A newly developed smart ring can measure as many as four distinct chemical biomarkers at once by sampling sweat from the finger - and it can do so without the wearer needing to exercise or visibly perspire.
Engineers describe it as the first fully integrated smart ring designed for continuous, everyday biochemical monitoring, with the ability to track glucose, ketones, vitamin C, uric acid, lactate and alcohol.
The work was carried out by engineers at the University of California, San Diego, in the laboratory led by Joseph Wang.
Their prototype is called CHARM - short for Continuous Health Analyzing Ring Module. It has a mass of 5.1 grams and an outer diameter of roughly 3 centimetres.
More than a fitness tracker
“Commercial rings only provide biophysical information, but they lack molecular information about biochemical markers that offer deeper insights about an individual’s health status,” said lead author Tamoghna Saha, a postdoctoral researcher in Wang’s lab.
Most smart rings currently sold focus on metrics such as heart rate, temperature and movement. By contrast, this ring adds a molecular layer by capturing biochemical markers that indicate what is going on in the body at a chemical level.
To make that possible, the engineers constructed the ring as two connected sections. One half houses the sweat-extraction unit, a sensor array and the microfluidic channels.
The other half contains the flexible battery and electronics, with the two sides joined via a connector pad.
Monitoring without breaking a sweat
Many sweat-based sensors rely on exercise or exertion to create enough perspiration for analysis, but this ring does not depend on that at all.
Instead, it pulls sweat passively through the skin by osmosis, using an approach that Saha specifically developed for this application.
Because collection is passive, the ring can capture biochemical measurements continuously during day-to-day life, whether the wearer is moving about or remaining still.
In tests, the osmotic extraction drew sweat at a relatively consistent rate across different fingers and across different people.
The technique yielded about five to six times more fluid than the skin would naturally provide at that location, while still avoiding visible sweating or discomfort.
“A ring capturing dynamic molecular information in real time would be extremely useful for making informed decisions regarding health, diet, and lifestyle,” Wang said.
Tested against medical devices
To evaluate accuracy, the researchers conducted trials involving both healthy volunteers and people living with type 1 diabetes.
Glucose values recorded by the ring closely mirrored readings from commercial continuous glucose monitors.
Its ketone measurements also aligned with results from commercial blood ketone meters, which is a notable cross-check given how widely those devices are already used in clinical and personal monitoring.
In one test session, a participant with type-1 diabetes wore the ring while eating meals, taking a ketone supplement, drinking alcohol, exercising and eating sweets to address a fall in blood sugar.
During that period, the ring registered post-meal glucose increases, a ketone rise following the ketone drink, a lactate jump after moderate exercise, and an increase followed by a gradual decrease in blood alcohol after a glass of wine.
Overall, those patterns matched reasonably well with standard blood-test results collected alongside the ring’s measurements.
Among healthy volunteers, the device likewise picked up smaller meal-related glucose fluctuations and ketone changes after a supplement drink.
It also registered shifts in uric acid after participants ate sardines - a purine-rich food known to increase uric acid levels.
Packed with tiny technology
The team produced the biomarker ring as a fully integrated prototype, combining biomarker sensing, low-power electronics and a flexible battery within the ring’s body.
Biomarker readings are sent wirelessly to a companion smartphone app.
For sweat collection, the ring uses an osmotic hydrogel - a soft polymer that creates a pressure gradient, allowing fluid to be drawn through the skin without pain.
The principle is comparable to the way water moves from soil into a plant through its roots and up into its leaves.
After collection, the sweat is assessed by an electrochemical sensor array built into the ring.
By taking repeated measurements over time, the system determines subject-specific calibration factors that translate raw electrical-current signals into concentration values.
This makes it possible to provide more personalised insight into how an individual’s biomarkers change over time.
Importantly, the personalised calibration remained valid for around two months before needing updating. As a result, wearers would not need to do a daily finger-prick comparison blood reading to keep the ring calibrated.
Packing everything into a ring
The ring is powered by a flexible, rechargeable zinc–silver oxide battery that can provide up to 12 hours of continuous use between charges.
The electronics board is smaller than a US quarter coin (around 24 mm across), a strikingly small footprint given the system’s requirements.
A 3D-printed polymer outer shell provides the ring’s final form.
The battery was also shown to withstand repeated bending and folding, maintaining a stable charge after being flexed into tight loops thousands of times.
“Such integration onto the small footprint of a ring form factor is amazing,” Wang said.
The technology still needs work
The researchers emphasise that the current prototype is not yet ready to be used as an everyday consumer product.
At present, the ring is not fully waterproof, although the team expects a more completely sealed design could address this in later versions.
They also point out that the device has not yet been evaluated in a large, diverse population of people with diabetes.
In addition, its performance has not been assessed across the full spectrum of blood-sugar extremes - including severe hypoglycaemia - that a commercial device would need to handle consistently.
Using the ring over multiple days rather than for a single day will probably require further improvements to the hydrogel and components that are easier to replace.
Before the device is practical for everyday, long-term use by people managing diabetes, developers will need to incorporate replaceable sensor cartridges or rechargeable battery modules.
Image credit: David Baillot/UC San Diego Jacobs School of Engineering
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