Biodegradability

Biodegradation is a physiological process, during which materials are gradually excreted from the body by dissolution, enzymatic hydrolysis, cell phagocytosis, etc. The tissue engineering scaffolds are not intended as permanent constructs. They should gradually biodegrade to allow the cells to produce their own extracellular matrix and eventually achieve the ingrowth of new tissues or the formation of new organs. The new tissues grow into the implantation site at the same time of material biodegradation. To achieve this goal, the scaffold degradation profile should be designed. At the time of scaffold material selection, the consideration of the coordination of its biodegradability and other components’ should be put emphasis on. Ideally, the degradation rate of the scaffold should match the new tissue formation rate so as to provide a smooth transition of the load transfer from the scaffold to the new tissue [35]. When the scaffolds are biodegraded completely, the new desired tissues fully replace the scaffolds and fill the implantation site. Additionally, biodegradation products should be removed from the body via metabolic pathways at an adequate rate that can keep the concentration of these degradation products in the tissues at a tolerable level [36]. Furthermore, the biodegradation rate of the scaffolds should be controllable to match the different tissue growth rate. For example, the degradation behavior of the scaffolds should vary based on the applications, such as 9 months or more for scaffolds in spinal fusion, 3-6 months for scaffolds in cranio- maxillofacial applications [29]. Moreover, tissue regeneration rate varies with the age and sex of the patients. To achieve controllable biodegradation rate, researchers usually develop biocomposites as tissue engineering scaffolds, which contain the components with faster biodegradation rate and the components with slower biodegradation rate. For example, Wu et al. [37] prepared porous scaffolds of zein/ poly(epsilon-caprolactone) biocomposites with satisfactory porosity and well interconnected network for bone tissue engineering. Their results indicated that the degradation rate could be tailored by adjusting the amount of the zein in the scaffolds. Another sample is that Mukundan et al. prepared Nanofibrous composite scaffolds of poly(ester amides) with tunable physicochemical and degradation properties by controlling the different additive amount of polycaprolactone.

 
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