Janus N,N-dimethylformamide as a solvent for a gradient porous wound dressing of poly(vinylidene fluoride) and as a reducer for in situ nano-silver production: anti-permeation, antibacterial and antifouling activities against multi-drug-resistant bacteria both in vitro and in vivo

The requirements for anti-permeation, anti-infection and antifouling when treating a malicious wound bed raise new challenges for wound dressing. The present study used N,N-dimethylformamide to treat poly(vinylidene fluoride) (PVDF) in order to obtain a dressing impregnated with in situ generated nano-silver particles (NS) via an immersion phase inversion method. Scanning electron microscopy (SEM) images showed that the film was characterized by a two-layer asymmetric structure with different pore sizes (top layer: similar to 0.4 mu m; bottom layer: similar to 1.8 mu m). The moisture permeability test indicated that the film had an optimal water vapor transmission rate (WVTR: similar to 2500 g m(-2) per day). TEM images revealed the successful formation of spherical NS, and Fourier-transform infrared spectroscopy (FTIR) demonstrated the integration of PVDF and NS (i.e., PVDF/NS). Correspondingly, the water contact angle measurements confirmed increased membrane surface hydrophobicity after NS integration. The inductively coupled plasma (ICP) spectrometry showed that the PVDF/NS displayed a continuous and safe release of silver ions. Moreover, in vitro experiments indicated that PVDF/NS films possessed satisfactory anti-permeation, antibacterial and antifouling activities against A. baumannii and E. coli bacteria, while they exhibited no obvious cytotoxicity toward mammalian HaCaT cells. Finally, the in vivo results showed that the nanoporous top layer of film could serve as a physical barrier to prevent bacterial penetration, whereas the microporous bottom layer could efficiently prevent bacterial infection caused by biofouling, leading to fast re-epithelialization via the enhancement of keratinocyte proliferation. Collectively, the results show that the PVDF/NS25 film has a promising application in wound treatment, especially for wounds infected by multi-drug-resistant bacteria such as A. baumannii.