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