Nanoparticle-Enabled Modulation of the Bone Immune Microenvironment for Enhanced Regeneration

Bone regeneration is governed by a tightly coordinated interplay between skeletal cells, immune cells, vascular components, and signaling networks within a dynamic microenvironment. Increasing evidence from osteoimmunology demonstrates that immune regulation is not merely supportive but mechanistically determinative of regenerative outcomes. Dysregulated or persistent inflammation can impair osteogenesis, whereas timely immune resolution promotes angiogenesis and matrix deposition. In this context, nanotechnology has enabled the development of nanoparticles (NPs) that function not only as delivery vehicles but also as active modulators of the bone immune microenvironment. Immunomodulatory NPs can be engineered to deliver bioactive agents, regulate cytokine networks, and influence immune cell phenotypes, particularly macrophage polarization, at defined stages of healing. Through tailored surface chemistry, targeting ligands, and stimuli-responsive release mechanisms, NPs can achieve spatially localized and temporally controlled modulation of inflammatory and reparative phases, thereby enhancing osteogenesis and vascular integration. This review provides a comprehensive overview of organic, inorganic, and hybrid NP platforms applied to bone regeneration, with emphasis on their mechanisms of immune modulation, strategies for cell-specific targeting, and approaches for sequential regulation of inflammatory resolution and tissue repair. By integrating advances in materials science and immunology, NP-enabled platforms have the potential to transform bone regeneration from passive structural repair into precision immune-guided healing.