Ultrasmall Amorphous Calcium Phosphate-Functionalized Hierarchical Scaffolds Promote Osteochondral Repair Via Synergic Effects of Immunoregulation and Osteogenesis

Abstract

The unique architecture of osteochondral tissue, characterized by the absence of both blood vessels and nerves, poses significant challenges for effective repair due to its distinctive tissue lineage and physiological properties. Polymer-induced liquid-precursor modified amorphous calcium phosphate (nCaP) has emerged as a promising candidate for bone tissue repair owing to its ability to mimic natural mineralization processes. However, its efficacy in repairing osteochondral defects with the features of complex anatomical and the associated therapeutic mechanisms remains inadequately investigated. In this study, a multifunctional nCaP-based hierarchical scaffold  was developed to repair osteochondral defects. Precisely defined hierarchical micro-scale structures within the scaffold provided efficient ways for endogenous cell infiltration and migration from the surrounding cartilage and subchondral bone tissues, while ultrasmall (~1nm) amorphous calcium phosphate (nCaP) promoted osteogenic differentiation of MSCs in vitro and blood vessel formation in vivo, achieving superior repaired outcomes of osteochondral defects. Bulk-seq RNA sequencing analysis proved that nCaP not only enhanced the expression of EGFL6, which promoted angiogenesis, but also diminished inflammation by downregulating TNFSF14 and inhibiting the NF-kappa B signaling pathway. Furthermore, nCaP activated the phosphoinositide 3-kinase (PI3K)-Akt signaling pathway while inhibiting osteoclast differentiation, thereby facilitating extracellular matrix mineralization and osteogenesis. This study highlights the potential of nCaP-based hierarchical scaffold as a viable therapeutic strategy for osteochondral defects and provides valuable insights into the underlying mechanisms of its action.

Note:
Funding declaration: This work was funded by the National Key Research and Development Program of China(2022YFA1104600) and the National Natural Science Foundation of China (82172403, 81972053). The authors thank Shuangshuang Liu from the Core Facilities, Zhejiang University School of Medicine for her technical support.

Conflict of Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Ethical Approval: Animal experiments were approved by the Experimental Animal Welfare Ethics Committee of Zhejiang University (Ethics batch number: ZJU20240420, ZJU20240841).

Keywords: Osteochondral Defect, Amorphous Calcium Phosphate, 3D printing, Osteochondral Scaffold