Regenerative potential of decellularized porcine nucleus pulposus hydrogel scaffolds: stem cell differentiation, matrix remodeling, and biocompatibility studies.

Nucleus pulposus (NP) tissue regeneration has been proposed as an early stage interventional therapy to combat intervertebral disc degeneration. We have previously reported on the development and characterization of a novel biomimetic acellular porcine NP (APNP) hydrogel. Herein, we aimed to evaluate this material for use as a suitable scaffold for NP tissue regeneration. Human-adipose-derived stem cells (hADSCs) were cultured for 14 days on APNP hydrogels in chemically defined differentiation media and were analyzed for an NP-cell-like mRNA expression profile, evidence of hydrogel remodeling including hydrogel contraction measurements, extracellular matrix production, and compressive dynamic mechanical properties. The innate capacity of the hydrogel itself to induce stem cell differentiation was also examined via culture in media lacking soluble differentiation factors. Additionally, the in vivo biocompatibility of non-crosslinked and ethyldimethylaminopropyl carbodiimide/N-hydroxysuccinimide and pentagalloyl glucose crosslinked hydrogels was evaluated in a rat subdermal model. Results indicated that hADSCs expressed putative NP-cell-positive gene transcript markers when cultured on APNP hydrogels. Additionally, glycosaminoglycan and collagen content of hADSC-seeded hydrogels was significantly greater than nonseeded controls and cell-seeded hydrogels exhibited evidence of contraction and tissue inhibitors of metalloproteinase-1 production. The dynamic mechanical properties of the hADSC-seeded hydrogels increased with time in culture in comparison to noncell-seeded controls and approached values reported for native NP tissue. Immunohistochemical analysis of explants illustrated the presence of mononuclear cells, including macrophages and fibroblasts, as well as blood vessel infiltration and collagen deposition within the implant interstices after 4 weeks of implantation. Taken together, these results suggest that APNP hydrogels, in concert with autologous ADSCs, may serve as a suitable scaffold for NP tissue regeneration.