Biocompatibility and selective antibacterial activity of a bismuth phosphinato-nanocellulose hydrogel

Antimicrobial hydrogels are of immense value in wound care applications. However, the rapid rise of antimicrobial resistance has made it necessary to look for new antimicrobial additives for such materials. In this study, a novel antimicrobial hydrogel for wound care applications has been developed. The material combines TEMPO-oxidized nanocellulose hydrogel with a new class of antimicrobial agent, phenyl bis -phosphinato bismuth (III) complex. The hydrogel was characterized using scanning electron microscope imaging to show the overall distribution of the complex particles within the nanocellulose hydrogel matrix phase. The rheological properties of the bismuth loaded hydrogel are comparable to commercial over-the-counter burn hydrogels and behave like true gels. Activity of the different concentrations of the complex was studied against a range of medically important bacteria and mammalian fibroblast cells. Bismuth complex target loading of 9 µg/g showed bactericidal activity against Acinetobacter baumannii and Pseudomonas aeruginosa and bacteriostatic effect against MRSA and VRE, while having no toxic effect on mammalian fibroblast cells. However, Escherichia coli was less susceptible to this concentration comparatively. Our study has identified a range of bismuth complex loading levels for the material at which the additive appears to be safe and active. This study is a step towards the design of a biocompatible and renewable hydrogel containing a safe antimicrobial additive, which has an excellent safety margin to pathogenic bacteria over mammalian cells and would appear to be a promising material for active wound dressing applications. Graphic abstract