On-body test configuration. (a) A photograph of Chem–Phys hybrid patch. (b) Location of the Chem–Phys patch for mounting on the human body—the fourth intercostal space of the chest. (c) Cycling resistance profile for on-body tests. (d) Effect of amperometric measurement on the electrocardiogram signal before cycling (no sweat state) and during cycling (sweating state).
Engineers at the UC San Deigo have developed the first flexible wearable device capable of monitoring both biochemical and electric signals in the human body. The Chem-Phys patch records electrocardiogram (EKG) heart signals and tracks levels of lactate, a biochemical that is a marker of physical effort, in real time. The device can be worn on the chest and communicates wirelessly with a smartphone, smart watch or laptop. It could have a wide range of applications, from athletes monitoring their workouts to physicians monitoring patients with heart disease.
Nanoengineers and electrical engineers at UC San Diego Center for Wearable Sensors worked together to build the device, which includes a flexible suite of sensors and a small electronic board. The device also can transmit the data from biochemical and electrical signals via Bluetooth.
(a) Schematic showing the screen-printing process. (b) Image of the Chem–Phys printing stencil. (c) An array of printed Chem–Phys flexible patches. (d) Image of a Chem–Phys patch along with the wireless electronics. (e) Schematic showing the LOx-based lactate biosensor along with the enzymatic and detection reactions. (f) Block diagram of the wireless readout circuit.
Researchers used screen printing to manufacture the patch on a thin, flexible polyester sheet that can be applied directly to the skin. An electrode to sense lactate was printed in the center of the patch, with 2 EKG electrodes bracketing it to the left and the right. Engineers went through several iterations of the patch to find the best distance between electrodes to avoid interference while gathering the best quality signal. They found that 4cm between the EKG electrodes was optimal.
In-vitro characterization of Chem–Phys hybrid patch.
Researchers also had to make sure the EKG sensors were isolated from the lactate sensor. The latter works by applying a small voltage and measuring electric current across its electrodes. This current can pass through sweat, which is slightly conductive, and can potentially disrupt EKG measurements. So the researchers added a printed layer of soft water-repelling silicone rubber to the patch and configured it to keep the sweat away from the EKG electrodes, but not the lactate sensor. The sensors were then connected to a small custom printed circuit board equipped with a microcontroller and a Bluetooth Low Energy chip, which wirelessly transmitted the data gathered by the patch to a smartphone or a computer.
The patch was tested on 3 males on their chest while doing 15 to 30 minutes of intense activity on a stationary bike. Two of the subjects also wore a commercial wristband heart rate monitor. The data collected by EKG electrodes on the patch closely matched the data collected by the commercial wristband. The data collected by the lactate biosensor follows closely data collected during increasing intensity workouts in other studies.
Next steps include improving the way the patch and the board are connected and adding sensors for other chemical markers, such as magnesium and potassium, as well as other vital signs. Physicians working with Wang and Mercier are also excited about the possibility of analyzing the data from the two signals and see how they correlate.
http://www.eurekalert.org/pub_releases/2016-05/uoc–etf051916.php http://www.nature.com/ncomms/2016/160523/ncomms11650/full/ncomms11650.html
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