Defining Spatial Relationships Between Spinal Cord Axons and Blood Vessels in Hydrogel Scaffolds

Abstract

Spinal cord injury (SCI) results in lifelong paralysis due to the poor regenerative capability of the central nervous system and the hostile microenvironment that is created from processes such as inflammation, scarring, axonal dieback, and demyelination. Hydrogel scaffolds facilitate a permissive regenerative environment and overcome these barriers by reducing scarring. One important other consideration for axonal regeneration is the availability of nutrients and oxygen, making it crucial to further investigate vascularization characteristics in the regenerating spinal cord.We previously described the close relationship between blood vessel formation and axonal regeneration. In this study, we focused on identifying the vascular -axonal relationship, as well describing novel techniques to analyze their interactions after a complete T9 spinal cord transection in rats. Following implantation of positively charged oligo-polyethylene glycol fumarate (OPF+) scaffolds containing Matrigel-only (MG), Schwann cells (SCs), or SCs with rapamycin-eluting poly-lactic-co-glycolic acid (PLGA) microspheres (RAPA), stereological methods were applied to measure core area, blood vessel number, volume, diameter, inter-vessel distances, total vessel surface and cross-sectional areas, and radial diffusion distances in each group 6 weeks after implantation.Immuno-histochemical and stereological analysis demonstrated a significantly larger core area in the RAPA group and found a total of 2,494 myelinated and 4,173 unmyelinated axons at 10 micron circumferential intervals around 708 individual blood vessel profiles within scaffold channels. We found that axon number and surface density in the SC group exceeded that seen in the MG and RAPA groups and that higher axonal densities correlated with smaller vessel crosssectional areas. Generally, axons were concentrated within a concentric distance of 200 microns

Comparing natural hydrogels to self-assembling peptides in spinal cord injury treatment: a systematic review

“…In total, 23 were excluded at this stage and only one record was selected for full-text review (Figure 1). Of the 23 articles excluded, 18 were because they did not evaluate a natural hydrogel in their study, [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] and five because they had not administrated a SAP in the study. [44][45][46][47][48] According to the single record included (Table 1), axonal regeneration of the administrated scaffolds was reported individually based on the type and the combination of scaffolds.…”

Open spaced ridged hydrogel scaffolds containing TiSAMP surface chemistry promotes regeneration and recovery following spinal cord injury

“…Histological and immunohistological analysis of tissue samples is a staple in neuroscience and regenerative medicine. After therapeutic intervention, such as after implantation of biomaterials, many aspects such as axon regeneration, immune infiltration, scarring, infiltration of endogenous cells, vascularization, and tissue preservation need to be measured 11,31–33,35 . The in-depth analysis of these parameters using manual methods is time consuming.…”

“…Rat Schwann cells were harvested from the sciatic nerve of 2-5 day of Sprague Dawley pup as previously described 11,31,32,37,38 . The cells were cultured in DMEM/F12 containing 10% fetal bovine serum, 100 U/mL Antibiotic-Antimycotic, 2 μM Forskolin (Sigma), 10 ng/mL neurgulinin-1 at 5% CO2 and 37°C.…”

“…While enhancement of axon regeneration is an important goal for treatment of SCI, any modifications (chemical or architectural) to implanted polymer scaffolds should not lead to increased negative side effects. Foreign body reactions leading to inflammation and scarring have been a long concern for neuroprosthetics and biomaterials 31,32,43,44 . The cell and protein attractive surface may lead to greater cell infiltration into the scaffold resulting in enhanced inflammation or fibrosis/scarring.…”

“…When fabricated in a multichannel design it can reduce scarring and cyst formation and can induce greater axon outgrowth than poly(lactic-co-glycolic acid) (PLGA) and poly(caprolactone fumarate) (PCLF) based scaffolds 26,27 . OPF can be easily utilized for combinatorial therapy by combining them with cells, drug eluting microspheres, extracellular matrix (ECM) proteins, or modifying the material with additional characteristics such as a positive charge or improved electroconductivity 11,[26][27][28][29][30][31][32][33] . All these modifications aim to improve regeneration and recovery following SCI.…”