have relatively low surface energies, however this property alone is not sufficient to achieve superhydrophobicity. superhydrophobic surfaces can be created in a number of ways, however most of the synthesis strategies are inspired by natural designs. the cassie-baxter model provides an explanation for superhydropbicity—air trapped in microgrooves of a rough surface create a “composite” surface consisting of air and the tops of microprotrusions. this structure is maintained as the scale of the features decreases, thus many approaches to the synthesis of superhydrophobic surfaces have focused on the fractal contribution. wax solidification, lithography, vapor deposition, template methods, polymer reconfirmation, sublimation, plasma, electrospinning, sol-gel processing, electrochemical methods, hydrothermal synthesis, layer-by-layer deposition, and one-pot reactions are approaches to the creation of superhydrophobic surfaces that have been suggested. making a surface superhydrophobic represents an efficient means of imparting antimicrobial activity. a passive antibacterial effect results from the poor ability of microbes to adhere to the surface. the area of superhydropboic textiles takes advantage of this and could have potential applications as antimicrobial coatings. fluorocarbons fluorocarbons and especially perfluorocarbons are excellent substrate materials for the creation of superhydrophobic surfaces due to their extremely low surface energy. these types of materials are synthesized via the replacement of hydrogen atoms with fluorine atoms of a hydrocarbon. nanomaterials nanoparticles are used for a variety of different antimicrobial applications due to their extraordinary behavior. there are more studies being carried out on the ability for nanomaterials to be utilized for antimicrobial coatings due to their highly reactive nature. nanomaterialcharacteristicapplication titanium dioxidephoto catalytic activity, low costuv protection, anti-bacterial, environmental purification, self-cleaning, solar cell efficiency organosilaneprevent adhesion by abrasive surface, low costantimicrobial coating with long-term effectiveness silverelectrical conductivity, low toxicityanti-microbial activity – bind and destroy cell membrane zinc oxide photo catalytic activity anti-microbial activity, used in textile industry copperelectrical conductivityuv protection properties, anti-microbial additive magnetite superparamagnetic antimicrobial activity, generate radicals that cause protein damage magnesium oxide high specific surface area antimicrobial activity, generate oxygen radicals that cause protein damage goldelectrical conductivityanti-bacterial, acne curing agent galliumsimilar to fe3+ (essential metabolic nutrient for bacteria)anti-bacterial against clostridium difficile carbon nanotubesantistatic, electrical conductivity, absorptioncnt/tio2 nanocomposits; antimicrobial surfaces, fire retardant, anti-static. there are quite a few physical characteristics that promote anti-microbial activity. however, most metal ions have the ability to create oxygen radicals, thus forming molecular oxygen which is highly toxic to bacteria. 2 h 2 o + 1 2 o 2 → metal ion 2 h 2 o 2 → h 2 o + ( o ) o} +\mathrm \ \xrightarrow \ 2\ \mathrm o_ \rightarrow \mathrm o} +(\mathrm )} self-cleaning coatings photocatalytic coatings are those that include components (additives) that catalyze reactions, generally through a free radical mechanism, when excited by light. the photocatalytic activity (pca) of a material provides a measure of its reactive potential, based on the ability of the material to create an electron hole pair when exposed to ultra-violet light. free radicals formed can oxidize and therefore breakdown organic materials, such as latex binders found in waterborne coatings. antimicrobial coatings systems take advantage of this by including photocatalytically active compounds in their formulations (i.e. titanium dioxide) that cause the coating to “flake” off over time. these flakes carry the microbes along with them, leaving a “clean” coating behind. systems like this are often described to be self-cleaning. antimicrobial additives instead of doping a surface directly, antimicrobial activity can be imparted to a surface by applying a coating containing antimicrobial agents such as biocides or silver nanoparticles. in the case of the latter, the nanoparticles can have beneficial effects on the structural properties of the coating along with their antibacterial effect. antimicrobial peptides antimicrobial peptides (amps) have gained a lot of attention because they are much less susceptible to development of microbial resistance. other antibiotics may be susceptible to bacterial resistance, like multi-resistant staphylococcus aureus (mrsa) which is known as a common relic in the healthcare industry while other bacterial strains have become more of a concern for waste water treatment in local rivers or bays. amps can be functionalized onto a surface by either chemical or physical attachment. amps can be physically attached by using oppositely charged polymeric layers and sandwiching the polypeptide between them. this may be repeated to achieve multiple layers of amps for the recurring antibacterial activity. there are, however, a few drawbacks to this mechanism. assembly thickness and polymer-peptide interactions can affect the diffusion of peptide to bacterial contact. further research should be carried out to determine the effectiveness of the adsorption technique. however, the chemical attachment of amps is also widely studied. amps can be covalently bound to a surface, which minimizes the "leaching effect" of peptides. the peptide is typically attached by a very exergonic chemical reaction, thus forming a very stable antimicrobial surface. the surface can be functionalized first with a polymer resin such as polyethylene glycol (peg). recent research has focused on producing synthetic polymers and nanomaterials with similar mechanisms of action to endogenous antimicrobial peptides. touch surfaces main articles: antimicrobial copper-alloy touch surfaces and antimicrobial properties of copper antimicrobial touch surfaces include all the various kinds of surfaces (such as door knobs, railings, tray tables, etc.) that are often touched by people at work or in everyday life, especially (for example) in hospitals and clinics. antimicrobial copper alloy touch surfaces are surfaces that are made from the metal copper or alloys of copper, such as brass and bronze. copper and copper alloys have a natural ability to kill harmful microbes relatively rapidly – often within two hours or less (i.e. copper alloy surfaces are antimicrobial). much of the antimicrobial efficacy work pertaining to copper has been or is currently being conducted at the university of southampton and northumbria university (united kingdom), university of stellenbosch (south africa), panjab university (india), university of chile (chile), kitasato university (japan), university of coimbra (portugal), and the university of nebraska and arizona state university (u.s.). clinical trials evaluating the efficacy of copper alloys to reduce the incidence of nosocomial infections are on-going 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. characterization designing effective antimicrobial surfaces demands an in-depth understanding of the initial microbe-surface adhesion mechanisms. scanning electron microscopy (sem) is used for nonliving samples. 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. contact angle measurements can be used to characterize micro/nano-pillars use for rupturing cell walls. the analysis of the zeta potential by the streaming potential method of either an antimicrobial coating or a self-disinfectant material in contact with an aqueous environment, or by electrophoretic light scattering of nanoparticle dispersions of antibacterial additives reveal information about surface and interfacial charge and let predict the electrostatic attraction or repulsion of microorganisms. application antimicrobial peptides and chitosan naturally occurring chitin and certain peptides have been recognized for their antimicrobial properties in the past. today, these materials are engineered into nanoparticles in order to produce low-cost disinfection applications. natural peptides form nano-scale channels in the bacterial cell membranes, which causes osmotic collapse. these peptides are now synthesized in order to tailor the antimicrobial nanostructures with respect to size, morphology, coatings, derivatization, and other properties allowing them to be used for specific antimicrobial properties as desired. chitosan is a polymer obtained from chitin in arthropod shells, and has been used for its antibacterial properties for a while, but even more so since the polymer has been made into nanoparticles. chitosan proves to be effective against bacteria, viruses, and fungi, however it is more effective against fungi and viruses than bacteria. the positively charged chitosan nanoparticles interact with the negatively charged cell membrane, which causes an increase in membrane permeability and eventually the intracellular components leak and rupture. silver nanoparticles silver compounds and silver ions also have been known to show antimicrobial properties and have been used in a wide range of applications, including water treatment. it is shown that silver ions prevent dna replication and affect the structure and permeability of the cell membrane. silver also leads to uv inactivation of bacteria and viruses because silver ions are photoactive in the presence of uv-a and uv-c irradiation. cysteine and silver ions form a complex that leads to the inactivation of haemophilus influenzae phage and bacteriophage ms2. medical and commercial applications surgical devices even with all the precautions taken by medical professionals, infection reportedly occurs in up to 13.9% of patients after stabilization of an open fracture, and in about 0.5-2% of patients who receive joint prostheses. in order to reduce these numbers, the surfaces of the devices used in these procedures have been altered in hopes to prevent the growth of the bacteria that leads to these infections. this has been achieved by coating titanium devices with an antiseptic combination of chlorhexidine and chloroxylenol. this antiseptic combination successfully prevents the growth of the five main organisms that cause medical related infections, which include staphylococcus epidermidis, methicillin-resistant staphylococcus aureus, pseudomonas aeruginosa, escherichia coli and candida albicans. peptide-based gel coating with intrinsic antibacterial activity against methicillin-resistant staphylococcus aureus, was also shown to inhibit colonization of titanium implants in mice. photocatalytic coatings photoactive pigments such as tio2 and zno have been used on glass, ceramic, and steel substrates for self-cleaning and antimicrobial purposes. 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. 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. titania has successfully be used as an antimicrobial coating on bathroom tiles, paving slabs, deodorizers, self-cleaning windows, and many more. copper touch surfaces main articles: antimicrobial copper touch surfaces and antimicrobial properties of copper copper alloy surfaces have intrinsic properties to destroy a wide range of microorganisms. 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. copper and copper alloys are unique classes of solid materials as no other solid touch surfaces have permission in the u.s. to make human health claims (epa public health registrations were previously restricted only to liquid and gaseous products). the epa has granted antimicrobial registration status to 355 different copper alloy compositions. 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 public facility applications, epa-approved antimicrobial copper products include health club equipment, elevator equipment, shopping cart handles, 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. a comprehensive list of copper alloy surface products that have been granted antimicrobial registration status with public health claims by the epa can be found here: antimicrobial copper-alloy touch surfaces#approved products. clinical trials are currently being conducted on microbial strains unique to individual healthcare facilities around the world to evaluate to what extent copper alloys can reduce the incidence of infection in hospital environments. early results disclosed in 2011 from clinical studies funded by the u.s. department of defense that are taking place at intensive care units (icus) at memorial sloan-kettering cancer center in new york city, the medical university of south carolina, and the ralph h. johnson va medical center in charleston, south carolina indicate that rooms where common touch surfaces were replaced with copper demonstrated a 97% reduction in surface pathogens versus the non-coppered rooms and that patients in the coppered icu rooms had a 40.4% lower risk of contracting a hospital acquired infection versus patients in non-coppered icu rooms. anti-fouling coatings marine biofouling is described as the undesirable buildup of