Research On Preparation And Application Of Usnic Acid /Silk Fibroin Composite Wound Dressing

As the largest organ of human body,skin plays a critical role in maintaining the stability of human internal environment and normal physiological function.However,chronic skin disease wounds often destroy the integrity of the skin and can cause severe trauma to the body through such as bacterial infection,inflammation,and tissue necrosis.To effectively treat wounds,wound dressings are often used to restore normal skin function and promote wound healing.Silk fibroin（SF）has become one of the preferred natural polymer materials for wound dressings due to its advantages of degradability,excellent biocompatibility and adjustable mechanical strength.In this paper,SF is used as base material,and usnic acid（UA）,a natural drug used as antibacterial agent,to prepare usnic acid/silk fibroin composite wound dressing（USCWD）by electrospinning,and which performance and application research are carried out.The specific research content and results are as follows:（1）Preparation and performance tests of USCWD.Natural silkworm cocoons were used to extract SF aqueous solution,and the concentrated SF solution was mixed with UA to prepare USCWD by electrospinning.The surface morphology,chemical structure,mechanical properties,in vitro degradability,gas permeability（Water Vapor Transmission Rate,WVTR）,and drug release of USCWD were characterized and tested.The scanning electron microscope（SEM）results showed that the nanofibers with an average diameter of 360±10 nm interwove with each other to form mesh structure which gives nearly twice WVTR of Tegaderm Hydrocolloid ^3M,a commercial dressing.By methanol treating for a short time can increase the internalβ-sheet content from 15.45%（before treatment）to 50.27%（after treatment）;when the concentration of SF is constant（20 wt%）,the UTS of USCWD can increased from 1.68±0.41 MPa（before treatment）to 2.61±0.61 MPa（after treatment）;Meanwhile,the rate of degradation in vitro was greatly reduced,and the drug release time was extended to 8 days,overcoming the explosive release of traditional dressing drugs.（2）Biological properties study of USCWD.Firsy,Gram-positive bacteria:Staphylococcus aureus（S.aureus）,Streptococci pyogenes（S.pyogenes）and Gram-negative bacteria:Escherichia coli（E.coli）,Pseudomonas aeruginosa（P.aeruginosa）were selected to prove the antibacterial activity of USCWD;Then,NIH3T3 fibroblasts were used to verify the biocompatabilityes of USCWD;Finally,the ability to promote wound healing and its possible mechanism were tested by using the full-thickness back skin wound model of mice.Studies have shown that under the two antibacterial methods of solid plat and bacterial suspension antibacterial,the USCWD exhibits ultra-high sensitivity to Gram-positive bacteria:the antibacterial index is as high as 2.02±0.09 and 12.01±0.25,and it can effectively inhibit the growth of Gram-negative bacteria:the antibacterial index is 1.65±0.08 and 1.19±0.01,respectively.NIH3T3fibroblasts are cultured in the soaking solution of USCWD,the survival rate is as high as 99%and the cell morphology is normal;the cell can carry out normal physiological activities on the USCWD.Compared with Tegaderm Hydrocolloid ^3M,the full-thickness skin wounds of mice have treated by USCWD showed obvious contraction on the third day,the staining results of pathological section also verified that USCWD had faster formation of Cytokeratin-10（CK10）and Vascular Endothelial Growth Factor（VEGF）than Tegaderm Hydrocolloid ^3M,and short the time of wound healing.In summary,in this study,the USCWD prepared by electrospinning using SF and UA has multiple advantages such as adjustable mechanical properties,good degradability,gas permeability,antibacterial properties,and biocompatibility.It can effectively promote wound healing,and providing potential applications for improving of chronic wound repair.