Solid-Liquid Interface Lubricating Hydrogels for Tendon-Bone Healing

A solid-liquid interface lubrication system composed of tissue and synovial fluid ensures the physiological functions of the tendon-bone (TB). However, after the TB tears, stress concentration and friction disrupt the solid-liquid interface lubrication of the TB and disturb its healing. Herein, solid-liquid interface lubrication hydrogels (MnCaP/HS) are constructed by encapsulating ion-coordinated calcium manganese phosphate microgels into covalent/ionic-cross-linked hyaluronic acid/sodium alginate dual networks. Solid lubrication interfaces are thus formed at the damaged TB through surface hydrogen bonding and ionic toughening and continuously release the biolubrication components into tissue fluid for rolling lubrication layers and liquid lubrication films. This long-lasting lubricating property and MnCaP synergistically improve the immune-regenerative microenvironment of the TB. In vitro, MnCaP/HS increases the toughness by 600% and reduces the friction coefficient at the solid-liquid interface by 60% compared with those of the phosphate-buffered saline group. Moreover, it releases metal ions to promote the anti-inflammation of macrophages and the cartilage-bone gradient differentiation of bone marrow mesenchymal stem cells. In vivo, the maximum load and stiffness of tendons in the MnCaP/HS group increase by 102% and 75%, respectively while exerting long-lasting anti-inflammation to inhibit scarring and complete microstructural reconstruction. Thus, MnCaP/HS provides new solutions for TB reconstruction by providing long-lasting lubrication and a regenerative microenvironment.