Silk patch monitors health, no sweat

By Paul Biegler

A team of scientists in China has created a wearable sweat monitor out of silk that measures a suite of health biomarkers in real time, including levels of glucose, lactate and potassium.

It’s a leap in materials science that promises new ways of tracking endurance and dehydration in exercise, as well as diseases such as diabetes and kidney failure. 

The research, led by Yingying Zhang from the Department of Chemistry at Tsinghua University in Beijing, took its inspiration from a small worm that has been punching above its weight for millennia.

The humble silkworm weaves a single, strong and uniform thread of silk up to 1.5 kilometres long in the process of building its cocoon.

That epic example of personal housing has fed the Chinese silk industry for over 5000 years and also, the researchers write, “[endows] silk fabric with good uniformity and high mechanical strength”.

Silk is famed for its comfort and breathability too, but none of the above a sweat sensor make. Which is where Zhang’s team availed themselves of some very deft new tech.

They heated silk up to 900 degrees Celsius, a natural process that induces a profound chemical change that “carbonises” the fibre.

Imbued with this new carbon structure, silk goes from one of the world’s most desirable fabrics to a top-of-the-range electrode, capable of measuring things in sweat that induce an electric current.

Using a laser device to construct six individual sensors in a patch of the material, Zhang’s team came up with a biscuit-sized swatch of fabric that could measure glucose, lactate, sodium, potassium, ascorbic acid and uric acid. {%recommended 9844%}

“[The] woven, porous structure provided the carbon textile good electrical conductivity… and good water wettability for efficient electron transmission and abundant access to reactants, enabling it to serve as an excellent working electrode in electrochemical sensors,” they write.

The researchers do not overstate the sweat patch’s potential, but its applications would appear to be many and vital. The six biomarkers are relevant to diabetes, endurance training, dehydration, kidney disease, tissue health and gout, among others.

Moreover, as the researchers point out, standard tests often involve pulling blood samples that have to be transported, with the associated time lag, to big expensive machines for analysis.

Zhang’s team, on the other hand, had five volunteers try out the patch worn on their upper arms while riding a stationary bike. The silk sensors then Bluetoothed to a smartphone that gave the cyclists an instantaneous readout of their health parameters.

And the results, write the authors, were accurate.

The team compared the glucose readings with samples sent off for the benchmark test, called high-performance liquid chromatography – mass spectrometry. The two levels were “comparable”.

The group also subjected the fabric to bending and repeated use for up to four weeks with “negligible changes” in performance.

“The versatility, high sensitivity, and remarkable stability of the sweat analysis patch, along with its facile fabrication process, hold promising practical applications in real-time monitoring of human health,” they conclude.

The study appears in the journal Science Advances.