Preparation And Properties Of High Strength Multi-crosslinked Network Hydrogels

Hydrogel is a kind of high molecular weight polymer with three-dimensional network structure,high water absorption capacity,a wide range of applications,including industrial,agricultural,sanitary,medical,pharmaceutical and other fields.In recent years,high-strength,biocompatible hydrogels have made up for the shortcomings of the lack of mechanical strength and application of traditional hydrogels,which have attracted the interest of researchers.The scientific researchers have developed a variety of high-strength hydrogels,such as double-network hydrogels,multi-crosslinked hydrogels,and hybrid hydrogels,which greatly enhance the hydrogel's Strength and biocompatibility,and extend the applications fields of hydrogels.This article combined chemical covalent bonds and physical cross-linking to prepare multi-cross-linked high-strength hydrogels,and further added physical cross-linking networks and interpenetrating networks on the basis of chemical cross-linking networks,through coordination among multiple networks,greatly improved the hydrogel's mechanical properties,and increased the hydrogel's mechanism of energy dissipation to make it have a certain application value in articular cartilage.This article mainly includes the following aspects:1.A multi-cross-linked PAM/PAA/PVA hydrogel was prepared using a one-pot two-step process.First,in situ radical polymerization of AM,AA monomers and cross-linker form a chemically cross-linked network,where Ca2+ and carboxylate of PAA is ionically coordinated to form a physical crosslink,while the coexisting PVA chain forms an interpenetration with a chemically cross-linked and physically cross-linked network.Then the hydrogel is subjected to freeze-thaw treatment to form a semi-crystalline region in the hydrogel,thereby forming physical cross-linking to enhance the toughness,tensile strength and compression performance of the hydrogel.The hydrogel prepared by this method has a compressive strength of 11 MPa and a tensile strength of 0.8 MPa.When subjected to external forces,the dynamic ion coordination bonds of PAA and Ca2+ and the semi-crystalline domains of PVA can be as effective sacrificial bonds to dissipate energy.This method introduces a variety of cross-linking methods to form a variety of cross-linked networks,which can effectively improve the mechanical strength of hydrogels.And the raw materials are cheap and easy to obtain,and they also have good biocompatibility,which makes the hydrogel have a good application value.2.A PAM/PVA/AS hydrogel was prepared by using a three-step process.Firstly,the AM,PVA,and AS are uniformly stirred,and the AM monomer was radically polymerized to form a chemically cross-linked network.Freeze-thaw treatment then proceeded to form semi-crystalline domains,forming a physically cross-linked network.Finally,the hydrogel was introduced into an ethanol/water solution of CaCl2.On the one hand,the guluronic acid(G unit)in different AS chains were cross-linked with Ca2+ for double bond ionization to form a dynamic reversible physical crosslinking network,on the other hand,dehydration of hydrogels increased the entanglement between the various molecular chains of the hydrogels formed phase separation,increasing the hydrogel's mechanical properties.The cross-linked physical networks by AS have dynamic reversibility and enormous energy storage.When subjected to external forces,broken ion bonds can dissipate energy,protect the chemical network to maintain the morphology of the hydrogel.And the hydrogels have the ability of self-repairing energy.The rapid recovery of ionic bonds can in turn store energy.The introduction of PVA to the hydrogels can improve the tensile strength and greatly improve the compression performance.The hydrogels have a compressive strength of 9 MPa,a tensile strength of 0.573 MPa,and an elongation rate of more than 1300%.So the hydrogels prepared by this method have better practice application.