Functional Nanoparticles For Anti-biofilms

Bacterial infection used to be the biggest threat to human health untill the discovery of antibiotics.With the broad application of antibiotics in clinic,the risk of bacterial infections has been greatly reduced.However,bacterial infections have once again become major threats to global health in recent years,due to the increasingly serious problem of antibiotic resistance.What is worse,in the past several decades,the speed of discovery of new antibiotics has fallen far behind that of development of antibiotic resistance.In 2013,the World Health Organization announced mankind has entered the"post-antibiotic era".Therefore,developing new antibacterial strategies has extremely important strategic significance.There are two main causes of the antibiotic resistance.One is the formation of bacterial biofilms and the other is the self-evolution of bacteria under the selective pressure of antibiotics.Due to the excellent size effect,physical and chemical properties and easy chemical modification,nanomaterials show great potential for treating bacterial infections.This paper proposes two types of therapeutic strategies.One is nanomaterial-based non-antibiotic therapy,including photothermal therapy and photodynamic therapy and the other one is antibiotic therapy assisted by nanomaterials,which refers to the method of using oxygen-loaded liposomes to assist antibiotic treatment.This article mainly contains the researches in the following aspects:1.pH-responsive gold nanoparticles for photothermal ablation of biofilmsGold nanoparticles were modified by mixed charged ligands(HS-（CH₂）₁₀-COOH)and(HS-（CH₂）₁₀-N（CH₃）₃Br).By adjusting the ratio of the two ligands,gold nanoparticles with excellent pH responsiveness were fabricated.The pH-responsive aggregation behavior of the nanoparticles in biofilms was studied.Further investigations were focused on whether these nanoparticles could achieve efficient photothermal killing of bacteria without damaging healthy tissues under the irradiation of near infrared（NIR）light.The results showed that the mixed-charged gold nanoparticles exhibited good dispersing stability and excellent resistance to non-specific protein adhesion at normal physiological pH.The dispersed gold nanoparticles showed no damage to healthy tissues since they had bare NIR light-heat conversion ability.At acid biofilm pH,gold nanoparticles could aggregate rapidly and adhere to the surface of bacteria.The aggregated gold nanoparticles had enhanced NIR absorbance and thus showed excellent photothermal ablation of biofilms.This kind of gold nanoparticles with pH responsiveness in acidic biofilms realized precise control of local temperature,resulting in that the high temperature generated by the photothermal effect was only focused on the bacterial infectious sites rather than healthy tissues,which greatly reduced the side effects of photothermal treatment.2.pH and GSH dual responsive supramolecular micelles for photodynamic therapy of biofilmsSupramolecular micellesα-CD-Ce6-NO-DA were fabricated by the host-guest interactions.The pH-responsive polyethylene glycol-polypeptide diblock copolymer（PEG-（KLAKLAK）₂-DA）acted as the guest molecule.The prodrug（α-CD-Ce6）ofα-cyclodextrin modified with chlorin e6（Ce6）and prodrug（α-CD-NO）ofα-cyclodextrin modified with nitric oxide（NO）donor served as guest molecules.Theα-CD-Ce6-NO-DA was used to study whether they could show pH-responsive penetration ability into biofilms and GSH-responsive NO release behavior in biofilms,thereby enhancing the effect of photodynamic therapy.The research results showed that in normal physiological environment（pH 7.4,GSH～2μM）,α-CD-Ce6-NO-DA had good long-term circulation stability and negligible cytotoxicity.In methicillin-resistant Staphylococcus aureus biofilm infectious site（pH 5.5,GSH～8m M）,the surface charge ofα-CD-Ce6-NO-DA could reverse by removing the shells of micelles,thereby promoting its penetration into biofilms.Once penetrating into biofilms,a large amount of NO could be released by the overexpressed GSH.On the one hand,NO could effectively kill numerous bacteria,on the other hand,it could consume GSH of biofilm,reducing GSH concentration and indirectly improving the efficacy of photodynamic therapy.High-efficiency photodynamic therapy can greatly reduce the dose of photosensitizers and laser intensity,reducing its cytotoxicity,thereby reducing the pain of patients during treatment.3.Oxygen-loaded liposomes for reducing biofilm hypoxia and enhancing therapeutic efficacy of antibioticsThe oxygen-loaded liposomes（lip@PFH@O₂）were fabricated by perfluorohexane encapsulated liposomes.The change of biofilm hypoxia was investigated by delivering oxygen-loaded liposomes into Pseudomonas aeruginosa biofilms,and then the changes of minimum bactericidal concentration（MBC）of antibiotics（aztreonam,ceftazidime,and piperacillin-tazobactam）were studied.The research results showed that after lip@PFH@O₂penetrating into biofilms,the hypoxia of biofilm was obviously reduced by continuous oxygen releasing of liposomes.After biofilm hypoxia reduced,the bactericidal ability of antibiotics was greatly improved,indicating that reducing hypoxia could effectively reduce the antibiotic resistance.Moreover,it was found that reducing biofilm hypoxia could not only reduce the secretion of alginate,but also inhibit the quorum sensing of bacteria and bacterial efflux pump,thereby weakening the bacterial resistance to antibiotics.This oxygen delivery system was firstly reported to reduce the antibiotic resistance of biofilms.It provided great significance for reducing the dose of antibiotics when killing biofilms and delaying the development of antibiotic resistance.