Preparation And Properties Of High-strength And Self-healing Hydrogel Based On Physical Crosslinking

Hydrogels are biocompatibility and stimuli-responsive materials that have achieved greater progress in tissue engineering,biomedicine,artificial intelligence,and software robots,etc.However,traditional hydrogels usually do not have high mechanical properties and limit their application.Physically crosslinked hydrogels are hydrogels that introduce physical crosslinks(hydrogen bonds,electrostatic interactions,ionic bonds,etc.)in the hydrogel network to increase the mechanical properties of hydrogels by dispersing stress.In this paper,we introduce of ionic bonds and hydrogen bonds in hydrogels,and then study the influences of the ionic bonds and hydrogen bonds on the mechanical properties of hydrogels.Studies have shown that ionic bonds and hydrogen bonds form energy dissipating mechanisms in hydrogels to improve the mechanical properties of hydrogels.The specific research results are as follows:1.Poly(acrylic acid)/diethylenetriamine(PAAc/DETA)hydrogels were prepared by free radical polymerization of acrylic acid(AAc)in small molecule diethylenetriamine(DETA).Commercialized small molecule with three amino groups,diethylenetriamine(DETA),is applied to crosslink polyacrylic acid(PAAc)chains via ionic bonding and the complex of PAAc chains and DETA form hydrophobic domain in the hydrogel network.The cooperation of ionic bonding and hydrophobic interaction drastically improve the mechanical properties that can be modulated by the molar ratio of PAAc and DETA.Due to the physical interaction of crosslinks,the hydrogels can self-heal rapidly.The thermal responsiveness of the rheologic property of hydrogels endow it with shape memory behavior.2.Poly(acrylic acid)/poly(allyl amine)(PAAc/PAH)hydrogels were prepared via one-pot free radical polymerization and characterized by mechanical testing and rheometer.The results indicated that multiple ionic bonds including strong and weak interaction were formed between the carboxyl groups of poly(acrylic acid)and the amino groups of poly(allyl amine).The weak ionic interaction breaks to dissipate the energy generated during the hydrogels stretching,consequently,the PAAc/PAH hydrogels exhibit excellent mechanical strength and toughness.The reversible ionic bonding also endows PAAc/PAH hydrogels with quick self-healing ability.The addition of counter-ions weakens the electrostatic interactions between polyelectrolytes to impair the strength of hydrogels,and the hydrogels can be recover to original mechanical properties after removing the counter-ions via dialysis.Therefore the cut hydrogels can be healed effectively by usage of saline and recovered to relatively high mechanical strength and toughness.3.L-polyglutamic acid is a polyamino acid with a secondary structure(α-helix)and contains a large number of hydrogen bonds in the molecule.The hydrogen-bonded physically cross-linked polyacrylic acid/L-polyglutamic acid hydrogel was prepared using acrylic acid as a monomer and an olefin-modified L-polyglutamic acid(allyl-L-PHPG)chemical crosslinker.Through the mechanical properties test,it has been shown that the secondary structure of allyl-L-PHPG in polyacrylic acid/L-polyglutamic acid hydrogel has the effect of enhancing hydrogel.The alternating change of storage modulus(G’)and loss modulus(G’’)in rheological experiments shows that Gel L has self-healing properties.Gel L self-healing was performed by shear self-repair experiment of Gel L hydrogel.Hydrogels have considerable self-healing properties.In this article,we have constructed PAAc/DETA hydrogel with high-strength,self-healing and temperature responsive shape memory by polymerizing diethylenetriamine as a crosslinking agent with acrylic acid.PAAc/PAH hydrogels with ionic bond crosslinker have strong mechanical properties.Hydrogen bonds of L-polyglutamic acid act as sacrificial bonds during stretching to increase the mechanical strength of the hydrogel.High-strength,self-healing hydrogels have potential applications in tissue engineering and biopharmaceuticals.