A research team from the King Abdullah University of Science and Technology (KAUST) has discovered ultrathin nanomaterials, known as MXenes, that are balanced to make it easier to monitor a person’s well-being by analyzing the pH levels of their sweat.
A team of KAUST researchers has developed a prototype wearable sensor, developed with a new MXene–hydrogel compound, which may prove valuable to athletes looking for real-time performance measurements. Image Credit: © 2021 KAUST; Olga Kasimova.
MXenes, like graphene, have a two-dimensional structure but are made up of non-toxic metals, like titanium, in combination with nitrogen or carbon atoms. MXenes are appealing options for biosensors that can detect minor changes in chemical concentrations due to their inherently high conductivity and strong surface charges.
In 2019, Husam Alshareef, Professor of Material Science and Engineering in the Physical Science and Engineering Division and Principal Investigator of Functional Nanomaterials & Devices Lab at KAUST along with his team, developed an MXene composite electrode, enclosed in a wearable armband sensor.
The tool, which had a modular design and utilized MXene inserts loaded with suitable enzymes, could absorb sweat and identify multiple analytes in human sweat, along with glucose and lactic acid.
Alshareef and his colleagues, in partnership with Sahika Inal’s research team at KAUST, recently attempted merging MXene sheets with hydrogels — water-filled polymers that are suitable for human tissue since they can stretch. However, the researchers discovered that high amounts of mobile ions in the hydrogel caused the polymer to be extremely sensitive to the mechanical strain experienced during the workout.
Initially the MXene sheets are randomly oriented within the hydrogel, but once you apply pressure to them, the sheets become more horizontally oriented. Because MXenes have a high concentration of negative charges on their surfaces, horizontal arrangements strongly affect ion movements within the hydrogel, and thus we can measure different levels of pressure change.
Husam Alshareef, Professor, Material Science and Engineering, King Abdullah University of Science and Technology
By generating discrete electrical resistance patterns as mechanical tension rose, a prototype wearable sensor built with the novel MXene–hydrogel compound was able to track muscle action. When the sensor was exposed to extra ions in the form of acidic or basic solutions, these patterns changed quickly.
As a result, the KAUST researchers realized that their gadget may be used to link sweat pH variations to fatigue-inducing acid growths in muscle cells.
As we exercise and our muscles get tired, the sensor sees the new chemical environment and produces different electrical resistance versus stress curves. By comparing these curves to reference curves for a given sensor, we can determine the pH of the sweat and how fatigued the muscle is.
Kang Lee, Study Lead Author, King Abdullah University of Science and Technology
Kang Lee was a postdoctoral scholar at KAUST.
Once the technology is improved, the MXene-based sensor could be useful to athletes searching for actual performance metrics, thanks to Bluetooth connectivity to surrounding digital devices.
The most serious challenge is the long-term stability of the sensor, so we’re looking at altering compositions and designs in future experiments.
Husam Alshareef, Professor, Material Science and Engineering, King Abdullah University of Science and Technology
Journal Reference:
Lee, K. H., et al. (2021) Muscle fatigue sensor based on Ti3C2Tx MXene hydrogel. Small Methods. doi.org/10.1002/smtd.202100819.