Stretchable, Breathable Skin Electrodes from Carbon Nanotubes

Introduction

Imagine a future where our electronic devices can seamlessly integrate with our bodies, monitoring our health and responding to our movements with ease. This vision is becoming a reality, thanks to the development of a new type of electrode that is both flexible and highly permeable to water vapor.

Researchers have created conductive nanosheets composed of

(

SWCNTs

This is an abbreviation for 'single-wall carbon nanotubes', which are the tiny, hollow tubes made of a single layer of carbon atoms.

 

) assembled on an

elastomeric polymer

A type of material that can stretch and bend without breaking, similar to rubber.

 

called

poly(styrene-b-butadiene-b-styrene)

A type of elastic, rubbery material that can stretch and bend without breaking. It is made up of three different chemical building blocks.

 

(

SBS

This is an abbreviation for 'poly(styrene-b-butadiene-b-styrene)', which is a type of elastic, rubbery material.

 

). These

SWCNT-SBS nanosheets

Thin, flexible sheets made by combining the single-wall carbon nanotubes and the elastic, rubbery material.

 

exhibit remarkable characteristics, including the ability to stretch and conform to the skin, as well as high

water vapor permeability

The ability of a material to allow water vapor to pass through it, which is important for maintaining skin health and comfort.

 

. This makes them an ideal candidate for use as

skin-conformable bioelectrodes

Flexible, thin electrodes that can attach to the skin and be used to measure biological signals, such as muscle activity.

 

in wearable devices.

Research Purpose and Motivation

Conventional stretchable electrodes often struggle with limitations, such as poor water vapor permeability and insufficient flexibility. This can lead to discomfort and skin irritation when worn for extended periods. The researchers set out to address these challenges by developing a new type of electrode that can overcome these limitations.

The primary goal of this research was to create conductive, stretchable, and water-vapor permeable nanosheets that can be used as skin-conformable bioelectrodes. By combining the unique properties of SWCNT networks and the elastomeric SBS films, the researchers aimed to develop a material that can seamlessly integrate with the human body, providing improved comfort and functionality for wearable devices.

Methodology and Study Design

The researchers fabricated SWCNT-SBS nanosheets with varying numbers of SWCNT coating layers, ranging from a single layer to three layers. They then characterized the water vapor transmission, mechanical properties, and electrical performance of these nanosheets.

To evaluate the skin-conformability and durability of the nanosheets, the researchers conducted a series of tests. They assessed the nanosheets' resistance to bending and exposure to artificial sweat, as well as their ability to detect

(

sEMG

This is the abbreviation for 'surface electromyography', which is a way to measure the electrical signals from muscles using electrodes on the skin.

 

) signals from the skin.

The

(

WVTR

This is the abbreviation for 'water vapor transmission rate', which is a measure of how easily water vapor can pass through a material.

 

) of the nanosheets was measured using the

dish method

A way to measure the water vapor transmission rate by placing a material over a container and measuring how much water vapor passes through it over time.

 

, which involves placing the nanosheet over a container filled with water and measuring the rate of water vapor loss. This allowed the researchers to compare the permeability of the nanosheets to that of conventional materials, such as filter paper and human skin.

The mechanical properties, including

and

elongation at break

The maximum amount a material can stretch or extend before it breaks. It's a measure of how stretchable or flexible a material is.

 

, were evaluated to determine the stretchability of the nanosheets. Electrical resistance measurements were performed during bending and exposure to artificial sweat to assess the durability of the nanosheets.

Finally, the researchers conducted sEMG measurements on human skin using the SWCNT-SBS nanosheets and compared their performance to that of traditional

. This allowed them to evaluate the nanosheets' ability to effectively detect and transmit electrical signals from the body.

Results and Significance

The SWCNT-SBS nanosheets exhibited remarkable water vapor permeability, with the SBS nanosheet having a WVTR that was 42 times greater than that of filter paper. The WVTR of the SWCNT 3rd-SBS nanosheet (the one with three layers of SWCNT coating) was found to be one to two orders of magnitude higher than that of human skin and previously reported textile electrodes.

In terms of mechanical properties, the SWCNT 3rd-SBS nanosheet demonstrated a significantly lower elastic modulus and higher elongation at break compared to the

, indicating greater stretchability. This is a crucial characteristic for ensuring the nanosheets can conform to the skin without causing discomfort or irritation.

The SWCNT 3rd-SBS nanosheet also showed excellent durability, with only a 1.1-fold change in electrical resistance during bending and exposure to artificial sweat at different pH levels. This suggests that the nanosheets can withstand the mechanical stresses and chemical challenges encountered during everyday use.

When used for sEMG measurements on the forearm, the SWCNT 3rd-SBS nanosheet displayed a

(

SNR

An abbreviation for 'signal-to-noise ratio', which is a way to measure the quality of a signal by comparing the strength of the desired information to the background noise.

 

) comparable to that of the conventional Ag/AgCl gel electrode. This indicates that the SWCNT-SBS nanosheets can effectively detect and transmit electrical signals from the body, making them suitable for use in wearable bioelectronics.

Conclusions and Implications

The development of the SWCNT-SBS nanosheets represents a significant advancement in the field of wearable electronics. By combining the conductive properties of SWCNT networks with the elastomeric nature of SBS films, the researchers have created a material that is both highly stretchable and highly permeable to water vapor.

The exceptional water vapor transmission rates and mechanical properties of the SWCNT 3rd-SBS nanosheet make it a promising candidate for use as a skin-conformable bioelectrode. The ability of these nanosheets to effectively detect and transmit electrical signals, while maintaining a low profile and high comfort level, opens up new possibilities for the design of next-generation wearable devices.

As the demand for seamless integration between technology and the human body continues to grow, the SWCNT-SBS nanosheets developed in this research could pave the way for a new era of comfortable, breathable, and highly functional wearable electronics. By addressing the limitations of conventional stretchable electrodes, this innovation has the potential to revolutionize the field of wearable bioelectronics and improve the overall user experience.