Drying testing of surfaces in real-world polluted environments - Joydeep Lahiri, Vice President and Program Director, Corning

The ravages of deadly viruses and drug-resistant bacteria are a major health threat to humanity.
the new coronavirus SARS-CoV-2 is a warning that uncontrollable highly contagious viruses can have a dramatic impact on our lives.
although human-to-human transmission of the virus is the main mode of transmission, both the Chinese Centers for Disease Control and Prevention and the U.S. Centers for Disease Control and Prevention have warned that exposure to surfaces with live viruses could also cause transmission.
1 While hand washing and proper cleaning with disinfectants are still necessary to prevent germs, the reality is that surface contamination is persistent and the cleaning effect is not long-lasting.
self-sterilizing surface materials and coatings containing antimicrobial components can continuously reduce viruses and bacteria and can be used as a complementary solution for routine disinfection measures.
, however, different self-sterilizing solutions contain different active ingredients, and their labeling statements follow different testing standards.
Recently, the U.S. Environmental Protection Agency announced that it would allow antimicrobial declarations on surfaces with long-term effects, but that they must be based on drying tests that simulate a realistic polluted environment, which need to be performed at low temperatures (23±4 degrees C) and take no more than two hours to test.
many regions around the world are still using "wet tests" as a benchmark for identification, such as JIS Z-2801, which is performed at high temperatures (37±4 degrees C) and has a 24-hour test time on the surface in wet conditions.
studies have shown that some common antimicrobial components, such as silver, can achieve effective antiviral and antibacterial levels at high humidity and high temperatures.
common sources of pollution in daily life do not meet these conditions.
materials, mainly copper, that are still performing well under dry test conditions, are very limited.
in order to provide additional protection for self-sterilizing surfaces, we advocate the widespread adoption of drying testing standards similar to those required by the U.S. Environmental Protection Agency for products sold in the United States.
of deadly viruses and drug-resistant bacteria is a major health threat to humanity today.
the new coronavirus SARS-CoV-2 is a warning that uncontrollable highly contagious viruses can have a dramatic impact on our lives.
at a time when the world is struggling to maintain normalcy and try to prevent a new outbreak, we must develop appropriate programmes to prevent the spread of the outbreak in public and private spaces.
, however, the virus can easily spread even when wearing a mask and maintaining a social distance.
although human-to-human transmission of the virus is the main mode of transmission, both the Chinese Centers for Disease Control and Prevention and the U.S. Centers for Disease Control and Prevention have warned that exposure to surfaces with live viruses could also cause transmission.
1 study showed that the new coronavirus SARS-CoV-2 can survive for hours to days on surfaces such as desktops and doorknobs, depending on the composition of the surface under contact.
2, how do we disinfect and control surfaces that people come into frequent contact with in the workplace and in public places? Before the outbreak, self-sterilizing surfaces and antimicrobial coatings were niche products.
companies are now actively looking for solutions that create a healthy environment for their customers and employees.
, such as homes and offices that house millions of people, urgently need to do more to reduce germs in crowded areas.
schools, hospitals, kindergartens and nursing homes also need to take more precautions to prevent the spread of germs.
there are still some people who are reluctant to step out of their homes to resume their daily lives, and the large-scale use of self-sterilizing surfaces can help improve the situation.
an environment where an object's surface can continuously kill bacteria and viruses on its own, reducing fear and stress and reassuring those who return to work and frequent public places.
the large-scale popularity of antimicrobial coatings is based on the establishment of a universal and standardized testing standard.
products with antimicrobial properties claim to inhibit microbial growth, but these claims are limited by their testing standards.
most commonly used test criteria for antimicrobial surfaces is the "wet test method" (JIS Z-2801).
the test was designed to assess the effectiveness of surface coatings on objects that inhibit microbial growth.
lot of liquid bacterial cultures are used during the test to keep the surface under test moist throughout the experiment.
test is required at a high temperature of 37±4 degrees C and at high humidity greater than 80%.
the test criteria, the active ingredient on the test surface had a full 24 hours to kill the microorganisms under test.
3 While wet testing does prove the efficacy of antimicrobial products, the test data represent only the established test environment, and these parameters do not fully simulate the environment in which we live and the true state of the antimicrobial surface.
, studies have shown that certain antimicrobial agents, such as silver-based antimicrobials, are highly active only at high temperatures and humidity.
4 Imagine that in an office that requires shared office supplies, a shared computer, and frequent access to doorknobs, the environmental conditions are quite different from those set by the wet test.
in the workplace, humidity and temperature are usually low and the environment is dry, and due to the high frequency of use, the surface of the object is likely to be contaminated with microorganisms more than once every 24 hours.
to raise the standard of self-sanitizing surfaces, we need to adopt a more accurate test standard widely.
The U.S. Environmental Protection Agency has created a "dry test" that can more realistically simulate everyday environmental and real-world pollution.
the test was conducted at ± 23 degrees Celsius (room temperature) and 40-50% ambient humidity.
products that pass the drying test must completely kill the surface microorganisms in 2 hours or less.
In October 2020, the U.S. Environmental Protection Agency announced its latest guidelines: establish a rapid review system to help surface disinfectant products gain faster access to performance statements against new coronavirus SARS-CoV-2, while the U.S. Environmental Protection Agency has expanded the category of antimicrobial products to cover solid surfaces and coatings as complementary long-acting antimicrobial products.
6 Although the testing standards for wet testing do not represent real living environments, many common surface antimicrobials are still being tested and validated with this standard.
currently existing wet tests include surface antimicrobial efficacy testing (ISO 221967, JISZ 28013 and GB/T 218668) and surface antiviral efficacy testing (ISO 217029).
is one of the most commonly used antimicrobial agents, and its efficacy in completely killing microorganisms on the surface of objects depends on the test environment of such wet testing methods.
at high humidity and high temperatures, and when the silver ions reach a sufficient amount, the silver-based antimicrobial agent can meet the killing standards of 99.9% of the other antimicrobial products.
4 When a drying test method closer to the real world is used for silver-based antimicrobial products, its antimicrobial efficacy often fails.
, copper, another well-known antimicrobial metal, has been shown to pass drying tests.
4, although the chemical mechanism behind this phenomenon is still controversial, several experiments have shown that copper is a more effective antimicrobial agent for self-disinfecting surfaces.
in drying tests conducted by researchers such as Harold T Michels, they compared three different types of surfaces: uncoated stainless steel surfaces, stainless steel surfaces coated with silver-based antimicrobial agents, and a variety of copper-containing surfaces.
4 analysis showed that in about 75 minutes, a variety of MRSA superbugs on copper-containing surfaces were completely killed, while the surface coated with silver-based antimicrobial agents remained large amounts of bacteria after 6 hours.
4 is necessary to promote the development of the self-sterilizing surface market, using a five-drying test method similar to that of the U.S. Environmental Protection Agency.
is more practical than traditional wet testing methods, which can better simulate real-world environments and help screen more efficient materials such as copper for self-sterilizing surfaces.
the future, the market demand for antimicrobial products will increase significantly.
widespread adoption of testing standards closer to the real world will help break through niche product barriers and expand the scope of application of antimicrobial technology, so as to better address the urgent needs for the benefit of the global community.
Reference 1.2.N van Doremalen et al. Aerosol and surface stability of HCoV-19 (SARS-CoV-2) compared to SARS-CoV-1. New England Journal of Medicine (2020). Japanese industry standard JIS Z 2801. Antibacterial processing products - antibacterial test methods and antibacterial effects (2000) 4.Michels H T et al. "Effects of temperature and humidity on the efficacy of methicillin-resistant Staphylococcus aureus challenged antimicrobial materials containing silver and copper." Letters in Applied Microbiology vol. 492 (2009) 5. U.S. Environmental Protection Agency. Protocol for The Evaluation of Bactericidal Activity of Hard Non-Porous Copper-Containing Surface Products (2016) 6. ISO 22196 - 2011 Plastics and other holeless surface antibacterial determination 8. China National Standardization Management Committee. GB/T 21866 - 2008 Antibacterial coating (paint film) antibacterial assay and antibacterial effect 9. International Organization for Standardization. ISO 21702 - 2019 Plastics and other holeless surface antibacterial determination