Study On The Self-Healing Mechanism Of Hydrogel Made From Sodium Alginate And Chitosan Quaternary Ammonium Salt

Self-healing hydrogel has high stability and long life characteristics,which structure can recover after being subjected to external force.Notably,the self-healing hydrogel based on electrostatic interaction can be easily prepared under mild gelation conditions,physiological conditions.Therefore,it has received extensive attention in biomedical fields.However,the self-healing mechanism of hydrogel based on electrostatic interaction are still not clear,which poses great difficulties to prepare hydrogel with different performance requirements.Herein,we reported a kind of self-healing hydrogel based on electrostatic interaction,which prepared by natural weak polyelectrolyte polysaccharide sodium alginate(Alg)and 2-hydroxypropyltrimethylammonium chloride chitosan(chitosan quaternary ammonium salt,HACC).The thermodynamics and molecular conformational of the formation of the polyelectrolyte composite were analyzed under different conditions.Then,we combined thermodynamics and conformational behavior about Alg-HACC polyelectrolytes to reveal the self-healing mechanism,which would offer improved approach to design special,functionally tunable Alg-HACC self-healing hydrogel.The research contents are including:First,the composite thermodynamic characteristics of the formation of the polyelectrolytes composite were investigated.The heat released from the reaction between Alg and CTS is AHAlg-CTS=-851 cal/mol,which mean that the binding was driven by enthalpy and entropy.While the heat released from the reaction between Alg-HACC is AHAlg-HACC=482 cal/mol,which is driven by entropy.The thermodynamic of the formation of Alg-HACC composite at different pH were also characterized.The results showed that there was a exothermic reaction when pH<3.93,but a endothermic reaction when pH>3.93.And the ratio between HACC and Alg decreased with the increase of ionic strength.When using Ac-replace Cl-,the interaction between HACC and Alg was enhanced,showing a exothermic reaction.Then,the conformational characteristics of polyelectrolytes and their composites were studied.The binding force between HACC and chloride ion is stronger than the binding force between CTS and chloride ion,resulting in weaker intramolecular electrostatic repulsion of HACC than that of CTS,and samller molecular size than that of CTS.Ions on the left side of the Hofmeister ion sequence is less hydrated than ions on the right side,which weaken the combination of ions on the left side and amino groups.So the molecular size of the Alg-CTS(Ac-)complexes was smaller than that of the Alg-CTS(Cl-)complexes.At last,the mechanical strength and self-healing properties of polyelectrolyte hydrogel prepared under different conditions were studied.Alg-HACC hydrogels have self-healing properties while Alg-CTS hydrogels did not have self-healing properties.The mechanical properties of the Alg-HACC hydrogel would be improved as the pH increased.And the storage modulus(G')of Alg-HACC was 18000 Pa,18500 Pa,20300 Pa when the pH was 3.93,4.1,7.0 respectively.The self-healing efficiency increased from 10%at pH=3.93 to 95%at pH=7.The macroscopic self-healing ability of the hydrogel would decrease after the counterion was dialyzed out from the Alg-HACC hydrogel.Based on these studies,we reported a complex self-healing model for Alg-HACC hydrogel.A reversible weak electrostatic interaction was formed between Alg and HACC.A part of the counterion was coated inside the gel after the formation of Alg-HACC which reached a dynamic binding equilibrium with the quaternary ammonium salt group.All these are the key to the self-healing ability of the gel.