Multiple Stimuli-responsive Hydrogels And Nanoparticles For Diagnosis And Therapy Of Bacterial Infections

Bacterial infections have become a global public health safety issue.Despite the great success in antibiotic treatment of infectious diseases,the conventional mode of administration suffers low bioavailability,poor selectivity,increasing resistance,low biofilm permeability,and ineffective intracellular bacterial clearance,leading to chronic and recurrent infections.Accurate and early diagnosis is a prerequisite for precise treatment of bacterial infection,and the separation of theranostics often leads to miss the best time for infection control.In this thesis,on the basis of different biochemical environmentsthe of planktonic bacteria,biofilm and intracellular bacteria infection,multiple stimuli-responsive hydrogels and nanoparticles were designed to convert markers into visual fluorescent signals or color changes for effective diagnosis.The synergistic sterilization effect of photodynamic therapy（PDT）,chemodynamic therapy（CDT）and antibacterial polymer was realized in reponse to external stimulation or self-initiation.The integrated theranostic system was constructed for several major bacterial infections.To alleviate the excessive infiltration of inflammatory cells in wound areas,the visible light-triggered injectable antibacterial hydrogels were constructed to promote wound repair by releasing immune adjuvant to regulate macrophage phenotypes.Black phosphorus nanosheets were irradiated with visible light to generate reactive oxygen species（ROS）like superoxide anion radicals as initiator,andε-polylysine（e PL）was grafted with acrylate polyethylene glycol（e PLG-acr）as macromolecular monomer to prepare e PLG@BP-Dex hydrogels after dexamethasone encapsulation.This crosslinking system avoids the toxicity of traditional small molecule initiators and ultraviolet irradiation,and hydrogels could capture bacteria via electrostatic interaction of e PL and confine bacteria within the diffusion range of ROS to realize e PL/PDT synergistic efficacy.Moreover,the macrophage phenotype is regulated through sustained release of dexamethasone to promote epidermal regeneration,collagen deposition,angiogenesis,and wound closure.To integrate the diagnosis and treatment process of wound infections,antibacterial hydrogels were constructed for visual imaging-guided antibacterial PDT and bacterial debris removal to promote wound healing.Ureido-pyrimidinone was conjugated on e PL to produce quadruple hydrogen bonding,and the inoculation of tetrakis（4-carboxyphenyl）porphyrin（TCPP）-loaded PDA nanoparticles（PTc）introduced Schiff base linkages in PLU@PTc hydrogels,which endowed mechanical strength,adhesion properties and self-healing ability.PDA could quench fluorescence emissions of TCPP,and the acidic microenvironment of bacterial infection triggers the release of TCPP and restores fluorescence emissions to achieve real-time diagnosis.The hydrogels produce e PL/PDT synergistic sterilization under660 nm-laser illumination,which is strengthened by the bacterial capture on hydrogels via electrostatic interaction.Furthermore,attributed to the excellent photothermal conversion ability of PDA,the temperature of PLU@/PTc hydrogel increases under near-infrared（NIR）illumination to break the quadruple hydrogen,and the PLU@PTc hydrogels with entrapped dead bacteria and debris could be removed from wound beds.In a wound infection model,PLU@PTc gel can diagnose bacterial infection,effectively kill bacteria and accelerate wound healing after removing dead bacteria.The quadruple-hydrogen cross-linked injectable hydrogels containing bacterial toxin-responsive nanoparticle were constructed for toxin-triggered specific detection of bacterial biofilms,efficient CDT/e PL therapy and then on-demand removal of bacterial debris and toxins to promote wound healing.Liposome-coated iron nanoparticles were constructed and combined with gallic acid and UPy-modified e PL to form Fe@Lip/PUG hydrogels.Hydrogels possess good adhesion properties and self-healing ability.The liposome could be disturbed by bacteria toxins,and the acidic microenvironment triggers iron nanoparticles to release Fe²⁺,which undergo a Fenton reaction with endogenous H₂O₂ to destroy biofilms and kill bacteria.The Fenton reaction generated Fe³⁺to chelate with gallic acid and turn hydrogels black for wound infection sensing.NIR irradiation of the chelates causes the temperature increase,destroy hydrogen bonds in the cross-linking system,and remove hydrogels with wrapped bacterial debris.In a biofilm-infected cutaneous defect model,Fe@Lip/PUG can effectively diagnose biofilm-infected wounds,remove toxins and accellerate wound repairing process.To address the challenges of limited penetration depth and phototoxicity of PDT,composite nanoparticles with equipped ultrasound-activated afterglow luminescence and toxin/enzyme-activated generation of photosensitizer in situ were designed for theranostics of intracellular bacterial infection in deep tissues.Mechanoluminescent Sr Al₂O₄:Eu²⁺（SAOE）and persistently luminescent Ca S:Eu²⁺（Ca S）nanodots were deposited on mesoporous silica to prepare m SC nanoparticles,and nitroreductase（NTR）-activatable theranostic probes（n MB）were loaded in bacteria membrane,which were used to encapsulate m SC to obtain m SC-n MB@BM composite nanoparticles.n MB could block PDT effect and fluorescence emission by means of electron transfer to eliminates the phototoxicity of m SC-n MB@BM in healthy tissues and phagocytes.Once arrival at the infection site,bacterial membranes on the nanoparticles mediate endocytosis by bacteria-infected macrophages through pathogen recognition patterns to increase the targeting efficiency.Toxins in the host phagocytes trigger the release of n MB,and NTR enzyme inside the bacteria converts n MB into methylene blue as the photosensitizer and fluorescent imaging agent.Ultrasound-activated SAOE nanodots generate green emissions to excite ZGC nanodots,providing interior and continuous light source for imaging-guided precise PDT.m SC-n MB@BM nanoparticles can specifically diagnose intracellular bacterial infection,remove bacteria from host cells,and effectively prolong the lifespan of mice.In summary,stimuli-responsive hydrogels and drug-loaded nanoparticles were prepared by using biochemical signals such as p H,toxin and enzyme in the microenvironment of planktonic bacteria,biofilm and intracellular bacteria infection.The stimuli-responsive kinetics,diagnostic and treatment mechanism and tissue repairing efficacy of injectable hydrogels and nanoparticles have been investigated.These theranostic systems could convert infection markers into visual fluorescence and color signals,and achieve the synergistic sterilization effect of e PL and ROS in reponse to external and endogenous stimuli to promote wound repairing.The theranostic design has shown broad prospects and clinical significance for infection control and reduction of bacterial resistance.