A wearable knee sleeve, knitted from stretch-sensing fibres that can detect human movement, has been developed by Australian researchers.

In the future such devices could be used to monitor how well people are regaining their range of movement after surgery or help train athletes to move in a way that prevents injury, the researchers said.

"This is the first fibre in a knitted structure that can measure strain, which is a measure of stretch," lead researcher Professor Gordon Wallace, from the University of Wollongong, said.

"The primary applications for us are in monitoring human movement, primarily joint movement."

For some years, scientists have been developing "smart" textiles to make garments that sense, store energy or process information.

One of the challenges here has been to create fibres that are stable and durable enough to cope with the strenuous process of being knitted together with commercially-available fibres.

Professor Wallace and his colleagues have now developed such a robust yarn, which can detect stretch resulting from human movement.

Spinning the yarn that has 'extraordinary mechanical property'

The yarn, reported in a recent issue of the journal Applied Materials & Interfaces, is pulled out of a solution made from a mixture of organic conducting polymers and polyurethane.

"It is like spinning nylon," said Professor Wallace.

"We can continuously make metres of fibre per minute."

After producing the sensing yarn, the researchers then knitted strands of it together with Spandex into an electrically conductive textile.

As the knitted textile stretches, the way the sensors in it interact decreases the textile's electrical resistance, giving a read-out of how much it has been stretched.

Professor Wallace and his colleagues knitted a knee sleeve that was then stretched on test rig in the lab to test how sensitive it was to movement.

Traditional strain gauges, typically made of metals, can sense around 5 per cent strain - the ratio of the final stretched length to the original length.

However, the new stretch-sensitive textile containing four strands of the new yarn, detected repeated strains of up to 160 per cent.

"That's an extraordinary mechanical property," Professor Wallace said.

"Most human movement applications wouldn't require that degree of strain."

The stretch-sensitive knee sleeve was also hooked up to a commercial wireless receiver so researchers could record stretch measurements remotely.

Professor Wallace said the team has been working with collaborators in biomechanics to trial the use of the knee sleeve in sports training.

"We've been involved in developing a device that trains AFL players how to have their knee bent at the appropriate angle when they land," he said.

The team has also been applying the technology to medical monitoring.

"We're working with orthopaedic surgeons to look at using the knee sleeve as a diagnostic tool before and after a knee replacement, for example," Professor Wallace said.

Seatbelts could even have built-in sensing capacities that might help them function better, he said.

Wearable batteries to power the sensors

For the final version of knee sleeves and related wearable stretch-sensors, there will need to be an onboard battery to power the sensor.

In a related development, accepted for publication in the journal Electrochemistry Communications, Professor Wallace and team have found a way of braiding fibre electrodes to make wearable batteries.

"It's never been thought of before that you could take fibres that can store energy and braid them in an appropriate way so you can create a battery structure," he said.

Professor Wallace said the braiding technique could be used in a mass fabrication process.

The braided batteries are highly flexible and have a high storage capacity, only 25 per cent of which is lost after bending the braid 1,000 times, he said.

The research is funded by the Australian Research Council.