Improvisations to electrospinning techniques and ultrasonication process to nanofibers for high porosity: Ideal for cell infiltration and tissue integration

Electrospinning is considered the most versatile for fabricating nanofibers in tissue engineering applications. Therefore, a bio-inspired morphology (e.g., micro/nanofibers) is highly desirable in which the cells can easily penetrate and increase their number. This can finally lead the synthesized material to be an integral part of a biological system. However, due to 3-D porosity at the surface level and highly compact nature deep inside, these nanofibers obviate cellular infiltration, failing to use them as potential candidates for subsequent tissue integration. Different strategies are put forward for loosening the fibers during and/or after electrospinning to promote cellular penetration into nanofibers. This review will focus on identifying those improvisations made to basic electrospinning techniques yielding highly-porous nanofibers, having immense internal permeability, and ultimately resulting in perfect cell growth. The paper will emphasize on creating advanced porosity in the nanofibers using salt-leaching, co-electrospinning, air-impedance, cold-plate electrospinning, and ultrasonication to loosen the individual fibers. Furthermore, this review will give the overall picture of using ultrasonication to yield highly porous nanofibers and its role in modifying as-spun fibers for future technological applications.