Recapitulation of angiogenesis and osteogenesis within an muscle pouch-based coral-derived macroporous construct organoid model.

BACKGROUND

Segmental bone defect is a challenging clinical problem that often requires autologous bone grafting, which has limitations such as donor site morbidity and insufficient supply. Bone tissue engineering aims to create functional bone substitutes that can mimic the properties and processes of native bone. However, the discrepancy between and conditions hinders the successful translation of bone tissue engineering from animal models to human applications. Organoids, such as muscle pouch-based models, are emerging as promising tools that can closely resemble the osteogenic niche and overcome some of the limitations of conventional models.

METHODS

In this study, we explored two distinct muscle-biomaterial based bone induction models: an heterotopic implantation model and a novel muscle pouch-based coral-derived macroporous construct organoid model. They both utilized the coral-derived constructs, specifically 13 % hydroxyapatite/calcium carbonate (13 % HA/CC) as the biomaterial. We implanted 72 coral-derived devices into rats' muscle, divided equally between and groups. Samples were harvested at 15, 30, and 60 days for molecular and histological analyses. We assessed the relative gene expression of angiogenesis markers ( and ) and osteogenesis signaling and structural markers (, , and ) using qRT-PCR. We analyzed tissue morphogenesis, angiogenesis and induction of bone formation by H&E and modified Goldner's Trichrome staining. Immunostaining was further used to detect the expression and localization of OCN, VEGFA and CD31 in both and models.

RESULTS

We demonstrated that muscle pouch-based coral-derived macroporous construct organoid model supported tissue survival up to 60 days with compromised tissue ingrowth compared to the model. Primary vascular structures formed at the tissue-scaffold interface in the organoid system with persistent up-regulation of and while comprehensive angiogenesis took place with early up-regulation of and . Proper bone formation was absent in both the and models, but the models showed an up-regulation of and in early phase and a delayed expression on day 30. The model showed connective tissue formation, comprehensive OCN deposition, and gene expression patterns mimicking trends but with some distinctions.

CONCLUSIONS

The muscle pouch-based coral-derived macroporous construct organoid model in this study can partially recapitulate angiogenesis and osteogenesis as compared to the model. However, key molecular signaling events that regulate these processes remained inactive. The study demonstrated that activating these events could enable the establishment of an tissue-based vascularized model.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

This study partly elucidated the molecular signaling events involved in the development of an tissue-based osteogenic organoid that closely resembled its counterpart. This would facilitate the development of well vascularized artificial bone grafts for treating segmental bone defects.