A joint research venture between the University of Birmingham and private firms NitroPep Ltd and Pullman AC has produced air filters that are highly effective at killing bacteria, fungi, and viruses, including the SARS-CoV 2 virus, the infamous coronavirus.
The secret of these filters’ effectiveness is a chemical called chlorhexidine digluconate (CHDG). This is a potent biocide that can kill pathogens within seconds of coming into contact with them. Air filters coated in this substance can prove to be a powerful tool against airborne pathogens around the world, according to the researchers that designed them.
Removing the gunk
“The COVID-19 pandemic has brought to the forefront of public consciousness the real need for new ways to control the spread of airborne respiratory pathogens. In crowded spaces, from offices to large indoor venues, shopping malls, and on public transport, there is an incredibly high potential for transmission of COVID-19 and other viruses such as flu,” says Dr. Felicity de Cogan, Royal Academy of Engineering Industry Fellow at the University of Birmingham, and corresponding author of the paper.
“Most ventilation systems recycle air through the system, and the filters currently being used in these systems are not normally designed to prevent the spread of pathogens, only to block air particles. This means filters can actually act as a potential reservoir for harmful pathogens. We are excited that we have been able to develop a filter treatment which can kill bacteria, fungi and viruses—including SARS-CoV-2—in seconds. This addresses a global un-met need and could help clean the air in enclosed spaces, helping to prevent the spread of respiratory disease.”
The filters were tested in both laboratory and real-life conditions to determine how effective they were at removing air-borne pathogens, and the results are stellar.
In the lab, the filters were covered with viral particles of the Wuhan strain of SARS-CoV-2, alongside control filters. They were then checked periodically over a period of more than one hour to see how these pathogens fared. While much of the initial quantity of viral particles remained on the surface of the control filters for the experiment’s length, all SARS-CoV-2 cells were destroyed within 60 seconds on the treated filters.
Experiments involving bacteria and fungi that commonly cause illness in humans — such as E. coli,S. aureus, and C. albicans— yielded similar results. This showcases the wide applicability of the filters.
To determine how well these fitlers would perform in real-life situations, treated filters were installed in the heating, ventilation, and air conditioning systems on train carriages in the UK alongside control filters in matched pairs on the same train line. These were left to operate for three months before being removed and sent to the lab for analysis — which involved the researchers counting any bacteria colonies that survived on the filters.
No pathogens were found on the treated filters, the team explains. Furthermore, this step showed that the treatment was durable enough to withstand three months of real-world use while maintaining their structure, filtration functions, and anti-pathogen abilities.
“The technology we have developed can be applied to existing filters and can be used in existing heating, ventilation and air conditioning systems with no need for the cost or hassle of any modifications,” Dr. de Cogan explains. “This level of compatibility with existing systems removes many of the barriers encountered when new technologies are brought onto the market.”
NitroPep Ltd is now building on these findings in order to deliver a final marketable version of the coating.
The paper “Efficacy of antimicrobial and anti-viral coated air filters to prevent the spread of airborne pathogens” has been published in the journal Nature Scientific Reports.
Although they’re relatively old technology in this day and age, there is renewed interest in iron lungs today against the backdrop of the coronavirus pandemic.
Few devices can boast having as terrifying — and cool — a name as the iron lung. These somewhat outdated medical devices were the earliest devices designed to help patients breathe. Compared to modern breathing aides, these devices were huge and quite scary-looking.
Still, iron lungs were a very important development at their time. In the aftermath of the COVID-19 epidemic, there has also been renewed interest in these devices as they can be used as an alternative to modern ventilators.
So let’s take a look at exactly what iron lungs are, and how they came to be.
So what are they?
Iron lungs are quite aptly named; unlike other modern ventilators, they function using the same mechanisms as our own lungs.
An iron lung is a type of negative pressure ventilator. This means that it creates an area of low-pressure or vacuum to move and draw air into a patient’s chest cavity. In very broad lines, this is the exact mechanism our bodies employ, via movements of the diaphragm, to let us breathe.
The concept behind these devices is quite simple. The main component of an iron lung is a chamber, usually a metal tube (hence the ‘iron’ part in its name) that can fit the body of a patient from the neck down. This acts as an enclosed space in which pressure can be modified to help patients breathe. The other main component of the device is mobile and actually changes the pressure inside the tube. Usually, this comes in the form of a rubber diaphragm connected to an electrical motor, although other sources of power have been used, including manual labor.
Patients are placed inside an iron lung, with only their head and part of their neck (from their voice box upwards) left outside the cylinder. A membrane is placed around their neck to ensure that the cylinder is sealed. Afterward, the diaphragm is repeatedly retracted and contracted to cycle between low and high pressure inside the chamber. Because the patient’s head and airways are left outside of the cylinder, when pressure is low inside it, air moves inside the patient’s lungs. When pressure increases inside the cylinder, the air is pushed back out.
The whole process mirrors the way our bodies handle breathing. Our diaphragm muscles draw on the lungs, increasing their internal volume, which pulls air in from the outside. To breathe out, the diaphragm muscle squeezes on the lungs, pushing air out. Iron lungs work much the same way, but they expand and contract the lungs alongside the rest of the chest cavity from outside the body.
This process is known as negative pressure breathing; low (‘negative’) pressure is generated in the lungs in order to draw in air. Most modern ventilators work via positive pressure: they generate high pressure inside the device to push air into the patient’s lungs.
One advantage of such ventilators is that patients can use them without being sedated or intubated. On the one hand this eases the pressure on medical supplies each patient requires; on the other, it slashes the risks associated with the use of anesthetics — such as allergic reactions or overdoses — and the risk of mechanical lesions following intubation.
“The desperate requests for ventilators in today’s treatment of patients in the grasp of the coronavirus brought to mind my encounter with breathing machines in the early 1950s polio epidemic, when I signed up as a volunteer to manually pump iron lungs in case of power failure at Vancouver’s George Pearson Centre,” recounts George Szasz, CM, MD, in a post for the British Columbia Medical Journal.
Iron lungs saw their greatest levels of use in developed countries during the poliomyelitis outbreaks of the 1940s and 1950s. One of the deadliest symptoms of polio is muscle paralysis, which can make it impossible for patients to breathe. The worst cases would see patients requiring ventilation for up to several weeks. Back then, iron lungs were the only available option for mechanical ventilation, and they saved innumerable lives.
As technology progressed, however, iron lungs fell out of use. They were bulky and intimidating machines, hard to transport and store despite their reliability and mechanical simplicity. With more compact ventilators, the advent of widespread intubation, and techniques such as tracheostomies, such devices quickly dwindled in number and use. From an estimated height of around 1,200 iron lung devices in the U.S. during the ’40s and ’50s, less than 30 are estimated to still be in use today
There are obvious parallels between those polio epidemics of old and today’s COVID-19 pandemic in regards to the need for ventilation. Machines such as the iron lung have been suggested as a possible treatment option for COVID-19 patients due to this. For most cases, such devices can help, but not for all.
In cases of severe COVID-19 infections, the tissues of the lungs themselves are heavily affected. A buildup of fluid in the lungs can physically prevent air from reaching the alveoli (the structures in the lung where gases are exchanged between the blood and the environment). While iron lungs can perform the motions required to breathe even for patients who are incapable of doing it themselves, they cannot generate enough pressure to push air through the tissues affected by a COVID-19 infection.
“Iron lungs will not work for patients suffering from severe COVID-19 infections,” explains Douglas Gardenhire, a Clinical Associate Professor and Chair of Respiratory Therapy at the Georgia State University (GSU) Department of Respiratory Therapy. “Polio interrupted the connection between brain and diaphragm and while some polio patients did have pneumonia, it was not the principal issue. For the most part, the lungs themselves did not have any change in their dynamic characteristics.”
“COVID-19 pneumonia physically changes the composition of the lungs,” adds Robert Murray, a Clinical Assistant Professor at the GSU. “The consolidation of fluid in the lungs will not respond with low pressure generated by the iron lung. The lungs of a COVID-19 patient will be a heterogenous mix of normal and consolidated lung tissue making mechanical ventilation very difficult.”
Still an alternative
Although patients with severe COVID-19 infections might not benefit from the iron lung, there are cases in which the device can prove useful. One paper (Chandrasekaranm, Shaji, 2021) explains that there still is a need for negative pressure ventilators in modern hospitals, especially for patients who have experienced ventilator-induced lung injuries. The use of negative pressure ventilators, especially in concert with an oxygen helmet, may also play a part in reducing the number of infections by limiting the spread of viruses through contaminated materials in cases where resources are stretched thin, the team adds.
While the concept is being retained, however, the actual devices are getting an upgrade. One example is the device produced by UK charity Exovent, which aims to be a more portable iron lung. Exovent’s end goal is to provide a life-saving device that will impose fewer limits on what activities patients can undertake. A seemingly-simple but still dramatic improvement, for example, is that patients can use their hands to touch their faces even while the Exovent device is in operation. Eating or drinking while using the device is also possible.
Exovent’s ventilator was designed before the coronavirus outbreak to help the millions of people suffering from respiratory issues including pneumonia worldwide. However, its designers are confident that, in conjunction with oxygen helmets, it can help patients who are recovering from a coronavirus infection — a process that leaves them with breathing difficulties for months.
All things considered, iron lungs have made a huge difference for the lives of countless patients in the past, and they continue to serve many. Although most of them today look like archaic devices, engineers are working to update and spruce them up for the modern day. And, amid modern ventilators, there still seems to be a role — and a need — for devices such as iron lungs.
New research at Purdue University measures how much pollution in your office or home is due to you.
We influence our surroundings just by virtue of being alive — we take oxygen and pump out CO2, our skin sheds, our hairs fall out, our heat dissipates out. Factor in elements like deodorant, and we have a surprisingly significant effect on the areas we spend our time in, such as an office or home. But, to find out just how large this influence is, a team of engineers at Purdue University has been conducting one of the largest studies of its kind in the office spaces of a building rigged with thousands of sensors.
The house of noses
“If we want to provide better air quality for office workers to improve their productivity, it is important to first understand what’s in the air and what factors influence the emissions and removal of pollutants,” said Brandon Boor, an assistant professor of civil engineering with a courtesy appointment in environmental and ecological engineering.
The present study is the largest of its kind to date. The team used an office space rigged with thousands of sensors to identify all types of indoor air contaminants and recommend ways to control them through adjusting a building’s design and operation. The building is called the Living Labs at Purdue’s Ray W. Herrick Laboratories and uses an array of sensors to monitor the flow of indoor and outdoor air through the ventilation system over four open-plan office spaces. The team further added temperature sensors (embedded in each desk chair) to keep track of people’s activities throughout the day.
People and ventilation systems have shown the greatest impact on the chemistry of indoor air in such environments, they explain. This chemistry is dynamic and “changes throughout the day based on outdoor conditions, how the ventilation system operates and occupancy patterns in the office,” Boor said.
In collaboration with researchers at RJ Lee Group, Boor developed an instrument called a proton transfer reaction time-of-flight mass spectrometer — a mechanical ‘nose’. Using this device, they recorded levels of volatile compounds in human breath, such as isoprene, in real-time.
These compounds linger in the office even after people have left the room. They also see greater build-ups when a larger number of people uses the same room.
“Our preliminary results suggest that people are the dominant source of volatile organic compounds in a modern office environment,” Boor said. “We found levels of many compounds to be 10 to 20 times higher indoors than outdoors. If an office space is not properly ventilated, these volatile compounds may adversely affect worker health and productivity.”
Ozone (considered an outdoor pollutant) breaks down inside office areas as it interacts with indoor compounds and furnished surfaces. The team adds that ozone and compounds called monoterpenes (these are aromatic compounds, such as those released by peeling an orange) break down into particles as small as one-billionth of a meter. At such a tiny size, they could be toxic as they can get into — and clog — pulmonary alveoli, the sacs in the lungs where blood-atmosphere gas exchange takes place.
Chemicals emitted from self-care products such as deodorant, makeup, and hair spray may elevate pollution levels outdoors as they are vented outside by the ventilation system, the team adds.
The team will present its initial findings at the 2019 American Association for Aerosol Research Conference in Portland, Oregon, on Thursday 16th, as the poster “Spatiotemporal Mapping of Ultrafine Particles in Buildings with Low-Cost Sensing Networks”.
The humble termite only has its body, saliva and some soil to work with, and the only blueprints it has are instinctual, based on variations in wind speeds and fluctuations in temperature as the sun rises and sets. Working with such limited resources, they still erect monumental mounds that, a new study reveals, rely on a surprisingly well-tuned mechanism for efficient ventilation, something architects today still struggle with.
Led by L. Mahadevan, Lola England de Valpine Professor of Applied Mathematics, of Organismic and Evolutionary Biology, and of Physics, a team of researchers that included Hunter King, a post-doctoral fellow and Samuel Ocko, a graduate student, both in the Mahadevan lab, has for the first time has described in detail how termite mounds are ventilated. The study reveals that the structures act akin to a lung, inhaling and exhaling once a day as they are heated and cooled.
Thermal images superposed on a photograph of a termite mound (photo 1). At night (left side) the flutes are cooler, so the air first moves down them and then up the central core. During the daytime (right), the warmer air reverses the process, moving air up the flutes and then down the central core. Occurring once a day, it allows CO2 from deep inside the mound to surface and diffuse through the porous walls (photo 2). Thus the mound works like a slowly breathing lung, powered by daily temperature oscillations. Credit: Hunter King and Naomi Ocko
The study is described in an August 31 paper in the Proceedings of the National Academy of Sciences (USA).
“The direct measurements essentially overthrow the conventional wisdom of the field,” Mahadevan said. “The classic theory was that if you have wind blowing over the mounds, that changes the pressure, and can lead to suction of CO2 from the interior…but that was never directly measured. We measured wind velocity and direction inside the mounds at different locations. We measured temperature, CO2 concentrations…and found that temperature oscillations associated with day and night can be used to drive ventilation in a manner not dissimilar to a lung. So the mound ‘breathes’ once a day, so to speak.”
On a trip to the National Center for Biological Sciences in India five years ago, Mahadevan was surprised to learn that many of the theories about how exactly the termites’ mounds function had not been rigorously tested. Working with Scott Turner, an Associate Professor at SUNY College of Environmental Science and Forestry, and author of a book that examines animal-built structures, Mahadevan, King and Ocko put together a plan to set out to find more definitive answers.
“It occurred to us that the internal flow profiles predicted by different potential mechanisms qualitatively disagree with each other,” King said. “By measuring them directly, we could easily identify the right one. The hard part was figuring out how to sensitively measure these small flows in a confined space defended by glue-and-mud-excreting termites.”
Over a period of several weeks they used a series of custom designed probes to conduct a variety of tests on both live and dead mounds that included temperature readings during the day or at night, covering the mounds with tarps, blowing air over the structures and even using vacuum cleaners to test suction throughout it’s internal passages.
“After months of hard thought and preparation, it all comes down to hiking through the woods at 4am with a laptop, a lantern, custom-built electronics, and a hole saw,” Ocko said. “The ‘aha’ moment made it all worth it.”
As they found out, the ventilation mechanism is in large measure built into the mounds themselves. There is a large central chimney that spans from the gallery — the underground chamber where most of the colony lives — to the top of the mound. The interior, structural walls that make up the core of the mound are larger, bulkier and more resilient, but the exterior ones are far thinner. While impermeable to winds, these outer walls allow for an exchange of gasses with the environment.
The interior structure of a termite mound. Image via matnkat
During the day, Mahadevan explained, as sunlight either directly or indirectly warms the mound’s outer walls, the air inside warms, causing it to rise.
“What you get is a convection cell,” Mahadevan explained. “The warm air can’t move through the walls quickly enough, but it has to go somewhere, and the only possibility is for it to go down into the interior through the central chimney. At night, as the exterior cools, the airflow reverses, and it pulls the air up from the central part of the mound.”
The end result is that while CO2 concentrations during the day can reach up to four or five percent in the center of the mound, the airflow at night pulls the gas to the exterior walls, where it can escape by diffusing through the wall.
“But what’s remarkable here is how the termites are using transients. The temperature outside the mound is oscillating, and they have developed a method to harness that to ventilate their mounds.” Mahadevan said.
While the study reveals for the first time how termite mounds truly work, it may also offer lessons human architects could benefit from.
“In a large building like the one we’re sitting in we have windows and doors that allow us a certain amount of seclusion and privacy, but that also means you have a harder time pushing air around from one part of the building to another,”
While the notion of designing buildings that can be more efficiently ventilated is not new, the principles described in the study might offer new ways to think about such passive ventilation systems.
“Could you drive large scale flows through a building like this one by cleverly opening and closing doors and windows ?” Mahadevan asked. “Rather than spending a great deal of energy for a fan and air conditioning in every room, with the end result being that some people are too hot and some people are too cold… perhaps we should think of the entire thing as a system and these new measurements suggest that if the architecture is appropriate, ventilation can occur by using environmental transients — something for us to think about.”