Preparation And Characterization Of Pectin-Based High Strength Hydrogel

Hydrogel,a kind of wet and soft smart materials,have been widely used in many fields,such as tissue engineering,drug delivery and so on.However,conventional hydrogels usually lack effective mechanical properties,which restrain their application in some fields,especially in the field of load-bearing tissues repair.Double network?DN?hydrogels based on the concept of“sacrificial bond”have made progress in enhancing mechanical properties largely through the cooperation of two networks.We prepared a newly pectin-based high strength hydrogel via a two-step method according to the concept of“double network”.Firstly,a pectin/PAAm single network hydrogel was prepared by photoinitiated free radical polymerization of acrylamide?AAm?and N,N-methylenebisacrylamide.Secondly,we acquired the pectin-Fe³⁺/PAAm DN hydrogel through introduction of Fe³⁺ions into SN hydrogel,which originated from complexation reaction between Fe³⁺ions and–COO^-of the pectin chain,achieving cross-linking between chains of pectin.During the process of experiment,the effects of the content of cross-linking agent,soaking time,solid content,concentration of FeCl₃ solution,and the ratio of the two network components on the mechanical properties of the obtained hydrogel were studied in detail and we obtained the optimum process parameters for the preparation of DN hydrogels,the resulting pectin-Fe³⁺/PAAm DN hydrogel demonstrated excellent performance with a high tensile strength of 0.9 MPa,a high stretch ratio of 1300%,elastic modulus of1.46 MPa,amazing toughness of 7.82 MJ/m³,excellent tearing energy of 3785 J/m²and more than 85%of equilibrium water contents.Through the tracking and testing of the mechanical properties of pectin-Fe³⁺/PAAm DN hydrogel during cyclic loading-unloading process,the toughening mechanism of DN hydrogel was proposed,ie,the first network unzipped to enhance energy dissipation and the second network provide elasticity to bridge cracks and keep the structure stable.Based on previous study,through introducing magnetic iron oxide nanoparticles into DN hydrogels,we endowed magnetic response to hydrogels without impairing mechanical properties.The results showed that the crystal structure of prepared iron oxide nanoparticles had a spinel crystal form with a particle size range of 10¹9 nm and exhibited good superparamagnetic properties.At the same time,the prepared magnetic DN hydrogel not only had high mechanical properties,but also exhibited excellent superparamagnetic properties.The research results will provide experimental basis for the design and application of high-strength hydrogels.