ABSTRACT
Although nanomaterials are used in many fields, little is known about the fundamental interactions between nanomaterials and microorganisms. To test antimicrobial properties and retention ability, 13 electrospun polyamide (PA) nanomaterials with different morphology and functionalization with various concentrations of AgNO3 and chlorhexidine (CHX) were analyzed. Staphylococcus aureus CCM 4516 was used to verify the designed nanomaterials' inhibition and permeability assays. All functionalized PAs suppressed bacterial growth, and the most effective antimicrobial nanomaterial was evaluated to be PA 12% with 4.0 wt% CHX (inhibition zones: 2.9 ± 0.2 mm; log10 suppression: 8.9 ± 0.0; inhibitory rate: 100.0%). Furthermore, the long-term stability of all functionalized PAs was tested. These nanomaterials can be stored at least nine months after their preparation without losing their antibacterial effect. A filtration apparatus was constructed for testing the retention of PAs. All of the PAs effectively retained the filtered bacteria with log10 removal of 3.3-6.8 and a retention rate of 96.7-100.0%. Surface density significantly influenced the retention efficiency of PAs (p ≤ 0.01), while the effect of fiber diameter was not confirmed (p ≥ 0.05). Due to their stability, retention, and antimicrobial properties, they can serve as a model for medical or filtration applications.
ABSTRACT
Electrospun polyamide (PA) nanofibers have great potential for medical applications (in dermatology as antimicrobial compound carriers or surgical sutures). However, little is known about microbial colonization on these materials. Suitable methods need to be chosen and optimized for the analysis of biofilms formed on nanofibers and the influence of their morphology on biofilm formation. We analyzed 11 PA nanomaterials, both nonfunctionalized and functionalized with AgNO3, and tested the formation of a biofilm by clinically relevant bacteria (Escherichia coli CCM 4517, Staphylococcus aureus CCM 3953, and Staphylococcus epidermidis CCM 4418). By four different methods, it was confirmed that all of these bacteria attached to the PAs and formed biofilms; however, it was found that the selected method can influence the outcomes. For studying biofilms formed by the selected bacteria, scanning electron microscopy, resazurin staining, and colony-forming unit enumeration provided appropriate and comparable results. The values obtained by crystal violet (CV) staining were misleading due to the binding of the CV dye to the PA structure. In addition, the effect of nanofiber morphology parameters (fiber diameter and air permeability) and AgNO3 functionalization significantly influenced biofilm maturation. Furthermore, the correlations between air permeability and surface density and fiber diameter were revealed. Based on the statistical analysis, fiber diameter was confirmed as a crucial factor influencing biofilm formation (p ≤ 0.01). The functionalization of PAs with AgNO3 (from 0.1 wt %) effectively suppressed biofilm formation. The PA functionalized with a concentration of 0.1 wt % AgNO3 influenced the biofilm equally as nonfunctionalized PA 8% 2 g/m2. Therefore, biofilm formation could be affected by the above-mentioned morphology parameters, and ultimately, the risk of infections from contaminated medical devices could be reduced.
