A new type of surface coating made from photosensitizer molecules kills viruses, bacteria, and other pathogens when applied to consumer and medical products.
Engineers have created a new type of surface coating that can effectively kill viruses, bacteria, and other pathogens when applied to different products. The researchers developed the surface by adding photosensitizer molecules that destroy drug-resistant microbes to polymers.
These biocidal molecules use energy from visible light to convert oxygen into “singlet” oxygen, which causes photodegradation in certain materials. In this usage, it effectively punches holes in viruses and bacteria. The new approach could help scientists develop consumer and health care products with more effective and reliable pathogen-killing surfaces.
“We have learned how to disperse the photosensitizer molecules in polymers to ensure that we have a material that continues to function against drug resistant pathogens for the duration of the lifetime of the product,” says Richard Spontak, professor of materials science and engineering at North Carolina State University. He is a co-author of the study, recently published in Applied Materials & Interfaces.
Drug resistant superbugs cause millions of illnesses each year in the United States alone, and many of these infections are caused by surface-transmitted pathogens. Applying a film of photosensitizer molecules to surfaces can effectively sterilize them.
“These molecules have the same oxidizing capability as bleach,” Spontak says. “Unlike antibiotics, which target specific functionalities, this photosensitizer approach is nonspecific, taking out various aspects of the microorganism simultaneously and making it impossible for the microbe to develop a defense against it.”
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Reza Ghiladi, associate professor of chemistry at NC State and co-corresponding author of a paper, and his team developed a method of grafting anti-infective photosensitizers to cellulose surfaces. Over time, however, the cellulose surface becomes abraded and worn through friction and contact, removing the photosensitizers.
Spontak and his team studied how to disperse anti-infective photosensitizers into thermoplastic elastomer materials, which are rubbery, waterproof, and mechanically resilient. Elastomers are used in many different products such as tubing and IVs used by hospitals, consumer goods such as athletic shoes, and more complex applications.
“We want to have photosensitizers available across the largest potential surface area, so these molecules, when exposed to oxygen and in presence of light, can start producing singlet oxygen,” says Spontak.
A photosensitizer-embedded polymer inactivated at least 99.89 percent of five bacterial strains and 99.95 percent of two viruses when exposed to light for 60 minutes in lab testing, the study noted.
Bharadwaja Peddinti, a postdoc at North Carolina State and a co-author of the study, worked out the process of dispersing photosensitizers through elastomer polymers. The first step is to dissolve an elastomer in a solvent to create a solution, add the photosensitizer molecules, and evaporate the solvent, leaving a film. Next, the polymer is hot-pressed at temperatures above its melting point to form a sheet, which is cut up, stacked, and hot-pressed again.
“This is basically the same process that a baker would do to get the best distribution of flour in creating a paste,” Spontak said. “By repeating this process several times, you would get very good dispersion of the photosensitizer throughout the whole film. If the surface is damaged, or contaminated, or worn off, there is fresh surface available with photosensitizer there to kill microorganisms.”
Developing products with anti-microbial photosensitizers has advantages over using titanium dioxide, which is used as an antibacterial agent but is ineffective against viruses. The Spontak team’s approach kills both bacteria and viruses. Activating titanium dioxide requires the use of UV radiation, which can have a detrimental effect on healthy cells. Moreover, the use of nanoparticles is increasingly being scrutinized for potential human health hazards when people are exposed to them.
This paper is proof of concept showing the ability to disperse these photosensitizers into a range of soft materials. Physically incorporating photosensitizers into harder materials could be limited if significant crystallization is present to block molecular oxygen from reaching photosensitizers.
“In a very hard material greater crystallization can reduce the efficacy of the approach, and it might take more time to kill microbes,” Spontak said. But the crystallization challenge in more rigid materials can eventually be overcome, allowing the integration of photosensitizers into tables, smart phones, door handles, stairway railings, and other high-touch products, he said.
Linen and screens used in health-care settings also spread infection. Many lives could be saved those and other materials could kill bacteria and viruses. “Textiles are really high on our list of a material class to try to incorporate these photosensitizers,” Spontak said.
The work was performed with support from the North Carolina State Nonwovens Institute and North Carolina State’s Analytical Instrumentation Facility, which is funded by the State of North Carolina and the National Science Foundation, supported the research. Frank Scholle, associate professor of biological sciences at North Carolina State, co-authored the paper.
John Tibbetts is an independent writer who focuses on technology.