Preparation Of Nano-Fibrous Aliphatic Polyesters And Their Composites Scaffolds Via Phase Separation

Biodegradable polymers have been widely used as scaffold materials to regenerate new tissues. To mimic natural extracellular matrix architecture, the scaffold should have a novel highly porous structure, which is a three-dimensional interconnected fibrous network with a fiber diameter ranging from 50 to 500nm. At present, many technologies have been developed with varying degrees of success at getting scaffolds, such as electrospinning, self-assembly, phase separation and so on. However, they have themselves advantages and disadvantages. To compensate for their shortcomings, we can combine different methods. The nano-fibrous matrices can also be prepared from the polymer solutions by a procedure involving thermally induced gelation, solvent exchange, and freeze-drying by phase separation. But gelation temperature is the key of the formation of fibrosis.In this study, phase separation and freeze-drying technologies were combined to fabricate the nanofibrous poly(L-lactide) (PLLA) scaffolds firstly. The effects of condensation temperatures and polymeric solution concentrations on the fiber morphology were investigated. It was found thatlower condensing temperature was more favorable for PLLA nanofibrosis. But at the same condensation temperature, the PLLA nanofibrosis could be observed only when the concentration of polymeric solution was in a proper arrange. Secondly, various composite nanofibrous PLLA scaffolds were prepared by adding carbon nanotubes, graphene, hydroxyapatite or -calcium phosphate naonoparticles into the PLLA solution followed by phase separation. The incorporation of inorganic particles into the PLLA fibrous matrixes could improve their mechanical properties. Besides, the composite scaffolds were biocompatible identified by the results of osteoblasts-scaffold coculture.In addition, sodium chloride or gelatin particles with particle sizes of 200-400 microns were applied with the phase separation method to produce nanofibrous scaffolds with interconnected macropores. Experimental results showed that the macroporous structure and morphology of the macropores depended on the shapes and sizes of the porogens.On the other hand, nanofibrosis of poly(lactide-co-glycolide) (PLGA) copolymers was also studied in this study. Different kinds of nonsolvents, including water, acetone and ethanol, were attempted to induce the nanofibrosis of PLGA75/25. It was found that mixed THF/H2O solvent pairs were a suitable solvent to obtain PLGA fibrosis scaffolds. The results showed that the key for the nanofibrosis of amorphous PLGA via phase separation was to find a proper solvent-nonsolvent system to get the PLGA gels at certain temperatures.