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Microcomputed Analysis of Nerve Angioarchitecture after Combined Stem Cell Delivery and Surgical Angiogenesis to Nerve Allograft
Mana Saffari, MD1, Femke Mathot, MD1, Allen T. Bishop, MD2 and Alexander Y Shin, MD3, (1)Mayo Clinic, Rochester, MN, (2)Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN, (3)Orthopaedic Surgery, Div Hand Surgery, Mayo Clinic, Rochester, MN

Introduction: Detailed three-dimensional (3D) evaluation of microvasculature is evolving to be a powerful tool, providing mechanistic understanding of angiomodulating strategies. The aim of this study was to evaluate the microvascular architecture of nerve allografts after combined stem cell delivery and surgical angiogenesis in a rat sciatic nerve defect model.

Materials & Methods: In 25 Lewis rats, ten mm sciatic nerve gaps were repaired with (i) autografts, (ii) allografts, (iii) allografts wrapped in a pedicled superficial inferior epigastric artery fascia (SIEF) flap to provide surgical angiogenesis, combined with (iv) undifferentiated mesenchymal stem cells (MSC) and (v) MSCs differentiated into Schwann cell-like cells. At two weeks, vascular volume was measured using microcomputed tomography (micro CT), and percentage and volume of vessels at different diameters were evaluated to describe vascular distributions.

Results: Revascularization of untreated nerve allografts occurred from both host stumps and left the mid longitudinal section of the nerve avascular. Allografts augmented with angiogenesis showed increase in the mesh network of microvessels sprouting into the nerve towards the mid-section. This was further increased when angiogenesis was combined with undifferentiated MSCs, resulting in microvessels along the entire length of the nerve graft. Objective quantification using micro CT showed that the vascular volume was significantly greatest in allografts treated with undifferentiated MSCs and surgical angiogenesis combined, compared to all experimental groups (P<0.01 compared to autografts, P<0.0001 to allografts, P<0.05 to SIEF and SIEF combined with differentiated MSCs, respectively). Evaluation of the nerve angioarchitecture allowed for determination of the distribution of blood vessels in nerve sample groups. Volume and diameters of vessel segments in nerve allografts were enhanced by surgical angiogenesis. These distributions were further improved when surgical angiogenesis was combined with stem cells, with greatest increase found when combined with undifferentiated MSCs.

Conclusions: The interaction between vascularity and stem cells remains complex, however, this study provides some insight into its synergistic mechanisms. The combination of surgical angiogenesis with undifferentiated MSCs specifically, results in the greatest increase of revascularization, size of vessels, and stimulation of vessels to reach the middle longitudinal third of the nerve allograft.

Figure legend: Micro CT images of unoperated control nerve (A), autograft (B), allograft (C), and allograft+SIEF flap (D), combined with undifferentiated MSCs (E) or MSCs differentiated into Schwann cell-like cells (F).

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