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New Durable, Low-Power, Wearable Paper-Based Device to Analyze Sweat

Various biomolecules contained in human sweat are being explored by researchers for noninvasive medical testing. However, analysis of sweat for research usually involves high cost, and devices tend to work reliably only for a limited duration.

The evaporation of sweat on paper pads could be used for fluid transport in wearables over long periods of time. The resulting dry layer of caked salts would preserve a “time-stamped” record of biomarkers of interest. Image Credit: Orlin D. Velev and co-authors, NC State University.

At North Carolina State University, scientists have developed a paper-based device as a wearable model that can gather, transfer, and analyze sweat as part of next-generation wearable technology.

The device uses a process called capillary action, similar to water transport in plants, to wick fluid mimicking the features of human sweat by evaporation to a sensor for up to 10 days or more. The researchers have described their study in the Biomicrofluidics journal from AIP Publishing.

The study was a collaborative work between Orlin Velev and Michael Dickey, supervising the research of graduate students Timothy Shay and Tamoghna Saha, as part of the NSF Center for Advanced Self-Powered Systems of Integrated Sensors and Technologies.

The aim of the researchers is to make use of the properties of paper to achieve the development of more cost-effective and durable devices.

For any device that analyzes sweat, one main issue is that sweat consists of salt, which, when evaporation occurs, gets deposited on the device and interrupts the fluid flow. The new device packs deposited salt crystals densely, enabling prolonged use and a means to examine the timing of when the chemicals are present in the sweat.

We expected that the flow of the model sweat will be suppressed by the deposition of a salt layer inside the drying pad. By following the flow of model sweat, we found, quite surprisingly, that such a simple paper construct can achieve continuous sweat pumping and disposal for very long periods.

Orlin D. Velev, Professor, North Carolina State University

Moreover, the paper microfluidic devices could be employed as wearable patches to evaluate the path of specific diseases or how well patients stick to drug regimens.

The biological markers or drug metabolites that seep in the patient’s sweat over a long period will be captured on the paper pad and preserved in a time-stamped manner to be analyzed later, similar to tree rings preserving the record of tree development.

Michael D. Dickey, Study Author, North Carolina State University

The device is driven by the wicking of the liquid via paper and avoids the need for external power. Its affordable price could also be helpful for economical medical testing in under-resourced patient populations who find it difficult to gain access to such testing. Skin patch assays of this type could eliminate the need to draw blood samples.

The researchers have started an array of human trials to investigate how the technology offers biomarker analysis for a longer duration, and they seek to restart the trials when pandemic safety measures make it possible to progress further.

Journal Reference:

Shay, T., et al. (2020) Principles of long-term fluids handling in paper-based wearables with capillary-evaporative transport. Biomicrofluidics.


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