The Preparation And Properties Of Lysine-Modified Poly(Lactic Acid) Microsphere Scaffolds

Polylactic acid(PLA),a synthetic polymer biomaterials,has become one of the commonly used biomaterials for tissue engineering scaffolds because of its excellent biocompatibility,biodegradability and non-toxicity of degradation products i.e.PLA microspheres can be used as cell carriers for tissue repair.The advantage of using PLA microspheres as tissue engineering scaffolds is that they can be administered relatively easily via simple injection without the necessity of surgery,so PLA microspheres have a good application prospect in the repair and treatment of irregular shape or small bone defects.However,PLA microspheres have a poor bioactivity resulting from their high hydrophobicity which makes their surface not suitable for the adhesion and growth of cells,so.some modifications are needed to be done to enhance the bioactivity of PLA microspheres by improving their hydrophilicity.Several modification methods of PLA microsphere scaffolds are mainly investigated in this thesis,the main research works and the obtained results are as follows:(1)Lysine was selected as a modifier to prepare modified PLA microspheres.Lysine molecule was grafted onto the molecular chain of PLA via the aminolysis reaction between one of its amino groups and ester group of PLA,so the hydrophilic amino group and carboxyl group were introduced into PLA molecule and then the modified PLA with improved hydrophilicity was obtained.The lysine-modified PLA nanofibrous microspheres were prepared by emulsion combined with thermally induced phase separation technique and characterized by means of SEM,FTIR,XPS,~1H-NMR and static water contact angle tester.The results of the study revealed that lysine was successfully grafted onto the molecular chain of PLA,and the prepared microspheres had an enhanced bioactivity due to the improved structure and hydrophilicity.(2)In order to further improve the hydrophilicity of PLA microspheres,a facile immersion-adsorption method was used to coat the surface of lysine-modified PLA nanofibrous microspheres with lecithin.The results of SEM,IR,XPS and the contact angle test confirmed that the surface of lysine-modified PLA nanofibrous microspheres had been successfully coated with lecithin and the hydrophilicity and bioactivity of PLA microspheres were further improved.(3)The hydrophilicity of PLA microspheres was further improved by immersing lysine-modified PLA nanofibrous microspheres in dopamine solution.The as-prepared dopamine-modified microspheres were characterized by SEM,IR,XPS and contact angle meter.It was found that coating a layer of dopamine on the surface of lysine-modified PLA nanofibrous microspheres could further improve the hydrophilicity and bioactivity of PLA microspheres.