| Background:Cardiac implantable electronic devices（CIED）therapy has become an important treatments for arrhythmias and severe heart failure,and can significantly improving patients’quality of life.CIED-related infection is one of the most common and serious complications after CIED implantation.However,the incidence of CIED-related infection is constantly increasing with the widespread use of CIED therapy,even outpacing the growth rate of CIED treatment.Despite tremendous advances in medical technology,the incidence of CIED-related infection within one year of implantation still ranges from 2.3%to 3.4%.The primary treatment currently used to prevent CIED infection is the use of preoperative antibiotics.However,with the rise of pathogen-related antibiotic resistance due to the misuse of antibiotics on a global scale,which has led to a decrease in the effectiveness of preoperative antibiotics.Therefore,there is an urgent need to develop a material that is not dependent on antibiotics and can effectively prevent CIED infections.Polyethylene glycol（PEG）hydrogel has been widely used in the biomedical field due to their high hydrophilicity and biocompatibility.Furthermore,PEG hydrogel can significantly reduce protein adsorption,bacterial adhesion,biofilm formation,and infection on biomaterial surfaces due to steric barrier,exclusion volume effect,and permeation exclusion effect.Chitosan is the only cationic polysaccharide in nature with amino groups and excellent biocompatibility.Its positively charged amino group can bind to anionic components such as lipopolysaccharide and surface proteins in microbial cell membranes and play a broad-spectrum antibacterial effect by destroying biological cell walls.However,the low solubility of chitosan limits its application as an antibacterial material in the microenvironment of human tissues.2′-O-hydroxypropyl trimethyl ammonium chloride chitosan（2’-O-HTACCS）prepared by chitosan quaternization reaction can not only improve the water solubility of chitosan,but also significantly enhance its antibacterial activity due to the increase in cationic groups.Meanwhile,we composed PEG and some other photosensitive materials into a photoresponsive PEG hydrogel,which not only has spatial and temporal controllability,but also can precisely control the shape of the hydrogel,thereby rapidly completing the surface modification of CIED before surgery.Therefore,this study aims to construct a fast-responsive photoresponsive PEG/2’-O-HTACCS hydrogel for the prevention of CIED pocket infection.Methods:1.Construction and characterization of photoresponsive PEG/2’-O-HTACCS hydrogel:Through chemical crosslinking and partial improvement of the process,we first synthesized photoresponsive PEG hydrogel and 2’-O-HTACCS.Titanium samples were sequentially treated with H2SO4/H2O2and 3-aminopropyltriethox-ysilane（APTES）to modify the hydroxyl and amino groups on the titanium surface.The pre-mixed PEG/2’-O-HTACCS hydrogel was homogeneously coated on the titanium surface,and the amino group of 2’-O-HTACCS,the hydroxyl group of PEG and the amino group on the titanium surface were chemically cross-linked under the UV light irradiation to make the hydrogel adhere to the titanium surface.Finally,the siliconization of the titanium was characterized by scanning electron microscopy（SEM）,X-ray photoelectron spectroscopy（XPS）,and contact angle analysis,and the adhesive force of the hydrogel on different titanium surfaces was examined by adhesion force test.2.Safety evaluation of photoresponsive PEG/2’-O-HTACCS hydrogel:We assessed the in vitro cytotoxicity of PEG/2’-O-HTACCS hydrogel using NIH/3T3cells.Implantation of hydrogel-coated titanium plates were into the subcutaneous pocket of SD rats to demonstrate the biocompatibility.In the in vitro experiment,NIH/3T3 cells were co-cultured with the impregnation solution of PEG/2’-O-HTACCS hydrogel,and the in vitro safety of hydrogel was assessed using the CCK-8kit to detect cytotoxicity of hydrogel and live/dead cells staining.In the in vivo experiment,silylated titanium samples loaded with hydrogel were implanted into subcutaneous pocket of SD rats,and the biocompatibility of the hydrogel was assessed by HE staining of subcutaneous pocket,heart,liver and kidney tissues,as well as blood routine,kidney function and liver function tests.3.Evaluation of antibacterial effectiveness of photoresponsive PEG/2’-O-HTACCS hydrogels:（1）In the in vitro antibacterial effectiveness experiment,four representative bacteria,including Gram-positive bacteria（Staphylococcus epidermidis,Staphylococcus aureus）and Gram-negative bacteria（Enterobacteriaceae,Pseudomonas aeruginosa）were selected for this study based on the microbiological characteristics of CIED-related infections.We co-cultured the four bacteria with samples from the control group（titanium samples）and the experimental group（silanized titanium samples loaded with antibacterial hydrogel）,and performed colony counting,live-dead bacteria staining and SEM to evaluate the antibacterial ability,resistance to bacterial adhesion and effect on bacterial membrane structure of PEG/2’-O-HTACCS hydrogel.（2）In the in vivo antimicrobial effectiveness experiment,two separate subcutaneous pocket were created on the bilateral backs of SD rats,and implanted with control and experimental samples and Staphylococcus aureus bacterial solution to construct a capsular pouch infection model.On the 3rd and 7th days after implantation,the pocket were re-opened.The degree of inflammatory response,the number of bacteria and bacterial viability were assessed by gross observation of the pocket,live dead bacteria staining and quantitative analysis of bacteria.HE staining of the pocket tissue was performed to reflect the inflammatory cell infiltration in the tissue around the pocket;immunohistochemistry and qPCR were performed to assess the expression levels of inflammatory factors IL-1βand TNF-αin the tissue around the pocket.Results:1.Construction and characterization of photo-responsive PEG/2’-O-HTACCS hydrogel:（1）SEM images found that the surface of pure Ti plates were typically flat.After alkali treatment,large surface irregularities with a roughness formed on Ti surface.Compared with the hydroxyl-modified Ti,nodular structures were emerged on the surface of silylated Ti.（2）XPS analysis results found that the oxygen on the surface of alkali-based titanium flakes increased significantly,and the nitrogen,carbon and silicon on the surface of silanized titanium increased to 9.32%,9.21%and42.82%,respectively;while the oxygen decreased to 37.19%and the titanium content decreased to 1.46%.（3）Water contact angle revealed that the water contact angle of alkylated titanium flakes decreased from 65.5±0.51°to 41.3±1.0°,and the hydrophilicity of the samples was enhanced;the water contact angle of silylated titanium surface increased to 76.3±2.6°.（4）The results of hydrogel adhesion force assay found that the adhesion performance of hydrogel with silanized titanium sheet was significantly improved compared with titanium sheet and alkylated titanium sheet group,and the adhesion performance increased by 2 times.In summary,this phase of experiments can confirm the successful silanization of titanium flakes and can lead to a significant increase in the adhesion of hydrogels.2.Safety evaluation of photo-responsive PEG/2’-O-HTACCS hydrogel:（1）In vitro safety evaluation:（1）The results of cell live-dead staining showed that the number and morphology of NIH/3T3 cells were normal after 1 and 3 days of co-culture with the hydrogel impregnation solution,and no significant cell death was observed.（2）The results of cell proliferation toxicity assay did not reveal any significant cytotoxicity of hydrogel after 1d,3d and 7d of co-culture.Besides,after co-culture for 3 d and 7 d,we found that the cell viability of the experimental group was higher than that of the control group.（2）In vivo safety evaluation:HE staining of the tissue around the pocket,myocardium,liver and kidney of the experimental groups did not show any significant inflammatory cell infiltration,vasodilatation,increased permeability and fibrosis on the 1st,7th and 14th days after implantation.Compared with the control group,no statistically significant differences were found in the experimental group in blood routine,liver function and renal function.In summary,this phase of experiments confirmed that PEG/2’-O-HTACCS hydrogels have good biocompatibility.3.Evaluation of antibacterial effectiveness of photo-responsive PEG/2’-O-HTACCS hydrogel:（1）In the in vitro antibacterial effectiveness experiment:（1）Colony count experiments found that the colony counts of the experimental group were significantly lower than those of the control group in all time periods of co-culture,especially in the groups of Staphylococcus epidermidis,Staphylococcus aureus and Pseudomonas aeruginosa,whose bacterial numbers decreased by more than 90%.（2）The bacterial live/dead staining showed that the bacterial staining on the surface of the samples in the experimental group were all red fluorescence,no obvious green fluorescence was seen,and the number of bacteria was significantly reduced.（3）The microbial SEM found that the number of adherent bacteria on the surface of the samples in the experimental group was significantly reduced,and the bacterial morphology was irregular,and even lysis was observed.（2）In the in vivo antimicrobial effectiveness experiments:（1）The gross observation of the pocket after incision showed a large amount of white purulent secretion in the control group,while no obvious purulent secretion was seen in the experimental group.（2）The quantitative analysis of bacteria and bacterial live/dead staining revealed that the number of bacteria and bacterial viability were significantly lower in the experimental group compared with the control group,and the difference was statistically significant.（3）HE staining showed that there was a large amount of exudate and obvious inflammatory cell infiltration in the fascial layer of the pocket tissue in the control group,while no obvious exudate and bacterial infiltration were found in the experimental group;（4）Immunohistochemistry and qPCR showed that the expression levels of inflammatory factors IL-1βand TNF-αwere significantly higher in the tissue around the pocket in the control group.In summary,this phase of experiments confirmed that PEG/2’-O-HTACCS hydrogel has excellent in vitro and in vivo antibacterial properties.Conclusion:In this study,we successfully constructed a photoresponsive PEG antimicrobial hydrogel,which not only possesses good biosafety but also excellent in vivo and in vitro antimicrobial properties as well a s can be rapidly immobilized on the CIED surface preoperatively.It provides a theoretical basis for the future clinical translation and application of photoresponsive PEG antibacterial hydrogel. 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