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Simmers P, Yuan Y, Sonner Z, Heikenfeld J. Membrane isolation of repeated-use sweat stimulants for mitigating both direct dermal contact and sweat dilution. Biomicrofluidics 2018; 12:034101. [PMID: 30867858 PMCID: PMC6404941 DOI: 10.1063/1.5023396] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Accepted: 04/04/2018] [Indexed: 05/27/2023]
Abstract
With the device integration of sweat stimulation, sweat becomes a stronger candidate for non-invasive continuous biochemical sensing. However, sweat stimulants are cholinergenic agents and non-selective to just the sweat glands, and so, direct placement of sweat stimulants poses additional challenges in the possibility for uncontrollable transport of the stimulant into the body and challenges in contamination of the sweat sample. Reported here is membrane isolation of repeated-use sweat stimulants for mitigating direct dermal contact, dilution of the sweat stimulant, and contamination of the sweat sample. The membrane dramatically reduces passive diffusion of the sweat stimulant carbachol by roughly two orders of magnitude, while still allowing repeated sweat stimulation by iontophoretic delivery of the carbachol through the membrane and into the skin. Both in-vivo and in-vitro validation reveal feasibility for reliable integration of sweat stimulants within a wearable device for use periods of 24 h or more. In addition, advanced topics and confounding issues such as stimulant gel design, osmotic pressure, and ionic impurities are speculatively and theoretically discussed.
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Affiliation(s)
- P. Simmers
- Department of Biomedical Engineering, University of Cincinnati, Cincinnati, Ohio 45221, USA
| | | | - Z. Sonner
- Department of Electrical Engineering and Computer Science, University of Cincinnati, Cincinnati, Ohio 45221, USA
| | - J. Heikenfeld
- Department of Electrical Engineering and Computer Science, University of Cincinnati, Cincinnati, Ohio 45221, USA
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Peng R, Sonner Z, Hauke A, Wilder E, Kasting J, Gaillard T, Swaille D, Sherman F, Mao X, Hagen J, Murdock R, Heikenfeld J. A new oil/membrane approach for integrated sweat sampling and sensing: sample volumes reduced from μL's to nL's and reduction of analyte contamination from skin. Lab Chip 2016; 16:4415-4423. [PMID: 27752680 DOI: 10.1039/c6lc01013j] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Wearable sweat biosensensing technology has dominantly relied on techniques which place planar-sensors or fluid-capture materials directly onto the skin surface. This 'on-skin' approach can result in sample volumes in the μL regime, due to the roughness of skin and/or due to the presence of hair. Not only does this increase the required sampling time to 10's of minutes or more, but it also increases the time that sweat spends on skin and therefore increases the amount of analyte contamination coming from the skin surface. Reported here is a first demonstration of a new paradigm in sweat sampling and sensing, where sample volumes are reduced from the μL's to nL's regime, and where analyte contamination from skin is reduced or even eliminated. A micro-porous membrane is constructed such that it is porous to sweat only. To complete a working device, first placed onto skin is a cosmetic-grade oil, secondly this membrane, and thirdly the sensors. As a result, spreading of sweat is isolated to only regions above the sweat glands before it reaches the sensors. Best case sampling intervals are on the order of several minutes, and the majority of hydrophilic (low oil solubility) contaminants from the skin surface are blocked. In vitro validation of this new approach is performed with an improved artificial skin including human hair. In vivo tests show strikingly consistent results, and reveal that the oil/membrane is robust enough to even allow horizontal sliding of a sensor.
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Affiliation(s)
- R Peng
- School of Optical-Elect. and Comp. Engin., Univ. of Shanghai for Sci. and Tech, PR China and Novel Devices Lab, Dept. of Electrical Engin. and Computing Sys., Univ. Cincinnati., USA. www.noveldevicelab.com
| | - Z Sonner
- Novel Devices Lab, Dept. of Electrical Engin. and Computing Sys., Univ. Cincinnati., USA. www.noveldevicelab.com
| | - A Hauke
- Novel Devices Lab, Dept. of Electrical Engin. and Computing Sys., Univ. Cincinnati., USA. www.noveldevicelab.com
| | - E Wilder
- Winkle College of Pharmacy, University of Cincinnati, Cincinnati, OH 45267, USA
| | - J Kasting
- Winkle College of Pharmacy, University of Cincinnati, Cincinnati, OH 45267, USA
| | - T Gaillard
- College of Nursing, University of Cincinnati, Cincinnati, OH 45267, USA
| | - D Swaille
- P&G Corp. Technical and Research Centers, Cincinnati, OH, USA
| | - F Sherman
- P&G Corp. Technical and Research Centers, Cincinnati, OH, USA
| | - X Mao
- P&G Corp. Technical and Research Centers, Cincinnati, OH, USA
| | - J Hagen
- Air Force Research Laboratory, 711th Human Performance Wing, Wright Patterson AFB, OH 45433, USA
| | - R Murdock
- Air Force Research Laboratory, 711th Human Performance Wing, Wright Patterson AFB, OH 45433, USA
| | - J Heikenfeld
- Novel Devices Lab, Dept. of Electrical Engin. and Computing Sys., Univ. Cincinnati., USA. www.noveldevicelab.com
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Sonner Z, Wilder E, Heikenfeld J, Kasting G, Beyette F, Swaile D, Sherman F, Joyce J, Hagen J, Kelley-Loughnane N, Naik R. The microfluidics of the eccrine sweat gland, including biomarker partitioning, transport, and biosensing implications. Biomicrofluidics 2015; 9:031301. [PMID: 26045728 PMCID: PMC4433483 DOI: 10.1063/1.4921039] [Citation(s) in RCA: 335] [Impact Index Per Article: 37.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2015] [Accepted: 04/30/2015] [Indexed: 05/02/2023]
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.
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Affiliation(s)
- Z Sonner
- Department of Electrical Engineering and Computer Systems, University of Cincinnati , Cincinnati, Ohio 45221, USA
| | - E Wilder
- Winkle College of Pharmacy, University of Cincinnati , Cincinnati, Ohio 45267, USA
| | - J Heikenfeld
- Department of Electrical Engineering and Computer Systems, University of Cincinnati , Cincinnati, Ohio 45221, USA
| | - G Kasting
- Winkle College of Pharmacy, University of Cincinnati , Cincinnati, Ohio 45267, USA
| | - F Beyette
- Department of Electrical Engineering and Computer Systems, University of Cincinnati , Cincinnati, Ohio 45221, USA
| | - D Swaile
- P&G Sharon Woods Innovation Center , Cincinnati, Ohio 45241, USA
| | - F Sherman
- P&G Beckett Ridge Technical Center , West Chester, Ohio 45069, USA
| | - J Joyce
- P&G Beckett Ridge Technical Center , West Chester, Ohio 45069, USA
| | - J Hagen
- 711 Human Performance Wing, Human Effectiveness Directorate, Air Force Research Laboratory , Wright-Patterson Air Force Base, Dayton, Ohio 45233, USA
| | - N Kelley-Loughnane
- 711 Human Performance Wing, Human Effectiveness Directorate, Air Force Research Laboratory , Wright-Patterson Air Force Base, Dayton, Ohio 45233, USA
| | - R Naik
- Functional Materials Division, Materials and Manufacturing Directorate, Air Force Research Laboratory , Wright-Patterson Air Force Base, Dayton, Ohio 45233, USA
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