Hypoxia-responsive microgels act as an intra-articular lubricant and inflammatory inhibitor for osteoarthritis therapy

The reduced oxygen concentration is a distinctive feature of osteoarthritic (OA) cartilage, whereas the mechanical friction also contributes to the inflammatory hypoxia microenvironment of OA. Herein, novel hypoxia-responsive methylprednisolone (MP) delivery microgels combining the capability of reactive oxygen species (ROS)-depletion and lubrication were constructed for regulating the microenvironment of OA. Methacrylate-modified sulfonated azocalix[4] arene (MACA) loaded with MP, the copolymers consisting of bioinspired lubricant 2-methacryloxyethyl phosphorylcholine (MPC), and polyethylene glycol-modified ROS-responsive poly(thioketal) (PEG-4PTK) were crosslinked together to construct the microgels. The zwitterionic MPC offered a lubrication effect, while the ROS-elimination was contributed by the PTK segments and the phenol groups in MACA. The microgels responsively released cargos in inflammatory environment and decreased inflammation by inhibiting the production of ROS and regulating the expression of inflammatory cytokines, and showed the lowest hypoxia-inducible factor-1α (HIF-1α) positive area and presented more deposition of glycosaminoglycans and collagen II with a smoother and integrated cartilage structure in therapy of OA in rats in vivo .