Fabrication and characterization of poly(l-lactic acid) 3D nanofibrous scaffolds with controlled architecture by liquid–liquid phase separation from a ternary polymer–solvent system

Poly(l-lactic acid) (PLLA) three-dimensional (3D) scaffold with macro/micropores and nanofibrous structure was fabricated by phase separation from a ternary PLLA/dioxane/water system. The pore size was mainly determined by the coarsening effects in the phase separation process, while the nanofibrous structure was due to the formation of PLLA microcrystallite domains in the gelation process. Increasing the gelation temperature or the content of water in the mixed solvent system, the pore size definitely increased and macropores up to 300 μm were observed. However, coalescence of nanofibers occurred, even platelet-like structure appeared at gelation temperatures higher than 12 °C or the proportion of water exceeded 12%. X-ray diffraction (XRD) and Differential Scanning Calorimetry (DSC) analyses demonstrated that the crystallinity degree increased with increasing the gelation temperature or the non-solvent volume ratio in the mixed system. Moreover, the results indicated that α′ was mainly corresponding to the nanofibers structure, while α crystal was detected in the platelet-like structure. Scanning electron micrograph (SEM) and methyl thiazolyl tetrazolium (MTT) assays indicated that the nanofibrous scaffold provided a better attachment and viability of MSCs (rat derived mesenchymal stem cells) than the platelet-like scaffold.