Antimicrobial surface
The most common and most important use of antimicrobial coatings has been in the healthcare setting for sterilization of medical devices to prevent hospital-associated infections, which have accounted for almost 100,000 deaths in the United States.
[2] In addition to medical devices, linens and clothing can provide a suitable environment for many bacteria, fungi, and viruses to grow when in contact with the human body which allows for the transmission of infectious disease.
Researchers today believe that the most important mechanisms include the following: Organosilanes create a network of electrically charged molecules on the surface, which rupture the cell wall on contact.
[11] It was also noted that antimicrobial agents such as Novaron AG 300 (Silver sodium hydrogen zirconium phosphate) do not inhibit the growth rate of E. coli or S. aureus when nutrient concentrations are high, but do as they are decreased.
Depending on the application, the ability to selectively combat certain microorganisms while having little detrimental effect against others dictates the usefulness of a particular antimicrobial surface in a given context.
Glass slides painted with the hydrophobic long-chained polycation N,N dodecyl,methyl-polyethylenimine (N,N-dodecyl,methyl-PEI) are highly lethal to waterborne influenza A viruses, including not only wild-type human and avian strains but also their neuraminidase mutants resistant to anti-influenza drugs.
[20] Additionally, in vitro studies have demonstrated that such an antifungal coating can inhibit the growth of yeast Candida albicans by 65% and completely stop the proliferation of filamentous fungus Neurospora crassa.
[21] Hence, the potential to help prevent the spread of fungi that cause human infections by using copper alloys (instead of non-antifungal metals) in air conditioning systems is worthy of further investigation.
Although simple, this approach suffers from the disadvantage of a relatively low grafting density due to steric hindrance from the already-attached polymer coils.
[24] For a process like this, grafting density depends on the concentration and molecular weight of the polymer as well as the amount time the surface was immersed in solution.
[24] As the antimicrobial activity depends on the concentration of quaternary ammonium tethered to the surface, grafting density and molecular weight represent opposing factors that can be manipulated to achieve high efficacy.
[22] A controlled polymerization allows for the formation of stretched conformation polymer structures that maximize grafting density and thus biocidal efficiency.
[3] Photocatalytic coatings include components (additives) that catalyze reactions, generally through a free radical mechanism, when excited by light.
[28] Recent research has focused on producing synthetic polymers and nanomaterials with similar mechanisms of action to endogenous antimicrobial peptides.
Clinical trials evaluating the efficacy of copper alloys to reduce the incidence of nosocomial infections are ongoing at hospitals in the UK, Chile, Japan, South Africa, and the U.S.
The United States Environmental Protection Agency (EPA) approved the registrations of 355 different copper alloys as “antimicrobial materials” with public health benefits.
Bacterial colony forming unit (CFU) counting requires overnight incubation and detects bacteria that readily grow on solid media.
Molecular dynamics (MD) simulation can be used to minimize the number of experiments with engineered substrates, with the quantification of time-lapse fluorescence microscopy images that can be processed in an hour.
The analysis of the zeta potential by the streaming potential method of either an antimicrobial coating[34] or a self-disinfectant material[35] in contact with an aqueous environment, or by electrophoretic light scattering of nanoparticle dispersions of antibacterial additives[36] reveal information about surface and interfacial charge and let predict the electrostatic attraction or repulsion of microorganisms.
[38] To reduce these numbers, the surfaces of the devices used in these procedures have been altered in hopes of preventing the growth of the bacteria that leads to these infections.
[38] Peptide-based gel coating with intrinsic antibacterial activity against Methicillin-resistant Staphylococcus aureus, was also shown to inhibit colonization of titanium implants in mice.
For photocatalytic bactericidal activity in water treatment applications, granular substrate materials have been used in the form of sands supporting mixed anatase/rutile TiO2 coatings.
[40] Oxide semiconductor photocatalysts such as TiO2 react with incident irradiation exceeding the material's electronic band-gap resulting in the formation of electron-hole pairs (excitons) and the secondary generation of radical species through reaction with adsorbates at the photocatalyst surface yielding an oxidative or reductive effect that degrades living organisms.
The US Environmental Protection Agency (EPA), which oversees the regulation of antimicrobial agents and materials in that country, found that copper alloys kill more than 99.9% of disease-causing bacteria within just two hours when cleaned regularly.
[31] In healthcare applications, EPA-approved antimicrobial copper products include bedrails, handrails, over-bed tables, sinks, faucets, door knobs, toilet hardware, intravenous poles, computer keyboards, etc.
In residential building applications, EPA-approved antimicrobial copper products include kitchen surfaces, bedrails, footboards, door push plates, towel bars, toilet hardware, wall tiles, etc.
In mass transit facilities, EPA-approved antimicrobial copper products include handrails, stair rails grab bars, chairs, benches, etc.
Clinical trials are currently being conducted on microbial strains unique to individual healthcare facilities worldwide to evaluate to what extent copper alloys can reduce the incidence of infection in hospital environments.
[47] More recently, copper-based anti-fouling paints have been used because they are less toxic than TBT in aquatic environments, but are only effective against marine animal life, and not so much weed growth.
Finally, microscopic prickles can be added to a coating, and depending on length and distribution have shown the ability to prevent the attachment of most biofouling.
