Question 6 a) Dscribe the three principles in tissue engineering and outline you

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Question 6 a) Dscribe the three principles in tissue engineering and outline your strategy to replace a 30 year old professional footballer's damaged cartilage identifying and justifying your choices for each of the three fundamental elements of a tissue engineering strategy [9 marks] Cartilage tissue engineering is dependent on a number of factors that will influence chondrocyte/matrix organisation and mechanical properties. Explain why these factors will influence cell behaviour and mechanical properties of the cartilage tissue engineered product. For each of these requirements, identify 1 example of b) how this could be implemented in the cartilage tissue engineering example above [4 marks]

Explanation / Answer

a). The principles of tissue engineering are

1. Isolation of living cells/tissue during biopsy and Culturing and proliferating them to gain a sufficient number of living cells.
2. Planting the cells onto a Scaffold (an artificial structure that is capable of regulating cell adhesion, proliferation and tissue formation in a 3-D space, taking into account the nutrient supply and uptake, pH, humidity, temperature and osmotoc pressure.
3. Control over the growth factors, such as hormones, vitamins

Now coming specifically to a damaged cartilage tissue engineering strategy.
1. The choice of cells and their isolation: Among chondrocytes, fibroblasts and stem cells; Chondrocytes and Mesenchymal stem cells are the widely used sources of chondrogenic cells for cartilage repair. This is because they have the ability to form Extracellular matrix and canbe isolated from different sources such as nasal septum, costal cartilage or articular and auricular cartilages.
2. The choice of Scaffold: We find protein-based matrices, polysaccharide-based matrices and a few synthetic matrices. Among the protein-based matrices, collagen or fibrin could be the components, out of which collagen-based is widely used. Among the polysaccharide-based matrices, hyaluronic acid, chitosan and cellulose could be the components used, out of which hyaluronic acid-based is widely used. And similarly for synthetic scaffolds, poly lactic-co-glycolic acid-based matrices are widely used compared to polylactic acid or polyethylene glycol based matrices.
However, all the above 3 matrices mentioned above may not be injected directly percutaneously.
Hence, self-hardening and injectable materials are to be used in order to transplant the chondrogenic cells percutaneously. For this, 'hydrogels' containing chains of macromolecules (either natural or synthetic) which can mimic the 3-D environment of chondrocytes are used as scaffolds.
3. Growth factors such as TGF beta (Transforming growth factor-b1 and 3) are the most commonly used to induce chondrogenesis of mesenchymal stem cells.
Articular cartilage being 'avascular' develops naturally in the presence of low Oxygen tension - 2 to 7%.

b).The answer to this question has been explained while answering a).
The mechanical properties will be discussed here. Articular cartilage is a tissue which is subjected to mechanical stimuli (such as shear stress, hydrostatic pressure). Recent studies have shown that collagen and glycosaminoglycan as part of the structural components of the extracellular matrix closely resembles that of a native cartilage of the human body.

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