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Posted by Okachinepa on 12/10/2024 @
Courtesy of SynEvol
Credit :Jihong Min
Similar to blood, sweat contains important health information, but it is much less intrusive to collect. Wei Gao, an assistant professor of medical engineering at Caltech, an investigator at the Heritage Medical Research Institute, and a Ronald and JoAnne Willens Scholar, developed wearable sweat sensors based on this idea.
Gao has improved these wearables over the last five years to identify a variety of health indicators, such as sugars, salts, uric acid, vitamins, amino acids, and even complicated compounds like C-reactive protein, which indicates specific health risks. In his most recent invention, Gao has fitted these sensors with a flexible solar cell for continuous, battery-free functioning. This was created in partnership with Martin Kaltenbrunner's group at Johannes Kepler University Linz in Austria.
Courtesy of SynEvol
Credit: Stepan Demchyshyn
The solar cell used by Gao’s lab is made of perovskite crystal, a material that shares the chemical structure first found in the mineral calcium titanium oxide. For a number of reasons, perovskite has drawn interest from solar cell developers. First, it is cheaper to manufacture than silicon (the primary material used in solar cells since the 1950s), which must be highly purified through multiple processes. Second, perovskite is as much as 1,000 times thinner than silicon solar cell layers, making them “quasi-2D” in Gao’s terms. Third, perovskite can be tuned to the spectra of different lighting, from outdoor sunlight to various forms of indoor lighting. Finally, and most enticingly for pioneers of solar energy, perovskite solar cells achieve a higher power conversion efficiency (PCE) than silicon, which enables them to produce more useful electricity from the light they receive.
In normal operation, the range is between 18 and 22 percent, however silicon solar cells have achieved PCE levels that range from 26 to 27 percent. In contrast, Gao's wearable sweat sensor's flexible perovskite solar cell (FPSC) boasts a record-breaking PCE of more than 31% when exposed to indoor light. Gao says, "We don't want to power our wearables only with strong sunlight." "Normative lighting in homes and offices is one of the more realistic conditions that we worry about. Strong sunshine increases the efficiency of many solar cells, but dim inside lighting does not. Gao claims that because "the spectral response of the FPSC matches well with the common indoor lighting emission spectrum," the sweat sensor's FPSC is especially well adapted to indoor lighting.
Courtesy of SynEvol\
Credit:Jihong Min
Gao's wearable sweat sensors were previously powered by large, cumbersome lithium-ion batteries that required external electricity to replenish. Gao's lab experimented with silicon solar cells in an attempt to find a lighter, more sustainable electricity source to power these high-demand gadgets, but they discovered that these cells were too inflexible, inefficient, and dependent on intense lighting. Additionally, they experimented with using body motion and the chemicals in human sweat (a readily available biofuel) to capture energy, but they discovered that these were either too unstable or needed too much work from the wearer.
Use of a FPSC has allowed Gao to create sweat sensors that can be worn for 12 hours a day, providing continuous monitoring of pH, salt, glucose, and temperature, and periodic monitoring (every five to 10 minutes) of sweat rate. Batteries or a specialized light source are not needed to achieve any of this. Furthermore, as the power source has become lighter and less cumbersome, the wearable has room for additional detectors to monitor a greater number of biomarkers simultaneously.
Courtesy of SynEvol
Credit: Jihong Min
Like its predecessors, this new wearable sweat sensor is put together like an origami, with distinct layers for various functions. There are four main interacting parts to the sensor. The first is dedicated to power management—disbursing the electricity harvested by the solar cell. The second enables iontophoresis, the induction of sweating without any exercise or exposure to high heat required on the part of its wearer. In Gao’s study, iontophoresis was performed every three hours to ensure that enough sweat was available to continuously monitor the biomarkers under observation. The third enables the electrochemical measurement of various substances in the sweat. The fourth manages data processing and wireless communication, which allows the sensor to interface with a cellphone app to display the ongoing results of the monitoring of sensors.
The sensor is 20 x 27 x 4 millimeters when fully built, and it is capable of withstanding the mechanical strain that comes with being worn on the body. Gao continues, "The majority of the sweat sensor's components, including the electronics and the FPSC, are reusable." “The only exception is the sensor patch, which is disposable, and it can be mass produced at a low cost using inkjet printing.” These sensor patches can also be customized according to what substances the user wishes to measure in their body.
As these solar-powered sweat sensors are put to use, they will be able to measure far more than any fitness or health tracker currently does. For example, they can be used for diabetes management (studies have shown that glucose in sweat is closely matched to glucose in the blood) and for the detection of a range of conditions such as heart disease, cystic fibrosis, and gout. Because they are noninvasive and can perform multiple measurements over short periods of time, these sensors can discern an individual’s baseline for substances such as cortisol, hormones, or the metabolites of various nutrients and medicines. Once the baseline levels for such substances are known, future deviations from these will provide a more effective means of diagnosis than a single Never could a blood draw. Additionally, it is hoped that the sensors, which are reasonably priced, would be a great diagnostic tool everywhere, even in underdeveloped nations.
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