Combinatorial Tissue Engineering Partially Restores Function after Spinal Cord Injury

Abstract

Hydrogel scaffolds provide a beneficial microenvironment in transected rat spinal cord. A combinatorial biomaterials based strategy provided a microenvironment that facilitated regeneration while reducing foreign body reaction to the 3-dimensional spinal cord construct. We used poly lactic-co-glycolic acid microspheres to provide sustained release of rapamycin from Schwann cell (SC)-loaded, positively charged oligopolyethylene glycol fumarate scaffolds. Three dose formulations of rapamycin were compared to controls in 53 rats. We observed a dose-dependent reduction in the fibrotic reaction to the scaffold and improved functional recovery over 6 weeks. Recovery was replicated in a second cohort of 28 animals that included retransection injury. Immunohistochemical and stereological analysis demonstrated that blood vessel number, surface area, vessel diameter, basement membrane collagen, and microvessel phenotype within the regenerated tissue was dependent on the presence of SCs and rapamycin. TRITC-dextran injection demonstrated enhanced perfusion into scaffold channels. Rapamycin also increased the number of descending regenerated axons, as assessed by Fast Blue retrograde axonal tracing. These results demonstrate that normalization of the neovasculature was associated with enhanced axonal regeneration and improved function after spinal cord transection.

Defining spatial relationships between spinal cord axons and blood vessels in hydrogel scaffolds

“…We have previously demonstrated that the use of OPF+ scaffolds containing rapamycin eluting microspheres were able to reduce the fibrotic reaction and improve functional motor recovery over 6 weeks (17). Here we sought to investigate the relationship of regenerating axons to the vasculature through OPF+ scaffolds containing Matrigel only (MG), Schwann cells only (SC), or Schwann cells with rapamycin (RAPA).…”

“…Scaffolds loaded with rapamycin-releasing microspheres were previously found to promote peripheral nerve regeneration when implanted in the early phase of sciatic nerve injury (32). Our lab has previously demonstrated that administration of rapamycin resulted in improved functional recovery following spinal cord transection, which was linked to improved axonal regeneration, possibly through increased BDNF and GDNF secretion of transplanted SCs (17). Although rapamycin was found to promote secretion of nerve growth factors, and has been suggested for application in peripheral nerve regeneration therapy (33, 34), our study found a significantly greater number of myelinated and unmyelinated axons per channel in the SC group, which were more clustered compared to the MG and RAPA group.…”

“…Drug-eluting microspheres were fabricated using a water-in-oil-in-water double emulsion and solvent evaporation technique, as we have previously described (17). Briefly, 250 mg of 50:50 D,L-poly-lactic-co-glycolic acid (PLGA) (50:50 DLG 4A, molecular weight 29 kDa, Evonik Industries AG, Essen, Germany) were dissolved in 1 ml of methylene chloride.…”

“…It may also reduce fibrosis in reaction to various implanted synthetic materials (15, 16). Loading OPF+ scaffolds containing Schwann cells with rapamycin releasing microspheres was recently shown to reduce the foreign body response and promoted functional recovery after spinal cord transection in rats and demonstrated the close relationship between revascularization and axonal regeneration following spinal cord transection (17).…”

Promoting neuronal outgrowth using ridged scaffolds coated with extracellular matrix proteins

“…This regeneration can be further improved by loading the channels with GDNF-secreting Schwann cells, leading to modest functional recovery [5]. We have also shown that the OPF+ material can be modified by incorporating the anti-fibrotic drug rapamycin in PLGA microspheres [27]. OPF+ multichannel scaffolds containing rapamycin microspheres were also combined with Schwann cells to help promote functional recovery following SCI.…”