Highly effective antimicrobial nanocomposites based on hydrogel matrix and silver nanoparticles: long-lasting bactericidal and bacteriostatic effects

Antimicrobial nanocomposites (NCs) are being used as an alternative antibacterial therapy for killing antibiotic-resistant pathogenic bacteria. The NCs are made of Ag nanoparticles (AgNPs) inside biocompatible hydrogel matrixes. The NCs were synthesized by the absorption of AgNO3 solution into a hydrogel matrix, followed by UV light irradiation, without using additional toxic reactants. The hydrogels used as matrixes are based on N-isopropylacrylamide (NIPAM) and copolymers with different functional groups: 2-acrylamide-2-methylpropanesulfonic acid (AMPS), N-hydroxyethylacrylamide (HEAA) and (3-acrylamidepropil)trimethylammonium chloride (APTMAC). Neutral, anionic and cationic groups were added to the matrixes in order to study their effects on the release of antibacterial species. The NCs were characterized by UV-visible spectroscopy and transmission electronic microscopy. The kinetics of the release of Ag+ ions from the NCs were followed by UV-visible spectroscopy at 300 nm. Biological experiments were based on the plate count method and agar diffusion testing against Pseudomonas aeruginosa. The bacterial death rate using the NCs is higher than when PNIPAM and nanoparticles in solution are used and seems to be related to the large amount of AgNPs contained inside the gels. In all cases, inhibition and diffusion halos were observed upon the exposure of bacterial cultures on agar to NC discs. The presence of both halos confirmed the bactericidal and bacteriostatic effects of the NCs. The reusability (prolonged use) of the materials was demonstrated until the Ag-NP content was exhausted. The NCs with a higher antibacterial capacity are based on a PNIPAM-co-6%APTMAC matrix. It was demonstrated that these NC materials have the capacity to maintain an aseptic/antiseptic zone for 7 to 15 days.