Antimicrobial s-PBC Coatings for Innovative Multifunctional Water Filters

Abstract

Biological contamination is a typical issue in water treatment. Highly concentrated microbial suspensions in a water flow may cause filter occlusion and biofilm formation, affecting the lifespan and quality of water purification systems and increasing the risk of nosocomial infections. In order to contrast the biofilm formation, most of the conventional strategies rely on the water chemical modification and/or on the use of filters functional coatings. The former is unsafe for huge chemicals spilling required; therefore, we focus on the second approach and we propose the use of a sulfonated pentablock copolymer (s-PBC, commercially named Nexar™) as innovative multifunctional coating for improving the performance of commercial water filters. S-PBC-coated polypropylene (PP) samples were tested against the pathogen Pseudomonas aeruginosa. The covering of PP with s-PBC results in a more hydrophilic, acid, and negatively charged surface. These properties avoid the adhesion and proliferation attempts of planktonic bacteria, i.e., the biofilm formation. Inhibition tests were performed on the as-modified filters and an evident antibacterial activity was observed. The results point out the possibility of using Nexar^TM as coating layer for filters with antifouling properties and a simultaneous ability to remove bacteria and cationic dyes from water.

Keywords: Pseudomonas aeruginosa; antibacterial coating; biofilm; filter; polypropylene; s-PBC; sulfonated polymers.

Figure 1

Photos and SEM images of polypropylene (PP) (on the left) and sulfonated pentablock copolymer (s-PBC)@PP (on the right) coupons.

Figure 2

Fluorescence microscopy images of reference PP and s-PBC@PP coupon before (A,C, respectively) and after (B,D, respectively) 20 days of incubation with Pseudomonas aeruginosa in water.

Figure 3

UV–Visible absorbance spectra of methylene blue (MB) solutions after dipping PP and s-PBC@PP for 1, 2, or 3 h. In the inset, a photo of the filters and dyes solutions after three hours of adsorption.

Figure 4

Growth test of P. aeruginosa at 20 days of incubation with s-PBC@PP (A,B), PP (C), Teflon (D), and glass (E) samples.

Figure 5

Fluorescence image of colonies of 5 × 10⁶ cells/mL (A,D) and 2.5 × 10⁶ cells/mL (B,C) P. aeruginosa, plated after 20 days of incubation in coupon-free water.

Figure 6

Modified Zone of Inhibition Test of P. aeruginosa after 24 h incubation with s-PBC@PP (A) and reference PP (B) coupons in dry state (on the left) and after adding 0.2 mL of water (on the right). The clear zone around the s-PBC@PP coupon is shown in detail (red dashed line).

Figure 7

Modified Zone of Inhibition Test of P. aeruginosa after 24 h incubation with reference PP (1) and s-PBC@PP (2) coupons containing a residual volume of water (A) and after the spotting of 0.2 mL (B) and 0.5 mL (C).

Figure 8

Modified Zone of Inhibition Test of P. aeruginosa after 24 h incubation with neutralized s-PBC@PP (A), PP (B), and standard s-PBC@PP (C) coupons spotted with 0.2 mL of sterile tap water. The clear zone around the standard s-PBC@PP coupon is shown in detail (D).

Figure 9

Schematic representation of P. aeruginosa death induced by s-PBC@PP and water: (A) acid s-PBC@PP in small volume system; (B) neutralized s-PBC@PP in small volume system; (C) acid s-PBC@PP in large volume system. Physiological (blue), damaged (red), and dead (gray) bacteria are indicated with different colors.