A Study On Polydopamine-based Nanoparticles Against Biofilms

The formation of bacterial biofilm is one of the main causes of most clinical infections.At present,antibiotics are mainly used to combat biofilms in clinical practice.However,bacterial biofilms exhibit high resistance to antibiotics,requiring large doses of antibiotics to treat biofilm infection,which not only accelerates the production of drug-resistant bacteria,but also produce toxic side effects on the human body.With the development of nanotechnology,it has been found that nanoparticles can pass through physiological and biofilm barriers,effectively kill bacteria within biofilms and destroy biofilms.and the penetration and accumulation of nanoparticles in the biofilms determine the final antibiofilm effect.Therefore,understanding the interaction between nanoparticles and biofilms,and controlling the penetration and accumulation of nanoparticles in biofilms are key issues for the development of nanoparticle based antibiofilm materials.In this thesis,polydopamine(PDA)nanoparticles,a kind of melanin-like material,were selected as the research object.Due to its good biocompatibility,excellent photothermal properties,and easy functionalization,PDA has shown great potential in the field of antibacterial in recent years.At present,the research on the anti-biofilm of PDA nanoparticles mainly focuses on the development of functional antibacterial materials using PDA as a carrier,while lack of in-depth understanding of their penetration and accumulation within biofilms.Therefore,this thesis systematically studied the effects of different factors on the penetration and accumulation ability of PDA nanoparticles in biofilms,including size,surface charge and external magnetic field,and then designed PDA-based anti-biofilm nanoparticles.(1)Firstly,from the perspective of size,we synthesized a series of small-sized PDA nanoparticles with hydrodynamic diameter of 7-17 nm,and preliminarily investigated their bactericidal effect on free bacteria.The outermost layer of bacteria is a dense cell wall,which makes it difficult for large sized nanoparticles to enter the interior of bacteria.Therefore,the development of small-sized nanoparticles(≤30 nm)is the basis for the construction of an ideal nanoparticle antibacterial platform.We have synthesized a series of PDA nanoparticles with hydrodynamic diameters ranging from 7 nm to 17 nm using a top-down method.After PEG modification,these small size PDA-PEG nanoparticles could stably disperse in phosphate buffer solution(PBS)for several months without aggregation.After further assembling the antibiotic levofloxacin(LVFX)with PDA-PEG,PDA-PEG-LVFX showed good photothermal effect and photothermal stability,and released antibiotics at the same time.Under an 808 nm laser irradiation,the bactericidal rates of PDA-PEG-LVFX nanoparticles against S.aureus and E.coli were both 100%.(2)Subsequently,we prepared a series of large-sized PDA nanoparticles with a hydrodynamic diameter of 60～200 nm and assembled them with different end groups of DSPE-PEG(DSPE-PEG-OCH3/COOH/NH2)to obtain PDA nanoparticles with different surface charges.Their interaction with S.aureus biofilms was studied.The results showed that the penetration and accumulation of PDA nanoparticles in the S.aureus biofilms was size-dependent.PDA nanoparticles with smaller size(～15 nm)could not remain in the biofilms,while PDA nanoparticles with larger size(～200 nm)was difficult to enter the biofilm,and PDA nanoparticles in the range of 60～90 nm have better penetration and accumulation ability.In addition,compared with the PDA nanoparticles with carboxyl and methoxy groups on the surface,the PDA nanoparticles with amino groups on the surface can further help the PDA nanoparticles to accumulate and distribute in the biofilms due to the negatively charged characteristics of the biofilms.Under the 808 nm laser irradiation,the PDA nanoparticles with amino groups exhibited a high bactericidal rate against S.aureus biofilms under 808 nm laser irradiation.(3)Finally,based on the work of the previous two chapters,we introduced magnetic nanoparticles(Fe3O4)core into PDA,that is,polymerized on the surface of magnetic nanoparticles to form PDA shell by oxidative self-polymerization method,and Fe3O4-PDA nanoparticles with core-shell structure was obtained.The results indicated that Fe3O4-PDA nanoparticles could target and accurately control the movement of PDA nanoparticles in the biofilms under the external magnetic field,which further improved the penetration and accumulation of nanoparticles in the biofilms.Meanwhile,to further enhance the anti-biofilm ability of PDA nanoparticles,we loaded the photothermally responsive NO donor molecule BNN6 on the surface of PDA through π-π stacking and hydrophobic interaction.Under the dual effects of laser irradiation and magnetic field,Fe3O4-PDA-BNN6 not only demonstrated the magnetic field enhanced photothermal-NO combined anti-biofilm effect,but also showed the ability to promote wound healing in vivo experiments.