A smarter outfit

Materials World magazine
,
1 Jan 2018

Ellis Davies rounds up recent developments in smart fabrics and clothing.

Clothing is getting smart. With the boom in wearable technology, such as smart watches and fitness trackers, the items we wear are no longer there for just looks, but functionality. Developments in materials science have helped power this move towards smart clothing and fabrics, with a greater understanding of graphene, polymers and other materials allowing researchers to begin to make headway on useful, non-intrusive additions to our everyday clothing. 

Developments include full, washable electronic circuits printed onto fabric at the University of Cambridge, UK, and phone charging pockets made from MXene – a nanosheet of titanium and carbon – created by researchers at Deakin University, Australia.

Pocket power

MXene is an atomically thin sheet 100,000 times thinner than A4 paper discovered in 2011. It is synthesised by chemically etching a ceramic material called MAX phase (Mn+1AXn), which removes the weak metallic bond, separating the MXene layers. These nanosheets, however, are small and cannot interlock, making them unsuitable for smart fabrics. Researchers at Deakin combined the sheets with graphene and used its spinnability in solutions to make MXene into a fibre. Graphene sheets act as a host and can accommodate a high amount of MXene – up to 88%.

Dr Shayan Seyedin, researcher at Deakin, explained how the material stores energy. ‘It’s different from typical batteries, where energy is stored through chemical reactions. These fibres act as supercapacitors,’ he said. Energy storage in graphene occurs at the interface between graphene sheets with ions, while MXene stores energy by ion insertion between their layers. ‘By combining graphene with MXene, we were able to take advantage of both charge storages,’ Seyedin said. As the fibres only hold a small charge, they are only good for a quick emergency charge of a smartphone, but are ideally suited for heart rate monitors and fitness accessories such as fitbits.

Seyedin estimates that several devices could together provide around the same amount of energy as an AA battery. They will also need to be charged in a similar manner to a portable battery or smartphone. ‘We are still working on these fibres to increase their energy storage performance and scale-up the fabrication process,’ said Seyedin.

The fabric has undergone mechanical properties testing, as well as electrical conductivity measurements and evaluation of the charge-discharge properties of the fibres. ‘We found that the MXene fibres are flexible enough to be knitted into small (~5cm2) textiles and that the energy storing performance is highly stable for 20,000 cycles, which means that if we recharge these fibre devices once a day, we may be able to use them for more than 50 years,’ said Seyedin.

However, another area still needs testing. The machine washability of the fibres has not yet been evaluated – a common challenge for wearable devices. Seyedin noted this as a research goal, and would be done by incorporating and encapsulating the fibres within standard fibres and yarns. Additionally, the team would like to make the fibres look more attractive. They are dark brown and the team is currently not able to produce them with similar properties that have different colours. However, ‘These fibres can always be incorporated within other yarns and fibres in the fabric or be hidden inside a pocket to improve the visual appeal of textiles made of them,’ Seyedin explained. 

As MXene is much more expensive than standard materials, the team does not intend to make whole items of clothing from the fibres anyway, but will instead opt to manufacture small patches, which they say can be made affordably. 

Washable circuits

As Deakin moves forward producing washable technology, researchers at the University of Cambridge are already there with washable, stretchable and breathable electronic circuits that can be printed onto fabric. These are comfortable to wear and can withstand 20 cycles in a standard washing machine, according to the researchers.

The circuits are printed using graphene-based inks. These are designed to be low-boiling and can be printed directly onto a polyester fabric, which can be modified by increasing its roughness to improve performance. The manufacturing process allowed the researchers to design electronic circuits that combine active and passive components, rather than just single transistors. 

Dr Felice Torrisi, of the Cambridge Graphene Centre said, ‘Other inks for printed electronics normally require toxic solvents and are not suitable to be worn, whereas our inks are cheap, safe and environmentally-friendly, and can be combined to create electronic circuits by simply printing different two-dimensional materials on the fabric.’

Wearable electronic devices are often rigid and attached to similar rigid materials such as plastic. This can limit interaction with the skin of the wearer and can make the devices uncomfortable. The method used at Cambridge will allow for the manufacture of fabric-based devices with electronic integrated circuitry that interact more naturally with the wearer. 

The circuits demonstrated by the team are simple, but the process is scalable. The researchers believe that if scaled-up, there are no obstacles to the development, complexity and performance, of wearable electronic devices. ‘Turning textile fibres into functional electronic components can open an entirely new set of applications from healthcare and wellbeing to the Internet of Things,’ said Torrisi. In future, our clothes could incorporate these textile-based electronics, such as displays or sensors, and become interactive.’

Smart clothing and fabrics have the potential to impact many areas, such as medicine and health. Whether they’re used for powering heart rate monitors or turning your clothing into an electronic circuit, their development will be watched with keen interest.