Spatiotemporally programming the immune-osteogenic cascade with a dual-immunomodulatory scaffold for functional bone regeneration.

Abstract

Functional repair of critical-sized bone defects is hindered by uncontrolled inflammatory microenvironments that disrupt endogenous regeneration. Conventional osteoimmunomodulatory biomaterials mainly emphasize direct regulating macrophage phenotype transformation, while neglecting the pivotal role of activating the immunomodulatory function of homing mesenchymal stem cells (MSCs) in immune-osteogenic cascade regulation. Herein, we present a dual-immunomodulatory bone scaffold (DIBS) to sequentially regulate the immune functions of macrophages and MSCs for repairing critical-sized bone defects. This scaffold integrates pH-responsive hydrogels containing oxidized xyloglucan (OXG) and metal polyphenol (Sr-PA) nanoparticles into a 3D-printed hydroxyapatite framework, enabling controlled release of immunomodulators and mineralization ions. The OXG first directs early M1-to-M2 macrophage transition to mitigate inflammation; then acidic-triggered release of Sr²⁺ and protocatechualdehyde from nanoparticles enhances the immunoregulatory function of homing MSCs. Additionally, hydroxyapatite framework provides essential mechanical stability and ion sources for late-stage osteogenic mineralization. Single-cell RNA sequencing and validation demonstrate that DIBS effectively induces the generation of immunoregulatory MSC subpopulations, which is associated with M2 macrophage activation through CCL2/CCR2 signaling axis, promoting angiogenesis and osteogenic differentiation. In vivo, DIBS effectively remodels the osteoimmune microenvironment, induces organized collagen arrangement and H-type vascularization, facilitating functional bone tissue repair. This study provides a new multicellular immunomodulatory strategy for endogenous bone repair.