Mechanical Cues in Spinal Cord Injury

Mechanical characteristics of spinal cord tissue by indentation

The mechanical properties of brain and spinal cord tissue have proven to be extremely complex and difficult to assess. Due to the heterogeneous and ultra-soft nature of the tissue, the available literature shows a large variance in mechanical parameters derived from experiments. In this study, we performed a series of indentation experiments to systematically investigate the mechanical properties of porcine spinal cord tissue in terms of their sensitivity to indentation tip diameter, loading rate, holding time, ambient temperature along with cyclic and oscillatory dynamic loading. Our results show that spinal cord white matter tissue is more compliant than grey matter tissue with apparent moduli of 128.7 and 403.8 Pa, respectively. They show similar viscoelastic behavior with stress relaxation time constants of τ1=1.38s and τ2=36.29s for grey matter and τ1=1.46s and τ2=46.10s for white matter, while the initial peak force decreased by 54 % for grey and 59 % for white matter tissue. An increase of the applied loading rate by two orders of magnitude led to an approximate doubling of the apparent modulus for both tissue types. Thermal variations showed a decrease in apparent modulus of up to 30 % after heating from 20 to 37.0 °C. Our dynamic tests revealed a significant influence of cyclic preload on the stiffness, with a drop of up to 20 % and a relative decrease of up to 60 % after the first cycle compared to the total modulus drop after five cycles for spinal cord grey matter tissue. Oscillatory indentation experiments identified similar loss moduli for spinal cord grey and white matter tissue and a higher storage modulus for white matter tissue. This work provides systematic insights into the mechanical properties of spinal cord tissue under different loading scenarios using nanoindentation.

Chronic spinal cord injury functionally repaired by direct implantation of encapsulated hair-follicle-associated pluripotent (HAP) stem cells in a mouse model: Potential for clinical regenerative medicine

Chronic spinal cord injury (SCI) is a highly debilitating and recalcitrant disease with limited treatment options. Although various stem cell types have shown some clinical efficacy for injury repair they have not for SCI. Hair-follicle-associated pluripotent (HAP) stem cells have been shown to differentiate into neurons, Schwan cells, beating cardiomyocytes and many other type of cells, and have effectively regenerated acute spinal cord injury in mouse models. In the present report, HAP stem cells from C57BL/6J mice, encapsulated in polyvinylidene fluoride membranes (PFM), were implanted into the severed thoracic spinal cord of C57BL/6J or athymic nude mice in the early chronic phase. After implantation, HAP stem cells differentiated to neurons, astrocytes and oligodendrocytes in the regenerated thoracic spinal cord of C57BL/6J and nude mice. Quantitative motor function analysis, with the Basso Mouse Scale for Locomotion (BMS) score, demonstrated a significant functional improvement in the HAP-stem-cell-implanted mice, compared to non-implanted mice. HAP stem cells have critical advantages over other stem cells: they do not develop teratomas; do not loose differentiation ability when cryopreserved and thus are bankable; are autologous, readily obtained from anyone; and do not require genetic manipulation. HAP stem cells therefore have greater clinical potential for SCI repair than induced pluripotent stem cells (iPSCs), neuronal stem cells (NSCs)/neural progenitor cells (NPCs) or embryonic stem cells (ESCs). The present report demonstrates future clinical potential of HAP-stem-cell repair of chronic spinal cord injury, currently a recalcitrant disease.

Hair-Follicle-Associated Pluripotent (HAP) Stem Cells Encapsulated on Polyvinylidene Fluoride Membranes (PFM) Promote Functional Recovery from Spinal Cord Injury

Our previous studies showed that nestin-expressing hair follicle-associated-pluripotent (HAP) stem cells, which reside in the bulge area of the hair follicle, could restore injured nerve and spinal cord and differentiate into cardiac muscle cells. Here we transplanted mouse green fluorescent protein (GFP)-expressing HAP stem-cell colonies enclosed on polyvinylidene fluoride membranes (PFM) into the severed thoracic spinal cord of nude mice. After seven weeks of implantation, we found the differentiation of HAP stem cells into neurons and glial cells. Our results also showed that PFM-captured GFP-expressing HAP stem-cell colonies assisted complete reattachment of the thoracic spinal cord. Furthermore, our quantitative motor function analysis with the Basso Mouse Scale for Locomotion (BMS) score demonstrated a significant improvement in the implanted mice compared to non-implanted mice with a severed spinal cord. Our study also showed that it is easy to obtain HAP stem cells, they do not develop teratomas, and do not loose differentiation ability when cryopreserved. Collectively our results suggest that HAP stem cells could be a better source compared to induced pluripotent stem cells (iPS) or embryonic stem (ES) cells for regenerative medicine, specifically for spinal cord repair.