Preparation Of Self-healing Alginate Hydrogel And PH-responsive Research Based On Reversible Covalent Cross-linked

The alginate hydrogel is a hydrophilic system that forms three-dimensional network space structure inside by cross-linking.Due to the wide range of raw materials of alginic acid,it has excellent properties such as non-toxicity and good biocompatibility,making alginate hydrogel widely used in biomedicine,drug release and other fields.In this paper,the reversible dynamic covalent bond was introduced into the alginate hydrogel.When the pH value of the external environment changes,the gel system reversible breaks and recombines,and the gel-sol interaction is realized.At the same time,the gel system has self-healing properties.In this work,oxidized sodium alginate with aldehyde group and polyethylene glycol with hydrazide group at the end and using both as raw materials and chitosan.Preparation of two types of self-healing alginate hydrogels with pH-responsive cross-linked based on dynamic covalent bonds.The results of the study are as follows:(1)Gelators’ synthesis:Oxidized sodium alginate(ADA)with aldehyde groups was obtained by sodium alginate oxidizing sodium alginate.The generation of aldehyde groups was proved by infrared spectroscopy.Three kinds of oxidized sodium alginate with the actual oxidation degree of 9.23、28.3、47.37 were obtained.Polyethylene glycol-dibenzoyl hydrazide(G2)with a hydrazide group at the end was synthesized by esterification,nucleophilic substitution,and ester hydrolysis.The structure was characterized by 1HNMR,and the end capping rate was 97%.(2)Preparation and characterization of alginate hydrogels:The aldehyde group of the oxidized sodium alginate(G1)with degree of oxidation of 50%and the hydrazide group of the polyethylene glycol-dibenzoyl hydrazide(G2)were cross-linked to form an acyl hydrazide bond to prepare a mass concentration of 10wt%hydrogel(HG1G2)system.Judging the formation of hydrogels by inverting legislation,characterized by FTIR analysis of G2 and hydrogel(HG1G2),the results showed that the hydrogel is chemical gel that is cross-linked by covalent bonds.The examination of the swelling rate showed that the swelling rate increased with time in 20 hours,and the mass increased to 1.95 times the original,reaching a balance of swelling in 50 hours.The rheological properties of the hydrogel(HG1G2)were measured by a rheometer,the results showed that the gel interior was closer to the three-dimensional network structure,which was presented in the gel state and had better elasticity.The SEM characterization of the hydrogel(HG1G2)showed that the internal surface was a three-dimensional network structure;The aldehyde group of the oxidized sodium alginate(G1)with degree of oxidation of 50%with the acyl group of PEG-dibenzoyl hydrazide(G2)and the amino group of chitosan(CS)to form an acyl bond and imine bond by covalent cross-linked,preparation of hydrogel(HG1G2CS)system with concentrations of 10wt%、20wt%、30wt%respectively.Judging the formation of hydrogels by inverting legislation,the FTIR analysis of G2、hydrogel(HG1G2CS)、chitosan(CS)showed that the hydrogel was chemical gel that was cross-linked by covalent bonds.The swelling rate of hydrogels(HG1G2CS)at different concentrations was examined.The results showed that the hydrogels(HG1G2CS)with 10%、20%、30 wt%concentration increased 1.81、2.17、2.75 times with time in 20 hours,reaching a swell balance in 50 hours.The mechanical properties were tested by an electronic universal material testing machine.The results showed that with the increase of the mass concentration,the cross-linked density is greater,the three-dimensional network system is more stable,and the mechanical properties of the gel are better.The SEM characterization of the hydrogel(HG1G2CS)results in a higher density of cross-linked due to the cross-linked of the two networks,the results show that the three-dimensional network structure of the internal surface is more stable.(3)pH response and self-healing of alginate hydrogel:Under acidic conditionsthe,the mass concentration of 10wt%hydrogel(HG1G2)system can achieve 5 gel-sol interactions and self-healing,the mass concentration of 30wt%hydrogel(HG1G2CS)system could achieve 14 gel-sol interactions;the mass concentrations of 10wt%、20wt%hydrogel(HG1G2CS)and different mass concentrations hydrogels(HG1G2CS)have self-healing properties under acidic conditions.Aniline accelerates the exchange of hydrazide bonds under neutral conditions to achieve self-healing.