Heterogenous hydrogel mimicking the osteochondral ECM applied to tissue regeneration

Inspired by the intricate extracellular matrix (ECM) of natural cartilage and subchondral bone, a heterogenous bilayer hydrogel scaffold is fabricated. Gelatin methacrylate (GelMA) and acryloyl glucosamine (AGA) serve as the main components in the upper layer, mimicking the chondral ECM. Meanwhile, vinylphosphonic acid (VPA) as a non-collagen protein analogue is incorporated into the bottom layer to induce the in situ biomineralization of calcium phosphate. The two heterogenous layers are effectively sutured together by the inter-diffusion between the upper and bottom layer hydrogels, together with chelation between the calcium ions and alginate added to separate layers. The interfacial bonding between the two different layers was thoroughly investigated via rheological measurements. The incorporation of AGA promotes chondrocytes to produce collagen type II and glycosaminoglycans and upregulates the expression of chondrogenesis-related genes. In addition, the minerals induced by VPA facilitate the osteogenesis of bone marrow mesenchymal stem cells (BMSCs). In vivo evaluation confirms the biocompatibility of the scaffold with minor inflammation and confirms the best repair ability of the bilayer hydrogel. This cell-free, cost-effective and efficient hydrogel shows great potential for osteochondral repair and inspires the design of other tissue-engineering scaffolds.