Acceleration of Bone Regeneration Induced by a Soft‐Callus Mimetic Material

Abstract

Clinical implementation of endochondral bone regeneration (EBR) would benefit from the engineering of devitalized cartilaginous constructs of allogeneic origins. Nevertheless, development of effective devitalization strategies that preserves extracellular matrix (ECM) is still challenging. The aim of this study is to investigate EBR induced by devitalized, soft callus‐mimetic spheroids. To challenge the translatability of this approach, the constructs are generated using an allogeneic cell source. Neo‐bone formation is evaluated in an immunocompetent rat model, subcutaneously and in a critical size femur defect. Living spheroids are used as controls. Also, the effect of spheroid maturation towards hypertrophy is evaluated. The devitalization procedure successfully induces cell death without affecting ECM composition or bioactivity. In vivo, a larger amount of neo‐bone formation is observed for the devitalized chondrogenic group both ectopically and orthotopically. In the femur defect, accelerated bone regeneration is observed in the devitalized chondrogenic group, where defect bridging is observed 4 weeks post‐implantation. The authors' results show, for the first time, a dramatic increase in the rate of bone formation induced by devitalized soft callus‐mimetics. These findings pave the way for the development of a new generation of allogeneic, “off‐the‐shelf” products for EBR, which are suitable for the treatment of every patient.

Evaluating material-driven regeneration in a tissue engineered human in vitro bone defect model

“…The copyright holder for this preprint this version posted August 5, 2022. ; https://doi.org/10.1101/2022.08.05.502914 doi: bioRxiv preprint alkaline phosphatase, were less successful in defect regeneration in vivo [29]. Thus, while in vitro mineralization might be mainly caused by the presence of alkaline phosphatase, in vivo there are likely a multitude of factors regulating mineralization and regeneration.…”

“…Furthermore, in this study, the implanted devitalized cartilage spheres showed initial mineralization after 14 days, similar to when implanted in vivo for 14 days. Previously, these devitalized cartilage spheres were already shown to stimulate subcutaneous endochondral bone formation and bone regeneration in critically sized long bone defects in rats [29]. In these in vivo defects, complete bridging of the gap was already observed with µ CT 4 weeks after implantation [29].…”

“…Previously, these devitalized cartilage spheres were already shown to stimulate subcutaneous endochondral bone formation and bone regeneration in critically sized long bone defects in rats [29]. In these in vivo defects, complete bridging of the gap was already observed with µ CT 4 weeks after implantation [29]. The successful mineralization seen in vivo and in vitro might be attributed to the presence of alkaline phosphatase in the spheres [29].…”

“…In these in vivo defects, complete bridging of the gap was already observed with µ CT 4 weeks after implantation [29]. The successful mineralization seen in vivo and in vitro might be attributed to the presence of alkaline phosphatase in the spheres [29]. However, cartilage spheres that were further differentiated into hypertrophic cartilage spheres and subsequently devitalized, containing higher levels of alkaline phosphatase, were less successful in defect regeneration in vivo [29].…”

“…The successful mineralization seen in vivo and in vitro might be attributed to the presence of alkaline phosphatase in the spheres [29]. However, cartilage spheres that were further differentiated into hypertrophic cartilage spheres and subsequently devitalized, containing higher levels of alkaline phosphatase, were less successful in defect regeneration in vivo [29]. Thus, while in vitro mineralization might be mainly caused by the presence of alkaline phosphatase, in vivo there are likely a multitude of factors regulating mineralization and regeneration.…”