After traumatic injury to peripheral nerves, recovery is poor. The current standard of care is coaptation of the proximal and distal ends of the nerve, or if the gap between the two ends is too large, the use of autologous nerve grafts. The insufficiencies of donor nerve in both diameter and number of available nerves has led to the development of nerve guidance channels, engineered constructs including both artificial and natural materials. However, most designs still underperform compared to autografts because they lack Schwann cells, the glial, or support cells of peripheral nerve. These cells deliver growth factors, substrate glycoproteins, and topographical cues that potentiate axon regeneration following injury, and nerve guidance channels that possess Schwann cells outperform those that lack them. One of the recent advances in guidance channel design is the incorporation of longitudinally aligned, electrospun fibers on the cell-length scale that direct the growth of regenerating axons by contact guidance. Electrospinning is a method of fabricating nano- and microfibers that resemble native extracellular matrix, and the development of these biomimetic constructs has accelerated advances in engineering of multiple tissue types. Combining the directional guidance of micro- and nanofibers by pre-seeding them with Schwann cells seems a straightforward strategy, but electrospun fiber matrices are disadvantaged by small pore sizes that limit the depth of cell penetration to only one or two cell diameters, leaving much of the electrospun matrix devoid of cells. Here we propose solving this problem by developing a means to integrate Schwann cells into fibers produced by a process similar to electrospinning, called jetting. Jetting eliminates th high forces that reduce cell viability when electrospinning cells into fibers. If successful, this process would disperse cells evenly throughout an aligned-fiber matrix. The goal of this project is to provide scientific evidence needed to allow for the rational development of microfibers with integrated Schwann cells.
In specific aim 1, we fabricate and test a novel side-by-side biphasic fiber design. One layer encapsulates Schwann cells as the fiber is made and rapidly degrades to release them. The second layer, produced simultaneously in this biphasic jetting process, degrades much more slowly and remains to provide a topographical cue to the released cells. Fiber morphology, diameter, degradation, and cell viability and proliferation are tested at all stages of development.
In aim 2, we test the ability of scaffolds containing prototype fibers with integrated Schwann cells to improve regeneration in a sciatic nerve gap injury model. After 1.5 or 4 months have elapsed following implantation, the number of transplanted versus native Schwann cells in each graft is determined. Then the number of axons and the distance they have grown in is assessed and compared to grafts containing both autologous nerve and aligned electrospun fibers. It is hoped that this project will serve to develop an enabling technology toward the improvement regeneration in the nervous system.
Nerve grafts are used to treat large nerve injuries. Because of inadequate number and size of grafts from the patient, artificial nerve grafts are needed. However, despite the best designs, artificial nerve grafts often produce results inferior to natural grafts. This is likely due to the absence of Schwann cells, the support cells that occur naturally in nerve. Here we propose how to combine Schwann cells with aligned fibers that guide nerve cells, to produce better nerve regeneration.
| Miller, Ryan J; Chan, Cheook Y; Rastogi, Arjun et al. (2018) Combining electrospun nanofibers with cell-encapsulating hydrogel fibers for neural tissue engineering. J Biomater Sci Polym Ed 29:1625-1642 |
