Design,Synthesis And Application Of Shape Memory Self-healing Hydrogels

Shape memory hydrogel is a kind of universal material with good tunability and machinability,whih has a wide range of applications in the fields of children’s toys,intelligent wearable and soft robots.However,the single shape memory hydrogels under external stress is vulnerable to the irreversible damage,serious limits its widespread application.In this paper,from different triggering mechanisms（such as water triggering based on ion hydrophobic action,p H and metal ion triggering based on imine bond and ionic bond,temperature triggering based on gelatin hydrogels）,we introduce shape memory and self-healing properties into hydrogels at the same time,and explore the potential applications of hydrogels.The main research conclusions are as follows:1,In order to make the water gel has shape memory performance and responsiveness to temperature,The temperature-sensitive monomer N-isopropyl acrylamide was copolymerized with amphoteric ions in this chapter,Through the synergistic action between hydrogen bond ion interaction and hydrophobic action,an ionic hydrogel with water-driven shape memory property and automatic transparency change with temperature change is formed（NIPAM-DMAPS）.Hydrogels can fix temporary shape in 20%Na Cl aqueous solution（within 20min）and restore permanent shape and transparency in deionized water（within 5min）.By changing the ratio between NIPAM and DMAPS,the hydrogel can achieve self-change in transparency at different temperatures.Therefore,we put NIPAM₁-DMAPS₂ hydrogel in a sandwich between two layers of transparent glass to prepare a sandwich structure of smart window.The upper limit transparency temperature of hydrogels can be adjusted between 10℃-30℃,and the transparency is more than 80%.At the same time,the shape memory performance of the hydrogel also enables the transparency of this smart window to be artificially interfered with by Na Cl solution.2.Self-healing hydrogels with various shape memory properties were prepared by one-step polymerization.The synergy between the physical network of dynamic electrostatic interactions and the chemical network provided by imine bonds gives hydrogels excellent tensile fracture strength and self-healing properties.Through the construction of reversible physical crosslinking points,the temporary shape of the hydrogel can be fixed under two different types of stimuli:p H value and metal ions(Ag⁺Zn²⁺,etc.),with a minimum shape fixation time of 15 seconds.In addition,the hydrogel is also used in the manufacture of resistive strain sensors and capacitive pressure sensors,both of which have high sensitivity,stability and circulability.The sensor can detect various types of body movements,such as finger flexing,swallowing and pulse.3.By adding host-guest interaction into gelatin hydrogels,the mechanical properties of hydrogels were not only enhanced,but also endowed with self-healing properties and shape memory ability.A self-healing hydrogels with direct writing ability for shape memory was prepared.With the introduction of host-guest network,gelatin hydrogels can be cured twice,which greatly enhances the mechanical properties of hydrogels.The weak non-covalent bond can be quickly reconstructed by host-guest recognition and random line conformation of gelatin molecules at high temperature when the hydrogels break,which makes the hydrogels have excellent self-repair and shape memory.At the same time,the rapid sol-gel transformation of gelatin hydrogels makes the hydrogels have the ability of writing directly.