Vascularization Strategies for Peripheral Nerve Tissue Engineering

Abstract

Vascularization plays a significant role in treating nerve injury, especially to avoid the central necrosis observed in nerve grafts for large and long nerve defects. It is known that sufficient vascularization can sustain cell survival and maintain cell integration within tissue-engineered constructs. Several studies have also shown that vascularization affects nerve regeneration. Motivated by these studies, vascularized nerve grafts have been developed using various different techniques, although donor site morbidity and limited nerve supply remain significant drawbacks. Tissue engineering provides an exciting alternative approach to prefabricate vascularized nerve constructs which could overcome the limitations of grafts. In this review article, we focus on the role of vascularization in nerve regeneration, discussing various approaches to generate vascularized nerve constructs and the contribution of tissue engineering and mathematical modeling to aid in developing vascularized engineered nerve constructs, illustrating these aspects with examples from our research experience. Anat Rec, 301:1657-1667, 2018. © 2018 The Authors. The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.

Keywords: degeneration; peripheral nerve; regeneration; therapies; vascularization.

Figure 1

Microcirculation system of a peripheral nerve. The extrinsic vessels (EV) and branch radicular vessels (RV) supply the intrinsic circulation of the vasa nervorum. The intrinsic circulation consists of longitudinally oriented vessels that course to the perineurium (Peri) (Lundborg and Hansson, 1988).

Figure 2

Self‐alignment of HUVECs and formation of tube‐like structures within tethered collagen gels. Confocal micrographs (A(i)) and immunofluorescence images (A(ii)) show aligned HUVECs forming vascular networks after 2, 4, and 8 days in culture, z‐distance 20 μm, step size 1 μm. Three‐dimensional image analysis was used to calculate the angle of deviation between HUVEC/tube alignment and the longitudinal axis of the gel (B). Boxes show interquartile range and median values, whiskers indicate maximum and minimum angles (N = 3 gels). The length of tube‐like structures (C), shape factor which determine how round the object is (values closer to 1 indicate more rounded shape) (D) and surface area (E) were compared in 2‐day, 4‐day, and 8‐day cultured gels. Graphs show mean value ± SEM. (N = 3 gels). Scale bars in (A(i)) = 120 μm and in (A(ii)) = 100 μm.

Figure 3

Aligned endothelial cells within collagen gels support and guide neurite growth in vitro. Neurites from explanted rat DRG (A) and from dissociated DRG neurons (B) elongated along the longitudinal axis of the gel and were associated with the aligned endothelial cells. Scale bars in A, B = 100 μm.