Abstract
Antimicrobial polymers and coatings are potent types of materials for fighting microbial infections, and as such, they have attracted increased attention in many fields. Here, a series of antimicrobial copolymers were prepared by radical copolymerization of 2-hydroxyethyl methacrylate (HEMA), which is widely employed in the manufacturing of biomedical devices, and the monomer 2-(4-methylthiazol-5-yl)ethyl methacrylate (MTA), which bears thiazole side groups susceptible to quaternization, to provide a positive charge. The copolymers were further quantitatively quaternized with either methyl or butyl iodide, as demonstrated by nuclear magnetic resonance (NMR) and attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR). Then, the polycations were characterized by zeta potential measurements to evaluate their effective charge and by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) to evaluate their thermal properties. The ζ-potential study revealed that the quaternized copolymers with intermediate compositions present higher charges than the corresponding homopolymers. The cationic copolymers showed greater glass transition temperatures than poly(2-hydroxyethyl methacrylate) (PHEMA), with values higher than 100 °C, in particular those quaternized with methyl iodide. The TGA studies showed that the thermal stability of polycations varies with the composition, improving as the content of HEMA in the copolymer increases. Microbial assays targeting Gram-positive and Gram-negative bacteria confirmed that the incorporation of a low number of cationic units into PHEMA provides antimicrobial character with a minimum inhibitory concentration (MIC) of 128 µg mL−1. Remarkably, copolymers with MTA molar fractions higher than 0.50 exhibited MIC values as low as 8 µg mL−1.
Highlights
In the last few years, antimicrobial polymers have attracted substantial scientific and industrial attention because of their unique properties and applications in the design and production of many materials, including medical devices, textiles, packaging, and purification systems [1,2,3]
The polycations obtained after quaternization followed the contrary trend; their Tg increased with the amount of the MTARI cationic units for both series of copolymers—those quaternized with methyl iodide (P(MTAMeI-co-hydroxyethyl methacrylate (HEMA))) and those quaternized with butyl iodide (P(MTABuI-co-HEMA))
The polycations obtained after the quaternization followed the series of copolymers—those quaternized with methyl iodide (P(MTAMeI-co-HEMA)) and those contrary trend; their Tg increased with the amount of the MTARI cationic units for both series of quaternized with butyl iodide (P(MTABuI-co-HEMA))
Summary
In the last few years, antimicrobial polymers have attracted substantial scientific and industrial attention because of their unique properties and applications in the design and production of many materials, including medical devices, textiles, packaging, and purification systems [1,2,3]. Sci. 2018, 19, x FOR PEER REVIEW surfaces and, prevent such infections have emerged as very efficient prophylactic strategies These coatings can either repel microbes, avoiding microbial attachment, or kill microorganisms upon contact or in the surrounding by biocidal release [6]. The use antimicrobial polymers contact-active coatings with inherent activity demonstrated highofefficiency and are typicallyasobtained by incorporating antimicrobial biocidal activity has gained importance, because antimicrobial polymers offer some advantages, such agents, including antibiotics [7,8], antimicrobial peptides [9,10], silver and copper compounds [11,12], as chemical stability, high and long-term activity, low toxicity, and reduced potential to generate zinc oxide [13], titanium dioxide particles [14,15], etc., onto the surface. Several copolymer compositions were prepared and evaluated for an adequate balance of structural, thermal, and antimicrobial properties
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