Preparation And Performance Of Stimuli-responsive Hydrogels Based On Spiropyran

Stimuli-responsive hydrogels respond to stimuli external environment,including color,swelling ratio,shape,mechanical properties,and gel-sol transition.Stimuli-responsive hydrogels have excellent controllability,smart responsiveness,and good biocompatibility,and are used in drug slow-release carriers,smart switches,information recording,display and storage,flexible wearable devices,actuators,and sensors,etc.However,the single functionality and weak mechanical properties of stimulus-response hydrogels generally limit their further applications.Therefore,in this paper,high strength multi-stimulus response hydrogels were prepared through structural design to enhance the mechanical properties and functionality of hydrogels.1.The organic dye spiropyran（SPMA）was introduced into the hydrogel macromolecular network through the method of micellar copolymerization,and the Poly（sodium acrylate-co-methyl acrylate-co-spiropyran）P（SA-co-MA-co-SPMA）photochromic hydrogel was successfully prepared.Physically cross-linked of Ca²⁺to obtain a high-strength ion hybrid cross-linked photochromic hydrogel.The research results show that the hydrogel has excellent mechanical properties.The tensile strength,elongation at break,work of tension,and elastic modulus are 3.22 MPa,658%,12.88MJ m^-3,and 10.3 MPa,respectively.This is mainly due to the metal coordination complexation of–COO^–and Ca²⁺.After UV irradiation,due to the ionic interaction between the zwitterionic MC and Ca²⁺formed after the SP ring is opened,the mechanical properties of the hydrogel are further enhanced.The tensile strength and elongation at break are 3.7 MPa and 756%,respectively,increasing by about 14.9%.Besides,the hydrogel has excellent light response behavior,reversible light conversion performance,and good anti-fatigue performance,so it has potential application prospects in repeatable information recording,flexible visual display and light-controlled switches.2.The light,heat and p H multiple stimuli-responsive Poly（N’-isopropylacrylamide-co-methylacrylate-co-spiropyran）hydrogel P（NIPAM-co-MA-co-SPMA）was prepared by a simple"one-pot"method.The mechanical properties of hydrogels can be enhanced through dual networks.After adding Poly-2-acrylamido-2-methyl propane sulfonate（PNa AMPS）,the tensile strength,elongation at break,work of tension,and elastic modulus are 320 k Pa,350%,548 k J m^-3,and 78 k Pa,respectively.The hydrogel has excellent sensitivity to multiple stimuli of light,heat and p H.The swelling/deswelling performance can be controlled by light,heat,or p H stimulation,and it has repeatability.Adjust the low critical solution temperature（LCST）of the hydrogel by changing the hydrogel network structure or acrylic acid（AA）concentration.Besides,the hydrogel has excellent photochromic and acidichromic properties.The coloring/fading kinetics shows that SP-MC has stable reversible conversion properties.By adjusting the temperature,the programmable shape memory and thermally actuated behavior of the hydrogel are realized,and it has potential application prospects in drug release,smart switches,and soft actuators.