Magnetically Actuated Microstructures with Programmable Degradation for Knee Cartilage Regeneration

Degenerative joint diseases, such as osteoarthritis, are increasingly prevalent in aging populations, yet current treatments like stem cell injections face limitations in targeted delivery and efficacy. In this study, we proposed a biodegradable magnetically actuated microstructure for knee cartilage regeneration. The microstructure is composed of calcium-crosslinked alginate hydrogel embedded with magnetic nanoparticles (MNPs), allowing for precise control using an external magnetic field generated by an electromagnetic actuation (EMA) system. Fabricated via a centrifugal micro-nozzle process, the microstructures exhibited tunable sizes and uniform morphology. The proposed microstructures were characterized for their morphological, chemical, and magnetic properties, and their biodegradability and targeting ability in a phosphate-buffered saline (PBS) environment were experimentally analyzed. Experimental results demonstrated that smaller microstructures degraded more rapidly and that fewer microstructures resulted in improved targeting accuracy. In contrast, microstructures clustered at the lesion site degraded more slowly, supporting sustained therapeutic release. These results suggest that the proposed system can enhance delivery precision, minimize off-target accumulation, and reduce inflammation risks associated with residual materials. The biodegradable magnetically actuated microstructures present a promising platform for minimally invasive and site-specific cartilage therapy.