Repairing a large bone gap is not just a construction problem. This study suggests the repair material may also need to coach the immune system—quietly at first, then more strongly as healing unfolds.
The immunoregulation of tissue-engineered bone has emerged as a prominent area for bone defect repair. While this field demonstrates considerable potential, effectively managing relevant factors and maintaining a balanced immune microenvironment in practical applications remain substantial challenges that require resolution. In this study, we tested a novel comprehensive hierarchical delivery system based on the requirements of a natural immune microenvironment for inflammatory factors, to optimize local immune responses through precise regulation of drug release. Quercetin (Que)-loaded zeolite imidazolate framework-8 (ZIF-8) nanoparticles were embedded in gelatin methacrylate to create a drug-release system featuring a Zn2+ shell and quercetin core. In vivo and in vitro studies demonstrated that this dual sustained-release hydrogel-ZIF-8 system can produce low concentrations of Zn2+ at an early stage, resulting in a mild anti-inflammatory effect and proliferation of bone marrow mesenchymal stem cells. Moreover, as inflammation advances, the release of quercetin works synergistically with Zn2+ to enhance anti-inflammatory responses, reconfigure the local microenvironment, and mitigate the inflammatory response that adversely impacts bone health by inhibiting the Nuclear Factor-kappa B (NF-κB) signaling pathway, thereby promoting osteogenic differentiation. This system is pioneering for sequential microenvironment regulation based on its diverse anti-inflammatory properties, offering a novel and comprehensive strategy for bone immune regulation in the clinical treatment of bone defects.
Transcript
Repairing a large bone gap is not just a construction problem. This study suggests the repair material may also need to coach the immune system—quietly at first, then more strongly as healing unfolds. Larger and more severe bone defects can require external intervention to facilitate bone regeneration and ensure overall health.
Bone grafts remain a standard treatment, but they can cause problems at the place the graft is taken from and may be limited in size. That is why scaffolds made from cells and biomaterials are being explored as a way to repair defects while mimicking the structure of natural bone.
The proposed system combines quercetin-carrying nanoparticles with an injectable GelMA hydrogel for immune modulation and bone regeneration in bone defects. Think of it as a two-stage delivery system: zinc and quercetin are released sequentially, targeting different stages of the bone immune response.
The aim is sequential release, so the treatment can address different stages of the immune response with both inflammation control and support for bone formation. The release curves showed a step-by-step pattern. At first, the gel released low amounts of zinc, while quercetin stayed almost entirely contained inside the particles.
As zinc increased, the particle framework began to dissolve, causing substantial quercetin release. In an acidic environment like the one associated with increased inflammation, both substances were released faster than in a neutral environment.
The result was sustained, step-by-step release that responded to an acidic environment. The complete system limited inflammatory M one activation comparably to the quercetin-free system, while its repair-supporting M two activation was reduced without quercetin.
The combined anti-inflammatory effect was therefore expressed mainly through enhanced M two polarization, the repair-supporting shift observed in these results overall. The complete system also produced significantly more repair-supporting immune cells than the other groups.
The results indicate that the combined anti-inflammatory effect was mainly expressed through this shift toward the repair-supporting state. The complete system produced the greatest mineralization and bone formation among the groups, and a second test of mineralized bone gave the same result.
Signs of early and later bone-forming activity were strongest in the zinc-releasing systems, consistent with sustained zinc release over time. Adding quercetin made these signals markedly stronger in the complete system, consistent with synergistic effects from zinc and quercetin together.
In the skull defects, the complete system produced the largest area of new bone. Without the gel, only a small amount appeared at the edges, and the gap did not become connected. Both gel systems produced the strongest measures of new bone, but the complete system had clearer advantages over the system without quercetin.
It increased bone mass and helped rebuild a more organized structure at the damaged site. The work reflects a broader change in bone repair: materials are being designed not only to be tolerated by the body, but also to influence the immune response.
Here, the particles and gel produced anti-inflammatory effects at different times and places. Tests in cells and animals found that this controllable change in the local immune environment accelerated bone regeneration in defects. The results support considering bone immune regulatory mechanisms during bone repair, an essential part of evaluating therapeutic effects in this context.
However, the connections among immune cells and their signaling pathways remain only partly understood, so current understanding is preliminary today. The animal model also differs from real clinical situations. Larger, more clinically relevant animals will be needed to assess safety and effectiveness accurately before this approach can be judged for patients.
A dissolving gel delivered two helpful substances in sequence: one early, one later. In tests, that timing softened harmful inflammation and supported more organized new bone, though clinical safety still needs larger, more realistic studies.
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Shiyue Fang, Pengfei Shen, Xinhai Qi, Fan Zhao, Yue Gu, Jiaxin Huang, Yan Li
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