NIBIB-funded engineers at UC San Diego have developed a flexible all-in-one epidermal patch that can simultaneously and continuously monitor cardiac output and metabolic levels of glucose, lactate, caffeine, or alcohol. The patch is a major step towards continuous non-invasive health monitoring of chronic conditions as well as early signals of disease development. 

Devices capable of non-invasive sensing of health status offer significant improvements in the management of chronic conditions such as diabetes and hypertension. A more ambitious goal is sensing indicators of disease onset, allowing for early intervention that may stave off a developing condition.

Now, a flexible skin patch sensor developed by engineers at the University of California San Diego (UCSD) is the most sophisticated of this type of technology to date.

“The UCSD team has figured out how to place ultrasound sensors—that monitor heart rate and blood pressure—and chemical sensors—that detect metabolites of glucose and other substances in body fluids—on the same small patch,” explained Randy King, Ph.D., director of the NIBIB program in Diagnostic and Interventional Ultrasound. “This is a great example of the type of innovative engineering NIBIB supports that has the real potential to make an enormous impact on healthcare in the U.S. and worldwide.”

The stretchable two-by- two-inch patch—and the electronic circuits printed on it—looks a bit like the face of a cartoon character with two large eyes and a mustache. The “left eye” is a chemical sensor that detects substances in sweat— lactate, which increases during exercise, as well as caffeine and alcohol. The “right eye” senses substances in the interstitial fluid (fluid in the space between cells in the body)—in this case, levels of blood glucose. The “mustache” is a row of ultrasound transducers that pulse sound waves into blood vessels and pick up the returning sound waves. Those returning signals measure blood pressure and heart rate.

The sensor is capable of measuring three parameters at once, one from each sensor. For example, simultaneous read-outs of blood pressure, glucose levels, and either lactate, alcohol, or caffeine. The lab is working on a more advanced design that would allow monitoring of all of the parameters simultaneously.

The patch has the potential to improve healthcare monitoring in a wide range of situations. "It could serve as a great tool for remote patient monitoring,” explained Sheng Xu, PhD, Assistant Professor of Nanoengineering, Bioengineering, and Electrical and Computer Engineering at UCSD and co-senior author on the study, “especially during the COVID-19 pandemic when people are minimizing in-person visits to the clinic."

The technology would benefit people in self-managing underlying conditions such as hypertension and diabetes. It could also be a game changer in more critical situations when placed on the neck or forearm of patients in intensive care units, including infants in the NICU, who need continuous monitoring of blood pressure and other vital signs—measures currently performed by invasively tethering patients to an armada of ungainly, expensive, and often noisy hospital monitors.

The new sensor patch was developed by overcoming a number of engineering hurdles. For example, the ultrasound transducers normally require a liquid gel to send and receive signals. But, that gel would interfere with the chemical sensors in close proximity on the small patch. The engineering solution was the development of a solid gel that worked with the ultrasound but could not flow into and block the function of adjacent chemical sensors.

In fact, the engineering requirements of the patch necessitated collaboration of two research groups at UC san Diego. The laboratory of Sheng Xu has pioneered work on electronic skin patches that are soft and can stretch with the skin and can monitor blood pressure. The laboratory of Joseph Wang, PhD., specializes in the development of wearables that can monitor multiple signals simultaneously—chemical, physical, and electrophysiological. Wang is the SAIC Endowed Chair and Distinguished Professor, Department of Nanoengineering at UCSD.

“The collaboration of our two labs has been absolutely essential for the development of this technology, explained Wang. “And this is just the beginning. Our combined expertise will allow us to pursue sensors that can collect even more information using this non-invasive and convenient style of patch. In addition, the current patch is still physically wired to a receiver. We are now working to add the receiver to the patch itself, which means no more wires. The patch will remotely send signals enabling extremely convenient continuous health monitoring in just about any setting.”

This research was supported by the UCSD Center of Wearable Sensors and National Institute of Biomedical Imaging and Bioengineering grant no. 1R21EB027303-01A1, CNPq, a UC MEXUS–CONACYT collaborative fellowship, the Fulbright Egyptian Scholar Program, and the Royal Golden Jubilee PhD scholarship of the Thailand Research Fund. The work was reported in Nature Biomedical Engineering.¹

1. An epidermal patch for the simultaneous monitoring of haemodynamic and metabolic biomarkers. Sempionatto JR, Lin M, Yin L, De la Paz E, Pei K, Sonsa-Ard T, de Loyola Silva AN, Khorshed AA, Zhang F, Tostado N, Xu S, Wang J. Nat Biomed Eng. 2021 Feb 15. doi: 10.1038/s41551-021-00685-1