Research progress in lubricating hydrogel coatings
[Significance]Medical devices such as catheters,endoscopes,guidewires,artificial joints,and stents are in prolonged direct contact with human tissue.Therefore,surface treatment must be performed to enhance their lubricity and biocompatibility.Among the surface treatment techniques,lubricating coatings are widely used.The coatings reduce friction between medical devices and biological tissues,thereby minimizing tissue damage,alleviating patient discomfort due to friction,reducing the risk of rejection,infection,and inflammation,and making the treatment process smoother.With their structure similar to biological tissues and their ability to interact and retain large amounts of water,hydrogels are easily modified and less likely to cause immune rejection,making them suitable for fabricating lubricating coatings.However,the application of hydrogels as lubricating coatings faces many challenges.Initially,the physicochemical properties of hydrogels are diverse and complicated,resulting in different friction and lubrication mechanisms,and targeted modification of hydrogels for lubrication is challenging.Additionally,because of the unique formation methods and structures of hydrogels,achieving stable and strong adhesion with other substrates is difficult.Therefore,summarizing the existing research is crucial to guide further development of lubricating hydrogel coatings.[Progress]In the study of the lubrication mechanisms of hydrogels,articular cartilage was an important reference,primarily involving boundary lubrication and hydrodynamic lubrication mechanisms,relying on the synergistic interaction of various charged or polar macromolecules.The lubrication theory of synthetic hydrogels was similar to that of articular cartilage.In terms of hydrogel-solid substrate friction,the repulsion-adsorption theory explained the impact of microscopic interactions between the superficial hydrogel polymers and the solid substrate on lubrication performance.The friction between hydrogel surfaces was more complex,requiring careful consideration of the surface properties of both hydrogel counterparts.Current research on hydrogel coating modification for lubrication purposes primarily focused on three aspects:modification based on the hydrodynamic lubrication mechanism,structural modification,and intelligent response modification design.The first modification could simply and effectively improve the lubricity of the hydrogel surface.Structural modification,often bioinspired from specific biological tissue structures such as articular cartilage,aimed to balance the lubrication performance and stable mechanical properties of hydrogels.The intelligent response modification endowed the hydrogels with various responsive characteristics in lubrication performance,such as pH,light,and shear stress responses.These typical enhancements greatly improved the functionality of the hydrogel coatings from multiple perspectives.Hydrogels were primarily formed on substrates via chemical interactions such as surface bridging,surface initiation,gel coating,and biological modification.The first three methods involved the polymerization and crosslinking of hydrogels,with similar principles but different procedures,whereas biological modification directly used bacteria or other microorganisms for adhesion and gel formation.These methods were adapted to different production scenarios and were suitable for various hydrogel materials and substrates.[Conclusions and Prospects]Current lubricating hydrogel coatings excel in lubrication,reliability,stability,and ease of modification,yet they fall short of the comprehensive excellence of articular cartilage.Further research into the lubrication mechanism of hydrogels,the integration of lubrication properties,and other functional modifications with coating methods are anticipated to considerably improve the design of various hydrogel coatings with superior performance,enabling their biomedical application in various conditions.
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