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A fast-acting tourniquet for Australia’s Future Soldier

29 March 2019
Vanessa Ha and Mark Ryan with the equipment used to stretch the yarn samples used in their shape-memory polymer research.
Vanessa Ha and Mark Ryan with the equipment used to stretch the yarn samples used in their shape-memory polymer research.

The Reactive Tourniquet is a multi-functional material project, one of several exciting research ventures for the Future Soldier program.Biomedical engineering undergraduate Vanessa Ha has been assisting Defence researcher Mark Ryan to develop shape-memory polymers in the form of a special wool yarn to create a fast acting tourniquet to stem arterial bleeding.

Shape-memory polymers are smart materials with the ability to return from a deformed state to their original shape when activated by an external stimulus such as temperature change or application of a liquid.

A combat uniform with shape shifting properties

Their material is woven from a special type of raw wool that is wet, stretched and left to dry under load. When it is wet again it shrinks back down. The team has shown that the wool they've selected will shrink back more or less to its original size, with quite a bit of force, after being activated (in this case, by applying water). The end goal is for the shape-memory polymer to be knitted into a fabric that is an integral component of the Future Soldier Combat Ensemble – creating a tourniquet ready to apply pressure to a wound at the first detection of haemorrhage.

According to Ryan, soldiers are trained to apply a tourniquet within about 15 seconds. "Our high-level concept with this smart material is to make the application almost instantaneous. They'll be wearing the tourniquet material and it will apply pressure as soon as it's needed."

In this pioneering phase the team is focusing on how the properties of the material can be changed by altering preparation methods, including stretching, knitting and sewing methods. Ha has focused on two parameters - material extension (how much it is stretched), and the extension rate (how fast it is stretched) – and has homed in on the combination that exerts the greatest shrinkage force when activated.

Measuring the force

After preparing the hanks with different combinations of stretch and stretch rate, the scientists worked with specialists at RMIT to knit the yarn into tubular hosieries that could form the arm or leg components of clothing. They are now designing a test rig to measure shrinkage force. The tourniquet will be placed over an instrumented limb simulator to deduce how much pressure the tourniquet applies.

It is envisaged that a purpose-designed patch built into a 'smart uniform' could be triggered manually or automatically, releasing moisture from sealed sections within the uniform at specific locations along the arms and legs to activate the tourniquet effect.
Other potential applications within the defence realm for a material that rapidly shrinks upon activation include shrink-to-size seals around chemical protection suits and personnel escape hoods in submarines.