Tissue engineering approaches to improve peripheral nerve regeneration

Abstract

Peripheral nerve injuries show a prevalence of about 5% of traumatic injuries (approximately 300.000 cases per year in Europe) and are a frequent cause of hospitalization, displaying a major burden to patients, and the social health-care systems and the economy. Injuries to peripheral nerves often result in large defects in the continuity of the severed nerve. Bridging of a large defect with an autologous interfascicular nerve graft is considered to be the gold standard. Albeit it is best available treatment, transplantation of an autologous nerve graft does not always provide a satisfactory outcome. In this thesis several alternative approaches have been developed to improve peripheral nerve regeneration. Schwann cells are a crucial factor in peripheral nerve regeneration. Isolation, culture and re-implantation to the defect site have been proven to be challenging. Alternatives to native cultures are mesenchymal stem cells differentiated into Schwann cell-like cells. Chapter I illustrates the method -Extracorporeal Shockwave Treatment- to facilitate native Schwann cell isolation and culture, and to improve differentiation of mesenchymal stem cells into Schwann cell-like cells. Nerve conduit luminal fillers have been topic of discussion for many years. Ideas of an ideal luminal filler range from gels, to single fibres of different diameters and number, to composite gel/fibre fillers, multiple channels containing different growth factors and/or cells. In chapter II we investigated electrospinning as a method to align fibrin/PGLA fibres to create a biomimicking tissue-like material seeded with Schwann cell-like cells in vitro for potential use as an in vivo scaffold. Chapter III focuses on a novel nerve conduit material, its fabrication and functionalization. Due to its excellent biocompatibility silk fibroin has attracted considerable interest as a biomaterial for use as a conduit in peripheral nerve regeneration. We describe a novel procedure to produce silk fibroin nerve conduits: a braided tubular structure of raw Bombyx mori silk is subsequently degummed with a borate buffer system and processed with the ternary solvent CaCl2/H2O/ethanol, formic acid and methanol to improve its mechanical and topographical characteristics. Furthermore a protocol has been established to covalently bind laminin to silk fibroin utilizing carbodiimide chemistry, resulting in improved adhesion, viability and proliferation of Schwann cells.