Research On Preparation And Properties Of Bioinspired Responsive Lubricating Hydrogels

Hydrogel materials have been widely concerned by researchers for many years because of their high similarity in physical and chemical properties with biological tissues and organs,excellent biocompatibility,and high designability.Hydrogels have been widely researched in biomedical,intelligent materials,sensors,actuators and other fields.In particular,intelligent responsive hydrogels are favored by researchers because they can mimic the"living state"of organisms to change their physical and chemical properties according to external stimuli.Generally,when intelligent responsive hydrogels perform their functions on surfaces and interface individually or in concert,they are all associated with friction.Therefore,responsive lubricating hydrogels,especially those with bioinspired living lubricating function,have shown great promise for applications in biomedical and intelligent soft actuators.Traditionally,responsive lubricating hydrogels achieve lubricating function by introducing lubricant or constructing responsive microstructure.However,organisms usually achieve this dynamic lubricating process through their own biological molecule assembly-disassembly process.Therefore,how to construct the hydrogels with responsive lubricating capability through bioinspired strategies becomes an important challenge in this field.In this paper,inspired by the living lubricating mechanism of organisms,the preparation of bioinspired responsive lubricating hydrogels is achieved by introducing responsive supramolecular system or dynamic covalent bonding system into polymerization framework,and the hydrogels obtained both variety responsiveness and favorable mechanical properties.The specific work is as follows:Firstly,based on the study of electric field responsive lubricating hydrogel,we found that the application of electric field will bring heat,which prompted us to think about the utilization of the generated heat and prepare dual responsive lubricating hydrogel.Therefore,a bioinspired electric/thermo dual responsive lubricating hydrogel was prepared by introducing supramolecular system into covalent polymer network,which silk fibroin with electric responsiveness and poly（N-isopropyl acrylamide）（PNIPAAm）with thermal responsiveness.This hydrogel can realize the electric responsive lubricating properity or thermo responsive lubricating properity under the action of electric field or temperature.On this basis,we introducing conductive materials（sodium chloride and conductive carbon dots）into the hydrogel,and the properity of electrothermal responsive lubricating can be realized only by the action of electric field.Secondly,considering that the physiological activities and matrix operation of the human body is inseparable from reactive oxygen species（ROS）,and the ROS is a"double-edged sword",the human body mainly balances the level of ROS through biological redox reactions in order to maintain health.Therefore,a bioinspired redox responsive lubricating hydrogel was prepared by introducing the redox responsive supramolecular system into the anti-swelling interpenetrating network,which is polyacrylic acid grafted cyclodextrin（PAA-CD）and polyacrylic acid grafted ferrocene（PAA-Fc）.This hydrogel has good anti-swelling property,excellent responsive lubricating and mechanical property.And can undergo a partial gel-sol transition in the presence of hydrogen peroxide（H₂O₂）and to form a sol layer,realizing the redox responsive lubricating properity.This partial gel-sol transition and the formed sol layer can regulate various physicochemical properties of the hydrogel.By controlling the ratio of hydrogel finely,the modulus and coefficient of friction（COF）of hydrogel can be adjusted,which can match and simulate tissues and organs in various ways,and make it possible to be used in biomedical fields.Thirdly,in order to further expand the design strategy of responsive lubricating hydrogels,we also introduced dynamic covalent bonding responsive systems into covalent polymer network.For example,a p H responsive polyvinyl alcohol-borax（PVA-borax）dynamic borate bonding system was introduced into the covalent polymer network.Meanwhile,in order to further enhance the lubricating and mechanical properties of the hydrogel,carbon dots（CDs）was introduced into the hydrogel,and a carbon dots enhanced bioinspired p H responsive lubricating hydrogel was prepared.Hydrogel can undergo a partial gel-sol transition at p H 6.0,forming a sol layer and realize the properity of p H responsive lubricating.Moreover,due to the introduction of CDs,the lubricating and mechanical properties are enhanced,and the CDs also endow the hydrogel with fluorescence properties,so that the sol layer,which is not easy to be observed,can be more clearly observed through fluorescence microscopy and can be semi-quantitatively analyzed and calculated.Finally,based on the glucose responsiveness of the dynamic borate bonding,combined with its p H responsiveness,a bioinspired glucose-p H dual responsive lubricating hydrogel was prepared by introducing sodium alginate grafted phenylboronic acid（Alg-PBA）and polyvinyl alcohol（PVA）responsive systems into the covalent polymer network.Since phenylboronic acid has a higher binding constant to glucose,when glucose is present in the system,it will competitively replace the cis-vinyl alcohol（PVA）that was originally bound with Alg-PBA,resulting in a partial gel-sol transition,forming a sol layer and realize the glucose responsive lubricating properity.Meanwhile,the change in p H also affects the binding of Alg-PBA with PVA,thus a partial,reversible gel-sol transition also occurs,forming a sol layer and realize the properity of p H responsive lubricating.The above bioinspired responsive lubricating hydrogels provide promising ideas for the preparation of single/multiple intelligent responsive hydrogels,as well as for expanding the application fields of hydrogels.