Creating better asthma inhalers through aerospace engineering

Millions of people around the world rescue their health, daily, with asthma inhalers. The device is life-saving, but curiously inefficient for a technology that has been around for more than 60 years. The uneven spread and size of particles, combined with the different ways people use the inhaler, means drug delivery can often be just 25 per cent of what it should be.

Inhalers release a turbulent jet of vapour, not dissimilar to what you would see in an engine fuel injector, and in fact it’s this sideways leap in thinking that led to engineers from Australia and the US turning their engine and aerospace expertise to this medicine.

Using a synchrotron beamline – a source of extremely bright light used for highly accurate atomic and molecular analysis – in Chicago, the group unlocked the secret of why asthma inhalers are inefficient and, more importantly, were able to see how they can be improved.

Following their analysis of the inhaler at work, they’re confident that improved nozzle designs could deliver asthma drugs more efficiently and cut the medication’s cost per dose.

The project is being led by Professor Damon Honnery, deputy head of the Department of Mechanical and Aerospace Engineering at Monash University. Professor Honnery, a mechanical engineer and also the joint head of the Laboratory for Turbulence Research in Aerospace and Combustion, is an expert on pollutant formation from engines and climate-change mitigation measures.

The researchers also want to develop a more versatile spray. They hope to tailor nozzles and sprays to different user groups, such as children or frail elderly people.

He explains that his laboratory has an extensive capability to measure sprays used in engines. And, quite remarkably, the components of those spray systems are very similar to the sprays used in asthma inhalers.

“So I like to think of the asthma inhaler as a fuel system, but with a cooler spray,” he says. “The canister is the fuel tank, if you like, and the nozzle and the spray actuator is the fuel delivery system.”

Professor Honnery was among a group of Australian and American researchers who used a special synchrotron beamline and X-ray techniques at Chicago’s Argonne National Laboratory to record for the first time what happens inside the plastic nozzle of an asthma inhaler.

They reported in 2016 that when the drug and liquid propellant mixture enters the millimetre-wide expansion chamber of the nozzle, it creates a foam with different-sized bubbles. “This foam has a complex structure, which varies over the entire ejection period, giving the spray an erratic quality,” he says.

The process that occurs inside the minute chamber of an asthma inhaler nozzle is actually more complex than that in the fuel injector, he says. “That’s because the inhaler liquid is a refrigerant that vaporises as it enters the nozzle, dropping the temperature to well below 0˚C.”

The aim of the new research project is to design nozzle components that “get more of the drug delivered into people’s lungs” and allow more precise control of doses.

The researchers also want to develop a more versatile spray. They hope to tailor nozzles and sprays to different user groups, such as children or frail elderly people.

The project is being undertaken jointly with Professor Paul Young, head of respiratory technology at the Woolcock Institute of Medical Research at the University of Sydney. It has received A$550,000 in funding from the European pharmaceutical company Chiesi, and an Australian Research Council (ARC) Linkage Grant.

Professor Honnery’s team, including ARC Discovery Early Career Researcher Award recipient Dr Daniel Duke, has already spent six months creating nozzle prototypes, and hopes to design about a dozen more.

The team will test these nozzles at the Monash laboratory and the Chicago synchrotron. Testing at the synchrotron, led by Dr Duke, will involve tens of thousands of sprays, 24 hours a day, for seven days.

“We’re trying to improve the spray process, so that a greater proportion of the drug falls into a particle size that can get into the lung,” Professor Honnery says.

If the researchers can ensure the drug is sprayed out at the right particle size, the canisters will deliver more doses, more precisely, increasing health benefits and reducing the risk of over or under-medicating. The inhalers could also potentially be used for other drugs that are far more dose-sensitive, such as insulin for diabetics, he says.