Optically Responsive, Smart Anti-Bacterial Coatings via the Photofluidization of Azobenzenes

Abstract

Antibacterial strategies sans antibiotic drugs have recently garnered much interest as a mechanism by which to inhibit biofilm formation and growth on surfaces due to the rise of antibiotic-resistant bacteria. Based on the photofluidization of azobenzenes, we demonstrate for the first time the ability achieve up to a 4 log reduction in bacterial biofilms by opto-mechanically activating the disruption and dispersion of biofilms. This unique strategy with which to enable biofilm removal offers a novel paradigm with which to combat antibiotic resistance.

Keywords: antibacterial and antifouling strategies; antibacterial coatings; azobenzenes; optically responsive materials; photofluidization; photoresponsive polymers; smart materials.

Figure 1.

Azobenzene change in conformation from trans to cis upon exposure to UV light (~365 nm) and from cis to trans upon exposure to visible light (~490 nm) or heat. However, when irradiated with intermediate wavelengths (430–480 nm), azobenzenes undergo rapid, transient, oscillatory trans–cis–trans isomerization (photofluidization effect) and can successfully disrupt biofilms on the surface of a material (panel a). The photofluidization effect can be used to disrupt biofilms from the surface of a substrate (panel b).

Figure 2.

Pseudomonas aeruginosa biofilms (gfp green) grown on an azopolymer coating on the surface of a glassy polymer substrate (red, rhodamine; panel a). On exposure to a clinical dental light at 430–480 nm (3 M Elipar DeepCure-S LED Curing Light) for 45 s at 700 mW/cm², the photofluidization effect initiated via the rapid trans–cis–trans isomerization of the azobenzenes result in biofilm disruption and ejection (panels b and c). As soon as the light is switched off, the oscillatory dynamics cease, and materials return to its native state. The azocoating after the second exposure shows the further absence of biofilm (panel d).

Figure 3.

Biofilms on the surface of the AZO substrates and the control substrates (No AZO) were exposed to light from a dental lamp (3 M Elipar DeepCure-S LED Curing Light) to initiate the fluidization effect and subsequently gently washed in PBS to remove the detached bacteria from the biofilm. This process was repeated 3 times for each sample. A live–dead stain before and after the light exposures and subsequent washes captures the ability of the photofluidization effect to remove bacterial biofilms from 4 different biofilms (3A–D). Our approach was not successful in removing biofilms formed via Streptococcus mutans in the presence of sucrose (3E).

Figure 4.

Quantification of the biofilms removed via the photofluidization effect after three light exposures and washes on AZO and no AZO (control subtrates) indicates that a significant loss of biofilm can be achieved in 4 out of 5 biofilms tested: 4A–D (n ≥ 3). The sucrose-dependent S. mutans biofilms (4E), however, did not respond to the photofluidization effect.