Injectable Extracellular Matrix Hydrogels as Scaffolds for Spinal Cord Injury Repair

Abstract

Restoration of lost neuronal function after spinal cord injury (SCI) still remains a big challenge for current medicine. One important repair strategy is bridging the SCI lesion with a supportive and stimulatory milieu that would enable axonal rewiring. Injectable extracellular matrix (ECM)-derived hydrogels have been recently reported to have neurotrophic potential in vitro. In this study, we evaluated the presumed neuroregenerative properties of ECM hydrogels in vivo in the acute model of SCI. ECM hydrogels were prepared by decellularization of porcine spinal cord (SC) or porcine urinary bladder (UB), and injected into a spinal cord hemisection cavity. Histological analysis and real-time qPCR were performed at 2, 4, and 8 weeks postinjection. Both types of hydrogels integrated into the lesion and stimulated neovascularization and axonal ingrowth into the lesion. On the other hand, massive infiltration of macrophages into the lesion and rapid hydrogel degradation did not prevent cyst formation, which progressively developed over 8 weeks. No significant differences were found between SC-ECM and UB-ECM. Gene expression analysis revealed significant downregulation of genes related to immune response and inflammation in both hydrogel types at 2 weeks post SCI. A combination of human mesenchymal stem cells with SC-ECM did not further promote ingrowth of axons and blood vessels into the lesion, when compared with the SC-ECM hydrogel alone. In conclusion, both ECM hydrogels bridged the lesion cavity, modulated the innate immune response, and provided the benefit of a stimulatory substrate for in vivo neural tissue regeneration. However, fast hydrogel degradation might be a limiting factor for the use of native ECM hydrogels in the treatment of acute SCI.

Dose-Dependent Differential Effect of Neurotrophic Factors on In Vitro and In Vivo Regeneration of Motor and Sensory Neurons

“…While GDNF has already been reported to promote neurite outgrowth of both populations, FGF-2 was described to preferentially enhance motor neurite outgrowth when measuring the length of longest neurites [15]. Since reliable measurements of neurite outgrowth analysis in organotypic cultures are complicated [21], we used a semiautomatic analysis that works as an adaption of the Sholl method [17] to improve accuracy and reproducibility as shown in other works [22, 23]. Thus, the differences in methods and variables to quantify neurite outgrowth in these studies may in fact explain some controversies.…”

Extracellular matrix hydrogels from decellularized tissues: Structure and function

“…While injectability may be related to the viscoelastic properties (ECM pre-gel viscosity and gelation time), injectability has been independently confirmed in vitro and/or in vivo for heart [55, 60, 74–81], spinal cord [82], small intestine [26, 51], umbilical cord [63], skeletal muscle [63, 64, 83], tendon [59, 84], dermal [23], lung [49], liver [57], cartilage [70], urinary bladder [21, 22, 24, 82] and adipose [50, 67] ECM hydrogels with reported 18–27 gauge syringes or catheters. For example, porcine myocardial gel (6 mg/mL) was confirmed to be injectable through a 27 gauge catheter [75] , and then confirmed to be injectable via NOGA guided MyoSTAR catheter (27 gauge), which is the current gold standard delivery device used in cellular cardiomyoplasty procedures [75].…”

The characterization of decellularized human skeletal muscle as a blueprint for mimetic scaffolds

“…Understanding the degradation rate of a scaffolding material is meaningful in light of research that suggests that degradation rate can influence regeneration [63]. In this study, the in-vivo degradation rate of the human skeletal ECM, measured as the half-life, was evaluated using a subcutaneous implant in a mouse model.…”