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Page 2 of 32 Zhao et al. Soft Sci 2024;4:18 https://dx.doi.org/10.20517/ss.2024.04

applications of sweat-based bioelectronic systems and proposes a vision for the future evolution of this promising
field.

Keywords: Sweat electronics, sweat sampling, sweat sensing, sweat-based energy harvester, data display

INTRODUCTION
Sweat, one of the most important body fluids, primarily consists of water (~99%) . It also comprises
[1]
+
metabolites (such as glucose, lactate, ethanol, etc.), ions [including potassium ions (K ), sodium ions (Na ),
+
ammonium ions (NH ), chloride ions (Cl ), etc.], hormones, small proteins and peptides, offering abundant
+
-
4
biochemical information regarding human physiological and metabolic status . For example, the
[2-9]
concentration of Cl is the benchmark for diagnosing cystic fibrosis; the level of Na is a key indicator for
-
+
athletes as it guides the fluid intake strategies and helps maintain the balance between hydration and
electrolyte levels [10-12] . Sweat glucose analysis has been employed to evaluate the glucose variation in blood
for diabetes in clinical applications [13-15] . Recently, sweat is also utilized in clinical pharmacokinetics studies
to examine the variation of some xenobiotics, such as drug molecules [16-18] . Among various biofluids, blood
and interstitial fluid can be continuously monitored but are invasive and require additional processing [19,20] .
Saliva, although easily obtainable, presents limitations such as reduced flow during the day, non-uniform
composition across different parts of the mouth, and susceptibility to contamination . Tear collection, on
[21]
the other hand, is a little uncomfortable for participants and easily accessible. However, the quantity of tears
collected is limited, and studies investigating their validity and reliability are scarce [22,23] . Additionally,
[24]
collecting sweat samples is generally less challenging than urine collection . Compared with other bodily
fluids such as blood, interstitial fluid, urine, saliva, and tears, sweat holds significant promise due to the
merits of safety, rapid processing, easy preparation, noninvasiveness, and so on [20,25-27] . Therefore, achieving
rapid and accurate monitoring of sweat serves a significant role in health management and medical
diagnosis. However, clinical use of sweat is presently limited by high costs, complex sampling procedures,
significant time and manpower consumption, and the requirement of large-scale medical equipment,
among other factors .
[28]

Advances in materials, biotechnology, and electronics have enabled flexible sweat electronics [27,29-31] . These
devices, with sweat sampling, biosensors, energy harvesters, and data displays, enable noninvasive and
continuous physiological monitoring [32-34] . They can harness energy from sweat using sweat-activated
batteries (SABs) or supercapacitors (SACs) [35-37] . Flexible sweat electronics offer real-time health updates and
clinical treatment alerts, making them increasingly important in healthcare [38-40] .

Several works have been reported on the progress of sweat capture, collection, and sensing
techniques [11,13,26,35,41-43] , comprehensively summarizing sweat sampling and sensing. This review explores
various aspects of flexible sweat electronics, including sweat sampling, sensors, energy harvesters, and data
display [Figure 1]. It compares traditional methods with flexible sweat electronics, covers advancements in
sweat biosensors, and discusses sweat-based energy harvesters such as sweat-based fuel cells, SABs and
SACs. The review also addresses data display methods and highlights scientific obstacles and future
opportunities. Overall, the main goal of this article is to thoroughly overview flexible sweat electronics that
will facilitate personal health management and finally cause a paradigm shift in medical care.

TRADITIONAL SWEAT-BASED PLATFORM
The sweat platform has made significant progress, with various methods used to collect sweat components.
One typical traditional approach in the 1990s involved full body washing to assess overall sweat electrolyte