Table 1.

Different metal and metal oxide nanoparticles added to polymer formulations increase their antimicrobial effect

Nanoparticle material	Antimicrobial characteristics	Applications	Toxicity	References
Titanium dioxide	Nanosized structured TiO2 have exhibited antimicrobial properties, due to TiO2-induced photocatalytic production of cytotoxic oxygen radicals. Previous reports have described the use of TiO2 for water treatment and air purification. Recent reports have mentioned usage of TiO2 nanoparticles to decrease Candida albicans adherence in an experimental PMMA for dentures.	Titanium nanoparticles have been applied in the pharmaceutical industry as drug delivery vehicles and in excipient formulations.	The composite material combines the high adsorption capability of apatite with the photocatalytic activity of titanium. Apatite coatings may thus become useful in the attenuation of the toxicological effects of inorganic metal oxide nanoparticles.	49,74–78
Iron oxide	Ferrite nanoparticles may be a source of cellular toxicity. The hematite crystalline phase of Fe2O3 nanoparticles decreased C. albicans adherence in an experimental PMMA for dentures. Transition metal-substituted cobalt ferrite nanoparticles formed a cubic spinel structure with a crystallite size in the range of 40–50 nm, that significantly improved antibacterial activity against Escherichia coli and Staphylococcus aureus.	Used in cellular therapy, such as cell labeling and targeting, and as a tool for cell biology research to separate and purify cell populations. Also used in: • tissue repair; • drug delivery; • magnetic resonance imaging; • hyperthermia; • magnetofection.	No toxicity reported.	49,79,80
Silver	PMMA/AgNPs have been proposed for dentistry applications as cytocompatible dental materials with antifungal properties. Silver is known for its antimicrobial properties and has been used for years in the medical field for antimicrobial applications; it has been shown also to prevent HIV binding to host cells. Modified tissue conditioner combined with AgNPs displayed antimicrobial properties against S. aureus, Streptococcus mutans, and C. albicans incorporated after a 24- or 72-hour incubation.	Used for covering urinary catheters, surgical instruments, and bone prostheses. Additionally, silver has been used in water and air filtration to eliminate microorganisms. AgNPs have been added to soft tissue conditioners for prosthetic devices.	Exposure of metal-containing nanoparticles to human lung epithelial cells generates ROS, which can lead to oxidative stress and cellular damage (AgNPs). Silver nanowires resulted in the strongest cytotoxicity and immunological responses, whereas spherical silver particles had negligible effects on cells when tested in human cells.	21,25,50,81–83

Abbreviations: AgNPs, silver nanoparticles; PMMA, polymethyl methacrylate; ROS, reactive oxygen species.