Battery-Free Sweat Sensor Technology Inspired by Plants
Jenn U posted on June 02, 2016 |
Advancement in microfluidics could improve wearable medical devices.
Coloured fluid is conducted past a sensor by evaporation and capillary action.
Coloured fluid is conducted past a sensor by evaporation and capillary action. (Image courtesy of Eindhoven University of Technology.)
There’s a lot you can tell about a person from their sweat, and medical and fitness technology has been working on ways to monitor this data.

Lactic acid in sweat can indicate muscular stress levels during exercise, acidity levels can indicate skin disease and saline concentrations can provide information about those with cystic fibrosis.

Wearable sweat sensors can collect this data and use it to provide this and other health information about the wearer.

In order to maintain continuous monitoring, however, a continuous flow of sweat is needed.  Ideally, this should be done without moving parts or electrical power sources, which could break while monitoring or cause injury to the wearer.

Fortunately, an engineering research team has developed a potential solution, inspired by the method plants use to transport water.

Copying Plants to Create Wearable Sweat Sensors

 Xylem is a material in plants that allows water to be transported from the roots to the shoots and leaves, hydrating the plant as well as transporting water-soluble nutrients by the process of transpirational pull. Evaporation at the top of the plant creates the necessary pressure difference to pull water through xylem tubes by capillary action. 

The team’s design uses similar micro-channels to conduct sweat past a sensor by the same capillary action. Sweat is collected from the skin using an absorbent paper and evaporates from a porous structure at the outlet analogous to the pores in a plant’s leaves.

The sensor prototype, as used in the experiments.
The sensor prototype, as used in the experiments. (Image courtesy of Eindhoven University of Technology)
These structures are created within three thin layers of PET, using laser microfabrication. The embedded sensor in the prototype electrochemically monitors pH levels; however, alternate designs could use a variety of sensors to measure sweat contents for other applications.

Although the sensor itself requires electricity, the mechanism of liquid flow allows this device to use much less power than previous wearable sweat sensor devices. This design is one of many recent examples of technology inspired by natural processes, demonstrating that engineering innovations can often benefit from nature instead of opposing it.

The research was conducted at Eindhoven University of Technology, headed by Professor Jaap den Toonder with PhD student Chuan Nie

More information about Professor den Toonder’s laboratory can be found here, and the full research article is available from Science Direct

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