Bacterial infection is a fairly common and potentially dangerous complication of wound healing, but a new “intelligent” dressing that turns fluorescent green to signal the onset of an infection could provide physicians a valuable early-detection system.
Researchers in the United Kingdom recently unveiled a prototype of the color-changing bandage, which contains a gel-like material infused with tiny capsules that release nontoxic fluorescent dye in response to contact with populations of bacteria that commonly cause wound infections.
Applied Materials and Interfaces - Prototype Development of the Intelligent Hydrogel Wound Dressing and Its Efficacy in the Detection of Model Pathogenic Wound Biofilms
All wounds get colonized by bacteria, often including pathogenic species, but small populations are generally not harmful, and the immune system can clear them. In some cases, though, a population of harmful bacteria grows too big for the immune system to handle, and clinical intervention is needed to clear it. “We believe that this transition normally happens several hours, if not longer, before any clinical symptoms become evident,” says Jenkins. Earlier detection might give doctors time to head off the infection even before such symptoms arise.
Jenkins says the transition is “almost certainly” associated with the formation of a so-called biofilm, a layer of microbes that work together and secrete a slimy substance to defend the colony against the immune system. At a high enough population density, the bacteria film switches on the production of toxins, says Jenkins. The new dressing works because the outer layer of the dye-containing capsules is designed to mimic aspects of a cell membrane. Toxins puncture the capsules like they would cells in the body, releasing the dye, which fluoresces when it is diluted by the surrounding gel.
The early detection of wound infection in situ can dramatically improve patient care pathways and clinical outcomes. There is increasing evidence that within an infected wound the main bacterial mode of living is a biofilm: a confluent community of adherent bacteria encased in an extracellular polymeric matrix. Here we have reported the development of a prototype wound dressing, which switches on a fluorescent color when in contact with pathogenic wound biofilms. The dressing is made of a hydrated agarose film in which the fluorescent dye containing vesicles were mixed with agarose and dispersed within the hydrogel matrix. The static and dynamic models of wound biofilms, from clinical strains of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis, were established on nanoporous polycarbonate membrane for 24, 48, and 72 h, and the dressing response to the biofilms on the prototype dressing evaluated. The dressing indicated a clear fluorescent/color response within 4 h, only observed when in contact with biofilms produced by a pathogenic strain. The sensitivity of the dressing to biofilms was dependent on the species and strain types of the bacterial pathogens involved, but a relatively higher response was observed in strains considered good biofilm formers. There was a clear difference in the levels of dressing response, when dressings were tested on bacteria grown in biofilm or in planktonic cultures, suggesting that the level of expression of virulence factors is different depending of the growth mode. Colorimetric detection on wound biofilms of prevalent pathogens (S. aureus, P. aeruginosa, and E. faecalis) is also demonstrated using an ex vivo porcine skin model of burn wound infection.
SOURCES - Technology Review, - Prototype Development of the Intelligent Hydrogel Wound Dressing and Its Efficacy in