An interleukin-4-loaded bi-layer 3D printed scaffold promotes osteochondral regeneration.

Multilayer scaffolds fabricated by 3D printing or other techniques have been used to repair osteochondral defects. However, it remains a challenge to regenerate the articular cartilage and subchondral bone simultaneously with higher performance. In the present study, we enhanced the repair efficiency of osteochondral defects by developing a bi-layer scaffold: an interleukin-4 (IL-4)-loaded radially oriented gelatin methacrylate (GelMA) scaffold printed with digital light processing (DLP) in the upper layer and a porous polycaprolactone and hydroxyapatite (PCL-HA) scaffold printed with fused deposition modeling (FDM) in the lower layer. An in vitro test showed that both layers supported cell adhesion and proliferation, as the lower layer promoted osteogenic differentiation and the upper layer with IL-4 relieved the negative effects of inflammation on murine chondrocytes, which were induced by interleukin-1β (IL-1β) and M1 macrophages. In a rabbit osteochondral defect repair model, the IL-4-loaded bi-layer scaffold group obtained the highest histological score (24 ± 2) compared to the nontreated (11 ± 1) and pure bi-layer scaffold (16 ± 1) groups after 16 weeks of implantation, which showed that the IL-4-loaded bi-layer scaffold promoted regeneration of both cartilage and subchondral bone with increased formation of neocartilage and neobone tissues. Thus, the IL-4-loaded bi-layer scaffold is an attractive candidate for repair and regeneration of osteochondral defects.