Nanotechnology in textiles

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There has been significant advances in the development of smart clothing incorporating nanomaterials for conductivity and monitoring.

Recent advances in stimuli-responsive surfaces and interfaces, sensors and actuators, flexible electronics, nanocoatings and conductive nanomaterials has led to the development of a new generation of smart and adaptive electronic fibers, yarns and fabrics for application in E-textiles. Wearable low-power silicon electronics, light-emitting diodes (LEDs) fabricated on fabrics, textiles with integrated Lithium-ion batteries (LIB) and electronic devices such as smart glasses, watches and lenses have been widely investigated and commercialized (e.g. Google glass, Apple Watch).

However, improvements in sensors, flexible & printable electronics and energy devices are necessary for wider implementation and nanomaterials and/or their hybrids are enabling the next phase convergence of textiles, electronics and informatics. They are opening the way for the integration of electronic components and sensors (e.g. heat and humidity) in high strength, flexible and electrically conductive textiles with energy storage and harvesting capabilities, biological functions, antimicrobial properties, and many others new functionalities.
There have been a number of recent research developments in nano-enabled wearable sensors, memory devices, energy storage devices and LEDs that show great promise for commercial application in the next decade. The development of flexible energy harvesting and storage devices is especially important for wearable smart textiles.

MARKET DRIVERS FOR APPLICATION OF NANOMATERIALS IN SMART CLOTHING AND WEARABLE ELECTRONICS

Increasing demand for wearable electronic devices
The market for wearable electronics has expanded considerably recently, with applications in personal health and fitness monitoring, immersive gaming and wireless communications. For successful widespread implementation in other markets (e.g. healthcare) next generation wearables must be lightweight, small size, flexible and stretchable, have low power consumption, and reliable sensing performance.
Nanomaterials solution: The unique properties of nanomaterials (e.g. graphene & carbon nanotubes), such as high elasticity, mechanical strength, thermal conductivity, very high electrical conductivity and transparency, make them good candidates for stretchable electronic textile applications. Application to now has mainly been via printable, conductive carbon nanomaterial inks and pastes. Nanomaterials potentially allow for the high performance of rigid electronic semiconductors such as silicon, gallium arsenide, and gallium nitride with enhanced flexibility.1 2 3

Growth in remote health monitoring and diagnostics
The world’s ageing population and the prevalence of chronic diseases has lead to demand for wireless and sensory vital signs monitoring utilizing wearable devices. The medical industry is transforming itself through the use of digital technologies. The “Internet of Things” will impact the healthcare industry through monitoring, personalized medicine and medical diagnosis.
The development of health sensing devices enables the creation of solutions that address mobility concerns of patients, especially those located on remote locations or facing mobility constraints. These devices are playing an increasing role in improving quality of life and in allowing prevention for chronic cardiac diseases. They also support remote health monitoring following hospitalization, during recovery and rehabilitation, or between regular doctor visits.
However, the actual clinical use of smart wireless, software-based, mobile medical devices does not meet the recently raised expectations.

Figure 1: Electronic skin patch incorporating silicon nanomembranes. Image credit: Center for Nanoparticle Research, Institute for Basic Science (IBS).

Nanomaterials solution: Main technology limitations for wearable medical devices include the difficulty in producing appropriate physiological transducers, lack of availability of bioelectronic components, and the difficulty in integrating various technologies on a single substrate. A typical integrated system for human health applications consists of multiple functions (e.g., sensing, fluid handling, computation, telemetry), multiple technologies (e.g., integrated circuits, microfluidics, transducers), multiple materials (e.g., semiconductors, metallics, polymers, biomaterials), and multiple manufacturing processes (e.g., thin films, molding, lamination). The diversity in the makeup of these devices represents a significant challenge to producing wearable medical monitoring and diagnostic devices that are low cost and high performance.
Nanomaterials enable new generation wireless communication, sensors and low-power electronics for connected health and are driving innovations in wearable medical devices. Wearable sensor systems based on flexible and stretchable nanomaterials have the potential to better interface to the human skin, whereas silicon-based electronics are extremely efficient in sensor data processing and transmission. Therefore, flexible and stretchable sensors combined with low-power silicon-based electronics are a viable and efficient approach for medical monitoring. However, nanomaterials allow for a combination of these qualities and are leading to the development of flexible medical devices designed for monitoring human vital signs, such as body temperature, heart rate, respiratory rate, blood pressure, pulse oxygenation, and blood glucose have applications in both fitness and sports performance monitoring and medical diagnostics (continuous diagnosis, wound care, drug delivery, and at-home diagnostics).
Nanomaterials enable improved sensor systems, sensing mechanisms, sensor fabrication, power, and data processing requirements and the construction of high performance optical and electronic systems that can flex, bend, fold and stretch, with ability to accommodate large (>>1%) strain deformation.
These technologies can be integrated intimately and non-invasively with the surfaces of important organ systems in the human body, allowing for ‘skin-like’, wearable electronics for continuous, clinical quality measurements of health status, high resolution mapping systems capable of resolving fast, transient behaviors in brain activity, and soft sensors and stimulators for advanced forms of cardiac electrotherapy.

NANOFIBERS
Nanofibers are utilized in wearable devices and smart textiles due to the following benefits:

• Solution processability and continuous, low cost deposition (electrospun nanofibers).
• High strain and deformation sensing.
• Highly conductive and transparent.
• Low power consumption.

Applications include:
• Water proof breathable materials incorporating
membranes in performance apparel.
• Sensors for detection of pH change in wound dressings.
• Wearable power generators (e.g. Li-ion batteries).4 5
• Sensing skin.
• Pulse rate and waveform monitoring.
• Wearable photosensors.6
• Drug loaded textile delivery systems.

Figure 2: Wearable blood purification system (a) and a zeolite–polymer composite nanofiber mesh (b). (c) The nanofiber is composed of blood compatible poly(ethylene-co-vinyl alcohol) as the primary matrix polymer and zeolites which are capable of selectively adsorbing uremic toxins. Image credit: Biomaterials Science.

SILVER NANOWIRES
Wearable devices using silver nanowires (AgNW) have been widely investigated and fabircated. Benefits of utilizing AgNWs include:
• Low cost.
• High conductivity.
• Low temperature processing.
• Ag-NWs possess superior yield strength and Young’s modulus over bulk silver.
• Low electrical resistance and excellent flexibility and stretchability.

Applications include:
• Active lighting, textile heating structures and personal thermal management.
• Stretchable and washable radio frequency identification (RFID) tags.7
• Smart gloves.8
• Strain sensors for body motion detection.

Figure 3: Wearable sensor that uses silver nanowires to monitor electrophysiological signals. Image credit: North Carolina State University

CARBON NANOTUBES
Single-walled carbon nanotubes (SWNTs) are prime candidates for application in wearable devices due to the following benefits:

• High electrical conductivity.
• High electron mobility.9
• Strain sensors with high durability, fast response and low creep.10
• High transparency coupled with flexibility.11

Applications include:
• Textiles for controlling static and electromagnetic interference shielding.
• Strain sensors for human-motion detection.
• Wearable memory devices.
• Wearable energy devices.12
• Shape memory.
• Wearable biosensors.
• Fabric sensors for temperature monitoring.

Figure 4: 3D printed carbon nanotube sensor. Image credit: Hebrew University.

GRAPHENE
Graphene is viewed as a key material for the development of new generation wearable electronic devices. Benefits graphene affords include:

• High conductivity.13
• High electron mobility.14
• Sensitivity to volatile organic compounds.
• Ultra-thin thickness allows for integration into wearable electronics.
• High transparency.15

Figure 5: Printable graphene antenna. Image credit: University of Manchester.

Applications under development include:

• Gas sensor textiles.
• Transparent electrodes on textile substrates.
• Sensory skins.
• Battery and supercapacitor textiles.
• Sensors for diabetes monitoring and therapy.

Figure 5: Graphene-based fabric sensor. Image credit: ETRI.16

Nanomaterials components utilized in wearable electronics are often developed in combination with other nanomaterials to produce hybrid devices. The development of high value-added products such as smart fabrics, wearable consumer and medical devices and protective textiles has increased rapidly in the last decade and nanomaterials will play a key role in their wider development and commercialization over the next few years.

REFERENCES

1. Stretchable and Foldable Silicon Integrated Circuits, http://science.sciencemag.org/content/320/5875/507

2. Flexible and Stretchable Electronics for Biointegrated Devices, http://www.annualreviews.org/doi/abs/10.1146/annurev-bioeng-071811-150018

3. Inorganic semiconductor nanomaterials for flexible and stretchable bio-integrated electronics, http://www.nature.com/am/journal/v4/n4/full/am201227a.html

4. Human walking-driven wearable all-fiber triboelectric nanogenerator containing electrospun polyvinylidene fluoride piezoelectric nanofibers, http://www.sciencedirect.com/science/article/pii/S2211285515000488

5. Piezoelectric electrospun nanofibrous materials for self-powering wearable electronic textiles applications, http://link.springer.com/article/10.1007%2Fs10965-014-0469-5

6. Highly Flexible Organic Nanofiber Phototransistors Fabricated on a Textile Composite for Wearable Photosensors, http://onlinelibrary.wiley.com/doi/10.1002/adfm.201503230/full

7. Wearable Electronics of Silver-Nanowire/Poly(dimethylsiloxane) Nanocomposite for Smart Clothing, http://www.nature.com/articles/srep13971

8. Ag Nanowire Reinforced Highly Stretchable Conductive Fibers for Wearable Electronics, http://onlinelibrary.wiley.com/doi/10.1002/adfm.201500628/abstract

9. Extraordinary Mobility in Semiconducting Carbon Nanotubes, http://pubs.acs.org/doi/abs/10.1021/nl034841q

10. A stretchable carbon nanotube strain sensor for human-motion detection, http://www.nature.com/nnano/journal/v6/n5/full/nnano.2011.36.html

11. Transparent and Flexible Carbon Nanotube Transistors, http://pubs.acs.org/doi/abs/10.1021/nl050254o

12. Stretchable, Porous, and Conductive Energy Textiles, http://pubs.acs.org/doi/abs/10.1021/nl903949m

13. Graphene as a flexible electronic material: mechanical limitations by defect formation and efforts to overcome, http://www.sciencedirect.com/science/article/pii/S1369702115000188

14. http://www.sciencedirect.com/science/article/pii/S0038109808001178

15. Fine Structure Constant Defines Visual Transparency of Graphene, http://science.sciencemag.org/content/320/5881/1308
16. Ultrasensitive and Highly Selective Graphene-Based Single Yarn for Use in Wearable Gas Sensor, http://www.nature.com/articles/srep10904

 

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