Polyesters PHAs preparation

Electrospinning of PHA is still relatively new in scaffold fabrication. To date, P(3HB) and P(3HB-co-3HV) are the most common microbial polyesters to be electrospun into tissue-engineering scaffolds. Suwantong et al. (2007) prepared ultrafine electrospun fiber mats of P(3HB) and P(3HB-co-3HV) as scaffolding materials for skin and nerve generation, hi their study, they evaluated the in vitro biocompatibility of these fibers using mouse fibroblasts and Schwann cells... 

Aliphatic polyesters may be classified into two groups, depending on the bond constitution of the monomCTs poly(hydroxy acid)s i.e. polyhydroxyalkanoates (PHAs)) and polyfalkylene dicarboxylate)s [68]. The former are polymers of hydroxy acids (a, p,...(i)-hydroxy acids), obtained by ring-opening polymerization or polycondensation reactions. The latter are S3uithesized by the polycondensation reaction of diols with dicarboxylic acids. Aldonic and aldaric acids can be used to prepare both groups of polyesters. 

Optically active polymers are important functional materials for several industrial and bio-m ical applications and are extensively used as chiral catalysts for asymmetric synthesis, packing materials of chromatographic columns and chiral materials for the preparation of liquid crystal polymers (7). Polymers such as poly hydroxy alkanoates (PHAs), naturally occurring microbial optically active polyesters, are important materials in biomedical applications owing to their biodegradability (2). In synthetic polymer chemistry, synthesis of optically active polymers has been one of the most challenging tasks. Most synthetic chiral polymers are prepared from optically pure starting materials which are, except when isolated from nature, in limited supply and difficult to prepare (7, 3). 

PHA solutions of various densities were used to prepare transparent flexible films. The surface properties of PHB and P(HB-co-HV) fllm scaffolds were similar to each other and to those of synthetic polyesters (polyethylene terephthalate, poly (methyl methacrylate), polyvinyl chloride, and polyethylene) (Shishatskaya 2(X)7X The scaffold s surface properties are important for cell attachment and proliferation. To enhance cell adhesion to the surface, improve the gas-dynamic properties of scaffolds, and increase their permeability for substrates and cell metabolites, the scaffolds can be treated by physical factors or by chemical reagents. Biocompatibility of PHA scaffolds has been enhanced by immobilizing collagen fllm matrices on the scaffold surface and coating with chitosan and chitosan/polysaccharides (Hu et al. 2003). 

Efforts to synthesize P(3HB) without impurities of natural origin have led to the development of chemical routes to PHAs, which include the ROP of butyrolactone and other different lactones. However, due to the inability to easily obtain optically active polyesters and the lower molecular weights of the obtained products compared to those achievable in the biosynthetic approaches, these routes to PHAs are not very significant, except for the preparation of otherwise unattainable copolymers. On the other hand, racemic P(3HB) obtained by ROP is less crystalline, with elastomeric properties, and can be of interest in some medical applications, such as drug delivery. 

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