Preparation And Antimicrobial Property Of Silk Fibroin Porous Material By Loading With Polyhexamethylene Biguanide(PHMB)

As the barrier of body surface,skin is easily damaged by thermal,chemical and mechanical factors.Timely coverage and protection with dressing is the basic method for treating wounds.Inhibiting bacterial growth and preventing wound infection are the key to accelerate wound healing.Silk fibroin(SF)has good biocompatibility and a wide application prospect as wound dressing.As a new type of environmental-friendly antimicrobial agent,polyhexamethylene biguanidine(PHMB)has strong broad-spectrum antibacterial property.This paper aimed to develop a new antibacterial silk fibroin wound dressing,the interaction of negatively charged silk fibroin with positively charged PHMB and the effect of PHMB on the molecule conformation of SF were investigated;the PHMB-loaded silk fibroin porous material was prepared by blending-freeze drying method,the release of PHMB in the porous material was investigated,and the relationship between the loading and antibacterial property of PHMB was studied;the PHMB-loaded porous silk fibroin material was further prepared by adsorption-secondary freeze drying method,and its antibacterial property against S.aureus and E.coli was investigated.Firstly,different proportions of PHMB/SF blend solutions were prepared.It was found that when a relatively small proportion of positive charged PHMB(1% or 2% by weight of silk fibroin)was mixed with the negative charged SF,the size of SF increased,and no aggregation occurred;when the proportion of PHMB/SF was 5%,the surface Zeta potential of the particles in the solution increased to +0.68±0.4 m V,and the particles aggregated with each other to generate a large amount of flocculation.The SEM showed that the flocculation had a porous network structure inside and contained a large number of flakes.The results of the test and analysis of CD,FT-IR and XRD showed that the molecular conformation of SF was not significantly changed and mainly based on random coil structure,after mixed with a relatively small proportion of PHMB(1% or 2%)or a large proportion(10%).When the blend proportion of PHMB/SF was 5%,the ?-sheet structure was apparently produced in the flocculation,and the supernatant contained a small amount of ?-type structure.Secondly,PHMB/SF antibacterial porous materials were prepared by blending-freeze drying method.From the observation by SEM,the pore size inside the SF porous material did not change significantly after mixing with PHMB,and no significant phase separation occurred,however,some new micron-sized holes were added to the pore wall of the materials.The results of FT-IR and XRD showed that the secondary structure of SF was mainly ?-sheet structure in PHMB/SF porous material.The release of PHMB was measured by UV spectrophotometer.The results showed that when the blend proportion of PHMB/SF was relatively small(0.5-2%),the PHMB loaded inside the porous material could hardly be released,and the cumulative release rates were about 10%-25% for 20d;when the blend proportion of PHMB/SF was relatively high(5-20%),the release of PHMB the porous was significantly increased,and the cumulative release amount were about 40-75% for 20 d.The inhibition zone and the inhibition rate test results showed that the PHMB/SF porous material had stronger antibacterial activity against S.aureus than E.coli.When the blend proportion of PHMB/SF was 2%,the PHMB/SF porous material have bacteriostatic effects on the two both bacterias;when the blend proportion reached to 5% or more,the material could kill 99% of S.aureus and E.coli.Finally,the SF porous material prepared by lyophilization method was immersed in the PHMB solution to adsorb PHMB,and the PHMB-loaded silk porous material was obtained after secondary freeze-drying.The inhibition zone and the inhibition rate test results showed that when the impregnation concentration of PHMB was 0.005wt%,the proportion of PHMB/SF was approximately 0.5%,which has antibacterial property on E.coli and S.aureus;and when the impregnation concentration of PHMB was 0.02wt%,the proportion of PHMB/SF was about 2%.The antibacterial rate of the two tested bacterials were more than 99%,and the antibacterial property was remarkable.Although the PHMB-loaded SF porous material prepared by the adsorption method needed to be freeze-dried twice,the short-term antimicrobial property was stronger than PHMB/SF porous material prepared by the blending method.