Preparation Of Polylactic Acid From Tissue Engineering Scaffold By Microporous Foaming And Its Characterization

Polylactic acid (PLA), a widely used synthetic polymer material, becomes especially popular in the fields of biology, pharmacy and food because of its good biodegradable and biocompatible properties. However, in order to meet various application of bioengineering, the fabrication and investigation of PLA tissue engineering scaffolds need to be further explored and improved both at home and abroad. In this study, the PLA scaffolds were fabricated by the solvent-free solid gas foaming technology with two kinds of foaming gases (CO2, Air) and two kinds of PLA (PLLA, PDLLA). Combined with scanning electron microscopy (SEM), reflection-fourier transform infrared (FTIR) analysis, wide angle x-ray diffraction measurement (WAXRD), enzymatic degradation and cell tests, thermal analysis technology (differential scanning calorimetry (DSC), step-scan differential scanning calorimetry (SSDSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA)) were used to analyze the scaffolds’structures, functional groups, crystallinities and so on. Furthermore, thermal stabilities, mechanical properties, biodegradation, cytocompatibility and the influence of preparation condition on the scaffold’s properties were investigated. Besides, the thermal decomposition kinetic coefficients of scaffolds were calculated based on the equations of Kissinger, Ozawa-Doyle and Vyazovkin. The results are showed as follow:Firstly, all the three scaffolds (PLLA-CO2、PLLA-Air and PDLLA-CO2) have smaller pore size and larger pore density with the increasing saturation pressure, which indicates that the pore size of all the scaffolds decreases exponentially with the increasing saturation pressure and the logarithm of pore density increases linearly with the increasing saturation pressure. Among the three kinds of scaffolds under the same saturation pressure, the pore size is in a decreasing order as:PDLLA-CO2> PLLA-CO2> PLLA-Air. The reason is that CO2 has higher gas solubility and diffusivity, and gas is more likely to dissolve in an amorphous polymer.Secondly, all the activation energy, thermal stability, lifetime and elasticity of scaffolds increased with the increasing sturation pressure. Enzyme degradation analysis showed that the enzymatic degradation preferentially occurred in the amorphous region of PLA. Scaffold with smaller pore size and higher porosity tend to have a slower degradation rate. For semicrystalline PLLA, the crystal phase contents in the PLLA-CO2 and PLLA-Air were improved. Moreover, it is observed that the PLLA-CO2 sacffolds treated at higher pressure have higher crystallinities and some rigid amorphous phase (4%-12%). While, the crystallinity of PLLA-Air scaffolds first increased and then decreased with the increasing saturation pressure and the rigid amorphous phase content was 0%. For amorphous PDLLA, there is no crystal phase in the PDLLA-CO2 even after foaming. Only a little of rigid amorphous phase (< 5%) was found in PDLLA-CO2.Lastly, cytotoxicity and cellular adherence of PLLA-CO2 scaffolds were assessed, which have better foamability and mechanical strength. Results showed that the scaffolds have good biocompatibility and the cytotoxicity of PLLA-CO2 scaffolds with smaller pore size in vitro is lower and beneficial for cell attachment and growth.In summary, this study might provide a better understanding of the influence of foaming pressure, foaming gas and PLA configurations on the pore morphology, crystallinity and rigid amorphous structure, thermal stability and mechanical property of microcellular PLA scaffolds. These findings would enable precise design and fabrication of PLA composite material scaffolds with controllable properties.