title: The microfluidics of the eccrine sweat gland, including biomarker partitioning, transport, and biosensing implications.
abstract: Non-invasive and accurate access of biomarkers remains a holy grail of the biomedical community. Human eccrine sweat is a surprisingly biomarker-rich fluid which is gaining increasing attention. This is especially true in applications of continuous bio-monitoring where other biofluids prove more challenging, if not impossible. However, much confusion on the topic exists as the microfluidics of the eccrine sweat gland has never been comprehensively presented and models of biomarker partitioning into sweat are either underdeveloped and/or highly scattered across literature. Reported here are microfluidic models for eccrine sweat generation and flow which are coupled with review of blood-to-sweat biomarker partition pathways, therefore providing insights such as how biomarker concentration changes with sweat flow rate. Additionally, it is shown that both flow rate and biomarker diffusion determine the effective sampling rate of biomarkers at the skin surface (chronological resolution). The discussion covers a broad class of biomarkers including ions (Na(+), Cl(-), K(+), NH4 (+)), small molecules (ethanol, cortisol, urea, and lactate), and even peptides or small proteins (neuropeptides and cytokines). The models are not meant to be exhaustive for all biomarkers, yet collectively serve as a foundational guide for further development of sweat-based diagnostics and for those beginning exploration of new biomarker opportunities in sweat.
authors.affiliation: Department of Electrical Engineering and Computer Systems, University of Cincinnati , Cincinnati, Ohio 45221, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Sonner
authors.affiliation: Winkle College of Pharmacy, University of Cincinnati , Cincinnati, Ohio 45267, USA.
authors.forename: E
authors.initials: E
authors.lastname: Wilder
authors.affiliation: Department of Electrical Engineering and Computer Systems, University of Cincinnati , Cincinnati, Ohio 45221, USA.
authors.forename: J
authors.initials: J
authors.lastname: Heikenfeld
authors.affiliation: Winkle College of Pharmacy, University of Cincinnati , Cincinnati, Ohio 45267, USA.
authors.forename: G
authors.initials: G
authors.lastname: Kasting
authors.affiliation: Department of Electrical Engineering and Computer Systems, University of Cincinnati , Cincinnati, Ohio 45221, USA.
authors.forename: F
authors.initials: F
authors.lastname: Beyette
authors.affiliation: P&G Sharon Woods Innovation Center , Cincinnati, Ohio 45241, USA.
authors.forename: D
authors.initials: D
authors.lastname: Swaile
authors.affiliation: P&G Beckett Ridge Technical Center , West Chester, Ohio 45069, USA.
authors.forename: F
authors.initials: F
authors.lastname: Sherman
authors.affiliation: P&G Beckett Ridge Technical Center , West Chester, Ohio 45069, USA.
authors.forename: J
authors.initials: J
authors.lastname: Joyce
authors.affiliation: 711 Human Performance Wing, Human Effectiveness Directorate, Air Force Research Laboratory , Wright-Patterson Air Force Base, Dayton, Ohio 45233, USA.
authors.forename: J
authors.initials: J
authors.lastname: Hagen
authors.affiliation: 711 Human Performance Wing, Human Effectiveness Directorate, Air Force Research Laboratory , Wright-Patterson Air Force Base, Dayton, Ohio 45233, USA.
authors.forename: N
authors.initials: N
authors.lastname: Kelley-Loughnane
authors.affiliation: Functional Materials Division, Materials and Manufacturing Directorate, Air Force Research Laboratory , Wright-Patterson Air Force Base, Dayton, Ohio 45233, USA.
authors.forename: R
authors.initials: R
authors.lastname: Naik