Oscillating Magnetic Field Induced Bone Injury Repair by using Drug-Free Micromotors

Bone injury repair remains a significant clinical challenge due to the tissue's limited self-healing capacity and the complex physiological environment at the defect site. Factors such as insufficient vascularization, poor retention of therapeutic agents, and the lack of effective mechanical stimulation further hinder the success of current minimally invasive treatments, which often rely on the delivery of drugs or stem cells. Here, magnetic gelatin/hyaluronic acid composite hydrogels micromotors are developed, capable of promoting bone regeneration through localized micromovement stimulation, eliminating the need for therapeutic payloads. By harnessing the mechanical forces generated by the micromotors under an oscillating magnetic field, the approach directly enhances osteoblast proliferation and differentiation, providing a novel mechanism for bone repair. The efficacy of this strategy is further validated in vivo using animal models of bone defects, where moderate micromovement stimulation is shown to significantly increase the volume fraction of newly formed bone by approximately twofold, accompanied by well-aligned collagen and organized mineralization, thereby demonstrating substantial regenerative effects. This work presents a paradigm shift in bone repair with a payload-free, minimally invasive solution that overcomes conventional limitations and offers new insights into microrobotics in regenerative medicine.