Thread-based dialysis-like microfluidic platform for tissue-embedded continuous monitoring

Reliable and continuous access to interstitial fluid (ISF) remains a major challenge for wearable and tissue-embedded biosensing systems. Conventional microneedle-based methods, while widely adopted, often exhibit variable sampling efficiency across different skin types and are prone to performance fluctuations during motion. Herein, we introduce a tissue-embedded thread-based open capillary microfluidics-based sampling that enables minimally invasive, pump-free, and reliable continuous monitoring of small molecules from ISF. The system employs open capillary-driven microfluidic channels in textile threads, which facilitate the partial separation of small molecules from complex biological matrices, mimicking a microdialysis process. The continuous sampling is achieved through evaporation-driven capillary pressure, eliminating the need for an external pump. The experimental results confirm the numerical simulation of diffusion-controlled and capillary-driven transport of analytes in ISF. The performance of the developed platform was validated in phantom skin (agarose gel) and porcine skin models, confirming stable, long-duration sampling and continuous biomarker detection in tissue fluid. For practical applications, the developed platform was validated for real-time measurement of glucose and pH utilizing flexible electrochemical sensors. The sensor exhibited sensitivities of 0.027 µA/glu (mg/dL) and −56.25 mV/pH change, respectively. These findings establish thread-based dialysis-like open capillary microfluidics sampling as a promising approach for reliable, tissue-embedded monitoring of biomarkers in ISF for tissue-embedded biosensing applications.