Femke Mathot

11 Summary and Dutch summary 187 SUMMARY In the general introduction, chapter 1 , the aims and scope of this thesis are elucidated. The overall goal of this thesis is to improve the results of autograft substitutes like processed nerve allografts and nerve conduits when used in peripheral nerve repair. MSCs are hypothesized to possess regenerative capacities beneficial for nerve regeneration in these nerve substitutes, which is most plausibly caused by their secretion of trophic factors. As Schwann cells are essential for the function and regeneration of nerves by excreting numerous trophic factors, MSCs differentiated into Schwann cell-like cells might excrete enhanced levels of trophic factors leading to improved nerve regeneration. With this thesis, we literally strained every nerve to determine if the addition of differentiated and undifferentiated adipose derived MSCs to nerve substitutes could provoke the desired improvement in peripheral nerve regeneration. In chapter 2 a reviewof the currently available literaturewas performed to create the fundament for our experimental research. An overview of the current available MSC-differentiating methods is provided, delivery strategies and cell dosing are discussed and previous in vitro and in vivo outcomes of naïve and differentiated MSCs are described. Optimal delivery and dosing of (differentiated) MSCs has not been explored extensively, but dynamic seeding seems to deliver undifferentiated MSCs in a timely and non-traumatic manner. The neural induction of MSCs by chemicals combined with growth factors is the preferred and most extensively described method to obtain Schwann cell-like differentiation. Although differentiated MSCs demonstrated more potential in vitro compared to undifferentiated MSCs, their beneficial effect has not been convincingly confirmed in previous in vivo studies. Since differentiation of MSCs requires extra preparation time and costs, convincing in vivo results are required to determine which type of MSCs has most clinical potential. Chapter 3 focuses on the development of a delivery strategy that is applicable to both undifferentiated and differentiated MSCs. To test whether differentiated MSCs could be dynamically seeded comparable to undifferentiated MSCs, the experimental set-up of the described study comprised multiple samples of 1x10^6 (undifferentiated or differentiated) MSCs that were placed in a conical tube containing a processed nerve graft, which was rotated for either 6, 12 or 24 hours. Viability, seeding efficiency and cell distribution on the outer surface of the nerve allografts were evaluated. We concluded that differentiated MSCs can be dynamically seeded, leading to a similar cell-distribution as seeded undifferentiated MSCs. Twelve hours of seeding was estimated to provide the most efficient cell adherence for both cell-types, but differentiated MSCs had a significantly higher cell adherence than undifferentiated MSCs (95% versus 80%). This might indicate that differentiation of MSCs improves in vitro cell adherence to processed nerve allografts. To understand the biological differences of undifferentiated and differentiated MSCs before and after seeding onto processed nerve allografts, the gene expression profiles of both cell-types are compared in chapter 4 . Gene expression of both cell-types was quantified by quantitative polymerase chain reaction (qPCR) analysis of neurotrophic, angiogenic,