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Tissue engineering is the new, very fast growing interdisciplinary branch of science which combines biology, biotechnology, chemistry, and materials science. The practical aim of this discipline is to create scaffolds for new tissue growth, meaning nothing other than regeneration of damaged tissue. Nowadays, using tissue engineering methods we can replace for instance damaged bone or skin tissue. But still, plenty of questions remain unanswered. Cartillage tissue or nerve tissue are still important challenges for research groups.
Porous cell scaffold
Transplantaton is still one of the most commonly used method to replace damaged tissue. However, this method entails a lot of serious problems. The most important is the need for a greate number of procedures and possibility of graft rejection. All problems connected with this way of treatment forced to search for new solutions.
The idea of replacing tissue by materials like polymers appeared many centuries ago, but even 50 years ago biomaterials as we think of them did not exist. However, in recent years, together with the development of new technologies and improvement of biomaterials, new idea of tissue regeneration had appear. Nowadays, in tissue engineering plenty of various materials and technologies are used. Reffering to current trends in tissue engineering, the most promising materials are polymers, both synthetic and biopolymers like PLA, PLGA, PGA, PCL, PU, chitosan, collagen, or gelatin. Thanks to their wide spectrum of properties (chemical, physical and mechanical), biocompability and biodegradability, they found use in such applications like scaffolds for bone and cartilage, skin tissue, heart tissue etc. The use of degradable polymers to induce tissue regeneration is particularly promising in case of s.c. critical size, i.e. non-healing defects. Once implanted, polymer should act as a temporary substitute of the native extracellular matrix, enabling the ingrowth of a new tissue by attracting cells from surrounding and providing suitable conditions for proliferation. The polymer scaffold is expected to degradate gradually as the formation of neotissue with native, self-produced ECM occurs. Sometimes polymer scaffolds are combined with ceramics (hydroxyapatite, calcium triphoshate) for special applications.
The main techniques for scaffold fabication are as follows:
- solvent casting,
- particulate leaching techniqes,
- gas foaming,
- phase separation,
- porogen leaching,
- fiber mesh,
- fiber bonding,
- self assembly,
- rapid prototyping,
- melt moding,
- membrane lamination,
- freeze drying.
Not every method of scaffolds production can be used in a given case. The method of scaffold formation leading to a particular morphology, internal structure and hence final properties of a product, should be correlated with specific application. For instance, the most important methods of scaffold preparation used in the regeneration of nerve tissue include electrospinning and phase separation technique. Common methods for preparing scaffolds for new blood vessel formation is the filament winding method and electrospinning.
Bone-forming osteoblasts on the scaffold
Finally, scaffold has to be populated by cell which will create new tissue. Initially cells have to be isolated, then amplified at in vitro conditions and introduced into scaffold structure. In the next stage scaffold with cells has to be placed in a bioreactor. There in suitable enviroment of growth and nutrient factors cells start grow up and proliferate. Finally all new tissue can be placed into place of tissue defect.
Although, we are potentially able to regenerate many different tissues, some applications are still extremely difficult. Currently, the most problematic is the reconstruction of complex organs such as the heart or kidneys. The main problem is to reconstruct a complex network of blood vessels and innervation of these tissues. Which are essential for keeping her alive. Nevertheless, numerous studies are conducted which show promise. Looking for new solutions for organs regeneration such as the liver, researchers use a so-called ,,natural skaffold''. Using dead tissue or tissue containing dead cells. Using a special procedure, all cells and cell debris are removed from the liver. Then, healthy stem cells are seeded to the empty tissue and vasculature is restored to promote growth. Lungs have also been successfully replaced using this technique (animal trials).
Restoration the specific conditions in which cells build the particular tissue is essential for the success of therapy. In addition to an appropriate chemical environment of living (nutrient, enzymes, hormones) also physical factors (loads, pressure, temperature) are very important for cells differentation. For example, articular cartilage cells differentiate into the correct way in the presence of loads which are relevant in the joints.
There is still a lot of fundamental research in the scaffolds design. Also plenty of clinical trials.that must be followed by extensive. This branch of science is changing rapidly, so the opportunities for the use of tissue engineering will surely change year-by-year.
1. Buddy D. Ratner, Allan S. Hoffman, Frederick J. Schoen, Jack E. Lemons, ,,Biomaterials Science: An Introduction to Materials in Medicine '', Academic Press
2. B. Subia, J. Kundu and S. C. Kundu, ,,Biomaterial scaffold fabrication techniques for potential tissue engineering applications'', Interchopen,