visceral mesoderm, neuroectoderm and endoderm characteristics in vitro. Most somatic cell types could be derived after this population of cells was injected into an early blastocyst (Jiang et al., 2002). These studies suggest mesenchymal stem cells maintained pluripotent properties. Chapter 2 Features of Articular Cartilage 2.1 Introduction Joint cartilage formed highly sophisticated structure during the evolutionary development. There have been considerable research interests related to the cartilage cells, chondrocytes. In the last decades these studies made cartilage the first and very successful tissue engineering treatment (Brittberg et al. 1994). 2.2 Categorization of cartilage tissues Cartilage tissue is categorised in three major types by different biochemical compositions and structures of their extracellular matrix (ECM). Elastic cartilage has a small concentration of proteoglycans (PGs), and a relatively high proportion of elastin fibres. It exists in the epiglottis, small laryngeal, the external ear, auditory tube, and the small bronchi, where it is generally required to resist bending forces. Fibrocartilage also possesses a small concentration of PGs, but far less elastins. The meniscus in the knee joint is made of fibrocartilage. Hyaline is the most widespread cartilage in the human body. It is resistant to compressive or tensile forces due to its special type II collagen fibril mesh filled with a high concentration of PGs. Hyaline cartilage can be found in the nose, trachea, bronchi, and synovial joints. In the latter case, it is termed as articular cartilage (Schulz and Bader, 2007). 2.3 Compositions of articular cartilage Chondrocytes contribute to only 1%- 5% of the tissue volume; the remaining 95%-99% being extracellular matrix (ECM). Chondrocytes sense and synthesize all necessary ECM components (Mollenhauer, 2008; Schulz and Bader, 2007). The ECM of articular cartilage consists of about 60-85% water and dissolved electrolytes. The solid framework is composed of collagens (10-20%), PGs (3-10%), noncollagenous proteins and glycoproteins. In articular cartilage, 95% of collagen in the ECM is type II collagen fibrils. The rest other types are collagen type IX and XI and a small fraction of types III, VI, XII and XIV. Normal articular cartilage does not present type I collagen, which is concerned with fibrous tissue. Unlike Type I and Type III collagens which form thick fibres and thin  ¬Ã‚ bres respectively, Type II collagen present in hyaline and elastic cartilages does not form  ¬Ã‚ bres. It forms very thin  ¬Ã‚ brils which are disposed as a loose mesh that strongly interacts with the groun d substance. Type II collagen provides tensile stiffness and strength to articular cartilage and constrains the swelling capacity generated by highly negatively charged glycosaminoglycans (GAGs) of the proteoglycans (PGs). The majority (50-85%) of the PG content in articular cartilage were presented by large molecule aggrecan. It consists of a protein backbone, the core protein, to which unbranched GAGs side chains of chondroitin sulphate (CS) and keratan sulfate (KS) are covalently attached (Figure 1.1). The composition of articular cartilage was extensively reviewed by Schulz and Bader (Schulz and Bader, 2007). Figure 1. Illustration of the extracellular matrix (ECM) organization of articular cartilage (Left) and the schematic sketches (Right) of the most relevant polysaccharides of proteoglycans (PGs) in articular cartilage. The PGs consist of a strand of hyaluronic acid (HA), to which a core protein is non-covalently attached. On the core protein, glycosaminoglycans (GAGs) such as keratan sulphate (KS) and chondroitin sulfate (CS) are covalently bound in a bottle brush fashion (Modified from Schulz and Bader, 2007 and Mow and Wang, 1999). 2.4 Low capacity of self-repair in articular cartilage The aneural and avascular nature of articular cartilage, coupled with its low cellularity, contribute to both the limited rate and incomplete nature of the repair process following damage (Heywood et al., 2004). The low mitotic potential of chondrocytes in vivo also contributes to its poor ability to undergo self-repair (Kuroda et al., 2007). Some researchers believe that cartilage lesions less than 3mm in diameter self-repair with normal hyaline-like cartilage (Revell and Athanasiou, 2009; Schulz and Bader, 2007). In animal studies, full thickness cartilage defects, extending into the subchondral bone, have been reported to heal with the formation of fibrous tissue, which contains relatively low amount of type II collagen and aggrecan, but a relatively high concentration of type I collagen which is not present in normal adult articular cartilage and accordingly exhibits impaired mechanical properties (Hjertquist et al., 1971). 2.5 Metabolism of articular cartilage Joint cartilage is supplied with nutrients and oxygen by the synovial fluid diffusion facilitated by compressive cyclic loading during joint movements which acts as a pumping function (Mollenhauer, 2008). Within synovial joints, oxygen supply to articular chondrocytes is very limited, from 7.5% at the superficial zone down to 1% oxygen tension at the deep zone. It is supposed to be even further decreased under pathological conditions, such as osteoarthritis (OA) or rheumatoid arthritis (RA). The metabolism of chondrocytes is largely glycolytic. Oxygen-dependent energy generated by oxidative phosphorylation is just a minor contributor to the overall energy in chondrocytes. Nevertheless, changes in O2 tension have profound effects on cell metabolism, phenotype, gene expression, and morphology, as well as response to, and production of, cytokines (Pfander and Gelse, 2007; Gibson et al., 2008). The most important component of this hypoxic response is mediated by transcription factor hypo xia-inducible factor-1 (HIF-1), which is present in most hypoxia inducible genes (Pfander and Gelse, 2007; Gibson et al., 2008). Moreover, the matrix turnover in articular cartilage is extremely slow. Proteoglycan turnover is up to 25 years. Collagen half-life is estimated to range from several decades up to 400 years (Mollenhauer, 2008). Chapter 3 Osteoarthritis (OA) 3.1 Prevalence Osteoarthritis (OA) is the most common form of arthritis. More than 40 million US American citizens (approximately 15% of the overall population of the USA) suffer from arthritis (Schulz and Bader, 2007). OA can occur in any joint but is most common in certain joints of the hand, knee, foot and hip. OA is the most common reason for total hip- and knee-joint replacement (Wieland et al., 2005). Among US adults 30 years of age or older, symptomatic disease in the knee occurs in approximately 6% and symptomatic hip osteoarthritis in roughly 3% (Felson and Zhang, 1998). 3.2 The symptoms and diagnosis The symptoms of OA include pain, stiffness and loss of function. OA can be monitored by radiography, magnetic resonance imaging (MRI), and arthroscopy, but radiographs are still considered the gold standard (Wieland et al., 2005). 3.3 The pathology of OA The pathologic characteristics of OA are the slowly developing degenerative breakdown of cartilage; the pathological changes in the bone, including osteophyte formation and thickening of the subchondral plate; the changes in the synovium such as inflammatory infiltrates; ligaments, which are often lax; and bridging muscle, which becomes weak. Many people with pathologic and radiographic evidence of osteoarthritis have no symptoms (Martel-Pelletier, 1999; Felson et al., 2000). A protease family of matrix metalloproteases (MMP) is responsible for the initial occurrence of cartilage matrix digestion. Of this family, collagenases, the stromelysins and the gelatinases are identified as being elevated in OA. Another group of MMP is localized at the cell membrane surface and is thus named membrane type MMP (MT-MMP) (Martel-Pelletier, 1999). Proinflamatory cytokines such as interleukin (IL)-1ÃŽ ², Tumor necrosis factor (TNF)-ÃŽ ±, IL-6, leukemic inhibitor factor (LIF) and IL-17 are first produced by the synovial membrane and then diffuse into the cartilage through the synovial fluid, where they activate the chondrocytes to produce proinflammatory cytokines. These proinflamatory cytokines are considered responsible for the catabolic pathological process (Martel-Pelletier, 1999). In OA cartilage, an increased level of an inducible form of nitric oxide synthase (iNOS) leads to a large amount of nitric oxide (NO) production (Pelletier et al., 2001). NO can inhibit the synthesis of cartilage matrix macromolecules such as aggrecans and can enhance MMP activity (Taskiran et al., 1994; Murrell et al., 1995). It is well stablished that proinflammatory cytokines such as IL-1ÃŽ ² act as the key mediators of cartilage breakdown and stimulate the release of inflammatory products (NO) and prostaglandin (PG)E2, via induction of iNOS and cyclo-oxygenase (COX)-2 enzymes (Chowdhury et al., 2008). 3.4 Risk factors Osteoarthritis is considered to be a systemic disease although severe joint injury may be sufficient to cause osteoarthritis. There are several systemic risk factors related to OA. (1) Age: Osteoarthritis increases with ages, the incidence and prevalence of disease increased 2- to 10-fold from 30 to 65 years of age and increased further thereafter in a community-based survey (Oliveria et al., 1995). (2) Hormonal status and bone density: women taking estrogen have a decreased prevalence of radiographic osteoarthritis (Nevitt et al., 1996). Before 50 years of age, the prevalence of osteoarthritis in most joints is higher in men than in women. After about age 50 years, women are more often affected with hand, foot, and knee osteoarthritis than men. In most studies, hip osteoarthritis is more frequent in men (van Saase et al., 1989). Evidence suggests an inverse relationship between osteoarthritis and osteoporosis (Felson et al., 2000). (3) Nutritional factors: evidence indicates that co ntinuous exposure to oxidants contributes to the development of many common age-related diseases, including osteoarthritis. McAlindon et al. reported a threefold reduction in risk for progressive radiographic osteoarthritis was observed in persons in the middle and highest tertile of vitamin C intake compared with those whose intake was in the lowest tertile (McAlindon et al., 1996a). Vitamin D intake was observed associated with the progression of OA although not associated with risk for new-onset radiographic osteoarthritis (McAlindon et al., 1996b; Lane et al., 1999). (4) Genetics: genetic factors account for at least 50% of cases of osteoarthritis in the hands and hips and a smaller percentage in the knees (Spector et al., 1996). Candidate genes for common forms of osteoarthritis include the vitamin D receptor gene, insulin-like growth factor I genes, cartilage oligomeric protein genes, and the HLA region (Felson et al., 2000). Local mechanical factors include the body weight and the pathological alterations of the mechanical environment of the joint. Persons who are overweight have a high prevalence of knee osteoarthritis (Felson et al., 1997). OA is also considered to be related to alterations in joint mechanical environments such as knee laxity, the displacement or rotation of the tibia with respect to the femur; proprioception, the conscious and unconscious perception of joint position and movement; knee alignment , knee position in reference to the hip and ankle (Felson et al., 2000). In addition, joint dysplasias, fractures of articular surfaces, and tears of menisci and ligaments that increase joint instability precede the development of osteoarthritis in a high percentage of affected joints. Risk factors for posttraumatic osteoarthritis include high body mass, high level of activity, residual joint instability or malalignment, and persistent articular surface incongruity (Buckwalter et al., 1997; Honkonen 1995). 3.5 Treatments The medicine treatment of OA was dominated by COX2 inhibitors (Flower 2003). The other medicines include glucosamine, chondroitin (McAlindon et al., 2000), and hyaluronic acid (Lo et al., 2003). In addition, both aerobic walking and muscle strengthening exercise reduce pain and disability from osteoarthritis (Roddy et al., 2005). Articular cartilage lesions, both of traumatic or pathological origin, do not heal spontaneously and often undergo progressive degeneration towards osteoarthritis (OA). The most frequently used treatments include the artificial joint replacement, mosaicplasty, marrow stimulation, and autologous condrocyte implantation (ACI) (Steinwachs et al., 2008). Total joint replacement is most commonly performed in people over 60 years of age. (NHS 2006; Brittberg et al., 1994) Mosaicplasty is an autologous osteochondral transplantation method through which cylindrical periosteum grafts are taken from periphery of the patellofemoral area which bears less weight, and transplanted to defective areas. This transplantation can be done with various diameters of grafts (Haklar et al., 2008; NHS, 2006). Marrow stimulation methods include arthroscopic surgery to smooth the surface of the damaged cartilage area; microfracture, drilling, abrasion. All marrow stimulation methods base on the penetration of the subchondral bone plate at the bottom of the cartilage defect. The outflowing bone marrow blood contains the mesenchymal stem cells which are stabilised by the clot formation in the defect. These pluripotent stem cells which are able to differentiate into fibrochondrocytes, result in fibrocartilage repair with varying amounts of type I, II and III collagen (Steinwachs et al., 2008). The ACI tissue engineering treatment will be discussed in the next chapter. Chapter 4 Tissue engineering and autologous chondrocyte implantation (ACI) 4.1 Overview of tissue engineering technologies Tissue engineering is defined as ‘‘the application of the principles and methods of engineering and the life sciences toward the fundamental understanding of structure-function relationships in normal and pathological mammalian tissues and the development of biological substitutes to restore, maintain, or improve tissue function† (Langer and Vacanti, 1993). Three factors are considered as the principles of tissue engineering, including the utilization of biocompatible and mechanically suitable scaffolds, an appropriate cell source, and bioactive molecules to promote the differentiation and maturation of the cell type of interest (Song et al., 2004). Potential applications of tissue engineering are involved in the following fields: skin, cartilage, bone, cardiovascular diseases, organs (e.g. liver, pancreas, bladder, trachea and breast), central nervous system (e.g. spinal cord), and miscellaneous (e.g. soft tissue, ligaments). Although research is being carried out in all these fields, only few products have already entered the market. The most successful products up to now are: tissue engineered skin which is mainly used for wound cover, autologous chondrocyte implantation (ACI), and artificial bone graft (Hà ¼sing et al., 2003). 4.2 Autologous chondrocyte implantation (ACI) In 1984, a study in rabbits reported successful treatment of focal patellar defects with the use of ACI. One year after transplantation, newly formed cartilage-like tissue typically covered about 70 percent of the defect (Grande et al. 1989). In 1987, Brittberg firstly performed ACI in 23 people with deep cartilage defects in the knee. ACI is described as the following procedure: cartilage cells are taken from a minor load-bearing area on the upper medial femoral condyle of the damaged knee via an arthroscopic procedure, cultivated for four to six weeks in a laboratory and then, in open surgery, introduced back into the damaged area as a liquid or mesh-like transplant; at last, a periosteal flap sutured in place to secure the transplant (Figure 2; Brittberg et al., 1994). Genzyme Biosurgery with its product Carticel ® was the first company which introduced ACI into market and is the market leader in USA. Carticel ® is a classic ACI procedure using the periosteal cover (Hà ¼sing et al., 2008). Today the periosteum is often replaced by an artificial resorbable cover such as collagen I/III and hyaluronan membrane, such as ChondroGide or Restore (De Puy, Warzaw, Indiana) (Gooding et al., 2006; Jones and Peterson, 2006). Another new method uses chondrocytes cultured on a tri-dimensional (3D), biodegradable scaffold. This kind of scaffold, cut to the required size, is fixed into the lesion by anchoring stitches or its sticky nature. The 3D cell seeded scaffold eliminates the using of cover, thus simplifies the surgery procedure, saves the surgery time, and opens up the possibility of an arthroscopic surgery instead of the open surgery which causes more tissue damage. HYALOGRAFT from Italy is one of the European market leaders. It is a cartilage substit ute made of autologous chondrocytes delivered on a biocompatible 3D matrix, entirely composed of a derivative of hyaluronic acid (Marcacci et al. 2005). 4.3 Clinical results of ACI Brittberg studied the long-term durability of ACI-treated patients, 61 patients were followed for at least five years up to 11 years post-surgery (mean 7.4 years). After two years, 50 out of 61 patients were graded good-excellent. At the five to 11 years follow-up, 51 of the 61 were graded good-excellent (Brittberg et al., 2003). Since 1997 the year FDA approved ACI, this method has been widely performed in more than 20,000 patients all over the world. It has been reported to be effective in relieving clinical symptoms, such as pain and function (Wakitani et al., 2008). In a randomised controlled study, Knutsen et al. studied 80 patients who needed local cartilage repair with lesions on the femoral condyles of 2-10 cm2. There were no signi ¬Ã‚ cant differences in clinical results at 5 years follow-up (Knutsen et al., 2007). In another randomised controlled study that compared mosaicplasty with ACI, there was no significant difference in the number of patients who had an excellent or good clinical outcome at 1 year (69% [29/42] and 88% [51/58], respectively). In the subgroup of patients who had repairs to lesions of the medial femoral condyle, significantly more patients who had ACI had an excellent or good outcome (88% [21/24]) compared with those who had mosaicplasty (72% [21/29]) (p Clinical results of ACI were reviewed by Gikas 2009 (Gikas et al., 2009). Generally speaking, the outcomes of ACI treatment have been encouraging. However, most randomised controlled studies showed no significant difference between ACI and traditional treatments. 4.4 Limitations of ACI Microfracture is a very simple and low-cost procedure whereas ACI costs about $10 000 per patient. If ACI is not found to be more effective for improving articular cartilage repair than microfracture, the procedure will not be continued (Wakitani et al., 2008). There are several possible reasons to be blamed for the limitations of the traditional ACI procedure. The cell source in ACI is the cartilage tissue derived via an arthroscopic procedure from the low load-bearing area on the upper medial femoral condyle of the damaged knee. However, Wiseman et al. found the chondrocytes isolated from the low loaded area of the knee joint respond to mechanical stimulations in a distinct manner with the chondrocytes from the high loaded area, which suggests the traditional cell source of ACI may not provide enough mechanical response and may further lead to the insufficient mechanical properties of the repaired tissue (Wiseman et al. 2003). As cultured in monolayer, chondrocytes undergo a process of dedifferentiation and adopt a more  ¬Ã‚ broblast-like morphology, which is accompanied by an increase in proliferation and an altered phenotype. Type II collagen, the major protein produced by chondrocytes in articular cartilage, are down-regulated in the culture, while collagen types I and III are increased (Glowacki et al., 1983; Stocks et al., 2002; Benya et al., 1978). The agregating proteoglycan aggrecan of articular cartilage, is down-regulated during dedifferentiation and replaced by proteoglycans not speci ¬Ã‚ c to cartilage, such as versican (Glowacki et al., 1983; Stocks et al., 2002). Therefore, monolayer cultured chondrocytes do not express the origninal phenotype, and their ability to regenerate damaged cartilage tissue is impaired. Upon implantation, dedifferentiated cells may form a  ¬Ã‚ brous tissue expressing collagen type I that does not have appropriate mechanical properties, which may lead to deg radation and failure of the repair tissue (Brodkin et al., 2004). Chondrocytes grown in conditions that support their round shape, such as plating in high-density monolayer (Watt, 1988) and seeding in 3D structure (Benya and Shaffer, 1982) can maintain their differentiated phenotype much longer compared to cells spread in monolayer cultures. Although ACI can still be considered to be one of commonly form of repair of cartilage defects, it does have a number of scientific limitations. Some of those can be resolved using more comprehensive tissue engineered strategies which incorporates cells, scaffold materials and potentially biochemical, biomechanical and/or physical stimulation in a controlled bioreactor environment. 4.5 Tissue engineering strategies for ACI Chondrocytes derived from the low load bearing area of the knee joint respond in a distinct manner with the chondrocytes from the high loaded area. Chondrocytes cultured in monolayer have a dedifferentiation phenomenon as described above. In addition, the limitation of the transplant volume is always a major problem in autograft to be overcome (Kitaoka et al., 2001; Vinatier et. al, 2009). Accordingly, potential cell sources are widely studied for the future improvement of ACI approach, which will be discussed in Chapter 4. Seeding in 3D structures (Benya and Shaffer, 1982) can maintain chondrocytes differentiated phenotype. Ideally, cell scaffolds for tissue engineering should meet several design criteria: (1) The surface should permit cell adhension and growth, (2) neither the polymer nor its degradation products should provoke inflammation or toxicity when implanted in vivo, (3) the material should be reproducibly processable into three dimensional structures, (4) the porosity should be at least 90% in order to provide a high surface area for cell-polymer interactions, sufficient space of extracellular matrix regeneration, and minimal diffusional constraints during in vitro culture, (5) the scaffold should resorb once it has served its purpose of providing a template for the regenerating tissue, since foreign materials carry a permanent risk of inflammation, and (6) the scaffold degradation rate should be adjustable to match the rate of tissue regeneration by the cell type of interest (Freed et al., 1994). Synthetic materials such as poly (glycolic acid) (PGA), poly (lactic acid) (PLA), and poly (lactic-co-glycolic acid) (PLGA) have been investigated for use as cartilage tissue engineering scaffolds (Cima et al., 1991; Vacanti et al., 1991). Both, in vitro and in vivo studies have demonstrated these scaffold maintained the chondrocyte phenotype and the production of cartilage extracellular matrix (ECM) (Barnewitz et al., 2006; Kaps et al., 2006). Moreover, PLGA is used as a scaffold material for matrix-based autologous chondrocyte transplantation clinically (Ossendorf et al., 2007). Natural materials have also been investigated in the application of tissue engineering scaffolds in ACI. Collagen-based biomaterials are widely used in todays clinical practice (for example, haemostasis and cosmetic surgery). Collagen is also be commonly used as main components in tissue engineered skin products. Several commercial ACI products have used collagenous membraneas as the replacement for the periosteum to close the defect, such as ChondroGide or Restore (De Puy, Warzaw, Indiana) (Cicuttini et al., 1996; Jones and Peterson, 2006). The combination of type I collagen with GAG in scaffolds had a positive effect on chondrocyte phenotype (van Susante et al., 2001). Hyaluronic acid is a non-sulphated GAG that makes up a large proportion of cartilage extracellular matrix (Schulz and Bader, 2007). Matrices composed of hyaluronan have been frequently used as carriers for chondrocytes. Facchini et al. con ¬Ã‚ rms the hyaluronan derivative scaffold Hyaff  ®11 as a suitable scaff old both for chondrocytes and mesenchymal stem cells for the treatment of articular cartilage defects in their study (Facchini et al., 2006). Sugar-based natural polymers such as chitosan, alginate and agarose can be formulated as hydrogels and in some cases sponges or pads. Although these materials are extensively used in in vitro research, their role in in vivo cartilage reconstruction is still limited (Stoop, 2008). Growth factors are proved to be able to promote the formation of new cartilage tissue in both explants and engineered constructs. Insulin-like growth factor-I (IGF-I), transforming growth factor-ÃŽ ²1 (TGF-ÃŽ ²1) increases, basic fibroblast growth factor (bFGF) can stimulate cell proliferation and/or biosynthesis in chondrocytes which were