Study Of Modification Of Magnetic Sensitive PVA Hydrogel Soaked In Alkaline Solution And Continuous Multi-phase Network

Hydrogel has attracted extensive attention in recent years due to its excellent biocompatibility,high moisture content and high flexibility.Various kinds of artificially prepared hydrogels have been proved to be applied in biomedical,tissue engineering,drug delivery and other frontiers of biological applications.Therefore,hydrogels are potential soft materials,but traditional hydrogels have poor controllability.However,the development of magnetic sensitive hydrogel materials in recent years has become a hot research material because of its ability to respond to external magnetic fields and overcome the shortcomings of hydrogel materials.For hydrogel materials,because of its complex application environment,the research on the mechanical behavior of hydrogel materials is always a key research topic.In this paper,polyvinyl alcohol(PVA)hydrogel was used as the research object.Magnetic PVA hydrogel was prepared by in-situ precipitation method.The relationship between mechanical properties and the concentration of solution as the main influencing factor was fully studied.Based on this,a continuous phase network distribution model was proposed,revealing the mechanism of tensile failure behavior of hydrogel under immersion.The main contents of this paper are as follows:(1)Using magnetic PVA hydrogel as matrix material,magnetic PVA hydrogel was prepared by mixing method and in-situ precipitation method.The effects of two preparation methods on physical properties and mechanical properties of the material were explored.It is found that the latter has advantages of uniform particle size and excellent mechanical properties when preparing magnetic particles.Combined with a variety of testing techniques and mechanical experiments,on the basis of experiments,it is concluded that the main factor affecting the properties of materials is immersion,which is the research focus.(2)PVA hydrogels soaked in alkaline solution were tested by mechanical experiments such as quasi-static uniaxial tension,uniaxial compression,pure shear test and cyclic loading under coaxial shear.First,aiming at the improvement of the traditional sliding mechanics experiment method in the loading slippage of PVA hydrogel,a tensile test method suitable for PVA hydrogel was developed.After studying the relationship between the concentration of sodium hydroxide solution and the mechanical behavior of hydrogels,it was found that the tensile strength and compression modulus of PVA hydrogel increased with the concentration of solution,while in high concentration solution.The toughness of the hydrogel increases,and the failure mode changes from brittle fracture to ductile fracture.On the basis of the above results,we observed the microstructures of the hydrogel after dyeing.We found the characteristics of the tensile fiber redistribution under the high stress of the phase separation PVA hydrogel,and combined with the mechanical characteristics of the phase separation network,we proposed the distributed fracture of the strong and weak fibers to explain the tear mechanical properties of the material.(3)In view of the mechanical behavior of PVA hydrogel after immersion phase separation,a continuous multiphase network constitutive model was proposed for the first time.The fracture limit and tensile modulus were used as parameters for continuous distribution.Combined with digital image technology and edge recognition algorithm,the true stress-strain relationship of hydrogels after large deformation and even fracture has been measured.The model corresponds well with the real stress-strain relationship of PVA hydrogel from tensile to fracture under various concentrations,which proves the rationality of the model.The ductile fracture of PVA hydrogel under immersion is a specific mechanical behavior than that of ordinary PVA hydrogel.Using this model as the tool,the ductile fracture behavior of PVA hydrogel immersed in phase separation is analyzed for the first time,revealing the relationship between the macroscopical failure behavior of hydrogels and the concentration of immersion.The study shows that the probabilistic multiphase network model can well describe the mechanical failure behavior of tensile phase separated hydrogels.