Preparation And Applications Of Multi-triggered Hydrogels

Hydrogel is a hydrophilic polymer network system with three-dimensional cross-linked structure.Stimulus-responsive hydrogel can trigger reversible phase transition under external factors,such as p H,light,and temperature,which demonstrates potential applications in drug delivery,clinical diagnosis,and tissue engineering.However,the majority of stimuli-responsive hydrogels reported up to now response to simple single response.Therefore,it is of great significance to develop multi-component hydrogels as a new generation of"smart"soft materials.In this work,multi-component supramolecular hydrogels and double-layer polymer hydrogels were prepared by self-assembly of graphene oxide（GO）,polymer chains,and biomolecules,respectively.Moreover,the stimuli-responsive behaviors of GO-based hydrogels were studied.The content of the dissertation is as followsThree representative hydrogels,including GO/PVA/G4/H,GO/PVA,andGO/G4/H systems,were prepared by a simple self-assembly strategy of GO nanosheets,polyvinyl alcohol（PVA）chains and G-quartet-hemin（G4/H）nanofibers,respectively.Next,the morphology and mechanical properties were characterized by using scanning electron microscopy（SEM）,rheological measurement and Raman spectroscopy,The SEM images showed that the prepared GO/PVA/G4/H hydrogel exhibited a honeycomb 3D network structure,while the GO/PVA and GO/G4/H samples showed irregular and porous discontinuous network structure,respectively.Moreover,the GO/PVA/G4/H hydrogel had the highest storage modulus is 14000 Pa which exhibited excellent mechanical strength,followed by GO/PVA is 10000 Pa and GO/G4/H is 2000 Pa.In addition,the gel exhibited a p H-stimulated responsive behavior,where a phase change could be performed between the gel state and the quasi-liquid state through p H triggering.The change could be repeated in a reversible and cyclic manner.Based on the reversible and cyclic phase transitions between solution and hydrogel states,the hydrogel could be used as an“ink”for injectable 3D printing of different shaped patterns,such as heart,star,etc.Due to the synergistic effect of catalysis of G4/H and GO nanosheets,the hydrogel demonstrated an excellent peroxidase-like activity which catalyzed the substrate TMB into its blue product in the presence of H₂O₂.Based on this,the hydrogel was coated on indium tin oxide（ITO）electrode,and an ultrasensitive detection of H₂O₂ was achieved by electrochemical methods.This biosensor demonstrated a dynamic detection spanning 7 orders of magnitude,with a detection limit as low as n M order.In addition,AND and OR logic gates based were bulit by coupling the p H-responsive properties and enzymatic reactions.In the logic gate,the inputs of glucose,lactose and Fe³⁺led to a sol-gel change as the output.More interestingly,two logic gates could be restored to the initial state by adding urea as reset agent.An asymmetric double-layer polymer hydrogel was developed by using GO nanosheets.The first layer was polymerized by GO and N-isopropylacrylamide（NIPAM）,which responded to temperature and near-infrared（NIR）light.Moreover,the second layer was prepared by GO,PVA,and chitosan by freezing and thawing,which responded to water and p H.It was found that the hydrogel containing two gel layers responded to multi-stimuli,such as p H,temperature,and NIR.It was reasoned that each layer contained independent stimulus-responsive element to control the switchable bending of this layer.The double-layer hydrogel demonstrated great potential in sensor,actuator,biomedicine,and intelligent robots.