Novel gradient bimetallic hydrogel promotes tendon-to-bone interface reconstruction by synchronous regeneration.

Due to the dynamic imbalance between osteogenesis and osteoclasis and the abnormal inflammatory microenvironment in situ, osteoporosis hampers the early osseointegration between implants and bones. To improve osseointegration with the osteoporosis, we first coated the titanium implants (Ti) with polydopamine (PDA) coating (Ti-PDA), followed by modification with strontium (Sr) to prepare the Ti-PDA-Sr implants. An osteoporotic rat model with femoral bone defect was verified to estimate the osseointegration of the implants. The Ti-PDA-Sr implants exhibited good biocompatibility with continuous release of Sr ions for up to 21 days. Ti-PDA-Sr implants promoted the osteogenesis of BMSCs and the polarization of BMMs to M2 phenotype compared to that of Ti and Ti-PDA implants, revealing the double-regulated effects in bone induction and immune regulation. According to the Micro-CT and histopathology results, Ti-PDA-Sr implants exhibited the most stable osseointegration between bone tissues and implants. According to the immunohistochemistry results, the Ti-PDA-Sr implants differentiated the BMMs to M2 phenotype, alleviating the abnormal inflammation in osteoporosis and preventing the consistent bone destruction between the implants and bone tissues. This study provides a practical and effective strategy in preparing bi-functional implants that can promote osseointegration with osteoporosis.

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.