Repid Preparation And Antibacterial Properties Of Self-healing Hydrogels

Bacterial infections or diseases caused by bacterial infections affect the health of people around the world.The overuse of antibiotics could induce bacterial resistance.Therefore,innovative antibacterial materials circumventing the use of antibiotics have attracted great interests.Hydrogels with tunable components and pore sizes have a three-dimensional network structure and are promising as antibacterial materials.Self-healing hydrogels are typically formed based on covalent or non-covalent interactions and their intermolecular bonds are easy to break and recover,which make the hydrogels be automatically healed after destruction by the external force.In this thesis,two kinds of self-healing hydrogels are prepared based on dynamic disulfide bonds or hydrogen bonds for potential antibacterial applications.The main contents of the thesis include the following three chapters.The first chapter mainly introduces the types and applications of hydrogels,and summarizes the research progress of hydrogels in the field of antibacterial apllications.The mechanism,preparation methods and appications of self-healing hydrogels and coacervates are also summarized.In the second chapter,we report a rapid assembly strategy for the preparation of hydrogels based on a thiol-disulfide cascade reaction and coordination interactions.The hydrogels were prepared by simply mixing 8-arm-PEG-SH,AgNO3,and 5,5’-dithiobis(2-nitrobenzoic acid)(DTNB)and had self-healing property due the presence of disulfide bonds.This method enables rapid formation of hydrogel at PEG concentrations of 1-5%.The thiol-disulfide bond exchange reaction was demonstrated by 1H NMR.Energy dispersive Spectrometry and scanning electronic microscopy(SEM)characterization proved the presence of evenly distributed silver in the hydrogels.The hydrogels can be further quickly functionalized by thiol-containing molecules.This method is also applicable for the preparation of other silver-containing hydrogels composed of thiolated polymers.Antibacterial experiments demonstrated that the hydrogel had a good antibacterial effect on both Gram-negative(e.g.,E.coli)and Gram-positive(e.g.,S.aureus)bacteria.In the third chapter,self-healing coacervate hydrogels composed of tannic acid,carboxymethyl chitosan and poly(ethylene glycol)(PEG)are introduced.The hydrogel can be instantly formed based on hydrogen bonds once mixing the componets..Confocal laser scanning microscopy measurements showed that coacervate droplets were evenly distributed in the hydrogel networks.The hydrogel three-dimensional networks were well arranged in an orderly manner due to the presence of coacervate droplets,which was observed form SEM.We further investigate the effect of molecular weight,number of arms,and end functional groups of PEG on the formation and mechanical properties of the hydrogels.Rhodamine B dye as a model drug could be encapsulated into the coacervate particles in hydrogels,which resulted in controlled release of model drugs.In addition,the components of carboxymethyl chitosan and tannic acid endow the hydrogels with antibacterial properties.