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Materials Science in Additive Manufacturing Functional materials for AM

through the integration of DIW printing and automated printed matrix and DIW-printed functional materials was
pick-and-place of electronic components within a unified achieved. The developed strain gauge exhibited a gauge
manufacturing platform. Ink using silver flakes as filler in factor of 251, indicating relatively excellent sensitivity.
a thermoplastic polyurethane (TPU) matrix is printed as a Advanced 3D printing techniques, such as multi-
strain gauge, along with a pick-and-place microcontroller material extrusion, hybrid printing, and coaxial printing,
and LED, resulting in the development of a large-area have emerged as powerful tools for fabricating soft sensors.
wearable strain gauge. The developed strain gauge outputs These 3D printing methods have particularly facilitated soft
LED readings according to joint bending. Similarly, a sensors embedded with metallic nanoparticles, enabling
moisture sensor was developed through a pick-and-place immediate fabrication on request. The integration of metal
hybrid procedure of DIW 3D printing and surface-mount particles into non-conductive polymer matrices imparts
electronic components (LEDs). Polyethylene oxide electrical conductivity, while the inherent flexibility of
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(PEO) composite with silver flakes as conductive filler polymers facilitates their applications in various fields,
was extruded and printed in the form of an induction such as strain sensors and wearable sensors. Despite their
coil. When immersed in water, the printed conductive advantages, metal particle-embedded soft materials face
traces undergo a reverse drying process and exhibit higher several challenges:
impedance. Under controlled moisture, the ink maintains (i) High-temperature sintering: Metal nanoparticles often
its printed shape and recovers to its initial impedance level require high-temperature sintering (typically above
after drying. 100°C) to enhance electrical conductivity, hindering
In addition, a flexible sensor was developed to detect the in situ fabrication within the human body.
deformation and posture of a snake-like soft robot based (ii) Cost limitations: Silver nanoparticles, the most
on liquid metal (Figure 4B). Liquid metal-based sensors commonly used, are expensive, thereby limiting their
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have the advantage of measuring large deformations suitability for mass production. Although copper
by remaining connected even after experiencing large nanoparticles are cheaper than silver nanoparticles,
deformations due to their stable electrical properties. they are less commonly used due to the aforementioned
Since liquid metal has low printability, silicon and liquid manufacturing difficulties.
metal are printed together coaxially. The sensor is printed (iii) Oxidation: The large surface area of nanoparticles
in the shape of a solenoid and can be installed on a soft makes them susceptible to oxidation, potentially
robot, such as a snake, to distinguish tensile and bending compromising their long-term performance.
deformations.
3.3. Perovskites
Extrusion-based 3D printing has been considered the
predominant approach for fabricating soft sensors embedded Perovskite materials have attracted considerable interest in
the semiconductor field due to their unique characteristics,
with metallic powder. However, a limited but notable such as strong absorption coefficients, excellent tolerance
alternative has been reported: vat photopolymerization to defects, and high charge carrier mobility. 76-78 Perovskites
printing. Photopolymerization-based printing is only generally possess ABX structure, where A and B represent
applicable to photosensitive resins, and metallic powders cations, and X represents an anion (A: MA or FA or
3
+
+
may absorb and reflect light, potentially impeding sufficient Cs , B: Pb or Sn , X: Cl or Br or I ). The enhanced
-
-
-
+
2+
2+
light penetration into the material. These limitations can photoluminescence quantum yield (PLQY) and superior
result in incomplete curing of the material and degradation color purity inherent to perovskites significantly enhance
of mechanical properties. In addition, metallic powders the power conversion efficiency (PCE) in solar cells. 79-83
have high thermal conductivity, which can concentrate Furthermore, their broad wavelength spectrum facilitates
heat energy generated during the photopolymerization the generation of diverse light colors in LEDs, which
process onto the soft material, leading to thermal damage plays a critical role in achieving high-resolution display
or deformation of the material. technologies. 84,85 Moreover, these properties are critically
To circumvent these limitations, hybrid 3D printing that harnessed in engineering highly sensitive sensors capable of
integrates the advantages of vat photopolymerization and detecting subtle environmental alterations. Conventional
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extrusion-based 3D printing was developed. This approach fabrication methods of perovskite devices include spin
has demonstrated strain gauge fabrication. The hybrid coating, spray coating, and blade coating. However,
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87
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3D printer combines DLP for high-resolution printing of spin coating often leads to substantial material loss, spray
a photosensitive matrix and DIW for printing conductive coating poses challenges in controlling the uniformity of
silver nanoparticle ink. Through optimization of printing perovskite layer thickness, and blade coating encounters
parameters, strong interfacial bonding between the DLP- difficulties in fabricating ultrathin films.
Volume 3 Issue 2 (2024) 10 doi: 10.36922/msam.3323