Abstract
● This review focuses on the integration techniques of conductive materials in
and onto textile structures for e-textile development.
● E-textiles can be created by applying conductive components to textile
surfaces or by manufacturing textile substrates using conductive materials.
● Conductive filament fibers can be integrated into conventional textiles during
fabrication or post-fabrication, and 3D/4D printing could further advance smart
textiles.
1. Introduction
● Smart textiles are materials that sense and react to environmental stimuli.
● "Smart textiles" can refer to smart textile materials or systems, with smart
materials interacting with their environment and smart systems exhibiting an
intended response.
● Smart textiles can be classified as passive, active, and very active or intelligent,
made with electronic materials, conductive polymers, and sensors.
Building Blocks of Smart Textile Systems
● Smart textile systems consist of functional building blocks like sensors,
actuators, interconnections, control units, communication devices, and power
supplies.
● Sensors detect physical properties, actuators influence the environment, and
interconnections link functional components.
● Control units direct operations, communication devices transmit data, and
power supply units provide power.
2. Search Method
● A comprehensive electronic search was conducted using keywords related to
smart textiles integration techniques.
● Articles were screened for relevance to smart textile building block integration,
excluding reviews and studies not using e-textile technology.
● A total of 138 articles met the inclusion criteria for the review.
3. Conductive Materials for Textiles
● Electrically conductive textiles are crucial for smart textile applications,
achieved by integrating metallic wires, conductive polymers, or other
compounds.
● Conductive materials for textiles include conductive inks, carbon-based
materials, intrinsically conductive polymers, and conductive polymer
composites.
● Metal-based conductive textiles offer high conductivity but can be heavy and
prone to corrosion, leading to exploration of alternative conductive compounds.
3.1. Conductive Inks
● Conductive inks, crucial for printed electronics, are categorized into
three-dimensional nanostructured materials (nanoparticles, nanowires,
nanotubes) or plate-like shapes.
● Functional conductive inks are developed from metals, metal oxides,
conductive polymers, organometallic inks, graphene, carbon nanotubes, or
their mixtures.
● Examples of conductive inks used in conductive textile development include
reactive silver and graphene ink.
3.2. Carbon-Based Conductive Materials
● Carbon-based materials such as graphene and carbon nanotubes are used to
develop electrically conductive textiles due to their affordability, corrosion
resistance, and flexibility.
● Graphene-based polyester conductive fabrics have been developed for
bio-potential monitoring.
● These materials can achieve different conductance levels depending on the
load content and integration techniques.
3.3. Intrinsically Conductive Polymers
● Intrinsically conductive polymers, discovered in the 1970s, are widely used in
electro-conductive textiles.
● Conductive polymers combine the electrical properties of
metals/semiconductors with the benefits of conventional polymers.
● Polypyrrole (PPy), polyaniline (PANI), and poly(3,4-ethylene
dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) are the most successful
conductive polymers in textile production.
3.4. Conductive Polymer Composites
● Conductive polymer composites improve electrical conductivity and
mechanical stability.
● These composites consist of conductive fillers like carbonaceous, metallic, and
conducting polymeric particles dispersed in a polymer matrix.
● Examples include PEDOT:PSS-polydimethylsiloxane and PPy-silver
nanocomposites.
4. Integration Techniques of Conductive Materials on/into a Textile Structure
● Smart materials are integrated into textiles via embroidering, knitting, weaving,
spinning, braiding, coating, printing, plating, and chemical treatments.
● Integration techniques are categorized based on the form of the starting
conductive material.
● Starting materials include conductive compounds, fibers, yarns, or sheets.
4.1. Integration of Conductive Compounds
● Conductive polymers and inks are incorporated via in-situ polymerization or
surface application.
● Methods include adding the compound to a polymer solution during fiber
spinning or coating/dyeing textile substrates.
● Electrospinning and printing are also used to integrate conductive compounds,
with direct-write printing depositing patterns without masks.
4.1.1. Fiber Spinning
● Conductive components are integrated during fiber spinning by adding them to
the polymer solution.
● Conductive fibers are produced via wet-spinning, where fiber conductivity and
tensile strength can be improved by annealing.
● Melt-spinning is another method used to create textile piezoelectric strain
sensors.
4.1.2. Dip-Coating
● Textile materials are immersed in a bath containing conductive dispersion.
● The process can be discontinuous or continuous, depending on the application.
● Dip-coating has been used to fabricate highly conductive cotton fabrics and
textile-based strain sensors.
4.1.3. Plating
● Plating involves adding a layer of metal components to the surface of textile
materials.
● Methods include electroplating, which requires a conductive surface, and
electroless plating, a chemical process for coating metals.
● Electroless plating is more convenient for traditional textiles, offering high
friction and corrosion resistance.
4.1.4. Screen Printing
● Screen printing is a cost-effective method for creating conductive patterns on
textile substrates.
● The process involves printing a viscous conductive paste through a patterned
stencil, followed by curing.
● Screen printing is widely used for textile electronics due to its simplicity in
fabricating flexible, strong, and thick functional layers.
4.1.5. Spray-Coating
● Spray-coating involves depositing a spray of conductive particles or droplets
onto a textile substrate.
● The technique has been used to develop textile-based organic solar cells.
● A power conversion efficiency of 0.4% was achieved.
4.1.6. Transfer Printing
● Transfer printing involves printing a design on a non-textile substrate and
transferring it to a textile fabric using heat and pressure.
● The film release transfer method is commonly used, where a design is held in
an ink layer and transferred from a release paper.
● This method produces flexible and lightweight conductive textiles for wearable
applications.
4.1.7. Inkjet Printing
● Inkjet printing is a direct-write deposition tool increasingly used in electronics
fabrication.
● It builds images and structures in a droplet-by-droplet fashion, offering design
flexibility and minimal material consumption.
● Nano-silver inkjet material can be used to develop microstrip antennas,
operating more efficiently than those made by screen printing.
4.2. Integration of Conductive Yarn and Conductive Filament Fiber
● Conductive filament fibers, yarns, and metallic wires are integrated into textile
structures by weaving, knitting, embroidery, and braiding techniques.
● The electrical and mechanical properties of the textile substrate can vary
significantly from the initial conductive material.
● This depends on placement, structure, density, and other factors.
4.2.1. Weaving
● Weaving allows for the integration of active elements during fabrication and
encapsulation of components between layers.
● Conductive yarn or filament can be integrated as warp and weft, or inserted
alongside non-conductive yarns.
● Weaving can be used to create entirely conductive fabrics or fabrics with
incorporated conductive threads or wires.
4.2.2. Knitting
● Knitting is a continuous and efficient fabric manufacturing process that allows
for the inclusion of active elements and conductive yarns during fabrication.
● It is a good candidate for rapid prototyping of smart clothing and wearable
textiles due to its relatively lower fabrication costs for small samples.
● Knitting can produce wearable antennas and textile-based triboelectric sensor
arrays for monitoring physiological signals.
4.2.3. Embroidery
● Embroidery involves applying conductive yarns or filament fibers on a textile
fabric using a needle.
● It offers the flexibility to design and embroider traces of required shapes on a
plane.
● Embroidery is a convenient alternative for complex and labor-intensive design
and production processes, enabling the integration of conductive threads into
finished fabrics.
4.2.4. Braiding
● Braided conductive fabrics are made by interlacing conductive yarns or strips
of fabric, creating entirely or partly conductive structures.
● The braiding technique has been used to produce conductive yarns with
copper filaments as the core and polyester multifilament yarn as the sheath.
● These braided yarns can be used to fabricate e-heating fabrics with superior
tensile performance and heat trapping.
4.3. Integration of Conductive Sheets: Laminating
● This technique involves placing a conductive sheet or stripe on textile fabrics
by stacking and laminating via welding, adhesive, or heat and pressure.
● It is a quick method for producing e-fabrics.
● Conductive sheet lamination has been used to develop textile-based patch
antennas based on coplanar waveguides.
5. Outlook and Future Prospects
● Standard textile production techniques may not be suitable for developing
e-textiles of specific forms.
● The choice of technique depends on the textile form, conductive material, and
required final product.
● 3D and 4D printing techniques hold promise for creating complex structures
and dynamic smart textiles.
6. Conclusions
● This review covers approaches for integrating electronic components into
textile structures.
● Achieving smart textile development relies on appropriate e-textile integration
techniques, with existing processes being modified.
● 3D printing and 4D structures could revolutionize smart textile materials.
