Macroporous-channel hollow microneedles enable vacuum-free interstitial fluid sampling and on-patch sensing

Microneedle (MN) devices that sample skin interstitial fluid (ISF) without an external vacuum offer strong point-of-care potential, but are often limited by insufficient extraction flux and fabrication complexity. Here, we present macroporous-channel hollow microneedles (MPCHMNs) that integrate three features in a single photopatterning step: a rigid polymer shell for mechanical support, an interconnected micrometer-scale porous network formed by porogen removal, and an axially enriched macroporous conduit formed by a percolated chain of interconnected spherical cavities. This architecture establishes multiscale capillarity that drives vacuum-free ISF sampling. When coupled to a paper-wick collector or an on-patch sensing module, the interface enables rapid wicking and on-device readout without pumps or tubing. In ex vivo skin models and in vivo rat studies, MPCHMNs achieved ISF yields and start-up times that were comparable to those of negative-pressure collectors under matched conditions, while maintaining agreement between ISF and paired blood measurements for representative electrolytes and metabolites. Electrochemical modules quantified potassium (potentiometry) and glucose (amperometry), and a colorimetric panel reported glucose, acetoacetate, and creatinine. Viewed as a capillarity-driven transducer, MPCHMNs link structure to function and reduce system complexity. The resulting disposable, compact format supports vacuum-free ISF sampling and on-patch analysis, offering a practical path toward minimally invasive, near-patient monitoring. STATEMENT OF SIGNIFICANCE: We introduce macroporous-channel hollow microneedles that combine a rigid polymer shell, an interconnected macroporous network, and an axial lumen created in a single photopatterning step. This architecture establishes multiscale capillarity that supports vacuum-free dermal interstitial-fluid sampling and enables on-patch electrochemical or colorimetric readout without pumps or tubing. Across ex vivo skin models and in vivo rats, sampling yields and analytical agreement with paired blood measurements were comparable to negative-pressure collectors under matched conditions, while reducing system complexity. Treating the microneedle as a capillarity-driven transducer links structure to function and offers a practical route to compact, disposable devices for minimally invasive, near-patient monitoring.