Smart cotton for biomonitoring

Materials World magazine
,
1 Feb 2009
Light emitting diode emission as a current passes through the carbon-nanotube coated cotton

A conductive cotton yarn that can be woven into soft fabrics could have health monitoring capabilities.

The ‘smart yarn’, coated in carbon nanotubes (CNT’s), could be used as an integrated sensor to detect blood when a soldier, firefighter, or police officer is injured. It would relay a signal to a control post, enabling the dispatch of assistance.

To create these textiles, single and multi-walled CNTs are dispersed in a nafion-ethanol and a polysodium solution, diluted in water. A general commodity cotton thread, 1.5mm in diameter, is then dipped into the CNT dispersions. After several dips in both solutions, the thread becomes conductive enough to illuminate a light emitting diode, powered by a battery.

Wearable electronics

Conductive metal wires and other rigid fibres have been used in the past to demonstrate wearable electronic devices, but these materials do not provide textiles with sufficient flexibility, durability and mobile comfort, says Nicholas Kotov, a Professor of Chemical Engineering at the University of Michigan, USA, where the cotton was developed.

‘Smart textiles made primarily of metallic or optical fibres are fragile, uncomfortable, and
can corrode, but cotton yarns, coated with CNT and polyelectrolytes, have overcome these problems,’ he explains.

‘Once the absorbed yarns are dried, it is impossible to remove the CNT from the fibres, even when exposed to solvents, heat, or a combination of both.’

Exposuring the yarn to different solvents imitating washing did not affect its electrical properties.

‘The flexibility of the CNTs allows them to conform to the surface of the cotton fibres, making them comfortable enough to wear. The only perceptible change to the yarn is that it turns black, due to the carbon,’ adds Kotov.

To exploit its conductivity, the team infused the yarn with the antibody anti-albumin, which reacts with albumin, a protein found in blood.

Extra strong

The strength of the CNT-cotton yarn is said to be more than twice that of the original thread due to a reduction in the overall diameter, and stronger adhesion of the fibres to each other.

Kotov believes that further development could include energy harvesting apparel with charge storage capabilites. ‘This could be the most challenging application, but is nevertheless suitable because of the supercapacity properties of carbon nanotubes,’ he explains. ‘The effects of long-term contact between skin and the yarns also needs to be investigated further.’