Sensitive, continuous monitoring systems are needed to assess the individual constitution, vitality and performance of patients and to take effective countermeasures quickly if their health deteriorates. The latest wearable technologies, which are worn close to the body and ensure continuous measurement of vital parameters, offer this continuous monitoring.

The so-called interstitial fluid can indicate the general condition of users. Like human blood, this fluid between human cells is rich in biomarkers. Ultrathin needles made of flexible polymer material, embedded in sensory wearable systems, could be used to aid the reliable testing and tracking of these biological markers. And here's the most exciting thing: They could be used to measure molecular parameters such as glucose or lactose concentrations of the person wearing them in real time, without taking blood samples or causing any pain.

In order to manufacture polymer-based microneedles, which are thinner than a human hair, with extreme precision, sophisticated production processes are required: Using an ultrashort pulse laser, the negative needle structure that needs to be implemented is first applied to a wafer-based glass embossing master. This structure is then molded onto a 140-micrometer thin polymer material under high mechanical pressure and at a high temperature using the hot embossing process.

“Despite the use of a flexible polymer substrate, the resulting fine needles, which are only one millimeter long, are extremely mechanically stable, which is necessary when in contact with the top layer of skin. The needles, which are only 300 micrometers in diameter, also have a hollow microstructure through which the interstitial fluid is fed into the fluid channel using capillary force and transported to a portable sensor system. This then makes it possible to analyze the vital parameters recorded and indicate possible treatment options,” says prizewinner Tom Enderlein, explaining the advantages of the microneedles, the production process for which was developed by the researcher at Fraunhofer ENAS and the Center for Microtechnologies (ZfM) at Chemnitz University of Technology.

Collective strength: An EU project to help rescue teams

Enderlein’s approach to producing ultrafine microneedles is the result of the EU H2020 research and innovation project “SIXTHSENSE” (smart integrated extreme environment health monitor with sensory feedback for enhanced situation awareness), which was successfully completed in 2023.

As part of this project, over 20 partners from all over Europe developed a portable monitoring system with a closed biofeedback loop for first responders whose health and performance needs to be reliably monitored during 24-hour operations. The system enables real-time detection of risk factors that indicate a deterioration in the condition of first responders, so that countermeasures can be taken immediately.

About the Smart Systems Integration Conference (SSI)

In order to develop and discuss intelligent and sustainable system solutions for the societal challenges of today and tomorrow, SSI regularly brings together leading experts in research, industry and politics to engage in discussion, network and exchange knowledge. This event is organized every year by Fraunhofer ENAS and the European Association on Smart Systems Integration — EPoSS in cooperation with Silicon Saxony.

Scientific publication

The conference paper and the results of the research activities were published on the IEEE Xplore platform:

T. Enderlein, A. Morschhauser, J. Nestler, G. Jobst, U. Stöhr, F. Selbmann, T. Otto, Hollow Microneedle Fabrication and Characterization for Interstitial Fluid Extraction in Minimally Invasive Sensors, IEEE Xplore, 2023 Smart Systems Integration Conference and Exhibition (SSI), https://doi.org/10.1109/SSI58917.2023.10387954