Femke Mathot

Chapter 7 122 Autografts were used as control group to test whether MSCs could improve outcomes of decellularized allografts up to a level equal to that of autografts. While an additional control group in which sham surgery is performed would also be interesting to have, it would require the undesirable and precious use of additional animals. Alternatively, outcomes of the operated side were normalized to the unoperated control side in order to relate the test- outcomes to normal nerve and muscle function. The significant differences between groups presented at 12 weeks and normalized after 16 weeks, insinuates that nerve regeneration in motor nerves in rats will occur after 12 weeks independently from the type of nerve repair. This finding might be correlated to the demonstrated finite survival of MSCs up to 29 days in vivo; it is suggested that MSCs significantly enhance nerve regeneration up to 12 weeks after which the superlative neuroregenerative capacity of rats takes over, due to the apoptosis of the MSCs. 42 The superlative neuroregenerative capacity of rats is a commonly described explanation and can be mitigated in a larger animal model. 26, 39 Absent significant differences when comparing cross-sectional tibial muscle areas is also a likely consequence of using a small animal model with small cross-sectional nerve areas, relatively leading to larger standard errors and less significant differences between groups. 31, 32 Future research should be performed on multiple time points in larger animal models with larger nerve gaps to potentially translate outcomes to humans. Considering the overall goal to improve outcomes of decellularized nerve allografts in clinical practice, clinical applicability should be considered when interpretating results. The use of autologous differentiated MSCs requires approximately 4-5 weeks of preparation time, against 2-3 weeks for undifferentiated MSCs. 16 Moreover, the costs of the differentiation cocktail required to differentiate MSCs into Schwann Cell-like cells are high and add to the costs of extended cell culture. Differences between undifferentiated an differentiated MSCs were not statistically significant in light of the analyzed factors, but undifferentiated MSCs improved functional outcomes of decellularized nerve allografts to a greater extent than differentiated MSCs. Taking all this in consideration, undifferentiated MSCs have the greatest potential for bench-to-bedside application. Hypothetically, at the day of presentation in a clinical setting, adipose tissue can be obtained using minimally invasive techniques from the patient with nerve injury, MSCs can then be derived from this tissue and cultured for approximately 2 weeks after which the MSCs can be dynamically seeded onto an off-the-shelf commercially available nerve allografts, 12 hours in advance of the nerve repair. Translation to a larger animal model to ensure the enhanced functional outcomes, study of the capacity of human MSCs to be seeded on clinically available nerve allografts and FDA approval are potential hurdles that need to be addressed prior to application of the presented strategy in clinical practice.