Surfaces with anionic block copolymers can inactivate different viruses within minutes by making the polymer-microbe interface very acidic. Such surfaces can continuously disinfect surfaces without the need for reapplication of disinfectant.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of the coronavirus disease 2019 (COVID-19) pandemic, is mainly transmitted by airborne particles. However,  studies have shown that the virus can remain active for several days on different surfaces. Touching such contaminated surfaces and then touching the face may also cause an infection.

Study: Rapid and Repetitive Inactivation of SARS-CoV-2 and Human Coronavirus on Self-Disinfecting Anionic Polymers. Image Credit: Kateryna Kon / Shutterstock

Many methods of disinfection and sanitization have been approved worldwide, which include chemical and radiative methods. Drawbacks of such methods include their continual use and their inability to prevent re-contamination. Repeated use of disinfectants containing chemicals such as quaternary ammonium compounds can also have harmful effects on the environment.

Another strategy would be to develop self-disinfecting materials that can continuously disinfect the surface. Such materials generally include metals or metal oxides. Cationic polymers are another type of material used for antibacterial surfaces. Other types of polymers that have been used are photoreactive polymers, which can kill a wide variety of microbes and remain active for long times.

Researchers recently reported a new type of disinfection material based on anionic copolymers. These polymers are negatively charged and have sulfuric acid groups on their backbone, and have been shown to kill several types of bacteria and viruses. The material acts by causing a sharp drop in pH, making the area very acidic at the pathogen surface.

In a new study, the researchers explored how these materials inactivate coronaviruses as a function of time. They reported their results in Advanced Science.

Testing virus inactivation with time

The authors used three types of polystyrene-based anionic block polymers, which have blocks of different types of polymers. One is a commercially available polymer called BIAXAM^TM (named here as TESET), and the other two were sulfonated polymers named TST and SEBS. The polymers had different levels of sulfonation.

They found complete inactivation of SARS-CoV-2 on one type of the TESET material in five minutes, the mechanism believed to be the extreme acidity caused by the sulfuric acid groups. The nanoscale morphology of the polymer changes when it comes in contact with water. The sulfur groups become exposed on the surface, which leads to the pH drop.

The team also observed similar behavior for another coronavirus, HCoV-229E, on TESET surfaces. A greater degree of sulfonation is more effective for inactivating the virus compared to the polymer with a lesser number of sulfur groups. Here, for the polymer with the lower sulfur groups, they did not observe any inactivation even after 30 minutes, suggesting there is a minimum level of sulfonation required for virucidal activity.

While the TESET polymers are thermoplastic elastomers, the TST polymers are comparatively brittle plastics. This polymer also inactivated HCoV-229E in about 20 minutes, with the ability again dependent on the amount of sulfonation. These results suggest this type of polymer could potentially inactivate other viruses too.

Advantageous approach

The authors also tested the virucidal activity of TESET polymers at different temperatures. They found the HCoV-229E virus was inactivated faster at shorter times as the temperature was increased. But, when tested for longer times, the virus was inactivated faster at a lower temperature (20 minutes at 4 ºC and 25 ºC) than at a higher temperature (30 minutes at 37 ºC). This may be because the pH increases at higher temperatures because the cations in the virus media are more mobile and neutralize the sulfuric acid.

Thus, these anionic polymers can inactivate viruses continuously until the sulfuric acid groups are neutralized. They can then be recharged by dipping in dilute acids for a short time. Since the inactivation depends on the surface pH of the material, a measure of the surface pH can act as a predictor of the inactivation capability of these materials.

It is possible that other anionic polymers can also inactivate viruses. Nafion is another such material used mainly in fuel cells. When the authors tested this material for virus inactivation, they found virus inactivation similar to TESET and TST.

One of the advantages of the disinfection approach using this type of polymer is that since it does not target specific chemical species on the pathogens, it is unlikely that there will be any danger of the development of microbial resistance. This approach will also be suitable for microbes that form protective spores or targeting many pathogens that may exist on surfaces synergistically. The polymers are not detrimental to the environment and can be recycled.

Written by

Lakshmi Supriya

Lakshmi Supriya got her BSc in Industrial Chemistry from IIT Kharagpur (India) and a Ph.D. in Polymer Science and Engineering from Virginia Tech (USA).