Study On The Mechanical Enhancement Mechanism Of Solvent-induced Cross-linked Composite Gels

Polymer hydrogels with three-dimensional cross-linked networks have promising applications in biotissue engineering,soft robotics and wearable electronics due to their good biocompatibility and mechanical compliance.However,the large amount of water contained in hydrogels is significantly affected by the environment.For example,when the temperature is high,the water evaporates rapidly or even boils;when the temperature is too low,the water freezes and the gel loses its original properties such as elasticity and transparency.These changes in physical state are also accompanied by a change or loss of chemical properties.In addition,in order to provide sufficient mechanical stability to soft gel materials,composite network structures are often designed to introduce structural mechanical enhancement mechanisms.However,the design of such structures is often based on the existing solution system of the hydrogel.Such reinforcement mechanisms are subject to significant environmental constraints due to the instability of water itself with respect to the environment.Therefore,the development of high-strength gel materials adapted to extreme environmental conditions and the development of new network structure enhancement mechanisms with extreme application environments is a common problem in the current gel research field.Based on the above analysis,this paper has constructed a high strength and high tenacity gel with antidrying and anti-freezing properties based on a double network structure based on the hydrogen bonding of polar groups and the design of biomass composite gels,using the strategy of solvent-induced cross-linking and the introduction of fibrous fillers into organic hydrogels in binary solvent systems,as follows:(1)Design solvent-induced cross-linking by a simple solvent replacement method to construct ductile double-network organic hydrogels with an energy dissipation mechanism.A first network of polyacrylamides is formed by covalent cross-linking,and a second network is formed by physical cross-linking between the alginate polymer chains using the solvation between the clusters formed by DMSO and water molecules and the carboxylic acid roots of the alginate chains.In addition,as DMSO is a poor solvent for sodium alginate,the gel shrinks in the poor solvent and to some extent the polymer molecular chains show a certain degree of aggregation,leading to enhanced interactions between the hydroxyl groups between the alginate molecular chains.As a result,the constructed PAAm-Alginate double network organo-hydrogels have a significant mechanical enhancement effect and have anti-drying and anti-freezing properties.The mechanism of the constructed double-network organo-hydrogels was investigated and analysed by structural characterisation,rheological tests under different conditions and tensile cycling tests.By controlling the mass fraction of sodium alginate in the physical cross-linked network or the content ratio of DMSO during solvent replacement,the double-networked organo-hydrogels with different degrees of mechanical enhancement were obtained.The results show that the higher the content of sodium alginate or DMSO,the more significant the mechanical enhancement of the double-networked organic hydrogels.(2)Based on the previous work,an anti-drying and anti-freezing composite gel with mechanical enhancement and additional biological tissue-like strain-hardening mechanical properties was designed by introducing short-cut fibers as fillers in the gel network.The viscosity of the prepolymer solution was adjusted by varying mass fractions of sodium alginate to homogenise the dispersion of the short-cut fibers in the three-dimensional gel;a DMSO/H2 O binary solvent method was used and its ratio adjusted to induce fiber bending in the fiber composite gel by controlled water loss shrinkage and to improve the temperature tolerance of the composite gel.On the one hand,the water loss and shrinkage of the gel strengthens the interactions between the polymer chains and fibers are introduced,thus increasing the mechanical strength of the gel;on the other hand,due to the bending of the fibers,the change from the flexural to the elongated state during tensile deformation produces strain-hardening properties similar to those of biological tissues,resulting in a significantly enhanced mechanical property of the gel with the fiber composite structure.Furthermore,the overall mechanical properties of the fiber composite gels can be further regulated by adjusting the fiber type,density and length-to-diameter ratio.