Poly[2-(dimethylamino)ethyl methacrylate- co-ethylene dimethacrylate]nanogel by dispersion polymerization for inhibition of pathogenic bacteria

Abstract

Bacterial infections and antimicrobial resistance are one of the major public health problems and various strategies to prevent potential threats have been developed. Protonated polymers were proven as efficient agents against several microbial pathogens. Poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) linear polymer and its copolymers represent one example of functional materials which inhibit the growth of both harmful Gram-negative and Gram-positive bacteria. However, the antimicrobial effect of positively charged PDMAEMA particles has been never tested. In this report, we deeply studied several parameters of free-radical polymerization, including the effect of crosslinking monomer, medium composition, solvency and polarity, and type and concentration of initiator and stabilizer, to fabricate high-quality poly[2-(dimethylamino)ethyl methacrylate-co-ethylene dimethacrylate] (PDMAEMA-EDMA) nanogel. We successfully found that dispersion polymerization in water/2-methoxyethanol medium (80/20 w/w), initiated with 0.2 wt% potassium persulfate (KPS) and stabilized with 0.5 wt% poly(vinyl alcohol) (PVA), produced a well-defined and sub-micron 167 nm PDMAEMA-EDMA nanogel. Bactericidal activity of the quaternized PDMAEMA-EDMA nanogel was assessed via time-kill curve assay against two Gram-positive and Gram-negative pathogenic bacteria, namely Staphylococcus aureus (S. aureus) and Acinetobacter baumannii (A. baumannii). The results illustrated that the quaternized PDMAEMA-EDMA nanogel acted as an effective bactericidal agent against both tested bacteria.

Fig. 1. SEM micrographs of PDMAEMA-EDMA nanogels prepared in water with 1 (a), 5 (b), 20 (c) wt% of EDMA and initiated with 0.15 wt% KPS and 20 (d) wt% EDMA initiated with 0.2 wt% KPS.

Fig. 2. SEM micrographs of PDMAEMA-EDMA nanogels prepared in water with 10 wt% EDMA and stabilized with 0.15 wt% SDS (a), in the mixture of water/EtOH (80/20 w/w) with 20 wt% EDMA and stabilized with 0.15 wt% SDS (b), and in the mixture of water/EtOH (80/20 w/w) with 20 wt% EDMA and without SDS (c). All polymerizations were initiated with 0.2 wt% KPS.

Fig. 3. SEM micrographs of PDMAEMA-EDMA nanogels prepared in a mixture of water/EtOH (80/20 w/w) with 20 wt% EDMA, stabilized with 1 wt% PVA and initiated with 0.2 wt% KPS (a); in a mixture of water/EtOH (80/20 w/w) with 20 wt% EDMA, stabilized with 0.5 wt% PVA and initiated with 0.2 wt% KPS (b); in a mixture of water/EtOH (70/30 w/w) with 20 wt% EDMA, stabilized with 0.5 wt% PVA and initiated with 0.2 wt% KPS (c); in a mixture of water/MeOH (80/20 w/w) with 20 wt% EDMA, stabilized with 0.5 wt% PVA and initiated with 0.2 wt% KPS (d).

Fig. 4. SEM micrographs of PDMAEMA-EDMA nanogels prepared in water/MeOH (80/20 w/w) with 20 wt% EDMA, stabilized with 0.5 wt% PVA and initiated with 0.25 wt% (a) and 0.3 wt% KPS (b).

Fig. 5. SEM micrographs of PDMAEMA-EDMA nanogels prepared in water/MetCel (80/20 w/w) with 20 wt% EDMA, initiated with 0.2 wt% KPS and stabilized with 0.15 wt% SDS (a), or with 0.5 wt% PVA (b).

Fig. 6. Experimental ¹³C CP/MAS NMR (solid line) and ¹³C MAS NMR (dashed line) spectra of PDMAEMA-EDMA25 (a) and quaternized PDMAEMA-EDMA25Q (b) samples recorded at 11 kHz spinning speed on 500 MHz NMR spectrometer.

Fig. 7. Antibacterial testing of the non-quaternized PDMAEMA-EDMA25 and quaternized PDMAEMA-EDMA25Q nanogels. Time-kill curve assay was carried out to estimate the effect of the nanogels on both S. aureus (a) and A. baumannii (c) counts after 1 and 4 h of the treatment at room temperature. The data indicate mean values ± SD. Asterisks represent a significant difference (***p < 0.001) when compared to non-treated control. (b and d) Representative photographs of corresponding agar plates with S. aureus ((b), 5 mg ml⁻¹, representative suspension dilution of 10⁻⁵) and A. baumannii ((d), 5 mg ml⁻¹, representative suspension dilution of 10⁻⁴) colonies including non-treated controls (NT).