Multi-layered macroporous three-dimensional nanofibrous scaffold via a novel gas foaming technique

In the past decade, considerable efforts have been made to fabricate the biomimetic scaffolds from electrospun nanofibers for tissue engineering applications. However, one of the major concerns with electrospun nanofibrous scaffolds is the densely packed fibers in two-dimensional (2-D) array which impedes their applicability in tissue regeneration. To overcome this problem, a simple and facile post-electrospinning procedure was developed to modify a densely packed 2-D electrospun membrane into low density three-dimensional (3-D) scaffolds. In this strategy, an electrospun nanofibrous mat was immersed in a sodium borohydride (SB) solution. The interconnected pores of a mat are filled with the SB solution driven by capillary forces where it undergoes hydrolysis to produce hydrogen gas. The in situ generated gas molecules form clusters to minimize the free energy resulting in pore nucleation that reorganizes the nanofibers to form a low density, macroporous, spongy and multi-layered 3-D scaffold. Electrospun mats of various polar and non-polar polymers were subjected to post-electrospinning process to monitor the fabrication process. It has been found that the solvent for sodium borohydride (either water or methanol) played a crucial role in post-electrospinning process. Only the electrospun mat of polar polymers were amended into 3-D architecture using aqueous SB solution while methanol solution was found equally effective for both polar and non-polar polymers. Moreover, the fabrication process was fast in methanol solution compared to an aqueous solution due to the rapid liberation of hydrogen gas from the methanolysis reaction compared to the hydrolysis reaction. This process will reveal a new approach for the fabrication of a three-dimensional, low-density, nanofibrous materials for biomedical and industrial applications using a wide variety of polymers.