Carbon dots-enhanced pH-responsive lubricating hydrogel based on reversible dynamic covalent bondings

Due to the various pH liquid environment in nature, the pH-responsive lubricating hydrogel is widely investigated and developed for tissue interface substitute. However, the applied liquid environment will lead to poor mechanical property and weaken the pH-responsive capability. In this work, a carbon dots-enhanced pH-responsive lubricating hydrogel is developed by combining a pH-responsive section of dynamic PVA-borax network into a PAAm covalent polymer network. The formed hydrogel presents a partial gel-sol transition under controlled pH environments. At low pH environments (<6.0), the formed lubricating layer originated from dynamic disassembly of PVA-borax hydrogel, and brings the lubricating properties on the hydrogel surface. Moreover, the mechanical strength and lubrication properties are well promoted by introducing the carbon dots into the hydrogel, the blue sol layer can be observed more visually under the fluorescence microscope. The pH-response also exhibits well reversibility. The prepared hydrogel broadens the idea for designing pH-responsive soft materials for soft lubricating actuator or robot.