A Personalized Electronic Tattoo for Healthcare Realized by On‐the‐Spot Assembly of an Intrinsically Conductive and Durable Liquid‐Metal Composite

Abstract

A notable technology in this regard is customized electronic (e-) skin that can be mounted directly on human skin with tailored design depending on its purpose, attached body part, and user's body shape. [3] Since skin contains various physiological data (e.g., electrophysiological signals, sweat chemistry, and pulse rate) such skin-attached e-skin can interpret the health state of the user. [4,5] Moreover, chronic muscular disease such as inflammatory myopathies and myofascial pain syndrome can be treated with electrical/ thermal stimulation using e-skin. [4,6] Currently, customized e-skins are usually made by patterning and/or printing metal, [3] 1/2D materials, [7] and organic materials [8] on supporting substrates using conventional fabrications strategies such as nozzle printing, [9] screen printing, [10] and lithography [11] in a laboratory or factory. However, devices fabricated in this manner suffer from: 1) limited scalability and flexibility in their design, incapable of on-the-spot implementation, 2) limited durability (i.e., low toughness causing easy tear-off), stretchability, disposability, and gas-permeability (i.e., non-breathability due to the presence of substrate covering the skin), Conventional electronic (e-) skins are a class of thin-film electronics mainly fabricated in laboratories or factories, which is incapable of rapid and simple customization for personalized healthcare. Here a new class of e-tattoos is introduced that can be directly implemented on the skin by facile one-step coating with various designs at multi-scale depending on the purpose of the user without a substrate. An e-tattoo is realized by attaching Pt-decorated carbon nanotubes on gallium-based liquid-metal particles (CMP) to impose intrinsic electrical conductivity and mechanical durability. Tuning the CMP suspension to have low-zeta potential, excellent wettability, and high-vapor pressure enables conformal and intimate assembly of particles directly on the skin in 10 s. Low-cost, ease of preparation, on-skin compatibility, and multifunctionality of CMP make it highly suitable for e-tattoos. Demonstrations of electrical muscle stimulators, photothermal patches, motion artifact-free electrophysiological sensors, and electrochemical biosensors validate the simplicity, versatility, and reliability of the e-tattoo-based approach in biomedical engineering.

Liquid Metal-Based Electronics for On-Skin Healthcare

“…Skin-attachable biosensors are of significance for healthcare monitoring and disease diagnoses such as diabetes and rehabilitation [101]. Carbon nanotubes (CNTs) can form an electrostatic interaction with LM particles with the help of negatively charged polyelectrolytes (poly(sodium4-styrene sulfonate) (PSS)) (Figure 10A) [102]. Based on this, an intrinsic electrical conductivity was imposed for carbon nanotubes on LM particles (CMP) whilst coated on human skin.…”

Carbon-based electrochemical biosensors as diagnostic platforms for connected decentralized healthcare

“…Electronic diagnostic tattoos (e-tattoos) are a new wave of devices with potential for personalized medicine 120 .Customized e-tattoos are generally made by patterning or printing conductive materials on supporting substrates or as standalone substrate-free films. The main requirements for e-tattoo development are: i) skin compatibility, ii) stretch-resistant electrical conductivity, iii) flexibility, and iv) mechanical durability 121 .Carbon nanostructures have the required characteristics to be used as a conductive interface for epidermal e-tattoos due to their electrical conductivity and high mechanical strength, making them ideally suited for skin-conformed electronics.…”

“…An e-tattoo developed using Pt-decorated CNTs deposited on a gallium-based liquid metal composite demonstrated potential as a skin-attached wearable biosensor for measuring oxidase enzyme substrates, i.e., lactate, glucose, and ethanol (Figure 11A) 120 .Another example of skinattachable electrochemical sensor for glucose and pH in human perspiration has been developed by coating CoWO 4 /CNT and polyaniline/CNT nanocomposite onto CNT-AuNS electrodes with a chlorinated silver nanowire as a reference electrode 123 .To obtain a skin attachable device, the patterned electrodes were encapsulated within a sticky silbione led. Silbione was found to provide superior adhesion behavior, high biocompatibility and mechanical stability, which makes it an ideal material for wearables.…”

Recent Advances in Materials, Designs and Applications of Skin Electronics

“…Not only bulk liquid metals can be used to print e-skins in situ, but liquid metal particles similarly. Lee et al [35] achieved high-precision mask printing of electronic tattoos directly on the skin based on liquid metal particle coated with Pt-modified CNTs. Hydrogel-based conductive materials have become a popular option as connecting components in skin electronics due to their biocompatibility, pluripotency, and functionality easy to extend and modify.…”