Antibacterial and antibiofouling clay nanotube-silicone composite

Abstract

Introduction: Invasive medical devices are used in treating millions of patients each day. Bacterial adherence to their surface is an early step in biofilm formation that may lead to infection, health complications, longer hospital stays, and death. Prevention of bacterial adherence and biofilm development continues to be a major healthcare challenge. Accordingly, there is a pressing need to improve the anti-microbial properties of medical devices.

Materials and methods: Polydimethylsiloxane (PDMS) was doped with halloysite nanotubes (HNTs), and the PDMS-HNT composite surfaces were coated with PDMS-b-polyethylene oxide (PEO) and antibacterials. The composite material properties were examined using SEM, energy dispersive spectroscopy, water contact angle measurements, tensile testing, UV-Vis spectroscopy, and thermal gravimetric analysis. The antibacterial potential of the PDMS-HNT composites was compared to commercial urinary catheters using cultures of E. coli and S. aureus. Fibrinogen adsorption studies were also performed on the PDMS-HNT-PEO composites.

Results: HNT addition increased drug load during solvent swelling without reducing material strength. The hydrophilic properties provided by PEO were maintained after HNT addition, and the composites displayed protein-repelling properties. Additionally, composites showed superiority over commercial catheters at inhibiting bacterial growth.

Conclusion: PDMS-HNT composites showed superiority regarding their efficacy at inhibiting bacterial growth, in comparison to commercial antibacterial catheters. Our data suggest that PDMS-HNT composites have potential as a coating material for anti-bacterial invasive devices and in the prevention of institutional-acquired infections.

Keywords: PDMS; antibacterials; halloysite; medical devices; nanocomposites.

Figure 1

SEM micrographs of PDMS coated with different concentrations of PDMS–b–PEO. (A) PDMS–0% PEO, (B) PDMS–1% PEO, (C) PDMS–2.5% PEO, and (D) PDMS–5% PEO. Surface roughness appeared to increase with the sequential increase of PDMS–b–PEO concentrations. Abbreviations: b, coblock; PDMS, polydimethylsiloxane; PEO, polyethylene oxide; SEM, scanning electron microscopy.

Figure 2

SEM micrographs of PDMS loaded with HNTs 10% (wt./wt.) and coated with different concentrations of PDMS–b–PEO. (A) PDMS–HNT–0% PEO, (B) PDMS–HNT–1% PEO, (C) PDMS–HNT–2.5% PEO, and (D) PDMS–HNT–5% PEO. Similar surface characteristics were observed with the HNT-loaded PDMS versions. Surface roughness appeared to increase with the sequential addition of PDMS–b–PEO. Abbreviations: b, coblock; HNT, halloysite nanotube; PDMS, polydimethylsiloxane; PEO, polyethylene oxide; SEM, scanning electron microscopy.

Figure 3

Water contact angle images of treated and untreated PDMS. (A) 103.3° at 20 seconds on PDMS, (B) 97.7° at 200 seconds on PDMS, (C) 8.2° at 20 seconds on PDMS–PEO, and (D) 3.9° at 200 seconds on PDMS–PEO. Images displayed that the PEO additive significantly altered the PDMS surface wettability. Abbreviations: PDMS, polydimethylsiloxane; PEO, polyethylene oxide.

Figure 4

Water contact angle images on treated and untreated PDMS loaded with 10% HNTs (wt./wt.). (A) 103.8° at 20 seconds on PDMS–HNT, (B) 90.8° at 200 seconds on PDMS–HNT, (C) 15.8° at 20 seconds on PDMS–HNT–5% PEO, and (D) 8.7° at 200 seconds on PDMS–HNT–5% PEO. Hydrophilic properties were observed for the PDMS–HNT–PEO composites and showed that wettability was maintained with the addition of HNTs. Abbreviations: HNT, halloysite nanotube; PDMS, polydimethylsiloxane; PEO, polyethylene oxide.

Figure 5

SEM micrographs of tensile-fractured PDMS and PDMS–HNT surfaces. (A, B) PDMS, (C, D) PDMS–10% HNT. Different fracture patterns were noticed for PDMS and PDMS–10% HNT. Normal PDMS appeared to fracture smoothly, while the HNT-loaded versions displayed rougher fracturing patterns. Abbreviations: HNT, halloysite nanotube; PDMS, polydimethylsiloxane; SEM, scanning electron microscopy.

Figure 6

Images of energy-dispersive spectroscopic elemental data analysis for (left) PDMS and (right) PDMS–10% HNT. Spectra showed an increase in silica content and the presence of aluminum from the HNTs. Abbreviations: HNT, halloysite nanotube; PDMS, polydimethylsiloxane.

Figure 7

(A)Thermal gravimetric analysis on PDMS and (B) PDMS with 1%–10% HNT addition. Note: Thermal gravimetric analysis curves of formulation with different concentrations of HNTs with temperature (°C) at x-axis and the rate of weight loss (dw/dt) at y-axis. Abbreviations: HNT, halloysite nanotube; PDMS, polydimethylsiloxane.

Figure 8

(A) Graph showing total drug load content for PDMS and PDMS–10% HNT after solvent swelling. (B) Image of PDMS (left) and PDMS–10% HNT (right) after solvent swelling in methylene blue–acetone solutions. This is the first time that HNTs have been shown to increase the total drug loading content in cured polymers using a solvent swelling method. Abbreviations: HNT, halloysite nanotube; PDMS, polydimethylsiloxane.

Figure 9

Images of Mueller–Hinton agar disc diffusion assays against Escherichia coli at 24 hours. (A) antibacterial catheter, (B) silver-coated catheter, (C) PDMS–HNT–PEO–nitrofurantoin, (D) 100% PDMS catheter, (E) PDMS–HNT–PEO, and (F) standard nitrofurantoin disc (100 mg). Abbreviations: HNT, halloysite nanotube; PDMS, polydimethylsiloxane; PEO, polyethylene oxide.

Figure 10

Images of Mueller–Hinton agar disc diffusion assay against Staphylococcus aureus at 24 hours. (A) antibacterial catheter, (B) silver-coated catheter, (C) PDMS–HNT–PEO–nitrofurantoin, (D) 100% PDMS catheter, (E) PDMS–HNT–PEO, and (F) standard nitrofurantoin disc (100 mg). Abbreviations: HNT, halloysite nanotube; PDMS, polydimethylsiloxane; PEO, polyethylene oxide.

Figure 11

Images of Mueller–Hinton broth assays against Escherichia coli and Staphylococcus aureus at 24 hours. (1) E. coli, (2) S. aureus: (A1) Broth, (B1) control E. coli, (C1) 100% PDMS catheter, (D1) silver-coated catheter, (E1) antibacterial catheter, (F1) PDMS–HNT–PEO–nitrofurantoin, (A2) Broth, (B2) control S. aureus, (C2) 100% PDMS catheter, (D2) silver-coated catheter, (E2) antibacterial catheter, (F2) PDMS–HNT–PEO–nitrofurantoin. Abbreviations: HNT, halloysite nanotube; PDMS, polydimethylsiloxane; PEO, polyethylene oxide.

Figure 12

A graphic representation of untreated and treated PDMS surfaces and the biological effects in vitro. Abbreviations: HNT, halloysite nanotube; PDMS, polydimethylsiloxane; PEO, polyethylene oxide.