Preparation And Study Of Antibacterial Agent Based On Polydopamine Hollow Microspheres

Objective:It is simple,convenient,green and economical to synthesize hollow polydopamine（PDA）microspheres to avoid the introduction of other substances or processes to remove the core.Based on the synthesized PDA hollow microspheres,which have good biocompatibility,a series of new antibacterial agents were designed and developed.Firstly,the preparation of Ag-PDA antibacterial agent by loading silver nanoparticles can not only solve the problem that silver nanoparticles are easy to aggregate in the process of use,but also reduce the toxicity of silver nanoparticles,which has the effect of reducing toxicity and increasing efficiency.Secondly,an antibacterial agent triggered by near infrared light was prepared to combat bacterial infection and promote wound healing.The antibacterial agent can release antibiotics on demand and generate local hyperthermia assist bacterial inactivation.Methods:ZIF-8 was prepared by simply mixing zinc nitrate hexahydrate and 2-methylimidazole.Using ZIF-8 as a self-sacrificing template,dopamine polymerized on the template to form hollow microspheres.Taking advantage of the weak reducibility and adsorption of PDA,the in-situ growth of Ag NPs on microspheres was realized,and the compound bacteriostatic agent Ag-PDA was prepared.On the basis of systematic characterization of the synthetic materials by means of Transmission electron microscope（TEM）,Scanning electron microscope（SEM）and X-ray powder diffractometer（XRD）,the bacteriostatic rate,bacteriostatic zone,minimum inhibitory concentration（MIC）and bacteriostatic kinetics were studied,and the bacteriostatic effect of the compound bacteriostatic agent was evaluated.The drug loading rate was greatly improved by using the internal cavity structure and rich chemical functional groups on the surface of hollow PDA microspheres,and CIP@PDA composite antibacterial agents were prepared.The Synthesis of antibacterial agent was supported by the results from TEM,UV-Vis and FTIR.The antibacterial agent was irradiated under an 808 nm near infrared（NIR）laser with different concentrations to study the photothermal properties.Release of CIP from the antibacterial agent was determined under different conditions.We observed antibacterial activity of the agent by spread plate method and bacterial growth curve.The infected wound was made on the back skin of mice,and the mice were treated with different methods to observe the healing process of the wound and study its influence on the wound healing.Results:The synthesized ZIF-8@PDA is a hollow spherical shell with a surface thickness of about 20nm,and the Ag-PDA with uniform Ag NPs distribution and complete shell can be obtained by increasing the concentration of Ag⁺to 0.24 mol L^-1.The synthesized Ag-PDA antimicrobial agent has a wide antibacterial spectrum and has better bacteriostatic effect on Escherichia coli（E.coli）than Staphylococcus aureus（S.aureus）.The antibacterial agent CIP@PDA exhibited sustained release under physiological conditions,but could boost CIP release upon NIR light irradiation.Meanwhile,NIR light irradiation could activate the photothermal conversion ability,and the generated local hyperthermia leading to inactivation of bacteria in a synergistic way.Moreover,the exceptional bacterial killing activity and outstanding wound healing ability of the agent were also verified by the S.aureus-infected mouse skin defect model.Conclusion:Ag-PDA compound bacteriostatic agent has good biocompatibility and broad-spectrum bacteriostatic performance,and shows better bacteriostatic effect on Staphylococcus aureus（G⁺）than Escherichia coli（G^-）.The synthesized antimicrobial agents CIP@PDA have excellent antibacterial effect in vitro,and still have good antibacterial effect and promote wound healing under the conservative power irradiation without causing skin damage in vivo.