Fabrication Of Shape Memory Hydrogels With Highly Mechanical Performances Based On Polysaccharides

Hydrogels,constituted by a three dimensionally hydrophilic network and entrapped plenty of water while preserving their network structure integrity,has several advantages to traditional material,such as high porosity ratio,high water content and high ion permeability.Due to its innate similarity to biological tissue,hydrogel has many potential applications in drug delivery,artificial organs,flexible sensor and biological engineering.Depending on difference in external stimuli,Shape-memory hydrogels?SMHs?as a type of hydrogels can remember one shape,and return to the original shape.Although some progress have been made,SMHs still obtain a deficiency in mechanical properties,which seriously impede its stability to more complex situation.In addition,most SMHs only can remember one shape in response to external stimuli,few SMHs gain multi-shape memory abilities,which could cause lack of competitiveness in more and more austere challenge from work environment.Moreover,it is urge to prepare hydrogel with high strength and multi-shape memory abilities in a simpler way.In recent years,significant advances on understanding energy dissipation mechanism has been made.Double network on SMHs rise in response to the proper time and conditions for reversing deficiency in mechanical performance.Therefore,high strength shape memory hydrogel based on polysaccharide was synthesized by‘one pot'method.A multi-physically crosslinked hydrogel with high strength and shape memory has been synthesized by polymerization of acrylamide in mixed solution of PVA,?-carrageenan and calcium chloride followed by freezing-thawing process.?-carrageenan as a highly sulfated natural polysaccharide extracting from certain species of algae often accompanied by the reversible formation of a helix conformation,and the coil-to-double helix transition can be adjusted by temperature,which could act as temporary crosslink point for shape memory ability.Besides,ionic interaction between Ca²⁺and polymer network can be as‘sacrifice bond'to dissipate energy.Due to the fully physical cross-links,the prepared hydrogels exhibited high fracture strength,extraordinary toughness?5.14 MJ/m³?and good stability on stress.The hydrogel could withstand at least twenty times strain deformation?10³00%?without any change in stress peaks,indicating its fatigue resistance.Moreover,unlike most reported hydrogels based on permanently chemical crosslinked network,hydrogels prepared in this work could repeatedly remodel its shape as needed for many times through heating.This property favors the recycle use of the hydrogels.Furthermore,on account of the existence of ions,the hydrogel are conductive and the conductive ability is strain sensitive,and it can produce stable electronic signals under repeat stretching,making the hydrogels as a promising sensor to monitor motion.In order to further improve performance both mechanical and shape memory abilities,we show a facial method to prepare high strength multiple SMHs by copolymerizing of negatively charged acrylic acid and hydrophobic stearyl methacrylate under the presence of chitosan quaternary ammonium and Tween 80.The electrostatic interactions between acrylic acid and chitosan quaternary ammonium together with the hydrophobic interactions of alkyl chains in stearyl methacrylate endow the hydrogel with great stain-stress?906%,1.64 MPa?and fatigue resistance.Furthermore,the prepared hydrogels exhibit excellent shape memory triggered by heat,pH and saline solution due to these reversible and independent interactions,which can be combined to achieve multiple shape memory properties.