Preparation And Characterization Of Photodynamic Antibacterial P(MMA-co-MAA)/MMT Electrospun Nanofibers

In recent years,owing to the overuse of antibiotics worldwide,the emergence of“superbugs”has caused great trouble for the treatments of clinical-infected diseases.Therefore,it is particularly important to develop a new kind of antibacterial therapy.As one of the most promising new antibacterial therapies,photodynamic antibacterial chemotherapy（PACT）is mainly based on the oxidative damage mechanism by the combination of light,photosensitizer and oxygen.Since there’s no possibility of drug resistance occurring upon the oxidative damage mechanism,PACT has great advantages in terms of convenience,antibacterial efficiency and anti-drug-resistance.In this study,solution intercalation followed by electrospinning technique were employed to prepare the P（MMA-co-MAA）/MMT composite nanofibers,and the carboxylic acid group on its surface and MMT were used to adsorb cationic photosensitizer,namely,methylene blue（MB）,resulting in the photobactericidal nanofibers.The main research contents and conclusions are as follows.A series of random copolymer P（MMA-co-MAA）with different monomer MMA:MAA molar ratio were prepared by emulsion polymerization using hydrophobic monomer methyl methacrylate（MMA）and hydrophilic monomer methacrylic acid（MAA）.The molecular weight and distribution,chemical structure,thermal stability and transparency of the polymer were tested and analyzed by means of gel permeation chromatography（GPC）,fourier-transform infrared spectroscopy（FTIR）,thermogravimetry analysis（TGA）and UV visible chromatography（UV-vis）etc.The results indicated that the proportion of monomer in the reaction is basically consistent with the proportion of monomer in the polymer chain.The molecular weight of the polymer is between 100,000 and 300,000 and the distribution is narrow.The polymer is high transparent with more than 80%light transmittance in the visible region.P（MMA-co-MAA）nanofibers were obtained by electrospinning based on a series of copolymer P（MMA-co-MAA）with different monomer MMA:MAA molar ratio.The effects of solvent composition on the properties of electrospinning solution（viscosity,conductivity and surface tension）were investigated.Then,scanning electron microscope（SEM）,FTIR,TGA and surfac tension meter were used to analyze the fibrous structure and their diameter distribution,chemical structure,thermal properties and surface wettability.The content of carboxyl groups on the surface of the nanofibers were determined by carboxyl titration.The kinetic properties and mechanism of the cationic MB adsorbed on the nanofibers were studied.Finally,the photo-oxidation property and antibacterial activity of the MB immobilized nanofibers were discussed.The results showed that the surface of the nanofiber was smoother with an average diameter of 444±88 nm when the solvent was composited of N,N-dimethylformamide（DMF）:trichloromethane（CHCl₃）=3:7（m/m）.With the increase of molecular weight,the average diameter of the nanofibers was significantly lager,and the smaller the dispersion coefficient,the more uniform the diameter of the nanofibers.the carboxyl content of electrospun nanofibers surface increased with the proportion of monomer MAA,contributing to the increase of hydrophilic properties,photosensitizer adsorption capability,antibacterial properties.Furthermore,the prepared antibacterial nanofibers have an antibacterial inactivation rate of 99%against S.aureus and E.coli.Finally,the polymer with a monomer MMA:MAA molar ratio of 2:1 was selected as the substrate for further study.Solution intercalation followed by electrospinning technique were employed in this process to prepare P（MMA-co-MAA）/MMT composite nanofibers.The effect of MMT addition on the properties of electrospinning solutions including viscosity,conductivity and surface tension was studied.SEM,and transmission scanning microscope（TEM）were used to analyze the fibrous structure,and the existence state and distribution of the MMT lamella in the nanofibers.Besides,FTIR and TGA were used to analyze the chemical structure and thermal properties.The kinetic properties and mechanism of MMT-adsorbed cationic photosensitizer MB were studied,and finally the anti-photobleaching property,photo-oxidation property and antibacterial activity of MB immobilized composite nanofibers were evaluated.The results revealed that the addition of MMT increased the viscosity and conductivity of the electrospinning solution,and could make beads appear in the fibrous structure,simultaneously,a narrower diameter distribution of the nanofibers with the increase of the MMT ratio.In addition,the prepared MMT and nanofibers were well combined,and the increase of MMT ratio in the composite nanofibers strengthened the rate and ability of the membrane to adsorb MB.Moreover,the presence of MMT not only hindered the photocatalytic degradation of MB to a certain extent,but also reduced the photo bleaching effect,and ultimately leads to enhancing the photosensitivity of the composite nanofibers.Importantly,when the MMT took up 6%,the prepared composite photodynamic antibacterial nanofibers would acquire excellent antibacterial effects on the S.aureus and E.coli for reaching 99.9%,and after 5 cycles,the rate can still reach over 99%with just a slight decay,demonstrating the reasonable reutilizing of the composite.