Preparation And Study Of Properties Of Biodegradable PLA-PCL Block Copolymers

In recent years, biodegradable polymers have attracted great interests in biomedical field. They are widely used in traditional applications, such as matrices for long-term drug delivery, short-term fixation devices in the orthopedic field and surgical sutures. Moreover, biodegradable polymers may act as temporary scaffolds that facilitate tissue regeneration or cell growth in the field of tissue engineering.Among the biodegradable polymers, great attention is paid to degradable aliphatic polyesters such as poly (lactic acid) (PLA) and poly (ε-caprolactone) (PCL) due to their excellent biodegradability, biocompatibility and bioresorbability. PLA is transparent and crystalline polymer with relatively high melting point and brittle properties. It has high strength and low elongation at break. PLA can be easily degraded by enzymatic or alkali hydrolysis. PCL is semi-crystalline polymer with ductility. It is of great interest because of its outstanding permeability to drugs and thermal properties. PCL has a hydrolytic biodegradability but at long term. Copolymerization provides worthwhile means to adjust the degradation rate, as well as physical and mechanical properties. However, these methods generally require a complex multi-step synthesis and high toxic organometallic catalysts. It is practically impossible to entirely remove the organometallic compounds and residues from these polyesters.Alternatively, it would overcome these shortcomings to treat PLA and PCL with chain extenders directly. It is quite reasonable to expect that the coupling of PCL and PLA with chain extending reagents may bring about either increased strength or improved flexibility compared with each individual component. It is also an effective way to achieve high molecular weight polyesters in mild reaction condition, which greatly reduces the cost of production. Typical chain extenders for polyesters containing–OH and–COOH are diepoxides, bisoxazolines, dianhydrides and diisocyanates. In this work, PCL-PLA multiblock copolymers were prepared via coupling reaction. We introduced hexamethylene diisocyanate (HDI) as chain extender, which reacted with both–OH and–COOH. A series of experiments had been designed:1 The (AB)n type multiblock copolymers of PCL and PLA were prepared by the new process, in which the oligomers of PCL and PLA were blended in solvent and then the copolymer was synthesized by coupling reaction between PCL and PLA oligomers with–NCO groups of HDI. The optimal experiment condition was decided. FTIR, 1H NMR, TGA and DTG spectra proved that the multiblock copolymers were synthesized. Tensile properties were appreciably improved. Materials with high flexibility, enhanced strength and superior extendibility were gained. Besides, interfacial adhesion was improved, which was supported by SEM micrographs.2 The A-B-A type multiblock copolymers of PCL-diOH and PLA were prepared. The chemical structures, thermal properties, the mechanical properties and molecular weight were characterized with 1H NMR, thermal gravity analysis (TGA), tensile measurements and GPC. The effect of the content of PCL-diOH in PLA-PCL-PLA on the mechanical properties, molecular weight, water absorption and hydrolysis was studied.3 The degradation experiments outside body were designed. The effect of lipase on degradation of PLA-PCL-PLA was debated.4 Multi-porous scaffold was prepared by electrospinning technology. The condition of spinning was discussed and the optimal experimental condition was decided. The morphology of scaffold was characterized with scanning electron microscopy (SEM). The effect of molecular weight on morphology of scaffold was discussed.