A biomimetic hydrogel can exploits a light-triggered antimicrobial effect to be used in post-operative surgical dressings to reduce the risk of potentially lethal hospital-acquired, and other, infections.

Writing in the journal Angewandte Chemie researchers from the Hebei University of Technology, Tianjin, China, Radboud University, in Nijmegen, The Netherlands, and the University of Queensland, in Brisbane, Australia, have demonstrated how red light activates the gel to generate reactive oxygen species that can kill bacteria and fungi. [Xing, C. et al., Angew Chem (2020); DOI: 10.1002/anie.201910979]

Hydrogels are polymer networks that can carry water within their matrix. The addition of antimicrobial components to the matrix can give us an antimicrobial hydrogel. However, there are pros and cons to such an approach to making medical dressing that way. The current team has instead used photodynamic antimicrobial chemotherapy. In their approach photosensitizers are also added to the system so that it is an active, excited state, only when irradiated with light at an appropriate range of wavelengths. Non-radiative transitions help generate the reactive oxygen species.

Critically, the new system is, unlike earlier designs, biocompatible and biodegradable, but relies on a biometic approach rather than using materials from biological sources, which bring with them issues of contamination and immune reactions as well as being less reproducible. The team used a polymer with a helical backbone - polyisocyanide with grafted ethylene glycol chains. This polymer can form porous, highly biocompatible hydrogels with a thread-like architecture that is not dissimilar to collagen and fibrin fibers. The photosensitizer used was based on a polythiophene.

In solution the photosensitizer forms disordered clumps and absorbs violet light but once incorporated into the spiralised hydrogel, it takes on a linear configuration that is instead activated in the red region of the visible spectrum. Red light penetrates more deeply and does not lead to bleaching of the photosensitizer.

The team has successfully tested their gel against common microbes Escherichia coli and Bacillus subtilis, and the fungal pathogen Candida albicans. The system is active even against strains that are resistant to antiobiotics. They suggest that the work is a good starting point for making wound dressings with what they refer to as "built-in infection stoppers".