Electrospinning 3D Scaffolds for use in Neural Tissue Engineering
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Electrospinning 3D Scaffolds for use in Neural Tissue Engineering Rachel Martin1, M. E. Mullins1, F. Zhao2, Zichen Qian2 1 2
Department of Chemical Engineering, Michigan Technological University, Houghton, MI Department of Biomedical Engineering, Michigan Technological University, Houghton, MI
ABSTRACT Polymer nanofiber scaffolds for use in neural tissue engineering have been fabricated via electrospinning of poly-L-lactic acid (PLLA) directly onto a 3D printed support. Previously, the investigators have shown success in promoting the directed growth of neural axons on highly aligned PLLA substrates both in vitro and in vivo. However, one criticism of the earlier in vitro studies is that by spinning fibers on a flat, two-dimensional surface, the growth of the axons is restricted to one plane. Thus the axon-to-fiber attachment may not be the sole mechanism for aligning the growth of the axons along the fibers, and the channels between the fibers and the substrate could contribute to the results. Using 3D-printing, elevated or “bridge” spinning stages were made with supports at varying heights, allowing the fibers to be suspended 2 to 5 mm above the substrate surface in different configurations. This 3D structure promotes better access of in vitro cell cultures on the fibers to the growth media during incubation, reduces substrate effects, allows more degrees of freedom for axonal growth, and more closely simulates the growth environment found in vivo. Using these 3D stages, we have electrospun free-standing, highly-aligned pure PLLA fiber scaffolds. We are exploring spinning coaxial fibers with a PLLA sheath and a second core polymer. These coaxial fiber scaffold structures offer additional opportunities for in situ delivery of growth agents and/or electrical stimulation for improved axonal growth results. INTRODUCTION Previous research using highly aligned PLLA fibers spun on flat, 2-D coverslips proved successful during in vitro studies in aligning neural outgrowth of the axons from chick dorsal root ganglia (DRG)[1]. It was found that the axons grew along the aligned fibers in a parallel fashion, which is important if directed axonal outgrowth from neurons is to be achieved in vivo. In addition, in vivo rat studies were performed at the Kennedy-Krieger Institute of Johns Hopkins University[2]. A high percentage of spinal cord regeneration in rats who had suffered a surgically severed spine was observed. However, Hind Limb Motor Function (HLMF) tests produced lower scores than anticipated, indicating that the desired degree of neural reconnection was not achieved[2]. One criticism of the previous research is that the success of the in vitro studies may not be solely due to the alignment of the nanofibers, since the fibers were spun onto a flat surface, thus restricting the outgrowth of axons within a 2D plane. However, the nanofiber scaffolds used for the in vivo studies were constructed within a 3-dimensional tubular structure. In this configuration, in addition to axonal growth along the fibers, the axons may a
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