Study On Synthesis And Application Of Self-healing High-Performance Stimulus-Response Hydrogel

Hydrogels have attracted wide attention due to the high water content,biocompatibility,self-healing,and smart responsiveness,and have been applied in tissue engineering,soft machinery,water treatment,sensors,and other fields.At present,the research on hydrogel applications,stimulating responsive hydrogels,and conductive hydrogels are the two most popular directions.Stimuli-responsive hydrogels,also known as smart hydrogels,the shape or color of hydrogels change under external stimulation,such as photosensitive hydrogels,p H-sensitive hydrogels,and temperature-sensitive hydrogels.Conductive hydrogels are mainly used as flexible sensor materials,which could detect the external stress and the movement of external objects.Compared with traditional chemical crosslinked hydrogels,physically crosslinked hydrogels(crosslinked structures formed by non-covalent bonds,such as hydrophobic association,π-π stacking,hydrogen bonding,and electrostatic interactions)often exhibit good self-healing properties.However,in recent reports,physical crosslinking hydrogel mainly faces two limitations,one is the limitation of strength and self-healing efficiency.High strength and self-healing ability are the two important properties for the practical application of physically crosslinked hydrogels.However,the two properties of high strength and high self-healing efficiency are often contradictory in hydrogels,and it is still challenging to prepare hydrogels with high strength and high healing efficiency.In our previous works,some general methods to improve the mechanical properties and self-healing efficiency of hydrogels have been proved,such as combining crystallization microdomains,ionic interactions,and hydrophobic association crosslinking to synthesis composite gel system with the supramolecular crosslinking network.The results show that the formation of various physical crosslinking structures is conducive to obtain high strength and high selfhealing hydrogels.The use of hydrogels with good mechanical properties and selfhealing properties will be the basis for our further research on hydrogel applications.Another limitation is the development and application of the healing property.Currently,the application of the healing property is mostly limited to the repair of damaged hydrogels,and some reports involve reshape and recyclability,but still far from showing the importance of healing properties for hydrogels.When need to prepare hydrogels with complex structures,such as double-layer structures and massive splice structures,complex molds or injection molding equipment are often used without taking full advantage of the healing properties of the hydrogels.One of the purposes of this paper is to combine the healing properties and functions of the hydrogels,which can bring about the processability of the hydrogels through selfhealing and remolding properties,and further combine with the functionality of the hydrogel to increase the functionality and application scope of the hydrogels.In order to explore the self-healing high-performance stimulus-responsive hydrogels and the potential application prospects,three parts of research work based on hydrophobic association polyacrylamide gels were processed firstly:1.For the purpose of obtaining a hydrogel with both high strength and high selfhealing properties,the hydrophobic association cross-linked network and the ionic cross-linked network were combined to obtain a physically cross-linked dual network hydrogel.In chapter 2,a semi-interpenetrating structure hydrophobic association polyacrylamide /sodium alginate composite hydrogel was prepared and immersed in an aqueous solution containing calcium or iron ions to obtain composite hydrogels with dual physical crosslinking network structures.The hydrogels exhibited excellent mechanical properties and special high healing properties and have a processing performance resulting from its healing properties.Through the healing and immersion treatment,the double layer non-uniform hydrogels with different cross-linking degrees were formed.Through this non-uniform structure,a simple hydrogel actuator was obtained.and artificial muscles such as the hydrogel can be made.It has a certain significance.This is of great significance in the manufacture of artificial muscles by hydrogel materials.2.The response speed of the gel driven by swelling-drying is slow.In order to obtain the hydrogel with rapid response,the physical hydrophobic association crosslinked network and chemical cross-linked network were combined in chapter 3,the hydrophobic association polyacrylamide hydrogel with good self-healing properties is combined with a thermal sensitive poly N-isopropylacrylamide hydrogel.A dual network structure hydrogel with good self-healing ability and fast thermal sensitivity was prepared.Because the thermal sensitivity is within the range of human body temperature,it can be used as a thermal sensitive material for human body temperature trigger.In addition,the self-healing ability brought the ability of the hydrogel to be spliced and remolded.Therefore,the hydrogel could be reconstructed into various shapes according to the specific needs,and it still maintained the fast response to temperature stimulation.According to the design sequence,hydrogel films with different thermal sensitive patterns were arrayed,and the patterns could be stimulated by the body temperature.Based on this characteristic,this hydrogel could be used as reusable materials for recording and displaying information.3.Compared with the physical dual network hydrogel,the self-healing efficiency of the physical-chemical cross-linked dual network hydrogel is significantly reduced.In order to improve the self-healing efficiency of the physical-chemical cross-linked dual network hydrogel,in chapter 4.the nano two-dimensional material MXene was introduced into the physical-chemical cross-linked dual network hydrogel.In this paper,we prepared composite hydrogel sensors contained MXene with temperature sensitivity and stress sensitivity based on poly N-isopropylacrylamide hydrogel and hydrophobic association polyacrylamide hydrogel as a matrix.The composite hydrogel exhibited excellent mechanical properties and could stretch to more than 14 times the original length.The tensile strength reaches 0.4MPa and exhibited a good self-healing ability.It is of great significance to the practical application of hydrogels.The conductivity of composite hydrogel was 1.092 S/m,which was 15 times that of the hydrogel without MXene.The potential of the composite hydrogel as an intelligent compression sensor was verified by conductivity tests.When the compressive strain sensor was combined with temperature sensitivity,the composite hydrogel showed a great difference in the rate of change of the current.Under the same test conditions,compared with the gel without thermal sensitivity,the current change of the composite gel was much more significant.So it could be used to distinguish whether the compressed object is a room temperature object(such as a glass chip)or a certain temperature object(such as a finger).Therefore,the hydrogel has the potential of application as an intelligent thermal-sensitive compression sensor.Although the composite gel with hydrophobic association hydrogel as the matrix exhibited a high self-healing ratio,the healing rate was still low,and it often takes three days or longer to achieve a high healing ratio.To achieve the requirement of fast healing,the fourth part was based on the hydrogen-bonded poly Nacryloylglycinamide gel:4.In chapter 5,we synthesized iron-loaded polydopamine nanoparticles(PDAFe)with excellent photothermal effect and a vinyl monomer,n-acryloyl glycine amide(NAGA),which has dual-amide in one side group.Furthermore,the composite gel containing water and glycerol as the mixed solvent was further synthesized,and then the composite gel was used as the conductive sensor.Without the addition of any chemical crosslinking agent,the composite gel formed by hydrogen bond crosslinking showed excellent mechanical properties and thermal healing ability.Its sensitive and accurate stress conductivity changes could meet the requirements of some sensor materials such as wearable devices.And its good water retention ensures long-term stable useability.Moreover,due to the addition of photothermal agent PDA-Fe,the gels showed good photothermal properties.Under the NIR laser irradiation,the temperature rapidly increased to the sol state,so the gel showed "weldability".The good photothermal effect and self-healing ability greatly expand the application scope of gel materials.The PNAGA-PDA-Fe composite hydrogel has potential application in artificial muscle,biological tissue engineering,medicine,and other fields.It is of great significance for the wider application of gels.