Osmotically Enabled Wearable Patch for Sweat Harvesting and Lactate Quantification

Abstract

Lactate is an essential biomarker for determining the health of the muscles and oxidative stress levels in the human body. However, most of the currently available sweat lactate monitoring devices require external power, cannot measure lactate under low sweat rates (such as in humans at rest), and do not provide adequate information about the relationship between sweat and blood lactate levels. Here, we discuss the on-skin operation of our recently developed wearable sweat sampling patch. The patch combines osmosis (using hydrogel discs) and capillary action (using paper microfluidic channel) for long-term sweat withdrawal and management. When subjects are at rest, the hydrogel disc can withdraw fluid from the skin via osmosis and deliver it to the paper. The lactate amount in the fluid is determined using a colorimetric assay. During active sweating (e.g., exercise), the paper can harvest sweat even in the absence of the hydrogel patch. The captured fluid contains lactate, which we quantify using a colorimetric assay. The measurements show the that the total number of moles of lactate in sweat is correlated to sweat rate. Lactate concentrations in sweat and blood correlate well only during high-intensity exercise. Hence, sweat appears to be a suitable biofluid for lactate quantification. Overall, this wearable patch holds the potential of providing a comprehensive analysis of sweat lactate trends in the human body.

A One-Dollar, Disposable, Paper-Based Microfluidic Chip for Real-Time Monitoring of Sweat Rate

“…Lost body water must be replaced to maintain normal physiologic processes; this is particularly important for body builders, athletes [ 5 ], firefighters, etc. Furthermore, sweat, like saliva and tears [ 6 ], is noninvasively induced from deeper in the body and carries a diverse array of biomolecules, ranging from small electrolytes (including Na + , K + , and Ca 2+ ) and metabolites (such as glucose, lactate [ 7 ], and ethanol [ 8 ]) to hormones and larger proteins [ 9 ], which may provide vital information about physiological status and fitness level [ 10 ]. Sweat analysis could become an alternative to invasive blood tests in the future [ 11 , 12 ], as Heikenfeld et al [ 13 ] demonstrated—for the first time in vivo—the complete correlation between continuous sweat data and blood data.…”

Wireless Wearable Electrochemical Sensing Platform with Zero-Power Osmotic Sweat Extraction for Continuous Lactate Monitoring

“…8−16 Lactate is also present in the blood where its concentration ranges from 0.5 to 2 mM for healthy subjects at rest. 2,8,9 Greater amounts of lactate begin to appear in the blood only when the body experiences high-intensity exertion (>120 W) and crosses the lactate threshold (LT) workout intensity. 2,8 For this reason, the blood lactate concentration can peak up to ∼11 mM upon surpassing the LT. 9 Therefore, under other physiological conditions (e.g., rest or medium exercise workout), the sweat lactate concentration usually ranges ∼2−10 times greater than the blood lactate concentration (∼1−3 mM) and follows a different trend.…”

“…2,8,9 Greater amounts of lactate begin to appear in the blood only when the body experiences high-intensity exertion (>120 W) and crosses the lactate threshold (LT) workout intensity. 2,8 For this reason, the blood lactate concentration can peak up to ∼11 mM upon surpassing the LT. 9 Therefore, under other physiological conditions (e.g., rest or medium exercise workout), the sweat lactate concentration usually ranges ∼2−10 times greater than the blood lactate concentration (∼1−3 mM) and follows a different trend. 2,8,10 Hence, a minute rise (with respect to rest) in the blood lactate concentration during medium exercise workout suggests that most of the lactate produced via glycolysis in the muscles is released in sweat.…”

“…2,8 For this reason, the blood lactate concentration can peak up to ∼11 mM upon surpassing the LT. 9 Therefore, under other physiological conditions (e.g., rest or medium exercise workout), the sweat lactate concentration usually ranges ∼2−10 times greater than the blood lactate concentration (∼1−3 mM) and follows a different trend. 2,8,10 Hence, a minute rise (with respect to rest) in the blood lactate concentration during medium exercise workout suggests that most of the lactate produced via glycolysis in the muscles is released in sweat. 8,10 Most state-of-the-art wearable sweat sensors determine the sweat lactate content using either colorimetry or electrochemistry.…”

“…2,8,10 Hence, a minute rise (with respect to rest) in the blood lactate concentration during medium exercise workout suggests that most of the lactate produced via glycolysis in the muscles is released in sweat. 8,10 Most state-of-the-art wearable sweat sensors determine the sweat lactate content using either colorimetry or electrochemistry. The biorecognition elements in these sensors typically use either lactate oxidase (LO x ) or lactate dehydrogenase (LDH) enzymes.…”