Continuous magnetic-gradient hydrogel with augmented mechanical span and reverse-directional polysaccharides distribution for integrated repair of osteochondral defects

Natural osteochondral structure exhibits a continuous mechanical gradient that reflects the distinct mechanical properties of cartilage and bone. However, few continuous gradient casting methods can fabricate gradient scaffolds that match the mechanical span of natural osteochondral tissue for repairing full-thickness osteochondral defects. This study presents a continuous magnetic-gradient hydrogel with augmented mechanical span, developed through magnetic field-induced casting and post-modification techniques, for integrated repair of osteochondral defects. Through post-modification crosslinking, the hydrogel's mechanical span reaches two orders of magnitude, which is closer to the physiological gradient of cartilage to cancellous bone. Additionally, based on the natural polysaccharide characteristics of cartilage, two traditional Chinese medicine polysaccharides (oxidized Cuscuta chinensis polysaccharide and astragalus polysaccharide) are incorporated to create reverse-gradient that promote cartilage and bone tissue repair. Coupled with the hydrogel's magnetic gradient, an external gradient magnetic field is applied to further enhance the repair effects. Experimental results, both in vitro and in vivo, demonstrate that mechanical span augmented continuous magnetic-gradient hydrogel significantly facilitates the integrated repair of osteochondral defects. This work proposes a novel strategy to augment the mechanical span characteristic of continuous gradient hydrogel, resulting in a biomimetic scaffold that closely mimics the mechanical span properties of natural osteochondral tissue.