Wash and wear

Electronically enhanced textiles that can be stretched and washed without losing conductivity are nearing reality as result of a recent development by Belgian researchers.

The work is being carried out by Belgium's Interuniversity Microelectronics Centre (IMEC), which includes labs at Ghent University, the University of Brussels, the higher polytechnical school of Bruges-Ostend and the University of Limburg.

The research team fabricated elastic interconnections that can stretch like rubber bands to more than twice their original length.

Researcher Fabrice Axisa, of Ghent University, said the development is a big step ahead for the integration of electronics in textiles. 'Smart fabrics exist, but at the moment the electronics are not embedded inside,' he said. 'If you want to wash the fabrics you have to take the electronics off and put it in the washing machine. We want to embed the electronics in the fabric so you can forget about it and just wash it.'

Fellow researcher Jan Vanfleteren said the group's electronic circuit is totally embedded in an elastic material, such as silicone or polyurethane, so that it can resist influences from the outside, such as water.

'The challenge here is that, next to water resistance, the electronics need resistance to cleaning agents like soaps and detergents, and most of all, mechanical stresses like crumpling and high-velocity rotations during the washing cycle,' Vanfleteren said, adding that the researchers are testing their connectors to make sure they can hold up under these sort of harsh conditions.

For their lab demonstration, the researchers constructed their 3cm-long elastic connectors by embedding 4µm-thick gold wires in a highly elastic silicone film. The wires were coated with a 2µm-thick nickel layer for soldering wires to the ends.

The group patterned the gold wires onto a substrate in a horseshoe-shaped form, instead of the usual elliptical shape, to reduce stress without initial electric resistance. The horseshoe shapes were then connected to create a wave-like pattern.

The researchers further increased the elasticity and minimised induced stress by splitting the wire conductor track into four thinner (15µm-wide) tracks. They tested a variety of different shaped connectors by stretching them to the point of electrical failure, which happens when there is a rupture in the metallic track. The best connector stretched from 3cm to 6cm without losing conductance.

However, all interconnections — even those that experienced electrical failure —recovered their conductivity when they returned to their normal length.

The group is now developing technology toward the incorporation of the elastic interconnections into full electronic circuits.

Axisa said commercial applications for the elastic connectors are still about two to three years away, but there should be a large market for them. Other research groups around the world are also trying to develop and commercialise textiles embedded with electronics.

One EU-funded project, for example, is developing intelligent textiles to measure the health of people working in extreme conditions. Electric, electrochemical and optical sensor systems will be embedded into a textile to create sensing patches that will monitor fluids such as the blood, sweat and urine of the wearer throughout the day.

However, Axisa said, the electronics developed by himself and his fellow researchers are the only ones that promise to be both flexible and washable.

Apart from smart textiles, the Belgian researchers are also looking to apply their integrated electronics in the biomedical field.

Axisa said the group is now focusing on applications such as implantable electronics.

'At the moment, most implants are made of titanium and are rigid,' Axisa said. 'The silicone we use to create these systems is accepted by the body and it is able to be compressed and has the same touch feeling as flesh.'