In vitro and in vivo evaluation of polySia and polySia based hydrodel in terms of survival, proliferation and differentiation of primary neurons and glial cells, immunological reaction and nerve regeneration

The recent study follows the aim to develop a novel, biocompatible, and bioresorbable material for peripheral nerve tissue engineering based on polysialic acid (polySia), a homopolymer of alpha 2, 8-linked sialic acid residues. To reach this goal, at first protocols for efficient coating of cell culture surfaces with soluble polySia were established. In addition, primary cells of the central and peripheral nervous system such as neonatal and adult Schwann cells, neural progenitor cells, dorsal root ganglionic neurons and embryonic spinal motoneurons which are all possible candidates for reconstructive therapies were cultured on polySia substrates. Respective cell cultures were evaluated with regard to cell survival and cell proliferation. PolySia turned out to be stable under cell culture conditions. Induced degradation of PolySia and its degradation products had no negative effects on cell cultures. Furthermore, polySia used as a cell culture substrate revealed its compatibility for the chosen several rat cell types derived from embryonic, postnatal and adult tissue of the central and peripheral nervous system. In a second attempt, a polySia based hydrogel was formed by cross-linking with diepoxyoctane. The surface microstructure of the hydrogel was characterized by means of scanning electron microscopy and maintained the topography of polySia reported elsewhere. PolySia hydrogel is completely degradable by endosialidase enzyme which may help to avoid explantation surgery of nerve guides after tissue recovery when used in reconstructive therapies. Viability assay demonstrated that the soluble components of polySia hydrogel did not cause any toxic effect on cultured Schwann cells in vitro. Moreover, green fluorescence protein (GFP) transfected neonatal and adult rat Schwann cells, neural progenitor cells as well as dorsal root ganglia cells (unlabelled) were able to adhere and grow on polySia hydrogel modified with poly-L-lysine, poly-L-ornithine-laminin or collagen. Water soluble tetrazolium salt assay (WST-1) revealed that modification of the hydrogel significantly improved cell adhesion and viability of these primary neural and glial cells. An in vivo study was performed to assess the impact or contribution of polySia and polySia based hydrogel in peripheral nerve regeneration and immunological reaction. Macroscopic analysis of the explanted silicone nerve guides three weeks after surgery demonstrated that all animals transplanted with a mixture of soluble polySia and Matrigel inside the nerve guides showed tissue cable regeneration bridging a 10 mm gap in sciatic nerves of adult rats. In contrast, none of the animals transplanted with nerve guides filled with polySia hydrogel exhibited tissue cable growth. Furthermore, immunohistological analysis of the regenerated tissue indicated that in vivo introduction of polySia or polySia based hydrogel did not change immunological reaction as compared to the control transplanted with matrigel-filled silicone nerve bridges. These results prove the immunologic inertness of polySia in vivo and demonstrate its biocompatibility and potential to be used as scaffold material in peripheral nerve tissue engineering.