Page 13 - MSAM-3-2

Materials Science in Additive Manufacturing Functional materials for AM

inside soft materials utilized in extrusion-based 3D printing, of a magnetic field. In addition, a soft robot gripper capable
such as DIW. Soft materials embedded with neodymium of detecting the size of the captured object by analyzing the
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magnet (NdFeB) particles, programmed through this changing induced magnetic field was demonstrated.
method, can undergo rapid transformations of complex In addition to extrusion-based 3D printing methods, the
shapes under the influence of an external magnetic field. design and fabrication of magnetically responsive soft materials
Building on this capability, a soft robot capable of crawling using light-based 3D printing methods have been reported.
and jumping was developed. Similarly, a method has been Compared to extrusion-based 3D printing, which typically has
developed that can program not only the direction but relatively lower resolution, light-based 3D printing generally
also the density of the magnetic domain on a voxel basis has high resolution. By utilizing this technology, an eight-
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in the printed filament using an evolutionary algorithm. legged paddle-crawling robot was developed by programming
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Through this approach, a four-legged soft robot mimicking magnetic domains into NdFeB particles embedded within
a trot (dog gaits) was developed from a soft material a magnetically responsive soft material. Demonstrations of
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embedded with NdFeB particles under an alternating the robot’s crawling motion on silicone oil were achieved by
magnetic field. This demonstration highlights the potential applying an alternating magnetic field. Furthermore, a micro-
for greatly expanding application possibilities beyond the scale robotic gripper was developed using the CLIP approach
brute-force approach used to program the magnetization instead of the slower SLA approach, which exhibits clear
domain of existing magnetically responsive soft materials. boundaries between layers. This gripper utilizes Fe O with
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3
4
A mechanism was proposed to reprogram the a diameter of 20 – 30 nm, considered a superparamagnetic
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magnetization profile by folding a hinge-designed material, as a filler for achieving fast closing motion. The low
magnetically responsive material into a desired shape residual magnetization enables rapid closing of the gripper by
and applying an impulse magnetic field exceeding its elasticity.
the coercivity. Using this mechanism, a multi-finger 3D printing technology has revolutionized the field of
soft robotic gripper exhibiting precise operation was magnetically responsive soft robots, enabling the creation of
demonstrated (Figure 4A). A rock-paper-scissors gesture complex designs and sophisticated functionalities that were
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was demonstrated by re-magnetizing a magnetically previously unattainable through traditional manufacturing
responsive NdFeB material that mimics the human hand. methods. Material extrusion 3D printing offers the ability
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For hard magnetic materials that are already saturated, the to program the magnetization direction of the printed
remanence can be initialized by heating and cooling above filament by applying an external magnetic field, allowing for
the Curie point of the material in addition to applying an customized designs. This technique has proven particularly
impulse magnetic field greater than the coercive force. useful for fabricating soft robots with intricate structures and
The self-responsive soft material is soft and flexible while tailored properties. Vat photopolymerization 3D printing
exhibiting excellent responsiveness, enabling expansion also provides the capability for localized magnetization
into a core-sheath structure through integration with a programming during layer-by-layer printing. Light-based
functional core. Several studies have explored its application 3D printing generally offers higher resolution and faster
in biomedical contexts. For instance, a soft robotic catheter printing speeds compared to extrusion-based methods.
was developed using a polymer matrix embedded with However, the use of dark magnetic materials can lead to
NdFeB particles as a sheath and inserting other functional reduced curing speeds, limiting the incorporation of high
materials coaxially into the core. This catheter robot, magnetic particle contents.
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featuring an optical fiber as its functional core and a Despite the rapid advancements in 3D-printed
magnetically responsive soft material coated with hydrogel magnetically responsive soft robots, several areas still
as its sheath, demonstrated laser delivery by reaching the require improvement:
target point within a 3D cerebrovascular phantom through (i) Real-time feedback-based autonomous control: In
flexible motion. Similarly, a coaxial printing method has soft robotic applications, such as navigating through
been developed, enabling the simultaneous printing of the blood vessels, real-time feedback is crucial for obstacle
core and sheath to yield structures with excellent magnetic avoidance and path planning. Vision-based feedback
reactivity and conductivity. This method involves using a systems can be integrated with electromagnetic
conductive liquid metal core and a magnetically responsive actuation systems to enable intelligent control and
soft material sheath structure embedded with NdFeB maneuverability.
particles. Employing this coaxial printing method, a (ii) Multi-material printing: The combination of materials
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soft robot gripper has been developed, capable of grabing with different magnetic properties using multi-
objects of various sizes by transforming under the influence nozzle printers opens up possibilities for creating

Volume 3 Issue 2 (2024) 7 doi: 10.36922/msam.3323