Improved devices have been proposed for collecting sweat for biochemical analysis — especially for determination of the concentration of Ca2+ ions in sweat as a measure of loss of Ca from bones. Unlike commercially available sweat-collection patches used previously in monitoring osteoporosis and in qualitative screening for some drugs, the proposed devices would not allow evaporation of the volatile chemical components (mostly water) of sweat. Moreover, the proposed devices would be designed to enable determination of the volumes of collected sweat. From these volumes and the quantities of Ca2+ and/or other analytes as determined by other means summarized below, one could determine the concentrations of the analytes in sweat.
A device according to the proposal would be flexible and would be worn like a commercial sweat-collection patch. It would be made of molded polydimethylsiloxane (silicone rubber) or other suitable material having properties that, for the purpose of analyzing sweat, are similar to those of glass. The die for molding the silicone rubber would be fabricated by a combination of lithography and electroplating. The die would reproducibly form, in the silicone rubber, a precisely defined number of capillary channels per unit area, each channel having a precisely defined volume. Optionally, electrodes for measuring the Ca2+ content of the sweat could be incorporated into the device.
The volume of sweat collected in the capillary channels of the device would be determined from (1) the amount of light or radio waves of a given wavelength absorbed by the device and (2) the known geometry of the array of capillary channels. Then, in one of two options, centrifugation would be performed to move the sweat from the capillary tubes to the region containing the electrodes, which would be used to measure the Ca2+ content by a standard technique. In the other option, centrifugation would be performed to remove the sweat from the device to make the sweat available to other analytical instruments for measuring concentrations of substances other than Ca2+.
This work was done by Daniel L. Feeback of Johnson Space Center and Mark S. F. Clarke of the University of Houston.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
: University of Houston Department of Health and Human Performance Laboratory of Integrated Physiology 3855 Holman St.
Room 104 Garrison Houston
TX 77201.
MSC-23625-1
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Improved Devices for Collecting Sweat for Chemical Analysis
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Overview
The document outlines an innovative device developed by NASA for the collection of human sweat samples, aimed at improving the accuracy and integrity of chemical analyses. This device addresses significant shortcomings of prior art, particularly in the context of clinical diagnostics, such as cystic fibrosis (CF) testing in infants. Traditional methods require a minimum sweat volume of 10 microliters and involve complex procedures that can alter the sample's integrity due to evaporation or condensation.
The core of this innovation is a "volumetric" absorbent pad made from a flexible polymer, such as PMDS (polymethyldisiloxane), produced using the LIGA process (lithography, electroplating, and molding). This pad is designed to be worn on the skin, utilizing capillary action to collect sweat while maintaining the sample's integrity. The device features precisely controlled capillary channels that allow for accurate measurement of the collected fluid volume through light or radio frequency absorption. After collection, the sweat can be recovered from the pad using centrifugation for further analysis.
The document emphasizes the device's potential applications in both clinical settings and research, particularly in monitoring biological markers related to bone loss during spaceflight. The non-invasive nature of sweat sampling makes it an attractive option for various health monitoring scenarios, including the analysis of osteoporosis markers and drugs of abuse.
Additionally, the innovation is positioned to overcome the limitations of existing sweat collection devices, which often require trained personnel and involve time-consuming procedures. By integrating analytical components directly into the collection device, the new technology allows for immediate analysis of the sweat sample, enhancing its utility in both healthcare and commercial markets.
Overall, this development represents a significant advancement in sweat collection technology, promising to facilitate more efficient and reliable analyses while being adaptable for use in diverse environments, including microgravity. The document serves as a technical support package, providing insights into the device's design, functionality, and potential commercial applications, while also highlighting the broader implications for health monitoring and research in space exploration.
