Tissue Engineering

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TISSUE ENGINEERING: HALLMARK OF MODERN MEDICINE BBS1224 | CELL&TISSUE CULTURE Made for printing

What is Tissue Engineering?

Animal Tissue Culture ↔ Tissue Engineering

The term “tissue engineering” only appeared in 1987 during United States’ National Science Foundation meeting, which they define as “a new inter-disciplinary initiative which has the goal of growing tissues or organs directly from a single cell taken from an individual”. Since then, this new emerging scientific spectrum become a focus of research institution across the globe, particularly at USA and Europe. UKM’s Tissue Engineering and Human Genetics Research Team is a pioneer and leader in this area in Malaysia. Animal tissue culture allows for the advancement of tissue engineering. Two main strategies in tissue engineering are: • grow cells in-vitro on transplant. • implant matrix and regenerate host cells.

Cells and tissues commonly involved in tissue engineering, in clockwise: cornea, skin, various human genes, biomaterial, bone, cartilage.

Why it is gaining interest nowdays?

Cost to repair damaged tissues allows to more than a trillion annually, globally. In USA alone, liver transplant and aftercare cost over a billion USD. More than 10,000 people have died during the past five years while waiting for an organ transplant. Tissue engineering potentially offers dramatic improvements in medical care for hundreds of thousands of patients annually, and equally dramatic reductions in medical costs; due to the availability of less expensive treatments and minimizing time waiting for compatible organ donor, since “engineered" replacement organs became reality.

INTRODUCTION

Tissue engineering is an emerging multidisciplinary field involving biology, medicine, and engineering that is likely to revolutionize the ways we improve the health and quality of life for millions of people worldwide by restoring, maintaining, or enhancing tissue and organ function. In other words, tissue engineering is the development of artificial tissue and organ systems. The term regenerative medicine is often used synonymously with tissue engineering, although those involved in regenerative medicine place more emphasis on the use of stem cells to produce tissues.

Typical Processes

Scaffold

Scaffold must meet some requirement: • high porosity • adequate pore size • biodegradability (after the new tissue built its own mechanical support) Natural scaffold are proteic materials, such as collagen or fibrin, and polysaccharidic materials, like chitosan or glycosaminoglycans (GAGs). A commonly used synthetic material is PLA - polylactic acid. As cell produce extracellular matrix and proliferate, synthetic polymer scaffold degrades. Growth Factor

1. Remove cells1; 2. Expand number in culture; 3. Seed onto an appropriate scaffold2 with suitable growth factors3 and cytokines4; 4. Place into culture5; 5. Re-implant engineered tissue repair damaged site. 1

From fluid tissues such as blood, cells are extracted by bulk methods, usually centrifugation. From solid tissues usually the tissue is minced, and then digested with the enzymes trypsin or collagenase to remove the extracellular matrix that holds the cells. 2

Artificial structure capable of supporting three-dimensional tissue formation. More information at right. 3

Protein capable of stimulating cellular proliferation and cellular differentiation.

4

Group of proteins and peptides that are used in organisms as signalling compounds

5

Sometime in bioreactor. More information at right.

The choice of growth factors depends solely on the types of culture. Rich medium formulations like 199 and simpler media like MEM are popular. Other combinations might include serum, additives like insulin, transferrin, ethanolamine and selenium. In order to reduce cell aggregation, Ca2+ and Mg2+ ions have to be omitted from the medium, or alternatively low levels of trypsin may be added to the medium. Ideal pH of the medium should between 7.0 to 7.4. Bioreactor

Custom-made devices called bioreactors allow for precise and continuous control of culture conditions and also allow for introduction of different stimuli to tissue cultures.

METHODS AND TECHNIQUES

Cells are often implanted or 'seeded' into an artificial structure capable of supporting three-dimensional tissue formation called scaffold. Functions of scaffold are as follows: • allow cell attachment and migration • deliver and retain cell and biochemical factors • enable diffusion of vital cell nutrients and expressed products

Jackpot : Artificial and Synthetic Blood

• skin tissue replacement for ulcerations. • scaffold that allows the slow release of an anticancer agent to combat a form of brain cancer. • artificial pancreas that help diabetes patient. • artificial bladder. • lab-grown cartilage used to repair knee cartilage.

Dozens of biotech companies from around the globe was involved in search of artificial and synthetic blood because of its huge economic potential. Blood supply is problematic: • viral infection risk: HIV, Hepatitis • storage conditions • supply shortages

From Laboratory to Commercial Venture

BioTissue Technologies Inc. have several products commercially produced, including skin repair, oral connective tissue, and cartilage. BD Bioscience specialize in artificial bones. BioHeart Inc. specialize in regeneration of heart cells in vitro. • inject heart cells into patient to repair damaged tissue • in third stage human clinical trials in Europe

Biopure Inc. Hemopure® is the first artificial blood that has been approved for clinical use - in South Africa (2001). It is purified cows hemoglobin. It has a 2 day half life. Side effect is an increase in blood pressure Polyheme® is hemoglobin extracted from expired blood. The product is supplied as a dried powder which is reconstituted and has longer shelf life. Oxygent® is synthetic blood which uses perfluoro-chemicals as the oxygen carrier. Surfactants, salts and water are added

Prospects and Challenges

Although future of tissue engineering is very promising, finding effective scaffold is still a major issue in the creation of more complex, large-scale structures. Some say fabrication of nanofibrous materials can provide the answer. At the other side, the question of whether and how to control the creation and use of technology raises ethical issues of great concern to society. Conclusion

As a foundation of tissue engineering, animal cell and tissue culture provides extensive probabilities for human being to improve health quality, today and tomorrow. But, there is still much to be done and learned, scientifically and economically, to ensure that the benefits of this technology will truly help everyone and without any notable, harmful side-effects.

APPLICATION AND PROSPECTS

Current Uses