An antimicrobial surface is coated by an antimicrobial agent that inhibits the ability of microorganisms to grow on the surface of a material. Such surfaces are becoming more widely investigated for possible use in various settings including clinics, industry, and even the home. 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. 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.
Antimicrobial surfaces are functionalized in a variety of different processes. A coating may be applied to a surface that has a chemical compound which is toxic to microorganisms. In alternative, it is possible to functionalize a surface by adsorbing a polymer or polypeptide and/or by changing its micro and nanostructure.
An innovation in antimicrobial surfaces is the discovery that copper and its alloys (brasses, bronzes, cupronickel, copper-nickel-zinc, and others) are natural antimicrobial materials that have intrinsic properties to destroy a wide range of microorganisms. An abundance of peer-reviewed antimicrobial efficacy studies have been published regarding copper’s efficacy to destroy E. coli O157:H7, methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus, Clostridium difficile, influenza A virus, adenovirus, and fungi.
Apart from the health industry, antimicrobial surfaces have been utilized for their ability to keep surfaces cleaned. Either the physical nature of the surface, or the chemical make up can be manipulated to create an environment which cannot be inhabited by microorganisms for a variety of different reasons. Photocatalytic materials have been used for their ability to kill many microorganisms and therefore can be used for self-cleaning surfaces as well as air cleaning, water purification, and antitumor activity.
Antimicrobial activity
Mechanisms
Silver
Silver ions have been shown to react with the thiol group in enzymes and inactivate them, leading to cell death. These ions can inhibit oxidative enzymes such as yeast alcohol dehydrogenase. Silver ions have also been shown to interact with DNA to enhance pyrimidine dimerization by the photodynamic reaction and possibly prevent DNA replication.
The use of silver as an antimicrobial is well documented.
Copper
The antimicrobial mechanisms of copper have been studied for decades and are still under investigation. A summary of potential mechanisms is available here: Antimicrobial properties of copper#Mechanisms of antibacterial action of copper. Researchers today believe that the most important mechanisms include the following:
Elevated copper levels inside a cell causes oxidative stress and the generation of hydrogen peroxide. Under these conditions, copper participates in the so-called Fenton-type reaction — a chemical reaction causing oxidative damage to cells. Excess copper causes a decline in the membrane integrity of microbes, leading to leakage of specific essential cell nutrients, such as potassium and glutamate. This leads to desiccation and subsequent cell death. While copper is needed for many protein functions, in an excess situation (as on a copper alloy surface), copper binds to proteins that do not require copper for their function. This "inappropriate" binding leads to loss-of-function of the protein, and/or breakdown of the protein into nonfunctional portions.
Organosilanes
Organosilanes create a network of electrically charged molecules on the surface, which rupture the cell wall on contact. This is due to their structure which consists of a hydrophobic element, and a cationic element. While the hydrophobic element may prevent adherence in the first place, it may also intercalate with the cell wall, whose rupture is aided by the cationic component.
Nutrient Uptake
The growth rate of E. coli and S. aureus was found to be independent of nutrient concentrations on non-antimicrobial surfaces. 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. This result leads to the possible antimicrobial mechanism of limiting the cell's uptake, or use efficiency, of nutrients.