A recent review published in Science and Technology of Advanced Materials by a Chinese scientist summarises the advances and drawbacks of stretchable electronics, a promising technology for a new-generation wearable devices, storing energy and military applications.
Wei Wu, materials scientist at Wuhan University, China, analysed the materials and stretchable components available now and their need for further development to turn them into commercially-viable products. The biggest challenge for making stretchable electronics is that each component must endure being compressed, twisted and applied to uneven surfaces while maintaining its performance.
Stretchable electronic components that already exist are conductors and electrodes made from silver nanowires and graphene. However, what’s urgently needed are stretchable energy conversion and storage devices, such as batteries. Zinc-based batteries are promising candidates, even though they still need more work before becoming commercially-viable.
Alternative to batteries are stretchable nanogenerators that produce electricity from various freely-available vibrations, such as the wind or human body movements. Stretchable solar cells could also be used to power wearable electronic devices. In addition, by integrating multiple stretchable components, such as temperature, pressure and electrochemical sensors, it is possible to create a material resembling human skin that could use sweat, tears or saliva for real-time, non-invasive healthcare monitoring, or for creating smart prosthetics or robots with enhanced sense capabilities. However, at present, fabrication of artificial skin remains time-consuming and complex.
Currently there are two main strategies for manufacturing stretchable electronics. The first is to use intrinsically stretchable materials, such as rubber, that can endure large deformations. Sadly, their main drawback is high electrical resistance.
The second method is to make non-flexible materials stretchable using innovative design. For example, brittle semiconductor materials like silicon can be grown on a pre-stretched surface and then allowed to compress, creating buckling waves. Another method involves linking ‘islands’ of rigid conductive materials together with flexible interconnections, such as soft or liquid metals. Origami-inspired folding techniques can be used to make foldable electronic devices. In the future, stretchable electronics may be enhanced with new capabilities, such as wireless communication, self-charging or even self-healing.
The next step after laboratory tests is to bring stretchable electronic devices to market. This requires cheaper materials and faster, scaleable manufacturing methods, concludes Wu.
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