Temperature-and PH Double Responsive Supramolecular Lubricating Hydrogel

With the increasing progress of science and technology,reducing the loss caused by friction has always been a difficult problem to be overcome in various fields such as industrial production,biological materials,and drug transportation.Smart responsive hydrogels provide a choice for the study of biomimetic tribology due to their unique stimuli-responsive networks,simple synthesis methods,and easy regulation and modification.Biomimetic lubricating materials,such as articular cartilage substitutes,need to have two necessary properties: one is to be able to adapt to the complex and changeable biological environment,and the other is to have sufficient mechanical and lubricating properties.Currently,designing hydrogels with multiple stimuli-responsive properties that meet the mechanical and lubricating properties required by articular cartilage remains a challenge.First,the friction coefficient of the cartilage surface increases when the articular cartilage is damaged,and the pH value of the environment decreases and becomes acidic.Inspired by the mechanism of articular cartilage lesions,chitosan with an amino group that responds intelligently to pH on the molecular chain is selected.In the environment below p Ka=6.5,the intelligent response disassembly of chitosan plays a lubricating role.In the environment of p Ka=6.5,the amino groups in chitosan form hydrogen bond assembly.The interpenetrating double network was constructed with polyacrylamide and poly-2-acrylamide-2-methylpropanesulfonic acid as the overall skeleton of the hydrogel to improve the mechanical strength of the hydrogel.The pH-responsive hydrogel was prepared by introducing chitosan into the interpenetrating double network hydrogel.After the response,the minimum friction coefficient of the hydrogel reached 0.0144,and the friction coefficient did not change significantly after multiple cyclic friction experiments.The minimum mechanical strength is 4.87 MPa,and the minimum mechanical strength of the hydrogel after response is 2.85 MPa.The pH-responsive hydrogel has good lubricating and mechanical properties.In addition,there is a difference between the ambient temperature in the living body and the external ambient temperature.The gelatin with a typical high critical solution temperature(36 ℃)intelligently responsive to temperature is selected as the temperatureresponsive component and introduced into the hydrogel,and the gelatin hydrogels at room temperature(24 ℃).Glue-to-gel assembly,intelligently responds to disassembly at human body temperature(37 °C)and plays a lubricating role,enabling the hydrogel to adapt to a more variable environment,and enhancing the lubricating performance of the hydrogel while ensuring the mechanical strength as much as possible.The lubricating properties and mechanical properties of the hydrogels with dual response to pH and temperature were tested.The minimum friction coefficient of the hydrogels after the response reached0.0107,and the minimum mechanical strength after the response was 1.13 MPa.The prepared hydrogels enhanced the lubricating properties and retention.The mechanical strength is also able to adapt to the changing biological environment.In summary,a dual-responsive hydrogel to pH and temperature has been successfully prepared.The specific network in the hydrogel responds intelligently to its specific external stimuli.The hydrogel exhibits a very low surface friction coefficient.Compared with the traditional hydrogel,the hydrogel exhibits excellent mechanical strength,and the strength before and after the response is above the megapascal level,which can be applied to the bionic lubricating material.The design provides ideas and possibilities for artificially designing articular cartilage substitutes.