Nanosilver-based antibacterial drugs and devices: Mechanisms, methodological drawbacks, and guidelines

Despite the current advancement in drug discovery and pharmaceutical biotechnology, infection diseases induced by bacteria continue to be one of the greatest health problems worldwide, afflicting millions of people annually. Almost all microorganisms have, in fact, an intrinsic outstanding ability to flout many therapeutic interventions, thanks to their fast and easy-to-occur evolutionary genetic mechanisms. At the same time, big pharmaceutical companies are losing interest in new antibiotics development, shifting their capital investments in much more profitable research and development fields. New smart solutions are, thus, required to overcome such concerns, and should combine the feasibility of industrial production processes with cheapness and effectiveness. In this framework, nanotechnology-based solutions, and in particular silver nanoparticles (AgNPs), have recently emerged as promising candidates in the market as new antibacterial agents. AgNPs display, in fact, enhanced broad-range antibacterial/antiviral properties, and their synthesis procedures are quite cost effective. However, despite their increasing impact on the market, many relevant issues are still open. These include the molecular mechanisms governing the AgNPs-bacteria interactions, the physico-chemical parameters underlying their toxicity to prokaryotes, the lack of standardized methods and materials, and the uncertainty in the definition of general strategies to develop smart antibacterial drugs and devices based on nanosilver. In this review, we analyze the experimental data on the bactericidal effects of AgNPs, discussing the complex scenario and presenting the potential drawbacks and limitations in the techniques and methods employed. Moreover, after analyzing in depth the main mechanisms involved, we provide some general strategies/procedures to perform antibacterial tests of AgNPs, and propose some general guidelines for the design of antibacterial nanosystems and devices based on silver/nanosilver.