Investigation On Preparation And Properties Of High Strength Stimuli-reseponsive Healing Hydrogels

Hydrogels are soft and wet materials with three-dimensional networks that can absorb water many times their volume,and have a wide range of applications in the fields of drug delivery,tissue engineering and artificial articular cartilage.They are also used as stimuli-responsive materials.In this work,two hydrogels of special properties have been synthesized with different chemicals and methods.The main contents and conclusions are shown as follows:(1)Using a facile two-step method,the researchers synthesized a pH-responsive double-network(DN)hydrogel with high strength and toughness,consisting of a B(OH)4-linked hydroxypropyl guar gum(HPG)network and a covalently cross-linked polyacrylamide(PAAm)network.The ion that can interact with 1,3-type hydroxyl substitution of HPG is B(OH)4-,certain effects of the B(OH)4-ions on complexation are due to the sodium borate hydrolysis.The resulting DN gel exhibited unique pH-responsive properties and excellent mechanical properties,with a fracture stress of 843 kPa,and an excellent extensibility of 1400%(12-14 times its initial length).It is interesting to find that the HPG/PAAm DN hydrogel possesses pH-responsive ability.Among the responsive hydrogels composed of natural polymer and synthesized polymer,the prepared DN gels are extremely tough.(2)In previous study,we obtained a tough and pH-responsive hydroxypropyl guar gum(HPG)/polyacrylamide(PAAm)hydrogel.The HPG networks in gels are linked by weak reversible dynamic covalent interactions,while the PAAm are covalently cross-linked,it only possesses self-recovery under small deformation.We report the facile synthesis of a hydroxypropyl guar gum(HPG)/poly(N,N-dimethylacrylamide)(PDMA)hybrid hydrogel with efficient and fast healing capability.HPG networks were formed by hydrogen bonds between the hydroxyl groups at HPG chains,and PDMA networks were self-cross-linked without any chemical cross-linker.The physical cross-linking also formed among the HPG and PDMA chains.We chose nano-silica solution as connectors,which have plentiful hydroxyl groups on the surface.The gels are demonstrated to fully heal at room temperature with the help of nano-silica,the healing efficiency can achieve 102% after 2 h.