We have all heard the timeless mantra that regular exercise, a healthy diet, and sufficient sleep are vital to our overall wellbeing. In recent years, fitness trackers and smartwatches have gained substantial popularity as tools for monitoring our daily activity and informing us of how well we are adhering to this three-point plan for healthy living. The average fitness tracker can provide data about distance traveled, heart rate, calories burned, and sleep patterns. However, beyond the in-app notifications that alert users to when they’ve fallen short of their fitness goals, there is no clear correlate for how the data collected will translate into health improvement. Fitness devices aren’t readily built to be that intuitive. Our bodies’ physiology already has a way of telling us when we’ve adopted bad eating habits, had a poor night’s sleep, or strayed away from the New Year’s resolution to exercise regularly.
The current market of wearables is still faced with several challenges.
First, most of these devices fail to make a lasting impression on users. A study by Endeavour Partners, a technology and digital business think tank, reported that a third of U.S. consumers abandoned their wearable devices within six months of purchase. This could be attributed to the average user neglecting to put the device back on after every recharging session. Users may view this as a limitation of the device because of the discontinuity in monitoring their activity. The next generation of wearable sensors needs to aim for a “wear-and-forget” concept that limits or completely eliminates the need for recharge. Additionally, It has become increasingly accepted that wearing a fitness monitor on your wrist is not a sufficient incentive to change human behavior to make better health conscience decisions. Typically, if the device can offer functionality that can help change the habits of users, then it has the potential to promote sustainable behavior in their physical activity and foster long-term health outcomes.
Furthermore, the accuracy of current wearable technology is still a center of controversy. On January 5, a nationwide class action lawsuit was filed against Fitbit, claiming that the heart rate monitor feature on two of the company's wrist-based devices dangerously underestimated rates during workouts by as much as 75 beats per minute when compared to readings from an electrocardiogram. In response to the claim, Fitbit issued a statement that its devices are not medical monitors and should not be regarded as a gold standard. The National Health Service has further stressed the limitations of current consumer fitness wearables by emphasizing that they are regulated under the “wellness” category, and by no means do they compare to the standards of medical equipment nor offer a solution for an effective, reliable method for health monitoring.
This poses two important questions:
How can wearable devices be leveraged to provide accurate data in real time that can improve quality of life and revolutionize health care? And, what if wearable technology meant we could be wired for life to get reliable readout of our body’s chemistry and monitor disease progression as well as to predict impending onset of bodily distress? A recent report by Forrester Research found that consumers have a preference for health-based wearable technology that is wrist-based (28%) or clipped onto clothing (29%). It is only a matter for the next big revolution for wearable devices to improve on the limitations of the modern fitness tracker and gage current consumer interests. This puts a considerable amount of pressure on wearable sensor developers to provide proof of principle that their device is capable of improving health outcome in users.
The most recent contender to try and bridge the gap between a fitness tracker and a medical sensor is a wearable sweat-sensing device created by Professor Ali Javey’s research team at the University of California, Berkeley. He and his colleagues reported the applications and features of this device this year in January 28th in the journal Nature with the goal of fully demonstrating the potential of wearable sensor technology for the realization of personalized medicine. Current applications for sweat analysis include disease diagnosis, drug abuse detection and optimization of athletic performance. However, across all these applications, the sample collection and analysis of the data requires several hours of laboratory processing.
Compared to other consumer health monitors, the sweat-sensor designed by Prof. Javey and his team is the first ever, fully integrated wearable sensor array (FISA) system to provide continuous, non-invasive monitoring of metabolites and electrolytes in sweat. Utilizing the most current advances in wearable technology, the FISA consists of a flexible electronics circuit board attached to the flexible biochemical sensor array that can be integrated into a wristband or headband. The key feature here is flexibility, which maximizes the skin-to-sensor contact and durability. Once sweat makes contact with the sensory array, electrical signals are amplified, filtered and calibrated by the skin temperature sensor. The fully processed data is transmitted via Bluetooth to a custom-designed smartphone app for user review. This is an impressive achievement, considering that the FISA is scalable to a smaller chip as well as readily adaptable to integrate additional biochemical sensors.
The fully-integrated sweat sensory array system can selectively and simultaneously multiplex the measurements of metabolites (glucose and lactate), electrolytes (sodium (Na+) and potassium (K+), and skin temperature to generate a ‘sweat profile’ for the wearer. This panel of five biosensors was selected based on how they can be immediate and effective biomarkers for understanding an individual’s physiological state.
Specifically, an excessive loss of Na+ and K+ could be utilized as predictors of hypokalemia, dehydration, electrolyte imbalance and cystic fibrosis diagnosis.
Additionally, several studies have reported that sweat glucose levels are well correlated with blood glucose. Therefore, monitoring of glucose in sweat can be a vital non-invasive biomarker for managing diabetes. Analyzing sweat lactate can serve as a good predictor of early signs of pressure ischemia, or lack of blood flow to a certain part of the body; lactate analysis can also monitor physical performance as a product of anaerobic metabolism, a back-up metabolic process that occurs after muscles under exertion have exhausted their glucose supply.
The wearer’s skin temperature can be clinically informative of cardiovascular health and skin injuries such as pressure ulcers. More importantly, inclusion of a temperature biosensor improves on the issue of accuracy previously associated in other sweat sensors by providing essential calibration functionality to compensate for the temperature variations across the chemical sensors.
The design team sees their device as a platform for providing vital personalized diagnostics and informing users of early warnings of sudden changes in their physiological state. “The idea is to have this thumbs-up or thumbs-down device that will give real-time information: it could provide an alarm that you need to take some medication, or that you are getting dehydrated and need to drink some water,” says Professor Javey. The scalable properties of this platform make it readily applicable for large-scale clinical studies for medical applications.
Professor Javey has applied for patents on the technology used in the FISA and admits that there are still several challenges to overcome before this sweat-sensory array can be integrated into a commercially available wearable fitness band. While the group reports that each biochemical sensor retains excellent selectivity and specificity across varying concentrations of target biomarkers, it is important to note that in their test conditions, a sufficient sweat sample had to be generated by users in order to collect enough data. Considering that we are not always sweating, steps would have to be taken to integrate a feature on the devices that locally stimulates sweat for applications outside athletic performance. Professor Javey further expands on the current stance of the NHS on wearable devices by reiterating that sweat sensors will never replace blood tests because the content of our sweat is too variable and not as tightly regulated at the molecular level as blood is.
The most important factor that will truly determine the success of wearable sensors like the FISA and others like it is whether it can improve human health behavior. Wearable devices have the potential to decentralize and personalize health care by making it more proactive in catering to the specific health needs of the wearer. The possibility of being wired for life for continuously monitoring of our own health status can fundamentally revolutionize how we interact with physicians and pave the way for precision medicine.
Wei Gao, Sam Emaminejad, Hnin Yin Yin Nyein, Samyuktha Challa, Kevin Chen, Austin Peck, Hossain M. Fahad, Hiroki Ota, Hiroshi Shiraki, Daisuke Kiriya, Der-Hsien Lien, George A. Brooks, Ronald W. Davis, Ali Javey. Fully integrated wearable sensor arrays for multiplexed in situ perspiration analysis. Nature, 2016; 529 (7587): 509 DOI: 10.1038/nature16521