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Silkworms help create high-tech wearables

Joseph Flaig

(Credit: iStock)
(Credit: iStock)

Materials scientist Yingying Zhang from Tsinghua University in China on creating flexible sensors with super-silk

We are interested in using materials developed in our lab to help protect or improve people’s health and quality of life. Our work mainly focuses on the structures of materials and their performance in devices we create. We use various techniques, including high-temperature annealing, electron microscopy and mechanical property testing.

We tried to use carbon nanotubes as a filtration material to remove PM2.5 – very small particles that can enter the lungs and cause health problems – from polluted air. However, due to the unknown toxic properties of carbon nanotubes, we decided to stop using them.

Instead, we tried to search for other materials that are safer. We found silk nanofibre membranes are an excellent candidate for PM2.5 removal, especially for respirators. Silk materials are naturally produced protein, they are biocompatible and safe for the human body. Silk in China is low-cost, making it an ideal material for fabricating wearables. 

Beside the project on air filtration, we started to use silk materials for wearable and flexible sensors for monitoring human health or activity. We chose silk as one of the main raw materials for electronic sensors.

We are trying two strategies to enhance the electrical conductivity of silk. The first is combining it with electrically conductive materials to make composites. One approach is feeding nanocarbons or other electrically conductive materials to silkworms to get spun silk fibres ‘doped’ with other fillers. However, this has not produced conductive silk yet. 

The other approach is to treat the silk with other materials to form composites, which is more straightforward. It involves treating silk materials with high temperatures in argon or nitrogen to transform them into partially graphitised carbon, so obtaining silk-derived carbon materials for wearable electronics.

If we have conductive silk, we can use it to make ‘smart textiles’ or electronic clothes. Beside the advantages of silk, such as its excellent mechanical softness, strength and lustrousness, new functions relying on electrical conductivity can be readily realised with the conductive fibres.

These include electrochromic functions (controlled changing of colour by tuning electrical currents in circuits where there are pigments), Joule heating (changing temperature with current in the circuit, which can be used in thermal therapy devices) and wireless communications (circuits that can transmit radio waves).

We are excited about the future of silk-based wearable smart electronics and we believe our work will have many applications. We have developed a series of wearables, such as: flexible strain and pressure sensors, which can monitor detailed pulse-wave, respiration, voice, sound, micro-expressions, subtle touch and sport activity; sensors that monitor the temperature of patients or babies; dual-function sensors such as temperature-pressure sensors; stretchable thermal therapy devices, which can supply a stable temperature to keep the body warm or help to relieve pain; flexible, stretchable and dry electrodes for long-term monitoring of electrophysiology signals, such as ECG; and super-stretchable fibre-shaped supercapacitors for supplying power to the textile electronics. 

We are still designing more wearables. By integrating new techniques in our lab, we believe silk-based electronic textiles that are comfortable, reliable and sensitive, and can be used to monitor health, activities and environment, will contribute to the improvement of quality of life. Parents could remotely monitor the temperature and noise of their baby with wearable skin-like sensors, and doctors could monitor the health of elderly people wearing smart clothes.

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