Microstructural characteristics and crystallization behaviors of poly(l-lactide) scaffolds by thermally induced phase separation

摘要

In this study, poly(l-lactic acid) (PLLA) was prepared by four typical approach systems, namely, solid-liquid phase-separation processes from PLLA-dioxane at -80°C, PLLA-dioxane-water at -80°C, PLLA-tetrahydrofuran (THF) at -80°C, and PLLA-THF at 18°C. The microstructural characteristics and crystallization behaviors of PLLA were investigated by scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, and Fourier transform infrared spectroscopy. In the PLLA-dioxane binary system and PLLA-dioxane-water ternary system, the solvent froze immediately after quenching to a low temperature, and this restricted the PLLA chain arrangement. Thus, the PLLA amorphous phase dominated in the scaffolds, and solid-walled structures were produced. THF was liquid throughout the entire process, which enabled free PLLA chain arrangement and further crystallization. Single crystals aggregated by crystal nucleation and growth at a critical temperature (T_c) of 18°C; this resulted in its most common and stable polymorph, the α form. However, α′-form crystals, which were assumed to be limit-disordered crystals of the α form, were produced at a low T_c (-80°C). Scaffolds with a plateletlike structure were produced at a T_c of 18°C, whereas a nanofibrous network was obtained at -80°C. PLLA crystallization competed with phase separation; thus, the crystal structure and scaffold morphology depended on the codevelopment of these two processes. Finally, the effects of the scaffold morphologies on the cell behaviors were studied, and the nanofibrous scaffold was found to have better cell adhesion and viability than the other three scaffolds.