The detrimental impacts of chronic wounds affect 200,000 patients in the UK alone, making them a significant worldwide healthcare concern. Bacterial infections are a major factor in the chronicity of wounds and raise the possibility of serious consequences including gangrene and amputation. To address this issue, we explored the development of a theranostic dressing with an infection-responsive system that targets pH as a biomarker and a collagen-based wound contact layer known for its wound-healing properties.

To establish a visual infection detection system, we incorporated Bromothymol blue (BTB), a halochromic dye, into the dressing. Achieving an impressive 99 wt.% loading efficiency of BTB, the dressing exhibited a near-instantaneous colour change within one minute of exposure to simulated wound fluid. Drop-cast samples demonstrated sustained dye retention, retaining up to 97 wt.% and 85 wt.% of BTB after 96 hours in healthy and near-infected wound environments, respectively. In contrast, fibre-bearing prototypes released over 80 wt.% of BTB during the same period.

The extended dye confinement and durable colour change were attributed to secondary interactions between the collagen-based hydrogel and BTB, evidenced by increased collagen denaturation temperature (DSC) and red shifts (ATR-FTIR). Cytocompatibility was confirmed by high L929 fibroblast viability (92%) in drop-cast sample extracts after 7 days.

Our study successfully realised a simple wound theranostic dressing prototype by leveraging the colour change capability of BTB at infection-associated alkaline pH and the development of secondary interactions within the collagen network. Importantly, the addition of BTB did not alter the morphology or mechanical properties of the collagen hydrogels, rendering this design simple, scalable, and cell/regulatory-friendly. This novel wound theranostic design provides a promising platform for advanced dressings, with the potential to enhance wound healing, reduce hospitalisation time, and facilitate informed and personalised variations in clinical care.