Electrospraying Electrospun Nanofiber Segments into Injectable Microspheres for Potential Cell Delivery

Nanofiber microspheres have attracted a lot of attention for biomedical applications because of their injectable and biomimetic properties. Herein, we report for the first time a new method for fabrication of nanofiber microspheres by combining electrospinning and electrospraying and explore their potential applications for cell therapy. Electrospraying of aqueous dispersions of electrospun nanofiber segments with desired length obtained by either cryocutting or homogenization into liquid nitrogen followed by freeze-drying and thermal treatment can form nanofiber microspheres. The microsphere size can be controlled by varying the applied voltage during the electrospray process. A variety of morphologies were achieved including solid, nanofiber, porous and nanofiber microspheres, and hollow nanofiber microspheres. Furthermore, a broad range of polymer and inorganic bioactive glass nanofiber-based nanofiber microspheres could be fabricated by electrospraying of their short nanofiber dispersions, indicating a comprehensive applicability of this method. A higher cell carrier efficiency of nanofiber microspheres as compared to solid microspheres was demonstrated with rat bone marrow-derived mesenchymal stem cells, along with the formation of microtissue-like structures in situ, when injected into microchannel devices. Also, mouse embryonic stem cells underwent neural differentiation on the nanofiber microspheres, indicated by positive staining of β-III-tubulin and neurite outgrowth. Taken together, we developed a new method for generating nanofiber microspheres that are injectable and have improved viability and maintenance of stem cells for potential application in cell therapy.