## 3 Fabrication Methods
### DW Methods
By precisely depositing the conducting polymer onto desired substrates, researchers have been able to create intricate electrode structures with enhanced conductivity and flexibility [187]. An innovative double-layered graphene conductor has been developed to enhance the optical and electrical properties of organic LEDs, offering a high surface area for improved performance [188]. A novel method called consecutive ink writing (CIW) has been developed to enable the printing of conducting polymer composites onto various flexible plastic substrates. This method involves an iterative extrusion process that produces a filament with a consistent diameter of 1.75 mm. By incorporating matrix polymers and carbon fillers, composite materials can be effectively used in 3D-printing applications. The CIW method provides a versatile approach for fabricating conducting polymer composites with precise control over the deposition process. The iterative extrusion ensures a uniform filament, which enhances the consistency and reliability of the printed structures. This method allows the integration of carbon fillers, enabling the customisation of electrical conductivity and mechanical properties of the printed composites. The ability to print conducting polymer composites on flexible plastic substrates opens a wide range of possibilities in the field of flexible electronics. These composites can be used to create functional components, such as sensors, electrodes, and interconnects, with enhanced electrical conductivity and mechanical flexibility. The versatility  
Figure 10: 3D designs: (**a**) micro-LED array [175], (**b**) fluidic antenna [184], (**c**) hybrid materials [180], and (**d**) six capacitors [186]. of the CIW method enables the fabrication of complex 3D structures, further expanding the potential applications of these composite materials in various industries, including electronics, robotics, and healthcare [189]. This novel CIW process makes it possible to quickly print composite materials with a lot of graphene filler onto different substrates in 2D and 3D shapes. The CIW method allows for 3D printing of PEDOT: PSS and graphene ink on both rigid glass and flexible polyimide substrates. This versatile technique offers precise control over the deposition process, enabling accurate and reliable printing of conducting polymers and graphene materials. The CIW method has significant potential in various fields, such as flexible electronics, sensors, and energy devices. Further research and development in this area will optimise the CIW technique, opening possibilities for creating complex and functional 3D-printed structures on different substrates; an example is shown in Figure 11a [190]. Recently, polymer 3D printing has been utilised in devices for healthcare applications; for example, tissue scaffolds have been designed using polyjet and stereolithography printing that can be used to achieve hierarchical forms that can mimic the bone. A conductive polymer can be used to create implants that do not degrade in the human body. Polymer 3D-printing methods such as extrusion, resin-based printing, and powder-based printing provide flexibility in material choices and support a wide range of design shapes, responses, layouts, etc. [191]. To create a textile-based sensing device to be used in healthcare applications, several designers have incorporated 3 Dp technology, including FDM and SLS; an example is shown in Figure 11b [192]. Spray coating is a DW method that can make a film deposition on a substrate, and which changes its dielectric values (\(\epsilon\)) (Figure 12). This method has been broadly utilised because of its high speed (200 mm/s). Inks with a wide range of viscosities from 0.7 to 2500 mPa can be printed. Antennas, which can be used on IoT devices, have been easily fabricated using a simple spray-on method. As an example, researchers fabricated a 1-mm-thick MXene RFID tag with a reading range of 8 m at 860 MHz [193].