Design And Synthesis Of Two Dimensional Black Phosphorus-based Antibacterial Materials And Study On Their Biomedical Applications

Infectious diseases caused by pathogenic bacteria remain a serious threat to human health.Although with the development of public health and biomedical technology,many bacterial infections have been effectively suppressed or even eliminated,morbidity and mortality are still chronically high.In particular,the overuse of antibiotics and the rapid transfer of resistance genes between bacterial populations has led to the alarmingly rapid development of pathogenic bacteria with resistance to traditional antibiotics.Researchers in relevant fields are therefore using a variety of methods in the quest to improve antibacterial efficiency against pathogenic bacteria,including developing new materials,structures,and approaches.Among the varied antibacterial materials,black phosphorus(BP)has become a new star in the two-dimensional family because it is a direct bandgap semiconductor with broad-spectrum optical response and good biocompatibility.Its biodegradability is instrumental in one strategy to solve drug resistance,raising its profile in comparison to other antibacterial materials.However,BP's antibacterial efficiency,mechanisms,and multifunctional synergistic applicability in the antibacterial field are not yet clear.This thesis thus takes BP as its main research object,examining the design and synthesis of pure BP nanosheets,as well as a variety of BP-based antibacterial composite and multifunctional materials,to clarify the potential ramifications of BP for the field of biomedicine,especially antibacterial studies.We also explore antibacterial efficiency and mechanisms,biocompatibility,and multifunctional applications of materials to multiple bacteria and media.The specific contents are as follows:(1)Multilayer BP nanosheets with a small number of layers were successfully prepared by basic solvent exfoliation.How the nanosheets'antibacterial activity and efficiency were affected by thickness,concentration,time,and light were determined in vitro.Cytotoxicity testing in vitro that assessed the material's influence on the growth and breeding of Caenorhabditis elegans showed its good biocompatibility,and hemolytic testing proved its excellent blood compatibility.To determine the material's antibacterial mechanism,several tests were conducted:the detection of reactive oxygen species,the degradation of BP,scavenging tests,and a dialysis bag experiment.Ultimately,it was determined to have a synergistic antibacterial mechanism combining photodynamic effects and direct physical contact.The rate and degree of antibacterial activity and the degradation products were favorable.During a 60-days drug-resistance test,BP retained effective antibacterial ability without generating bacterial drug resistance.The above findings were simultaneously verified by experiments and theoretical calculations.(2)A BP-based magnetic composite antibacterial material modified by an N-halamine polymer(BP-Fe₃O₄@PEI-pAMPS-Cl)was designed and synthesized,and its application for blood disinfection was investigated.On a BP base,the N-halamine,which had renewable antibacterial ability,and Fe₃O₄nanoparticles,which could be magnetically recovered,were combined by electrostatic interaction.The existence of active chlorine in the material and its‘recharging'ability were confirmed by iodometric/thiosulfate titration and cyclic experiments.Magnetic hysteresis loop and leaching experiments were also used,to verify the material's strong magnetism and stable recyclability.In vitro tests of its antibacterial ability and cyclic characteristic showed BP-Fe₃O₄@PEI-pAMPS-Cl had excellent synergistic antibacterial activity and stability for 20 cycles.Other experiments tested its stationary and in-flow antibacterial activity at two flow rates,as well as hemolysis rate,clotting time,and blood composition after antibacterial exposure,proving it has excellent prospects for application in the field of blood disinfection.(3)A BP-based cytomembrane mimic(BP-PQVI)inspired by endotoxin release behavior was constructed,and its antimicrobial action in response to stimulation was investigated.Based on the similarity between BP and a cell membrane,antimicrobial quaternary ammonium salt(PQVI)was deposited onto the BP surface through controlled electrostatic interaction to simulate the release behavior of endotoxins on cell membranes.By regulating the elemental content,surface potential,and thickness of BP-PQVI,a cell membrane could be fully simulated.Theoretical calculations as well as experiments showed that the electrostatic interaction between BP and PQVI could dissociate in response to ion concentration,other competitive forces,temperature,and pH,improving the simulation of endotoxin-associated release behavior.In addition,the controllable release of PQVI induced by the electrostatic interactions resulted in controllable antibacterial behavior by the cytomembrane mimic,yielding high antibacterial efficiency and promoting healing at wound sites.(4)A two-dimensional BP-based multifunctional antibacterial material (MAG/VAE@SiO₂-BP)modified by Eu³⁺/carbohydrate was designed and synthesized to be used for targeting,imaging,and anti-infection treatment of bacteria.After SiO₂microspheres were prepared and gradually modified,Eu³⁺(fluorescence imaging)and carbohydrate(specific targeting)were successfully modified by free radical polymerization,and P-Eu coordination bonds were formed between Eu³⁺and BP in the final composite.The strong characteristic emission and obvious red fluorescence of Eu³⁺in the material were confirmed by testing its luminescence properties.After subsequent co-culturing with bacteria,it was found that MAG/VAE@SiO₂-BP could specifically target E.coli K12,which presented clear red fluorescence during imaging.In vitro bactericidal experiments further proved the material's targeted bactericidal ability,showing its activity against E.coli K12 to be significantly better than against S.aureus.(5)A BP-based conductive hydrogel was prepared for smart release in response to electrical stimulation at a wound site.An HA-DA substrate was successfully prepared by an amidation reaction.HA-DA hydrogel was synthesized by coordination between the catechol groups of DA and Fe³⁺.The BP-based conductive hydrogel(HA-DA@BP)was successfully obtained by coating the substrate with BP.By adjusting the amount of HA-DA and the pH,the hydrogel could be changed from sol-phase to gel-phase under electrical stimulation,forming a gel in an alkaline environment but decomposing to sol in a slightly acidic environment.The effective continuous release of BP was confirmed by monitoring the hydrogel's degradation process.The addition of BP gave the hydrogel excellent conductivity.The results of in vitro cytotoxicity and antibacterial tests showed that BP could be released from the hydrogel under slight acidity and electrical stimulation,which would not affect the survival rate of normal cells but could achieve synergistic antibacterial properties and promote the rapid healing of wounds.