Preparation And Properties Of High-Strength And Toughness Composite Silicone Hydrogels

As the most typical soft matter material,hydrogel has attracted the attention of many researchers due to its fascinating properties,especially in the field of medical materials.Among them,polyvinyl alcohol hydrogel has been widely used in the field of biomedicine due to its advantages of degradability and non-toxicity.However,the single-network PVA gel prepared only by the freeze-thaw method still has problems of low strength and poor toughness,so its application is also limited.In order to improve the application breadth and depth of PVA in the field of medical materials,researchers have developed various strategies to enhance PVA hydrogels.Inspired by silicone rubber,we combined inorganic silicates and polyvinyl alcohol（PVA）to develop a physical double network hydrogel with low swelling,high strength,and excellent friction resistance.The details are as follows:（1）PVA/Si O₂double network composite hydrogels were prepared by a simple freeze-thaw and soaking method.That is,the polyvinyl alcohol hydrogel obtained from three freeze-thaw cycles was soaked in an aqueous solution of sodium metasilicate,and a second silicon gel was formed in situ in the PVA gel network through the hydrolysis and polycondensation of sodium metasilicate.glue network to obtain PVA/Si O₂double network composite hydrogel.The performance study on it shows that the double network composite gel exhibits excellent mechanical properties,its toughness is as high as6.00MJ/m³,and the maximum elastic modulus can reach 1.91MPa,which are 30 times and 25 times higher than that of the single network pure PVA hydrogel,respectively.In addition,PVA/Si O₂hydrogels also have excellent fatigue resistance,low swelling and good biocompatibility.（2）On the basis of a simple freeze-thaw soaking method,we introduced urea into the preparation system of PVA-sodium metasilicate,using the inhibitory effect of urea on the hydrogen bonds between the PVA molecular chains and the interaction between urea and sodium metasilicate.It can catalyze and induce the formation of the silica gel network to a certain extent,making the silica gel formed in situ in the PVA network more dense and uniform,so as to obtain a strong and tough dual network hydrogel with better performance,namely PVA（Urea）/Si O₂hydrogel.Compared with the PVA/Si O₂hydrogel prepared without urea,the tensile strength and tensile toughness of the PVA（Urea）/Si O₂hydrogel reach 8.10 MPa and 44.45 MJ/m³,respectively,which are 41 times and 222times of those of the pure PVA hydrogel.Likewise,PVA（Urea）/Si O₂hydrogels have excellent fatigue resistance,low swelling and good biocompatibility.In addition,in the tensile recovery test results,it was found that with the increase of recovery times,the PVA（Urea）/Si O₂hydrogel appeared self-enhancement,that is,the maximum stress under a specific strain increased abnormally compared with the initial state.（3）The lubricating properties of hydrogel materials are as critical as their toughness for many medical applications,especially cartilage repair and replacement materials.We incorporated a small amount of lecithin into the PVA/Si O₂composite hydrogel,and embedded lipid micelles into the network of the composite gel to prepare PL/Si O₂and PL（Urea）/Si O₂composite hydrogels.The hydrophilic phosphorylcholine head group in the amphiphilic phospholipid is easily aggregated on the surface of the hydrogel to form a thin water-lubricating boundary layer,which improves the lubricity and friction resistance of the hydrogel.When the gel is squeezed and rubbed by an external force,the water-lubricated boundary layer can effectively reduce the friction coefficient and reduce the wear of the hydrogel.At the same time,the phospholipid micelles inside the hydrogel can continuously provide phospholipid molecules to ensure the durability of wear resistance.The performance study results show that the friction coefficient of PL/Si O₂composite hydrogels containing lecithin micelles is significantly lower than that of the corresponding hydrogels,and the compressive ability of PL/Si O₂and PL（Urea）/Si O₂composite hydrogels is also obvious.better than the corresponding PVA/Si O₂and PVA（Urea）/Si O₂composite hydrogels.