Antibacterial Property And Mechanism Studies Of Curcumin-loaded ZIF-8 Nanomaterials

Antibiotic treatment is commonly used to fight bacterial infections,but the abuse of antibiotics has spawned drug-resistant bacteria,which poses a major public health threat worldwide.Therefore,it is urged to develop environmentally friendly and efficient antibacterial materials Photodynamic sterilization is a hotspot in the development of antibacterial materials with advantages of high sterilization efficiency,small side effects avoiding the emergence of drug-resistant bacteria.Curcumin is a natural active product widely used in the food field,and can also be used as photosensitizer in photodynamic therapy.It has the advantages of low toxicity and fast removal rate in the body,and is an ideal antibacterial photosensitizer.However,curcumin has poor water solubility and unstable chemical properties,which limits its utilization.In order to solve these problems,the ZIF-8 was used to encapsulate curcumin in this study.ZIF-8 is acid-responsive which means it can selectively release the encapsulated drugs and Zn²⁺in the micro-acid environment where bacteria grow,and play an antibacterial effect.In this study,curcumin was encapsulated by a one-step method using metal-organic framework material ZIF-8,and the synthesis method was fast and simple.The physical and chemical properties of ZIF@CCM nanoparticles were characterized to verify the inclusion,protection and acid-responsive release ability of curcumin by ZIF-8.In the antibacterial experiments,standard strains（Escherichia coli and Staphylococcus aureus）and resistant Staphylococcus aureus were selected as experimental strain to investigate the antibacterial ability and mechanism of ZIF@CCM under blue light.And aiming to expand the application range of the materials,ZIF@CCM nanoparticles and polycaprolactone（PCL）were blended into a film,and the morphology of the composite film was characterized.What’s more,the antibacterial properties of the membrane were evaluated,providing new ideas for the antibacterial application of curcumin.1.One-step method was chosen to synthesize the ZIF-8 and encapsulate the curcumin,forming the ZIF@CCM nanoparticles.By optimizing the reaction time and the addition of curcumin,the ZIF@CCM nanoparticles was synthesized to had a higher encapsulation rate（82.76±3.18%）and drug loading efficiency（11.57±0.17%）.Several methods,such as Powder X-ray powder diffraction（PXRD）,scanning electron microscopy（SEM）,infrared spectroscopy（FT-IR）,thermogravimetric analysis（TGA）,ultraviolet-visible spectroscopy（UV-vis）,fluorescence spectroscopy（PL）,specific surface area analysis（BET）,particle size analysis（DLS）,and thermal stability analysis（TGA）,were used to analyze the physical and chemical properties of the material.The experimental results showed that the material had good thermal stability and played a good role in protecting curcumin under neutral and alkaline conditions.It could also quickly release the entrapped curcumin and Zn²⁺in a slightly acidic environment which has good acid responsiveness.2.The effects of ZIF@CCM,ZIF-8 and curcumin on the growth of E.coli and S.aureus were observed under blue light and dark environment.It was found that ZIF@CCM had better antibacterial effect than pure ZIF-8 or curcumin.Curcumin had no antibacterial ability in dark environment,ZIF-8 had similar antibacterial effect in blue light and dark environment.Under the blue light,curcumin and ZIF@CCM exhibited excellent antibacterial effect.ZIF@CCM almost killed all the E.coli and S.aureus.By the bacterial fluorescence staining,intracellular K⁺efflux,morphological observation,and the detection of the amount of singlet oxygen produced by ZIF@CCM under blue light,it was showed that the antibacterial effect of ZIF@CCM under blue light,resulted from the bacterial cell membranes damage caused by the singlet oxygen produced by the light response of curcumin and the bacterial cell walls damage caused by the Zn²⁺in the ZIF-8 structure.And it had excellent antibacterial effect on drug-resistant S.aureus and could completely kill drug-resistant bacteria.3.Different amounts of ZIF@CCM nanoparticles and polycaprolactone（PCL）were blended into a cast film to synthesize ZIF@CCM@PCL composite film.The film materials were characterized and it was found that the structure of ZIF@CCM was not been damaged.When the amount was not higher than 15%,the surface was flat.Tests on the antibacterial properties of the film materials found that the film loaded with ZIF@CCM under blue light had excellent antibacterial effects and the properties decreased under dark treatment.Under light and dark conditions,the membrane material added with ZIF@CCM had better antibacterial adhesion ability,and the number of viable bacteria adhered was significantly lower than that of the control group.The number of viable bacteria in the blue light treatment group was almost zero.From the bacterial recovery experiment,it could be concluded that ZIF@CCM@PCL composite film under blue light treatment had excellent antibacterial effect,and the composite film material had the ability on generating singlet oxygen under blue light irradiation.