Femke Mathot

11 Summary and Dutch summary 189 per time point) isometric tetanic force, compound muscle action potentials, muscle mass, histology and immunofluorescence analyses were performed. Both cell-types significantly improved part of the functional outcomes of processed allografts and equaled the majority of autograft results at 12 weeks of follow-up. Differences between undifferentiated and differentiated MSCs were not statistically significant. Considering the increased preparation time and costs of differentiated MSCs, undifferentiated MSCs are more clinically applicable. In chapter 8 a preliminary but essential step towards translating the use of dynamic seeding into a clinical setting is described. The purpose of the study was to examine if human adipose derived MSCs could be dynamically seeded onto the clinically available Avance® Nerve Graft (processed nerve allograft) and the NeuraGen® Nerve Guide (hollow collagen conduit). Viability of MSCs, seeding efficiency and cell distribution were determined for both nerve substitutes. The viability of MSCs was not negatively affected by the composition of the nerve substitutes. The optimal seeding duration was 12 hours, leading to a significant higher seeding efficiency of NeuraGen® Nerve Guides compared to Avance® Nerve Grafts (94% versus 65% of the administered dose of MSCs). This was hypothetically related to the cell distribution on both nerve substitutes; dynamic seeding led to a uniform distribution of MSCs over the surfaces of both nerve substitutes, but only to adherence of MSCs on the inner surface of the NeuraGen® Nerve Guide. These results demonstrate that human MSCs can be effectively and efficiently seeded on commercially available nerve autograft substitutes in a timely fashion. The interaction between human adipose derived MSCs and the extracellular matrix of the clinically available Avance® Nerve Grafts and NeuraGen® Nerve Guides was assessed in chapter 9. Quantitative PCR analyses onmultiple time points (up to 21 days) after MSC-seeding demonstrated the course of the expression of neurotrophic (NGF, GDNF, PTN, GAP43, BDNF), myelination (PMP22, MPZ), angiogenic (VEGF-a, CD31), extracellular matrix (COL1A1, COL3A1, FBLN1, LAMB2) and immunoglobulin (CD96) genes. The interaction resulted in a change and mostly an upregulation of the expression of numerous genes important for nerve regeneration over time. Despite the absence of micro-environmental signals in this in vitro study, the (timing of) upregulation of most genes could be correlated to processes occurring during Wallerian degeneration and axon regeneration of injured peripheral nerves. It was hypothesized that the biological composition of the Avance® Nerve Grafts (i.e. neural tissue) would lead to more expression of neurotrophic genes, but the in vitro interaction of MSCs with the NeuraGen® Nerve Guide was greater, particularly in the long-term results. These outcomes suggest that clinically available nerve autograft substitutes could benefit from the addition of MSCs. In chapter 10 , the main findings of this thesis are described and placed in a broader perspective. Suggestions for future research are illustrated and substantiated. By enhanced expression of trophic factors leading to increased vascularization and axon regeneration, dynamic seeding of MSCs leads to improved functional outcomes of decellularized allografts. Seeding of undifferentiated MSCs is more cost-efficient than differentiated MSCs and can be applied to clinically available nerve graft substitutes.