The rapidly developing area of additive manufacturing, usually known as 3D printing, encompasses a wide range of applications, including aerospace, automotive, biomedical, construction, and textiles [
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2]. The evolution of 3D-printed fashion shows is well-known among designers as the future of fashion, a trend that gained significant momentum in 2011 when Iris van Herpen’s 3D-printed dress debuted at Paris Haute Couture Fashion Week and was later recognized by Time magazine as one of the best inventions [
3]. This dress, created by scanning the wearer’s body for individualized customization, attracted considerable attention for its unique characteristics. In 2014, the “Ice Dress,” a transparent resin creation featuring intricate 3D-printed materials, was showcased exclusively on the catwalk [
4]. For the 2015 Chanel Haute Couture Show, Karl Lagerfeld utilized SLS printing to develop innovative mesh designs on fabric. At the 2016 Met Ball, Claire Danes' Zac Posen gown created a stunning visual effect in the dark through the use of cutting-edge lighting. In the same year, Paris introduced water-soluble clothing that disintegrated to reveal new styles. In 2019, glow-in-the-dark fashion technologies made a splash with Richard Nicoll’s dress at his London show and Zendaya’s fairy dress at the Met Gala, both of which stood out as leading innovations due to their unique formability and artistic expression. From the past decade, 3D printing has expanded large acceptance in the realm of smart textiles, inspiring increased interest among academics and industry professionals in recent years [
5]. Takagi introduced the concept of smart materials in 1990 as those that respond to environmental changes optimally. Smart materials began in Japan in 1989 with shape memory silk yarn, and by the early 2000s, the first textile electronic components were produced [
6]. Smart textiles, or intelligent textiles, are fabrics embedded with electronics like conductive fibers and sensors that detect and respond to stimuli from the human body, such as thermal, chemical, and biological changes, creating wearable clothing that monitors temperature, tracks health condition monitoring, and enhances interaction with the environment [
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10]. In healthcare, fashion, entertainment, and defense, smart textiles hold significant potential to enhance conventional materials, with comfort being crucial for consumer adoption [
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3D printing technology merges traditional textile techniques with innovative production methods, enhancing the industry's versatility and enabling precise, customizable designs through computer-aided design (CAD), while also offering complex designs at a lower cost, often unattainable with conventional production processes. Smart textile devices necessitate a multidisciplinary approach to circuit design in the development of intelligent textiles integrating knowledge of intelligent materials, microelectronics, and chemistry with a profound understanding of textile manufacturing to get optimal outcomes.
Figure 1 illustrates how 3D-printed smart textiles, embedded with integrated sensors, provide a sophisticated solution for the continuous monitoring of various health conditions in the human body. They fulfill various roles in technical textiles—such as thermal insulation, safety, and energy storage—as well as in security applications like identification and monitoring, and aesthetic features such as color changes and light emission [
12]. Nowadays, several 3D printing methods are leveraged in the production of customized smart textiles, including FDM, SLS, DIW, and PolyJet printing [
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14]. Different materials used in 3D printing for smart textiles require specific attributes depending on the application of the final product. Various polymers are employed in 3D printing, each with distinct characteristics and purposes. Polylactic acid (PLA) is a popular choice due to its wide range of colors, designs, and biodegradability [
15]. PLA composites produced through FDM-based 3D printing are versatile, with applications in bioprinting, sensor development, four-dimensional (4D) printing, smart textiles, and luminescence technologies [
16]. TPU-based flexible conductive filaments enable direct 3D printing onto textiles for electronic textile applications, offering flexibility that allows the printed material to bend and flex with the fabric [
17]. Acrylonitrile butadiene styrene (ABS) is well-suited for durable applications [
18], while thermoplastic elastomers (TPE), TPU, and thermoplastic copolyester (TPC) are known for their high durability and flexibility [
19]. Nylon is commonly used for applications that demand long-lasting parts, such as tools, functional prototypes, or mechanical components [
20]. Smart materials like shape memory alloys (SMA), ferrofluid, magnetorheological fluids, electroactive polymers (EAPs), piezoelectric materials, and chromogenic materials are also integrated into 3D printing [
21]. Resins, colloids, filament/paste, powder, and solid sheets are the primary materials for 3D printing. The technical requirements of the embroidery machine influence the choice of cord and ground fabric. Materials such as conductivity threads that are active metal wires, layered polymers, and carbon fibers are often employed [
22]. Conductive threads, in particular, are valuable for creating circuits for sensors, actuators, heating elements, sound transmission, or LED contact points.