Divergent effects of premineralization and prevascularization on osteogenesis and vascular integration in humanized tissue engineered bone constructs.

Osteogenesis (bone formation) and vascularization (blood vessel formation) are two central and interconnected physiological-relevant processes in bone formation. Prevascularization of humanized tissue-engineered bone constructs (hTEBCs) has been proposed to better mimic the human bone microenvironment by enhancing vascular integration and facilitating greater osteogenic capacity. Here, we investigated the effects of premineralization and prevascularization on bone and vasculature development in an ectopic hTEBC model using a scaffold-hydrogel composite approach. Human osteoblast cells (hOBs) were cultured under osteogenic conditions (OM), with or without a 3-day mineralization boost (OM+) period for 4 weeks prior to implantation in vivo in a supporting porous polycaprolactone (mPCL) scaffold. Separately, photocrosslinkable fish gelatin-derived hydrogels placed within supporting mPCL scaffolds showed formation of elongated vascular networks as early as day 3 with in vitro coculture of human umbilical vein endothelial cells (HUVECs) and human bone marrow mesenchymal stem/stromal cells (MSCs). The OM and OM+ cultured constructs were subcutaneously implanted into immunocompromised rats with and without the prevascular hydrogels, resulting in four subgroups: OM, OM+, OM/Vas, and OM+/Vas. Our results demonstrated that the OM+ group led to more rapid osteoinduction and enhanced osteogenic differentiation in vivo with woven bone structure and active remodeling. Conversely, prevascularization (OM/Vas, OM+/Vas groups) led to reduce in vivo bone volume and density but promoted the development of human endothelial networks and successful anastomosis with host vasculature. Our study highlights the distinct contributions of premineralization and prevascularization, where premineralization is critical for robust bone formation and prevascularization enhances vascular integration, providing important insights for advancing the physiological relevance of hTEBC models in animal hosts. STATEMENT OF SIGNIFICANCE: This study demonstrates the development of humanized tissue engineered bone constructs incorporating a vascular niche using a rat. By integrating innovative premineralization and prevascularization techniques within scaffold-hydrogel composites, we show that premineralization accelerates bone formation, while prevascularization promotes endothelial network formation and integration with host vasculature. Photocrosslinkable, low-stiffness LunaGel™ hydrogels enhanced microcapillary-like structure formation and endothelial sprouting in in vitro co-culture. However, by combining osteogenic and vascular cues within a biodegradable composite, this work advances the bone tissue engineering field by creating a model that more accurately reflects the divergent and competing nature of vascularization and bone formation. This platform has broad applicability for studying bone-vascular interactions and may inform strategies to improve the design of biomaterials for regenerative therapies.