Engineering multifunctional microspheres for sequential regulation of osteoimmune microenvironment and bone remodeling balance to promote regeneration of osteoporotic bone defects.

OBJECTIVES

Osteoporotic bone defect repair remains clinically challenging due to persistent low-grade inflammation, excessive reactive oxygen species (ROS), and dysregulated bone metabolism. Approaches relying solely on osteoclast inhibition are often insufficient, particularly for irregular osteoporotic bone voids. This study aimed to develop a multifunctional microsphere system capable of sequential osteoimmune regulation and bone metabolic remodeling.

METHODS

Gelatin microspheres grafted with alendronate and loaded with epigallocatechin gallate (Gel@ALN@E) were fabricated via an emulsion-chemical crosslinking method to enable controlled dual-drug release. In vitro evaluations included ROS scavenging, inflammatory modulation, macrophage polarization, osteoclast differentiation, and osteogenic responses of rat bone marrow mesenchymal stem cells. Transcriptomic analysis was conducted to investigate immunoregulatory mechanisms. An osteoporotic rat bone defect model was used for in vivo assessment.

RESULTS

Gel@ALN@E effectively reduced oxidative stress and inflammatory responses by promoting macrophage M2 polarization, while concurrently suppressing osteoclastogenesis and restoring bone metabolic balance. This coordinated regulation significantly enhanced osteogenic differentiation. Transcriptomic analysis revealed the downregulation of related inflammatory pathways. In vivo, Gel@ALN@E markedly improved new bone formation, trabecular organisation, and cortical bone healing in osteoporotic defects.

CONCLUSION

This sequential drug release system offers a promising platform for both immunomodulation and bone regeneration in osteoporotic defect repair.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE: The composite engineered microsphere system Gel@ALN@E integrates local immunomodulatory and osteoclast-inhibitory functions to directly address key pathological microenvironmental features of osteoporotic bone defects. This integrative design highlights its comprehensive pro-regenerative capacity and provides support for its translational application in the clinical treatment of irregular osteoporotic bone defects.