Cranial Regeneration Using Stem Cells Encapsulated in Fast-degrading Thiol-acrylate Hydrogel

Objectives: The objective of this study is to evaluate the in vivo bone formation induced by bone marrow- and dental pulp-derived stem cells encapsulated in two thiol-acrylate hydrogels of different degradation rates in rabbit cranial defects.
Methods: Nine New Zealand White rabbits (~4kg) were used. The rabbits were divided equally into three groups: (1) cells encapsulated in 5wt% PEGDA hydrogel, (2) cells encapsulated in 15wt% PEGDA hydrogel, (3) control groups. Four 5 mm defects were created in the craniums. For experimental groups, two defects were filled with DPSCs and two defects for BMSCs encapsulated with the specific PEGDA hydrogel and cultured in basal medium and osteogenic medium. Empty defect, returned bone plug, and two hydrogels without cells served as controls. Six weeks post-implantation, the samples were retrieved. New bone formation was assessed and quantified by microcomputed tomography (µCT) followed by dynamic histomorphometry. Samples were then sectioned and stained with Von Kossa-MacNeals, H&E, Tartrate-resistant acid phosphatase, and Goldner’s Trichrome staining. All the data were evaluated by a blinded pathologist with statistical significance at p<0.05.
Results: Histological analyses revealed that the 5wt% PEGDA hydrogel degraded faster within six weeks compared to 15wt% PEGDA hydrogel and control group and showed lower residual hydrogel volume in the defects with higher bone formation, conforming to the profile of the degrading gel. There was less bone formation in 15wt% PEGDA (54µm to 211µm) compared to 5wt% PEGDA groups (537µm to 593µm). µCT analysis of 5wt% PEGDA group cultured in osteogenic medium demonstrated higher percentages of new bone volume (7.9% BMSCs and 9.2% DPSCs) compared to groups cultured in basal medium. Dynamic histomorphometry showed higher mineral apposition rate in the 5% PEGDA group. Minimal, localized inflammatory reactions were observed in brain tissue.
Conclusions: Stem cells encapsulated in fast-degrading thiol-acrylate hydrogel can potentially be an effective way to repair large cranial defects.