Electrospun Fiber - Hydrogel Composites for Nucleus Pulposus Tissue Engineering
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Electrospun Fiber - Hydrogel Composites for Nucleus Pulposus Tissue Engineering Daniel G. T. Strange1, Khaow Tonsomboon1 and Michelle L. Oyen1 1 Cambridge University Engineering Department, Trumpington St, Cambridge, CB2 3BU, United Kingdom ABSTRACT New materials are needed to replace degenerated intervertebral disc tissue and to provide longer-term solutions for chronic back-pain. Replacement tissue potentially could be engineered by seeding cells into a scaffold that mimics the architecture of natural tissue. Many natural tissues, including the nucleus pulposus (the central region of the intervertebral disc) consist of collagen nanofibers embedded in a gel-like matrix. Recently it was shown that electrospun micro- or nano-fiber structures of considerable thickness can be produced by collecting fibers in an ethanol bath. Here, randomly aligned polycaprolactone electrospun fiber structures up to 50 mm thick are backfilled with alginate hydrogels to form novel composite materials that mimic the fiber-reinforced structure of the nucleus pulposus. The composites are characterized using both indentation and tensile testing. The composites are mechanically robust, exhibiting substantial strain-to-failure. The method presented here provides a way to create large biomimetic scaffolds that more closely mimic the composite structure of natural tissue. INTRODUCTION Tissue engineering offers a paradigm shift in the treatment of back pain. Engineered intervertebral discs could replace degenerated tissue and overcome the limitations of current treatments, which significantly alter the biomechanical properties of the spine. The center of the disc, the nucleus pulposus, is a collagen-proteoglycan composite with a substantial bound water content. It can resist large compressive loads. The nucleus pulposus is a mechanically functional tissue and a successful tissue engineered construct will need to demonstrate adequate mechanical properties. New materials are needed to act as scaffolds for new tissue during the regenerative process, providing a template for new growth. By mimicking the structures present in the intervertebral disc, we may be able to create materials that support tissue regeneration while maintaining comparable mechanical function. Hydrogels, which have a similar water content to native tissue, have been frequently considered as substitutes for the nucleus pulposus but they lack much of the structural complexity and mechanical performance of the native tissue. Electrospun nanofibers that mimic the fiber structure of collagen have been previously used to reinforce hydrogels for arterial tissue engineering [1]. However, with conventional electrospinning techniques it is difficult to achieve material thicknesses greater than 1 mm, preventing this technique from being applied to larger tissues like the nucleus pulposus. Hong and Kim [2] recently demonstrated that it was possible to create porous electrospun polycaprolactone (PCL) micro- or nano-fiber structures over 20 mm thick by immersing the ground electrode of the el
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