Preparation And Poperties Of Bacterial Cellulose–Based Photosensitive Antibacterial Materials

As a result of the overuse of antibiotics,diseases such as drug-resistant bacterial infections are spreading around the world,increasing health risks and financial burdens.Antimicrobial photodynamic inactivation(aPDI) has recently attracted significant attention due to its advantages such as highly effective broad-spectrum inactivation and no pathogen resistance.It has broad prospects and great practical significance for infection prevention,however,the development and application of aPDI are hindered by unsatisfactory photosensitizer,poor reusability and difference in antimicrobial activity against different strains.To that end,this study immobilized the naturally-occurring photosensitizer hypocrellin(Hc) on bacterial cellulose(BC) to prepare photosensitive material and evaluated and further improved its photodynamic antibacterial ability.Firstly,naturally-occurring photosensitizer hypocrellin(Hc)was covalently appended on bacterial cellulose(BC) by coupling agent agent cyanide chloride(TCT)to creating a photodynamic material(Hc-BC).Then,the loading of Hc onto the BC membrane was determined and evaluated.The resultant Hc-BC membrane was characterized by both physical(SEM,TGA,XRD) and spectroscopic(IR,diffuse reflectance UV-visible)methods and its basic morphology,chemical structure and thermal stability were analyzed.Also,indirect cytotoxicity tests employing mouse skin fibroblast(L929)cells was carried out to investigate the biocompatibility of Hc-BC membrane.The results showed that Hc-BC had good photosensitizer loading of 155 nmol Hc/mg membrane.The addition of Hc improved the hydrophobicity and thermostability of BC,slightly decreased its crystallinity.After a 24 h extraction,no harmful components were leached out of HC-BC membrane,demonstrating its good covalent fixation and good biocompatibility to mammalian cells.Secondly,the antibacterial activities of the membranes before and after the loading of Hc was invastigated against S.aureus(Gram-positive)and E.coli(Gram-negative)strain in light/dark conditions.Besides,the photodynamic antibacterial ability and durability of HC-BC membrane were investigated under different conditions(soaking time,illumination time and recycle times).The potentiation of the antibacterial efficacy of the Hc-BC membrane with potassium iodide(KI)were investigated and the antibacterial principle of potassium iodide oxides was explored.The results demonstrated a 99.5+%(2.7 log units)reduction against S.aureus upon 30 min illumination(Xe lamp,65±5 m W/cm~2,420?780 nm),however,no statistically significant inactivation of E.coli was observed.Although the antibacterial activity of HC-BC membrane was improved by increasing the irradiation duration to 60 min,it was still not ideal for E.coli(49.5%).The photosensitizer HC on the HC-BC fiber membrane did not leach out through time,confirming its good covalent coupling.However,the reusability was not iseal as the antibacterial activity of HC-BC against S.aureus was only43.2% after 4 recycle times.Potentiation with potassium iodide was found to increase the antibacterial efficacy of Hc-BC against S.aureus to 99.997%(4.8 log units)at 10 m MKI,while E.coli was inactivated by 99.1%(2 log units)at 100 m MKI,with the increase in inactivation being attributable to short-lived reactive iodide radicals(I·/I2·?)that are the major biocidal agents in the potentiation of Hc-BC by KI.Finally,bacterial cellulose/chitosan(BC/CH)composite was prepared by adding chitosan(CH)into the BC scaffold.And Hc was also covalently loaded on the BC/CH membrane by coupling agent TCT to prepare photodynamic antibacterial membrane(Hc-BC/CH).Then,the morphology,crystallinity,chemical structure and thermostability of the nanofibrous membrane before and after the addition of CH and Hc were compared by physical(SEM,TGA,XRD)and spectroscopic(IR,diffuse reflectance UV-visible)characterization.The antibacterial ability to S.aureus and E.coli were also investigated in light/dark conditions.The results showed that the addition of CH could improve the Hc loading to 198 nmol/mg membrane.And the loading of Hc make the surface of the nanofibrous membrane uneven,slightly decreased its crystallinity and thermostability.More importantly,the Hc-BC/CH membrane showed good antibacterial effect against S.aureus and E.coli(?90%) in the dark due to the antibacterial ability of CH,furthermore,the antibacterial effect against S.aureus and E.coli reached 99.9999% and 99.49% rescepectively under illumination due to the synergy of Hc and CH.In addition,the antibacterial efficacy of HC-BC/CH against S.aureus remained at 85.42%,indicating that the addition of CH could improve the antibacterial ability and reusability.Taken together,these aPDI materials processed excellent practical value to prevent pathogen transmission in the future.