Bioburden-responsive antimicrobial PLGA ultrafine fibers for wound healing.

Despite innovation in the design and functionalization of polymer nanofiber wound healing materials, information on their interaction with the biochemical wound environment is lacking. In an earlier study, we have reported the interaction of fusidic acid-loaded PLGA ultrafine fibers (UFs) with wound bacteria. Massive bacterial colonization and the formation of a dense biofilm throughout the mat were demonstrated. This was associated with a marked enhancement of initial drug release at concentrations allowing eradication of planktonic bacteria and considerable suppression of biofilm. The present study aimed at extending earlier findings to gain more mechanistic insights into the potential response of the fusidic acid-laden UFs under study to controlled microbial bioburden. Initial drug release enhancement was shown to involve surface erosion of the ultrafibrous mats likely mediated by microbial esterase activity determined in the study. Release data could be correlated with microbial bioburden over the inoculum size range 10³-107 CFU/ml, suggesting a bioburden-triggered drug release enhancement mechanism. Moreover, the effectiveness of fusidic acid-laden UFs in the healing of either lightly contaminated or Staphylococcus aureus heavily infected wounds in a rat model suggested in-use relevant antimicrobial release patterns. Findings indicated active participation of polymer ultrafine wound dressings in a dynamic interaction with the wound milieu, which affects their structure-function relationship. Understanding such an interaction is fundamental to the characterization and performance assessment of wound materials under biorelevant conditions and the design of polymer-based infection-responsive biomaterials.

Antimicrobial PLGA ultrafine fibers: interaction with wound bacteria.

The structure and functions of polymer nanofibers as wound dressing materials have been well investigated over the last few years. However, during the healing process, nanofibrous mats are inevitably involved in dynamic interactions with the wound environment, an aspect not explored yet. Potential active participation of ultrafine fibers as wound dressing material in a dynamic interaction with wound bacteria has been examined using three wound bacterial strains and antimicrobial fusidic acid (FA)-loaded electrospun PLGA ultrafine fibers (UFs). These were developed and characterized for morphology and in-use pharmaceutical attributes. In vitro microbiological studies showed fast bacterial colonization of UFs and formation of a dense biofilm. Interestingly, bacterial stacks on UFs resulted in a remarkable enhancement of drug release, which was associated with detrimental changes in morphology of UFs in addition to a decrease in pH of their aqueous incubation medium. In turn, UFs by allowing progressively faster release of bioactive FA eradicated planktonic bacteria and considerably suppressed biofilm. Findings point out the risk of wound reinfection and microbial resistance upon using non-medicated or inadequately medicated bioresorbable fibrous wound dressings. Equally important, data strongly draw attention to the importance of characterizing drug delivery systems and establishing material-function relationships for biomedical applications under biorelevant conditions.