Interstitial fluid mirrors many biomarkers found in blood and has attracted growing interest as a target for painless diagnostics. Microneedles offer a way to access this fluid through the skin, but existing designs face major limitations. Hollow needles can clog. Swellable and conventional porous needles often extract fluid too slowly or break under mechanical stress. Increasing porosity usually weakens the needle, while strengthening the structure slows fluid flow. In many porous designs, poorly connected pores further limit fluid extraction performance. Based on these challenges, there is a strong need for microneedles that combine fast fluid extraction with reliable mechanical strength.
A research team from the University of Tokyo and Seoul National University reports (DOI: 10.1038/s41378-025-01103-1) a new microneedle design in Microsystems & Nanoengineering, in 2025, that dramatically improves how quickly interstitial fluid can be collected from skin. The team built porous microneedles with precisely controlled internal channels that guide fluid efficiently while preserving structural integrity. In laboratory skin models, the microneedles extracted fluid at record rates and enabled fast glucose detection using a simple paper-based sensor, highlighting their potential for painless, point-of-care diagnostics.
The breakthrough comes from rethinking how pores are formed inside microneedles. Instead of creating random voids, the researchers assembled uniform polymer microspheres into needle-shaped molds and bonded them together. The spaces between the spheres formed continuous microchannels that acted as highways for fluid flow.
By adjusting the size of monodisperse microspheres, the team could fine-tune the width of these channels. This control proved critical. Channels that were too wide reduced capillary force, while channels that were too narrow disrupted connectivity. With the optimal design, the microneedles achieved an in vitro extraction rate of about 0.95 microliters per minute per needle, the highest reported for porous microneedles.
Surface treatment further improved performance. A thin hydrophilic coating increased fluid flow without blocking the channels or weakening the needles. Mechanical optimization ensured the microneedles penetrated skin models cleanly, without bending or breaking.
To demonstrate real-world use, the researchers integrated the microneedles with a color-changing paper sensor. Extracted fluid spread evenly through a diffusion layer, producing clear and uniform color changes. The color intensity increased linearly with glucose concentration, confirming accurate and rapid sensing directly from skin models.
"Speed and reliability are critical for practical microneedle diagnostics," said the study's senior author. "Our results show that controlling pore connectivity and channel size makes a decisive difference. We achieved both high extraction speed and sufficient strength for skin penetration, which has been difficult to realize at the same time. This design also uses low-cost, biocompatible materials, making it well suited for disposable and wearable diagnostic devices."
These microneedles could support a new generation of painless, blood-free diagnostic tools. Rapid interstitial fluid extraction enables fast monitoring of glucose and could be extended to other biomarkers such as electrolytes, metabolites, and proteins. Because the sensing method relies on simple color changes, the technology is well suited for low-cost, point-of-care testing without complex electronics. With further development, the platform could enable wearable health monitors, early disease screening, and decentralized diagnostics, particularly in settings where traditional blood testing is impractical.
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References
DOI
10.1038/s41378-025-01103-1
Original Source URL
https://doi.org/10.1038/s41378-025-01103-1
Funding information
This research has been funded and supported by Japan Science and Technology Agency SPRING (Grant number: JPMJSP2108), Japan, and Japan Society for the Promotion of Science Core-to-Core Program A (Grant number: JSPSCCA20190006), also partially supported by 2025 Hyper-Convergence Research Support Program (0681-20250036) at Seoul National University.
About Microsystems & Nanoengineering
Microsystems & Nanoengineering is an online-only, open access international journal devoted to publishing original research results and reviews on all aspects of Micro and Nano Electro Mechanical Systems from fundamental to applied research. The journal is published by Springer Nature in partnership with the Aerospace Information Research Institute, Chinese Academy of Sciences, supported by the State Key Laboratory of Transducer Technology.