Engineering an electroactive bacterial cellulose-carbon nanotube composite membrane against Staphylococcus aureus

Abstract

Staphylococcus aureus is the leading cause of skin infections in the U.S., and its rapid evolution and resistance to antibiotics create a barrier to effective treatment. In this study, we engineered a composite membrane with bacterial cellulose and carbon nanotubes (BC-CNT) as an electroactive dressing to rapidly eradicate vancomycin-intermediate S. aureus. Nonpathogenic Komagataeibacter sucrofermentans produced the BC membrane at an air-liquid interface. Then, carboxyl-functionalized multi-walled CNTs were integrated into decellularized BC to create stable and electrically conductive BC-CNT dressings. The electric potential and ionic flux across BC-CNT were modeled and standardized via chronoamperometry for experimental validation. We found that treatment with electroactive BC-CNT increases S. aureus sensitivity to vancomycin and prevents macro-scale biofilm formation. The bactericidal efficacy of the composite membrane is consistent with electrochemical stress caused by voltage mediated with BC-CNT. After a single hour of combinatorial electrical and drug treatment, biofilm-forming capacity was inhibited by nearly 92 %. These results advance applications of electrochemistry in medicine and create a new direction to overcome S. aureus infections on skin and soft tissues.

Keywords: Bacterial cellulose (BC); Electrochemical bandage; Multi-walled carbon nanotubes (CNTs); Staphylococcus aureus.

Fig. 1

Electroactive BC–CNT bandage and proposed antibacterial mechanisms. (A) Schematic representation of the electrochemical bacterial cellulose-carbon nanotube bandage with a superimposed potential map. (B) CNTs deposited on cellulose fibers, endowing the bandage with electrical conductivity. (C–F) The electrochemical bandage proposed mechanisms of bacterial elimination, including stunted biofilm-forming capabilities, degradation of bacterial membranes, ROS-induced oxidative stress, and potentiation and permeation of antibiotics.

Fig. 2

Structural and morphological characterization of bacterial cellulose–carbon nanotube composites. a) Pristine BC and (b) BC-CNT. (c) CNT loaded into BC-CNT after processing in 5 % CNT solution. (d) CNT released and percent CNT retention in BC-CNT over 48 h. (e) Surface and internal pore areas measured from top-view and cross-sectional SEM images. (f) TEM images of BC fibers with and without CNTs at 50,000 × (scale bar = 300 nm) and zoomed areas at 300,000 × (scale bar = 50 nm). (g) SEM images of top-view and cross-sectional fibers in pristine BC and BC-CNT at 10,000 × (scale bar = 2 μm) and 50,000 × (scale bar = 300 nm).

Fig. 3

Electrochemical impedance and conductivity analysis of BC–CNT composites. (a) Nyquist plot of pristine BC (black circles), 1 % loaded CNT in BC-CNT (red triangles), and 5 % loaded CNT in BC-CNT (purple triangles). Inset focuses on the high-frequency region of the Nyquist plot for solution resistance. (b) Calculated conductivity of each sample based on the fitted equivalent circuit. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 4

Electrochemical modeling and validation of ion flux in BC–CNT membranes. (a) BC-CNT electrode configuration. (b) Diagrammatic representation of experimental electrochemical cell. (c) Surface electric potential modeled across BC-CNT. (d) Simulated Na⁺ and (e) Cl⁻ ion flux between terminal electrodes. (f) Phenol red colorimetric pH map across UFTYE agar lacking S. aureus after voltage exposure for 1 h. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 5

(a) Representative panel of UFTYE and BC-CNT disks with S. aureus-GFP following electrochemical treatment. Scale bar = 7.5 mm. (b) and (c) Graphical representation of mean biofilm areas from replicate experiments with standard deviation and statistical significance for UFTYE and BC-CNT disks, respectively.