Femke Mathot

10 General discussion and future perspectives 175 BENCH TO BEDSIDE TRANSLATION Considering the discussed gene expression profiles and their effect on angiogenesis, nerve regeneration and functional outcome, no scientifically funded specific preference can be expressed for either undifferentiated or differentiated MSCs. Usage of undifferentiated MSCs requires approximately half of the preparation time and even less than half of the costs of differentiated MSCs. Like previously described, applying a combination of differentiated and undifferentiated MSCs to processed nerve allograft might have undiscovered potential, but will reduce the ease of MSC-seeding per definition since both culturing techniques would need to be combined. As clinical applicability is crucial when estimating future potential of both cell-types, usage of undifferentiated MSCs is advised for future studies. Anticipatory to a clinical setting, we envision that adipose tissue is derived from patients with peripheral nerve injury as soon as possible after trauma, using a minimally invasive technique which can be performed on the ER or outpatient clinic. MSCs are obtained from this adipose tissue and cultured for approximately 2 weeks. Thereafter, the MSCs are dynamically seeded for 12 hours onto an off-the-shelf available nerve allograft, immediately prior to surgery. To test whether this would be technically possible in the future, we examined in chapter 8 if human MSCs can be dynamically seeded onto nerve substitutes currently available in clinic; the NeuraGen® Nerve Guide and the Avance® Nerve Graft. Surprisingly, MSCs adhered significantly more efficient to the surface of NeuraGen® Nerve Guides. This is attributed to the adherence of MSCs to both the inner and the outer surface of the nerve guides, while MSCs only adhered to the outer surface of Avance® Nerve Grafts as expected. Although the adherence of MSCs on the inner surface of NeuraGen® Nerve Guides hypothetically leads to enhanced concentrations of trophic factors that reach the regeneration site in NeuraGen® Nerve Guides, in vivo studies should indicate whether the MSC adherence location truly has implications for their effect on axon regeneration. The interaction between (undifferentiated) MSCs and both clinically available nerve substitutes resulted in an altered gene expression profile of the MSCs, described in chapter 9 . Most trends of the expression curves were relatable to physiological Wallerian degeneration and axon regeneration processes, implying potential benefit of the addition of MSCs to regenerating nerves. 56 Contrary to expectations considering the biological material components of both nerve substitutes, MSCs on NeuraGen® Nerve Guides demonstrated most gene expression adjustments appropriate for nerve regeneration. These results are hopeful, but like demonstrated with the rat MSCs in chapters 4, 5 and 6, the in vitro findings might not be completely relatable to in vivo results. Due to the neural tissue composition of Avance® Nerve Grafts, the interaction with the MSCs and the micro-environment might be more significant than NeuraGen® Nerve Guides. Contrarily, effects of MSCs on NeuraGen® Nerve Guides might be more prominent since part of the adhered cells lie protected on the inner surface, being closer to the regenerating nerve and avoiding mechanical stress during surgery. Besides this in vitro analysis, the result of the interaction between MSCs and the Avance® Nerve Graft and the NeuraGen® Nerve Guide on a gene-expression level should therefore be analyzed in vivo as well.