A prototype smart ring that analyses sweat in real time could push wearable health tracking beyond fitness metrics, offering researchers a glimpse into how future devices may continuously monitor key metabolic biomarkers without the need for repeated blood tests.
Study: A fully integrated smart ring for daily biochemical monitoring. Image credit: PeopleImages/Shutterstock.com
A prototype smart ring that continuously tracks multiple biochemical markers in sweat could bring laboratory-style metabolic monitoring to the finger. The wearable device can simultaneously measure up to four biomarkers, including glucose, ketone, uric acid, lactate, ascorbic acid, and alcohol, to provide real-time insights into metabolic health. The study is published in Nature Communications.
Smart ring expands health tracking beyond vital signs
Wearable smart rings are gaining popularity worldwide, mainly because of customizable features, compact design, and comfort of wearing. Several big companies are making smart rings that can simultaneously monitor various biophysical parameters, including skin temperature, sleep pattern, heart rate variability, calories, and blood oxygen levels.
These smart rings, mainly used as wellness and fitness trackers, can alert users about potential health irregularities. However, these devices can provide only physiological information, lacking features to track molecular and metabolic changes that drive physiological health.
Researchers at the University of California San Diego developed and validated a Continuous Health Analyzing Ring Module (CHARM), a compact, fully integrated wearable smart ring capable of continuous real-time monitoring of multiple biomarkers in sweat.
Continuous measurements of biomarkers are crucial for gaining timely and personalized insights, as episodic measurements often fail to detect rapid biomolecular dynamics critically related to favorable or adverse health outcomes.
CHARM – key features
CHARM is a highly compact smart device with an external diameter of 3 centimeters that can be worn comfortably at the ring location. The device can measure several biochemical markers, including glucose, ketone, ascorbic acid, uric acid, lactate, and alcohol from sweat, which is passively harvested at the skin surface using an osmotic hydrogel that creates a pressure gradient, without requiring exercise or electrical stimulation.
This fully integrated device contains all necessary biomarker sensors, low-power electronics, and a flexible battery. The left compartment of the device is designed to draw sweat passively using an osmotic hydrogel, a soft polymer that creates a pressure gradient to pull fluid from the skin painlessly.
The sweat is then analyzed by multiplexed electrochemical sensor arrays within the same compartment, leading to simultaneous and real-time tracking of four biomarkers at a time. The researchers established subject-specific calibration factors through repeated measurements in order to convert the measured sensor current at the ring site into estimated blood-equivalent concentration values. These calibration factors enable more personalized insight into the biomarker trends. In repeated experiments with newly prepared sensor patches, this personalized calibration remained stable for up to 2 months.
The right compartment of the device contains a flexible zinc-silver oxide rechargeable battery that supplies power for up to 12 hours of operation between charges. Biomarker information generated through sensors is wirelessly transferred to a connected Bluetooth-enabled device for real-time display; the prototype experiments used a custom MATLAB interface rather than a consumer smartphone app.
Functional validation
CHARM’s biomarker monitoring efficacy was validated under diverse conditions. The findings indicated that the device performed well in initial temperature, cytotoxicity, and on-body compatibility tests. It also demonstrated high analytical accuracy in preliminary studies involving healthy participants and individuals with type 1 diabetes, highlighting its potential for non-invasive metabolic monitoring.
Specifically, the researchers examined the relative change in sensor current and blood concentration from a specific stimulus, and used a personalized calibration model to convert the measured sensor current over time into an estimate of the corresponding blood glucose concentration based on sweat measurements.
The calculated estimated sweat-based blood glucose concentration showed a mean absolute relative difference of approximately 13.7% against its corresponding blood concentration values. The other biomarkers also showed strong correlations with their respective blood profiles, highlighting the effectiveness of the device as a promising minimally invasive, sweat-based monitoring approach, although the study involved a limited number of participants and larger clinical studies are still needed.
Prototype accurately tracked multiple biomarkers during testing
The study describes the development and validation of a compact, user-friendly, wearable smart ring, CHARM, which exhibits high accuracy in simultaneously tracking multiple sweat biomarkers in real-time, providing a promising platform for future metabolic health, diabetes, disease monitoring and nutritional tracking. Continuous monitoring of glucose and ketone can potentially provide additional information to support diabetes management decisions in the future. However, the device was not evaluated for insulin dosing or closed-loop therapy.
Notably, the integrated sensor–microfluidic architecture used in the device maintained participant-specific calibration coefficients for approximately two months in repeated testing with newly prepared sensor patches. This suggests that frequent recalibration may eventually be reduced, although the system still relies on initial reference measurements and requires further validation under broader real-world conditions.
The researchers believe that the device can be improved further by making it more waterproof. This can be done by changing the hinge-lock design to a fully enclosed concentric configuration, in which all components would be sealed within a comfortable, rubber-like, stretchable cover.
The researchers did not account for the physiological time lag correction between blood and sweat biomarkers. However, they mentioned that, as commonly used in commercial continuous glucose monitors, lag correction algorithms can be easily implemented in the electronic circuit of this device.
The device needs further validation in diverse clinical settings and across large diabetic cohorts. To enable long-term, multi-day monitoring, the hydrogel technology needs further improvements for prolonged sweat extraction. The authors also note that additional studies are needed to evaluate performance across a wider range of physiological conditions and to strengthen evidence for long-term clinical use.
The researchers are planning to develop multimodal chemo-physical hybrid rings to measure key vital signs. For the clinical deployment of CHARM as a practical, user-friendly multi-biomarker tracking device, they highlight the need to address commercial issues such as insurance coverage and reimbursement.