Self-sanitizing surfaces -
Can antimicrobial products withstand day-to-day real-life wear and tear if the antimicrobial material is part of the product and not only a coating?
A study in Switzerland tried to find out. Coatings of antimicrobial products on high touch surfaces do not last long in real life situations, but with multiresistant pathogens on the rise, something must be done. In Switzerland, a study was conducted on devices with the antimicrobial product built in.
To discuss this idea, Infection Control Today ® ICT ® spoke to Andreas Widmer, MD, MS, president of the National Center for Infection Control, University of Basel in Basel, Switzerland, lead author of the study; and Frédéric Loyrion, sales manager at Sanitized, also in Switzerland, about the study that Widmer and his team conducted using a Sanitized product to combat multiresistant pathogens on high contact surfaces.
The study was presented at the Clean Hospitals Day Conference held on October 20, , in Geneva, Switzerland. ICT ® : Dr. Widmer, would tell us the key points of the study? Andreas Widmer, MD, MS AW: Yeah, I think we all know that the environmental contamination of multiresistant pathogens is a major issue.
It has been part of the COVID pandemic where contact also is an issue. And after SARS 1, my colleague [W.
In our area, we couldn't afford the human resources to clean it repetitively. Knowing that recontamination occurs even in the hospital within 4 to 6 hours after disinfecting the room.
One of the [answers] would be self-disinfecting areas and devices, which we already know from intravascular catheter wherever used very successfully and other medical devices.
But in the environment, it was more difficult because you have a coating which has been used, then with the physical aberration and say, more or less abuse of the hospital staff with carts and devices, this coating falls apart, and the effect of self-disinfection is gone.
We already did some tests, and it didn't work more than 2 to 4 weeks. And then this coating was not effective anymore. There was a need for [a] new device or new technology, and then we came up to Sanitized, which produces a product that's in the device.
It's not a coating; it's in the device. Even if you have kind of physical attacks by our health care workers, the injured part is still effective. And that's the reason why our federal [Swiss] government subsidized the study, to make sure that this product is not only working in the laboratory, but also in a daily practice in a university hospital setting.
ICT ® : What was the goal of this research? AW: The goal of the research was to identify, in particular, multiresistant pathogens. In the past, a lot of studies were done with just bacterial load. And we have good bacteria and bad bacteria.
That brought us that we don't want to eliminate all bacteria in the hospital. Now we have a new technology available [within the last] couple years that allows you to do it at a much lower cost. And that's the reason why we were able to identify all bacteria and separate good bacteria [from] the bad bacteria, and the basic study results that we could [get] with this product, you have a significant difference between non-Sanitized surfaces versus Sanitized surfaces, and, in particular, a significant reduction of the multiresistant pathogens.
ICT ® : What are the specific takeaways for infection preventionists and environmental service professionals? AW: We, at least for new building, we should allow to have some products that have antimicrobial efficacy and effectiveness not on the surface but within the product in I would say these high touch surfaces where repetitive cleaning is physically not possible or for financial perspective not feasible.
If you have an automatic cleaning, and this particular is for vancomycin resistant Enterococcus, that really helped the alternative which is also an add on is using ultraviolet UV light that also disinfects the surfaces because we know from this study but also from other UVC studies, that even if you have almost perfect cleaning, you have residual multiresistant bacteria.
So the physical cleaning, even if it's done under supervision, is not perfect. And for certain areas, I would say for transplant units, multiresistant pathogens are an issue, for operating rooms ORs , everywhere where people have high touch surfaces, including elevator knobs.
That was in the preface of this study that the identified bacteria is on public areas, like airports, train stations. They realize that bad bacteria, pathogenic bacteria are more prevalent in this area than in hospitals. ICT ® : What was the contribution of Sanitized within this study?
Frédéric Loyrion: Sanitized made the initial tests in the lab in order to choose the suitable PVC film composition, the formulation for running the study. And the film was provided by one of our customers located in France, Hexis, who is manufacturing self-adhesive films.
That was the main goal of Sanitized, providing the right formulation, and then providing the right film for the study. It looks quite simple, but it was not.
Then putting this material safely on the screen or on the toilet seat that is physically not damaging. This was quite challenging, and the support we got was excellent. So that's the big advantage to have onsite test because in the lab, you will just have to control an active compound, but there's no physical damage.
When bacteria attach to a surface, they form communities that create a layer of slimy, slippery biofilm that protects the microbes from scrubbing, disinfectants and even antibacterial compounds. This technology could be important in the battle against superbugs. According to Health Canada, antibiotic resistant superbugs are currently the fourth leading cause of death in our country — a problem experts expect to get a lot worse as more bacteria evolve resistance to our current roster of antibiotic medications.
If you were to zoom right down to the surface of the lotus leaf, you'd see a structure kind of like a series of rolling hills, covered in trees and then flowers on those trees. This surface is slippery because these structures trap air pockets between themselves and water droplets, for example.
The water droplets then slide like pucks on an air-hockey table. Didar and his colleagues created a surface that emulates this. In includes microstructures 10 times smaller than the width of a human hair, which he said are the equivalent of the rolling hills.
On top of the microstructure, they added nanostructures times smaller than a human hair that you can think of as the trees. A photocatalytic reaction was the foundation for the first commercially available self-cleaning window s. By introducing molecules catalysts that take part in a chemical process without being consumed, the pace of a photoreaction in which one or more reacting components absorb light may be changed.
There is a very thin coating of titanium dioxide on these windows. Coatings made with TiO2 seem to be self-cleaning. TiO2 interacts with water under sunlight to produce hydroxyl radicals, which decompose biological compounds and microorganisms adhered to the surface.
The hydrophilic TiO2 layer allows rainwater to easily flow over its surface, washing away contaminants. A TiO2 coating is a great way to keep surfaces like doorknobs clean during a pandemic, when cleanliness is of the utmost importance.
The idea of self-cleaning has a wide range of applications and benefits across many different domains. Specifically, self-cleaning materials provide a significant potential for improvement across all industries and sectors as a result of the time, material, energy, and cost savings that may be realized throughout the production process.
This technology not only reduces the amount of time and money spent on cleaning, but it also helps to preserve water and energy, which is beneficial to the environment.
Experimental development is carried out continuously to discover new smart materials and the way they contribute to the concept of self-cleaning.
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The first instance of a self-cleaning surface was created in created a transparent titanium dioxide TiO 2 film that was used to coat glass and provide the ability for the glass to self-clean.
The first commercial application of this self-cleaning surface, Pilkington Activ, was developed by Pilkington glass in This product implements a two-stage cleaning process.
The first stage consists of photocatalysis of any fouling matter on the glass. This stage is followed by the glass becoming superhydrophilic and allowing water to wash away the catalyzed debris on the surface of the glass.
Since the creation of self-cleaning glass, titanium dioxide has also been used to create self-cleaning nanoparticles that can be incorporated into other material surfaces to allow them to self-clean. The ability of a surface to self-clean commonly depends on the hydrophobicity or hydrophilicity of the surface.
Whether cleaning aqueous or organic matter from a surface, water plays an important role in the self-cleaning process. Specifically, the contact angle of water on the surface is an important characteristic that helps determine the ability of a surface to self-clean.
This angle is affected by the roughness of the surface and the following models have been developed to describe the "stickiness" or wettability of a self-cleaning surface. Young and colleagues proposed Young's model of wetting that relates the contact angle of a water droplet on a flat surface to the surface energies of the water, the surface, and the surrounding air.
This model is typically an oversimplification of a water droplet on an ideally flat surface. This model has been expanded upon to consider surface roughness as a factor in predicting water contact angle on a surface.
Young's model is described by the following equation:. When a water droplet is on a surface that is not flat and the surface topographical features lead to a surface area that is larger than that of a perfectly flat version of the same surface, the Wenzel model is a more accurate predictor of the wettability of this surface.
Wenzel's model is described by the following equation:. For more complex systems that are representative of water-surface interactions in nature, the Cassie-Baxter model is used.
This model takes into consideration the fact that a water droplet may trap air between itself and the surface that it is on. The Cassie-Baxter model is described by the following equation:.
Control over surface wettability is a critical aspect of self-cleaning surfaces. Both superhydrophobic and superhydrophilic surfaces have been used as self-cleaning materials.
Superhydrophobic surfaces can be created in a number of different ways including plasma or ion etching, crystal growth on a material surface, and nanolithography to name a few.
The ultimate goal in developing superhydrophobic surfaces is to recreate the self-cleaning properties of the Lotus Leaf that has the inherent ability to repel all water in nature.
The basis for superhydrophobic self-cleaning is the ability of these surfaces to prevent water from spreading out when in contact with the surface. This is reflected in a water contact angle nearing degrees. Superhydrophobic self-cleaning surfaces also have low sliding angles which allows for water that is collected on the surface to easily be removed, commonly by gravity.
While superhydrophobic surfaces are great for removing any water-based debris, these surfaces likely will not be able to clean away other types of fouling matter such as oil.
Superhydrophilicity allows for surfaces to clean away a wide variety of dirt or debris. This mechanism is very different than the aforementioned superhydrophobic surfaces. For superhydrophilic self-cleaning surfaces, cleaning occurs because water on the surface is able to spread out to a great degree extremely low water contact angle to get between any fouling debris and the surface to wash away the debris.
One of the most commonly used self-cleaning products, titanium dioxide , utilizes a unique self-cleaning mechanism that combines an initial photocatalytic step and subsequent superhydrophilicity.
A titanium dioxide coating, typically on glass windows, when exposed to UV light, will generate free electrons that will interact with oxygen and water in the air to create free radicals.
These free radicals will in turn breakdown any fouling organic matter deposited on the surface of the glass. Titanium dioxide also changes the normally hydrophobic glass to a superhydrophilic surface.
Thus, when rainfall occurs, instead of water beading up on the window surface and instantly falling down the glass, rain drops will rapidly spread out on the hydrophilic surface. The water will then move down the surface of the window, as a film rather than a droplet, essentially acting like a squeegee to remove surface debris.
Heating of the surfaces via passing current through a conductive transparent film has been shown to repel and remove contamination. It has been used in inkjet printers to reduced ink contamination on sensor windows.
Cleaning surfaces in environments without water has been a challenge. Electric curtain devices were designed to remove particles by creating electric fields on the surface and carrying away particles due to their charged nature.
It has been used in solar panels as well as 3D printers. The lotus flower has been known as a symbol of purity in some Asian cultures.
This ability, called self-cleaning, shields the plant from dirt and pathogens and plays a vital role in providing resistance towards invading microbes. Indeed, numerous spores and conidia of pathogenic life forms, mainly fungi, need water for germination and taint leaves within the first signs of water.
These cells generate papillae or microasperties which make surface very rough. On top of microscale roughness, the papillae surface is superimposed with nanoscale asperities consisting of three-dimensional 3-D hydrophobic hydrocarbons: epicuticular waxes.
Basically, the plant cuticle is a composite material composed of a network of cutin and low surface energy waxes, designed at different hierarchical levels. Hence, the lotus leaves represent remarkable superhydrophobicity.
Static contact angle and contact angle hysteresis of the lotus leaf are determined around ° and 3°, respectively. In plants world, the lotus leaf is not the only example of natural superhydrophobic surfaces.
For instance, taro Colocasia esculenta leaves were found to exhibit self-cleaning behavior, too. India canna Cannageneralis bailey leaves and the rice leaves whatever the kind of rice also represent superhydrophobicity, arising from the hierarchical surface morphology.
The Nepenthes carnivorous pitcher, widespread in a lot of countries such as India, Indonesia, Malaysia and Australia, possesses a superhydrophilic surface, on which wetting angle approaches to zero to create uniform water film. Therefore, it increases the slipperiness of the surface and the prey slides off from its rims peristome.
The second order ridges are quite small in size and generated by straight rows of overlapping epidermidis cells. The surface of epidermidis cells are smooth and wax-free.
The absence of wax crystals and microscopic roughness enhance the hydrophilicity and capillary forces, in doing so, water can swiftly wet the surface of rim. Butterfly wings possess not only ultra-hydrophobic trait but also directional adhesive characteristics.
On the other hand, if droplets stand against the opposite direction, they are pinned at the surface, leading adhesion and securing the flight stability of the butterfly by preventing deposit of dirt on the wings near the center of the body.
SEM micrographs of wings exhibit hierarchy along the RO direction, arising from aligned microgrooves, covered by fine lamella-stacking nanostripes. Water striders Gerris remigis , most commonly called Jesus bugs, have an extraordinary ability that lets them walk on the water.
In a fashion similar to superhydrophobic plants, their legs are highly water repellent due to their hierarchical morphology. They are built up with hydrophobic waxy microhairs, microsetae, and each hair is covered with nanogrooves. As a result, air is entrapped between micro- and nanohairs, which repels water.
measured how deep the leg can dip into water and the contact angle of the leg. They found the contact angle at least ° and the maximum depth reported 4. Gecko feet are the most famous reversible adhesion mechanism in nature. The anti-fouling ability of feet allows geckos to run on dusty ceilings and corners without the accumulation of dirt on their feet.
In , Autumn et al. Moreover, each setae is composed of a smaller hair, and each hair is tailed with a flat spatula and these spatulae are bonded by the van der Waals forces. This surface feature, regardless of the surface type hydrophobic, hydrophilic, dry, wet, rough etc.
In addition to strong adhesion, the gecko foot has a unique self-cleaning property which does not require water as the lotus leaf. Shark skin is another example of antifouling, self-cleaning and low adhesion surfaces.
This hydrophobic surface allows sharks to maneuvers fast in water. Shark skin is composed of periodically arranged diamond-shape dermal denticles, superimposed with triangular riblets. To fabricate synthetic self-cleaning surfaces, there are a variety of methods [10] used to obtain the desired nanotopography and then characterize surface nanostructure and wettability.
Templating utilizes a mold to add nanostructure to a polymer. Nanocasting is a method based on soft lithography which uses elastomeric molds to make nano-structured surfaces.
For example, polydimethylsiloxane PDMS was cast over the lotus leaf and used to make a negative PDMS template.
PDMS was then coated with an anti-stick monolayer of trimethylchlorosilane and used to make a positive PDMS template from the first. As the natural lotus leaf structure enables pronounced self-cleaning ability, this templating technique was able to replicate the nanostructure, resulting in a surface wettability similar to the lotus leaf.
Imprint nanolithography also utilizes templates, pressing a hard mold into a polymer above the polymer glass transition temperature Tg. Thus, the driving forces for this type of fabrication are heat and high pressure.
To achieve this, the polystyrene was heated well above its Tg to degrees Celsius and pressed against the template.
The template was then removed by dissolving the aluminum and producing either nanoemboss or nanofiber surfaces. Increasing the aspect ratio of the nanofibers disrupted the uniform hexagonal pattern and caused the fibers to form bundles.
Ultimately, the longest nanofibers resulted in the greatest surface roughness, which significantly decreased surface wettability. Similar to imprint nanolithography, capillary nanolithography employs a patterned elastomeric mold.
However, instead of utilizing high pressure, when the temperature is raised above the Tg, capillary forces enable the polymer to fill the voids within the mold.
Suh and Jon used molds made from poly urethane acrylate PUA. These were placed on spin coated, water-soluble polymer, polyethylene glycol PEG , which was raised above PEG's Tg. This study found that the addition of nanotopography increased the contact angle, and this increase was dependent on the height of the nanotopography.
One study used capillarity to fill PDMS molds with PUA, first partially curing the polymer resin with UV light. After microstructures were formed, pressure was applied to fabricate nanostructures, and UV curing was used again.
This study is a good example of the use of hierarchical structures to increase surface hydrophobicity. Photolithography and X-ray lithography have been used to etch substrates, often silicon. A mask is applied above the resist that often consists of gold or other compounds that absorb X-rays.
The region exposed to light either becomes soluble in a photoresist developer e. radical species or insoluble in a photoresist developer e. crosslinked species , ultimately resulting in a patterned surface.
X-ray sources are beneficial over UV-visible light sources as the shorter wavelengths enable production of smaller features. Plasma treatment of surfaces is essentially a dry etching of the surface.
This is achieved by filling a chamber with gas, such as oxygen, fluorine, or chlorine, and accelerating ions species from an ion source through plasma. The ion acceleration towards the surface forms deep grooves within the surface. In addition to the topography, plasma treatment can also provide surface functionalization by using different gases to deposit different elements on surfaces.
Generally, chemical deposition uses liquid or vapor phases to deposit inorganic materials or halides onto surfaces as thin films. He and his team were inspired by the lotus to create an innovative solution to curb the spread of bacteria, including potentially deadly antibacterial resistant bacteria.
Didar and his colleagues at McMaster University in Hamilton, developed a non-stick coating they could apply to plastic that in turn they can shrink-wrap onto surfaces — such as a stethoscope or a doorknob.
This could prevent bacteria from colonizing these objects and forming a fortress-like biofilm. When bacteria attach to a surface, they form communities that create a layer of slimy, slippery biofilm that protects the microbes from scrubbing, disinfectants and even antibacterial compounds.
This technology could be important in the battle against superbugs. According to Health Canada, antibiotic resistant superbugs are currently the fourth leading cause of death in our country — a problem experts expect to get a lot worse as more bacteria evolve resistance to our current roster of antibiotic medications.
If you were to zoom right down to the surface of the lotus leaf, you'd see a structure kind of like a series of rolling hills, covered in trees and then flowers on those trees.
This surface is slippery because these structures trap air pockets between themselves and water droplets, for example. The water droplets then slide like pucks on an air-hockey table. Didar and his colleagues created a surface that emulates this.
In includes microstructures 10 times smaller than the width of a human hair, which he said are the equivalent of the rolling hills. On top of the microstructure, they added nanostructures times smaller than a human hair that you can think of as the trees.
Then on top of that layer, they added Teflon-like fluorinated chemicals to mimic the lotus leaf's waxy layer, equivalent to the flowers on the trees.
Self-sanitizing surfaces Humphreys, Self-disinfecting and Microbiocide-Impregnated Surfaces Self-sannitizing Fabrics: What Potential in Gluten-free cookies the Spread Body neutrality Healthcare-Associated Infection? Innovative Gluten-free cookies Self-sanitzing identified approaches to developing self-disinfecting surfaces or Self-santizing to minimize Self-ssnitizing infection HCAI. These Self-sanitizing surfaces altering Self-sannitizing structure or surface to minimize the attachment of microbes or to delay the development of biofilm, using compounds that are activated in the presence of light to reduce the microbial burden, and incorporating a heavy metal such as silver or copper with intrinsic antimicrobial activity. However, apart from copper -impregnated surfaces, there have been few trials in a clinical setting. Copper-impregnated surfaces result in reduced microbial surface counts on surfaces commonly found in clinical areas compared with controls, and 1 study has assessed HCAI and colonization rates.
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