Graphene electronic tattoos are unique devices used in healthcare systems for personalized applications. Monolayered graphene electronic tattoos are used to monitor different electrophysiological signals in humans. Despite their innovative functionality, these devices suffer from an impermeability to sweat and difficulties in reproducibility.
Study: Graphene electronic tattoos 2.0 with enhanced performance, breathability and robustness. Image Credit: Tex vector/Shutterstock.com
In an article recently published in the journal npj 2D Materials and Applications, an enhanced version of graphene electronic tattoos was introduced. This update is wearable on the skin with sweat permeability, superior electrical properties, and robustness. While the older systems suffered scattered electrical properties due to growth or transfer-related discrepancies, the reported graphene electronic tattoos with graphene nanoscrolls (GNS) or multilayered graphene structures showed enhanced properties.
The devices were analyzed systematically by stacking different layers of graphene. The graphene monolayers stacked within a single tattoo significantly improved electronic properties. On the other hand, stacking the tattoos with multilayered graphene resulted in a 2.5-fold reduced skin impedance, 3.5-fold decreased sheet resistance and a 5-fold reduction in standard deviation.
Graphene Electronic Tattoos for Wearable Bioelectronics
Wearable bioelectronics has found applications in various healthcare fields. Consequently, electronic elements based on metal and silicon are being replaced slowly and persistently by lightweight skin-like materials with a softer texture and without any impedance to their functionality. To this end, simplifying the operation of the bioelectronics process can make them easily accessible and wearable.
Graphene electronic tattoos are atomically thin and used in wearable bioelectronic elements.
Initial designs featured approximately 85% transparency and the ability to adhere to the skin via van der Waals forces. Additionally, the electronic tattoos showed about 40% stretchability allowing their facile application on the skin, preventing strain-induced performance artifacts and motion-induced noise.
These graphene electronic tattoos were fabricated on a small scale. Moreover, the crucial properties such as sheet resistance, interface impedance, and water vapor transmission rate (WVTR) of graphene electronic tattoos were not optimized accurately.
Thus, previously reported graphene electronic tattoos suffered limitations such as average electronic performance and higher impedance than monolayered graphene electronic tattoos and inconsistencies such as large cracks or grain boundaries and folds induced during graphene transfer reducing their overall performance. In addition to these problems, the monolayered graphene electronic tattoos lacked reproducibility leading to large performance distribution.
Fabrication of Graphene Electronic Tattoos 2.0 with Enhanced Properties
In the present study, improved multilayered graphene electronic tattoos were reported with efficient sweat perspiration capacity and superior electrical properties. The devices were then analyzed for their bioelectronic and electronic properties.
The primary parameter of interest in the present study was the number of monolayers per tattoo. Since the electronic properties were hampered in monolayered graphene electronic tattoos due to the microcracks and defects and consequent imperfect growth, multilayered (bi- and trilayer) graphene electronic tattoos were created alongside their monolayered counterparts.
The fabricated trilayered devices showed a 3.5-fold improved sheet resistance and a 2.5-fold enhanced interface impedance over their monolayered counterparts. Moreover, the monolayered structure incorporated with GNS demonstrated improved performance due to its enhanced physical and mechanical properties.
Additionally, the drawbacks of previous graphene electronic tattoos were covered by the embossment of microholes in the topographical structure of the new graphene electronic tattoos. These microlayers allowed enhanced multi-planar skin contact with graphene electronic tattoos, paving the way for next-generation hybrid wearable systems.
To summarize, robust and multipurpose graphene electronic tattoos with permeability to sweat and superior electrical properties were prepared as unobtrusive and lightweight wearable tattoo sensors.
Incorporating the GNS into monolayered graphene electronic tattoos improved their performance due to decreased skin impedance, decreased sheet resistance, and lower standard deviation with improved reproducibility of the results.
The main drawback of the updated device was its impaired electronic properties due to minor cracks or disorders on its topological surface. Thus, GNS or multilayered graphene tattoos helped enhance their electronic properties due to the formation of an intercalated network that bridged any imperfections in the bulk graphene layer.
Moreover, an extensive study on multilayered graphene electronic tattoos revealed their robustness and favorable electrical properties for their applications in wearable electrophysiological recordings. The bilayered graphene electronic tattoos exhibited two-fold enhancement in the skin impedance compared to their monolayered counterpart.
Nevertheless, due to the time-delayed assembly of trilayered graphene electronic tattoos without significant enhancement in electrical properties, the bilayered graphene electronic tattoos can serve as potential next-generation graphene tattoos over their trilayered counterparts.
Kireev, D., Kampfe, J., Hall, A., Akinwande, D. (2022) Graphene electronic tattoos 2.0 with enhanced performance, breathability, and robustness. npj 2D Materials and Applications.