Antibacterial activity of electrospun nanopolymeric fibers embebbed with silver nanoparticles for biomedical applications

Background: Nowadays, producing nanopolymeric fibers with diameters in the nanoscale range by the electrospinning method has attracted much increased attention. In fact, their high surface area and porosity make them particularly attractive to a large number of medical applications, mainly wound dressing and drug delivery. Furthermore, silver is a desirable candidate among other known antimicrobial agents to control wound curing as it reduces the inflammation, impedes the contraction, and enhances the epithelialization; consequently a considerable interest on the use of silver nanoparticles has developed. The purpose of this work was to evaluate the antibacterial activity of both nanopolymeric poly lactic acid (PLA) fibers and PLA containing nanoparticles of silver (Ag) produced by an alternative, one-step, electrospinning method. Material/methods: The nanopolymeric fibers (PLA and PLA+Ag) obtained by an electrospinning technique have been characterized morphologically by SEM and TEM, and subsequently tested to evaluate their antibacterial activity against two reference bacterial strains: Staphylococcus epidermidis (ATCC 35984) and Escherichia coli (ATCC 25922). PLA and PLA+Ag fibers were sterilized by UV, placed in the presence of a bacterial inoculum of 107 CFU/ml and then incubated for 15, 24 and 48 hours at 37°C. Controls without nanopolymeric fibers were also performed. After the incubation time, for each sample the number of CFU/ml was quantified by trypticase soy agar (TSA) plate count. All the experiments were performed in triplicate, and the results were analyzed by descriptive statistics and tested by unpaired T-test (p<0.05). Results: Nanopolymeric fiber morphologies were observed using SEM and TEM photographs. These analysis showed that the electrospinning process, with optimized parameters results, led to uniform nanofibers for each sample and the resultant fibers exhibited uniform morphology with silver nanoparticles distributed throughout (Figure 1A). The antibacterial assays on PLA and PLA+Ag, evaluated against both gram positive and gram negative bacteria using CFU/ml counting, demonstrated that no antibacterial activity was detected for the PLA nanofibers. In contrast, for the PLA embedded with Ag, a significant (p<0.01) more pronounced activity against both S. epidermidis and E. coli, highlighted by a reduction in the CFU/ml, was observed during the course of the experiments (Figure 1B). Conclusions: Combining antimicrobial agents with nanopolymeric fibers is considered as an effective way to develop an antibacterial wound dressing for decreasing the risk infection, which is a considerable concern in wound healing. Although there has been only a partial Ag release from nanopolymeric fibers during the experiment times, a significant in vitro antimicrobial activity, exerted by PLA+Ag against two common types of pathogens, was detected and related to the presence of Ag nanoparticles. As a result, these nanopolymeric fibers have a good potential for use as a biocompatible and antimicrobial wound dressing in the biomedical field.