The skin acts as a hardy barrier against the messy outside world, but when left exposed, infections can take hold. From burns, scrapes, and cuts, skin wounds are some of the most common wounds and they require a delicate repair process (1). Bacterial infections can occur in up to 32 percent of all wounds, and what worries doctors and researchers is the that nearly 25 percent of these infections are resistant to multiple antibiotics (2,3). The need for improved wound healing outcomes is high, but technology has struggled to keep up with the demand.

A team of researchers recently designed a smart wound dressing that addresses the threat of antibiotic resistant infections surrounding wounds (4). They combined a real-time infection monitoring system with a precise method of ridding the infection without the need for antibiotics. 

“I have been researching this work for at least 15 years,” said Yan Sun, study coauthor and chemist at Henan University. “We were excited to develop timely methods to treat emergent bacterial infections, yet one big challenge was how to organize the small entities; they're still just nanometers. It wasn’t until four years ago that I first got the macroscopic size developed.”

Assembling the dressing

The team combined the strength and flexibility of silk with the unique bacteria-sensing capabilities of a chemical stain called N,N′-dimethylated dipyridinium thiazolo[5,4-d]thiazole (MPT) to produce a colorimetric infection monitoring system. When bacteria create energy via respiration, the final step in that biochemical pathway allows them to reduce MPT to a radical form. This radical form causes the silk to change from a yellow color to deep purple. They then took this MPT treated silk and used it to coat a centimeter of a self-assembled platinum-metal organic cage (Pt MOC) film (5). Metal organic cages are complex geometric chemical building blocks that house reactive metals at their cores, providing both structural support and bacterial killing machinery.

The team activated the dressing’s antibacterial properties using a simple red laser that shines light with a 660-nanometer wavelength.  The bacteria-induced MPT radicals absorb the light and release toxic reactive oxygen species (ROS) that effectively kill the bacteria. The heat produced by the radicalized MPT inside the dressing rises above 55°C, which also kills the bacteria. However, the MPT is not the only source of antibacterial weaponry.

The researchers found that this specific wavelength of light causes the disassembly of the Pt MOC superstructure. The freed platinum metal core can then bind to the surface of the bacteria, where it disrupts the membrane, ultimately killing the bacteria. 

“Their bacterial sensing component of the dressing is amazing,” said Raghu Ram Achar, a biochemist at Jagadguru Sri Shivarathri Academy of Higher Education and Research who was not involved in this study. “They have taken care addressing each and every component of the dressing in a proper manner and addressed common areas of concern found in the field of tissue engineering.” 

Dressing effectiveness

The researchers tested their design against two common skin pathogens, Staphylococcus aureus and Escherichia coli using in vitro and rat models. Carefully, they created small wounds on the surfaces of the rats’ skin and covered the areas with different combinations of their engineered wound dressing. On day 12 of the experiment, they found that the smart dressing made with three layers and treated with light helped wound healing the most; less than one percent of the initial wound remained.

“My coauthors and I were surprised with the effectiveness of the dressing,” said Sun. “It shows good activity towards the bacteria but also causes little to no harm to the regular, normal cells.” 

Altogether, this dressing provides a detection system and a three-pronged attack on invading bacteria — radicals, heat, and metals. It lays a strong foundation for the innovative biomaterials of the future.

“My one concern is with scalability and cost-effectiveness,” said Achar. “Silk is a very expensive fabric. The biocompatibilities and biostability of the chemicals used need to be studied before taken to the clinical setting.”

Sun added that she and her team will continue studying their wound dressing and design ways to enhance it.

“I hope one day this technology can be scaled to be used as a flexible, wearable device for human healthcare settings,” said Sun. 

References:

1. Guo, S. & DiPietro, L. A. Factors Affecting Wound Healing. J Dent Res  89, 219–229 (2010).
2. Ashoobi, M.T. et al. Incidence rate and risk factors of surgical wound infection in general surgery patients: A cross-sectional study. Int Wound J  20, 2640–2648 (2023).
3. Puca, V. et al. Microbial Species Isolated from Infected Wounds and Antimicrobial Resistance Analysis: Data Emerging from a Three-Years Retrospective Study. Antibiotics  10, 1162 (2021).
4. Li, W.-Z. et al. Supramolecular coordination platinum metallacycle–based multilevel wound dressing for bacteria sensing and wound healing. Proc Natl Acad Sci USA  121, e2318391121 (2024).
5. Sun, Y., Tuo, W. & Stang, P. J. Metal–organic cycle-based multistage assemblies. Proc Natl Acad Sci USA  119, e2122398119 (2022).