Preparation And Properties Of UV-crosslinked PDMA-based Hydrogel

Poly（N,N-dimethylacrylamide）（PDMA）is a very useful hydrophilic biocompatible polymer.PDMA-based linear polymers,hydrogels,interpenetrating polymer networks and mixtures are widely used in molecular biology,DNA sequencing and other fields.However,there are still some problems in the preparation and application of PDMA based hydrogels,such as long crosslinking time and poor mechanical properties.Based on the study of PDMA-based hydrogel,the effects of crosslinking agent content,water content,illumination time,light distance and whether deoxygenation by N₂on the cross-linking of UV-crosslinked PDMA-based hydrogels were studied.By doping metal ions in PDMA-based hydrogels,the effects of different metal ions on the mechanical properties,friction properties and self-healing properties of photocrosslinked PDMA-based hydrogels were studied.By adjusting the doping ratio of different ions,a photocrosslinked PDMA-based hydrogel with excellent comprehensive properties was obtained,and its main applications in friction reduction,repair and replacement of artificial articular cartilage were explored.1.By changing the content of light crosslinking agent,water content,illumination time and light distance,whether N₂was deoxygenated,the effect of crosslinking agent content,water content,illumination time and illumination distance on the crosslinking of UV-crosslinking PDMA based hydrogels by N₂deoxygenation was investigated.The best formula for preparing UV-crosslinked PDMA based hydrogels was 0.1 g content and 15 ml of water content.The illumination time is 5 min and the illumination distance is 10 cm.Besides,N₂is added to remove the oxygen in the hydrogel solution to reduce the inhibition of the existence of oxygen on the crosslinking of the hydrogel.2.Doping different metal ions in the PDMA-based hydrogel,the metal ions form ionic coordination bonds with the carboxyl group in the hydrogel.In addition,Mg²⁺and Ca²⁺will interfere with the relationship between the carboxylic acid group and octadecyl methacrylate.The interaction between them reduces the hydrophilic groups in the network.From the test results,it can be seen that Mg²⁺ions can effectively improve the self-healing rate of UV-crosslinked PDMA based hydrogels,and Ca²⁺ions can significantly improve the mechanical properties of UV-crosslinked PDMA based hydrogels.Na⁺and Mg²⁺can reduce the friction coefficient of UV-crosslinked PDMA based hydrogels,and adding Ca²⁺to generate inorganic substances will increase the roughness of the hydrogel surface,thereby increasing the friction coefficient of the hydrogel surface.We simulated the body fluid at human joints with water,and the friction coefficients of PDMA-based hydrogels doped with different metal ions were significantly reduced under the condition of water lubrication.This indicates that when water is used as the lubricant,during the friction process,water molecules are brought into the wear surface and form better lubrication between the friction pairs.3.Mg²⁺and Ca²⁺ions were co-doped into the PDMA based hydrogels and the ratio of them were optimized,the prepared hydrogel had a uniform structure and clear pores,similar to the structure of natural articular cartilage,and had similar swelling behavior to articular cartilage.From the test results of thermogravimetric,load,contact angle,friction,self-healing and other properties,it can be seen that when the ratio of Mg²⁺and Ca²⁺ions incorporated into the UV-crosslinked PDMA-based hydrogel is 2:1,the hydrogel has the toughness,wear resistance and low friction of repairing articular cartilage.The results of the in vitro toxicity test of the hydrogel cells show that the cytotoxicity of the PDMA-based hydrogel is first-class,without cytotoxicity,and meets the medical standards of biomaterials.It has great application potential in the field of artificial articular cartilage repair and replacement.