Synthesis And Characterization Of Supramolecular Hydrogel With Thermo-Sensitivity Driven Large-Scale Crack Self-Healing

Inspired by the self-healing properties of organisms,scientists have extensively designed and imparted self-healing properties to polymer materials.Because hydrogels are close to biological tissue,researchers in this field are committed to transforming traditional hydrogels into smart materials with self-healing capabilities.As one of the most common thermo-sensitive hydrogels,poly?N-isopropylacrylamide??PNIPAAM?has been extensively studied.Since its volume phase transition temperature?VPTT?is around 32?,the volume of the hydrogel will undergo significant expansion or contraction changes with temperature varying around the volume phase transition.However,there still exist some problems for most of the environmentally responsive self-healing hydrogels:On the one hand,the internal networks of the traditional hydrogels are relatively simple,lacking design for regular structure and uniform network,which limits smart hydrogels'comprehensive performance.On the other hand,most of the current studied self-repairing hydrogels are only capable of self-repairing microcracks with a crack width less than 250?m.When larger crack happened,it is often necessary to put the separated surfaces into contact manually,otherwise,the traditional hydrogel mechanism cannot play its role.Accordingly,a temperature-sensitive supramolecular hydrogel capable of self-repairing large cracks was designed and prepared in thisresearch.According to our design,atom transfer radical polymerization?ATRP?and click chemical reaction were first applied for the controllable synthesis of the building blocks.In this study,adamantane as the core and N-isopropyl acrylamide?NIPAM?as monomer were used to synthesize the dual-arm temperature-sensitive polymer Ad-?PNIPAM-?CD?₂ with terminal?-cyclodextrin and the four-arm temperature sensitive polymer Ad-?PNIPAM-Ad?₄with terminal adamantane.The two polymer units were then constructed into a supramolecule self-healing hydrogel by reversible self-assembly between the?-cyclodextrin hosts and the adamantyl guests.The formed hydrogel has a uniform,regular,porous network structure.The test results showed that the hydrogel had a VPTT of about 31?,with a volume swelling ratio of 22.58%in the range of 50?to 15?,so the hydrogels have the basic conditions for regulating the crack scale.Systematic study on the self-healing properties was then carried out for the prepared hydrogel.The rheological test shows that the hydrogel has fast and reproducible self-healing properties at both 37?and 27?,and the self-healing efficiency of the hydrogel adhered for 5 minutes after cutting can reach 93.20%.Further,we tested the self-healing process of hydrogels by Raman spectroscopy.The self-healing mechanism of the hydrogel were verified from a microscopic perspective that the self-repairing ability of the hydrogel was mainly due to the reversible self-assembly of the adamantane guest and the?-cyclodextrin host on the hydrogel crack surfaces.Due to the temperature sensitivity of PNIPAAM in the main chain,the hydrogel can adjust its volume according to the temperature,so that the damaged large crack can be automatically self-repaired.For example,the hydrogel sample with a length of 3 cm can self-repair large cracks with a maximum width of 3.5 mm,and the repaired hydrogel can be repeatedly remolded and repeatedly self-repair large cracks.Finally,through a simple temperature-controlled water valve device that was made in our laboratory,it was more visual to verify the hydrogel's powerful ability to self-repair large cracks under temperature regulation.Cytotoxicity and cell encapsulation experiments showed that the obtained hydrogel has low cytotoxicity and good biocompatibility.In view of the new structural design,excellent overall performance and unique self-repairing large crack function,we believe that this research not only has important theoretical significance for the study of new topological polymers and self-repairing hydrogel materials,but also plays an important role in promoting the application of hydrogel materials in biomedical,intelligent sensing,and intelligent textiles.