# Additively Manufactured Polymers for Electronic Components
## 4 Applications in the Electronic Field of Additively Manufactured Polymers
### Actuators  
Shape memory polymer (SMP) actuators can mimic human muscular response to multiple stimuli--i.e., light, electricity, magnetism, temperature, pH, or moisture levels. Although they have limitations like fatigue and slow responses, 3D printing of SMP materials has shown the possibility of fabricating SMP actuators cheaply and with a fast responsive ability to various stimuli, including light, electricity, magnetism, heat, pH changes, and moisture [150]. SMPs also offer several advantages, including low density, large strain recovery, biocompatibility, and biodegradability [151]. For example, 3D-printed SMPs were used to produce a simple gripper. The research studied the effect of multiple parameters, such as nozzle temperature control and filament speed during the extrusion process, to optimise the quality of the actuator in terms of part density, dimensional accuracy, and surface roughness [152]. Additionally, different deformations, referred to as predetermined self-evolving behaviours, were achieved by 3D-printed polymer materials after water immersion (Figure 13c) [153]. Bi-stability is another intriguing property of SMPs, allowing structures with zero degrees of freedom to have two or more stable positions under specific conditions. These structures can pass from a stable configuration to another with a slight deformation. For example, a 3D-printed bi-stable actuator made of nylon was successfully fabricated (Figure 13d) [154]. Soft actuators can be manufactured very effectively using 3D printing technology [155; 156; 157]. These soft actuators can achieve substantial strain, up to nearly 200%, due to their low Young's modulus and high elastic energy density. For instance, a two-layer dielectric elastomer (DE) actuator was 3D printed using an acrylic-based photopolymer, leading to the creation of a facial robotic system that mimicked human facial muscles [150]. Moreover, 3D printing has enabled the creation of generators using dielectric elastomers, which can be applied for energy harvesting, as in orthotic shoe inserts that capture energy during gait. In another application, a hexapod robot with multiple degrees of freedom was created using 3D-printed DE soft actuators, with all parts manufactured through 3D printing [158]. Soft piezoelectric materials, or piezoelectric polymers, are also used as actuators due to their flexibility, softness, transparency, and lightweight properties. They can convert electrical voltage into mechanical strain, making them suitable for various applications. While many piezoelectric actuators are produced via electrospinning, an exception is a polyvinylidene fluoride actuator created using inkjet printing. This actuator was used as a reciprocating membrane pump in a smart lab-on-a-chip system, showing its practical utility [159]. Furthermore, a cost-effective approach for producing active piezoelectric nanoparticles was developed using microscale dynamic optical projection stereolithography. This innovative method enhanced printing resolution and throughput compared to traditional SL techniques, particularly for 3D printing of piezoelectric polymers [160]. Figure 12: Wearable strain sensors made through aerosol-jet printing have important healthcare applications. (**a**) One example is a sensor printed on a commercial bandage and cured with laser sintering, used to monitor wrist joint mobility. (**b**) Another sensor, printed on an elastomer, maintains its shape and adhesion even when the skin wrinkles, ensuring its effectiveness in practical use. Adapted and reprinted with permission from ref. [149]. Figure 13: (**a**) Spontaneous and sequential shape recovery process of the helical SMP component with a graded hinge section, reactive to thermal stimulus. (**b**) SMP gripper printed using FDM and heated above T\({}_{\text{g}}\). (**c**) The initial joint and its folding after immersion in water, with their corresponding spring-mass systems. (**d**) Three-dimensional-printed nylon bi-stable structure using a compliant mechanism.