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Materials Science in Additive Manufacturing 3D-printed LMPA-integrated soft robots

to as 3D printing, a method that joins materials to create parts utilizing a two-nozzle extrusion 3D printer to achieve
from 3D model data, typically in a layer-by-layer manner. integrated printing of a soft gripper that has the function
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The versatility of 3D printing is evident across various domains, of lock in place. Our approach involves integrating low-
including aerospace, medicine, marine engineering, 15-19 melting-point alloys (LMPA) into soft robots. LMPAs,
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food, 20-23 functional structures, 24-27 and bioscience. 28-32 In the which include elements such as tin (Sn), indium (In),
realm of soft robotics, 3D printing plays a pivotal role due to bismuth (Bi), and gallium (Ga), can transition between
its capacity to construct intricate designs. 33-35 solid and liquid states at relatively low temperatures
(generally below 300°C). The advantages of LMPA include
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Soft robots, characterized by their flexibility and
adaptability, have been increasingly deployed in ease of handling, good thermal and electrical conductivity,
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applications ranging from delicate object manipulation reusability, and mechanical strength. LMPA usually
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to operation in hazardous environments where human incorporates low-melting-point elements. The applications
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intervention is not feasible. The inherent compliance of of LMPA include bionics, clean energy applications,
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soft robots allows them to interact with their surroundings thermal management, biomedical applications, and
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and handle objects with varying degrees of flexibility. electromagnetic shielding.
However, a significant limitation persists in the operation In this study, we attempted an innovative methodology
of pneumatic soft robots: they often require continuous for designing and fabricating a soft robotic gripper
external power or force to maintain their grip on objects embedded with LMPA using material extrusion 3D
during transportation, leading to unnecessary energy printing, specifically fused deposition modeling. 50,51 This
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consumption. This is particularly problematic for long- approach leverages the state-changing properties of LMPA
distance transportation, where maintaining a sustained to create a soft robot that can transition between a pliable,
grip results in considerable energy consumption. soft state, and a rigid, solid state. The basic operating
principle involves heating the LMPA above its melting
To address this challenge, Tang et al. explored the
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use of elastic instabilities to enhance the performance point to allow the soft robot to change its shape for holding
and grasping objects. While holding or grasping the object,
of soft robots. They designed a bistable hybrid soft the LMPA is cooled to room temperature so that it turns
actuator inspired by the spine of a cheetah, utilizing a into a solid state to enable the robot to continue holding
pre-tensioned linear spring and soft pneumatic actuators the object without consuming additional power.
to achieve rapid and high-force movements. The bistable
mechanism enables the actuator to switch between two By utilizing 3D printing techniques, we can precisely
stable states, providing dynamic operating regimens control the placement and integration of LMPA within the
for high-speed crawling and swimming. Wang et al. soft robot, ensuring optimal performance. The proposed
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introduced an inflatable particle-jamming gripper that grippers that can maintain a grip without continuous
combines positive pressure and partial filling to enhance energy input represent a significant advancement in soft
grasping performance. The gripper adapted its shape to robotics, addressing issues in both energy efficiency and
objects through particle jamming, presenting significant mechanical strength. Furthermore, the incorporation
compliance and robust grasping capabilities. The particle of LMPA into soft robots can enhance their operational
jamming technique offers a robust way to lock the gripper’s capabilities. The solidified LMPA not only maintains the
shape. Li et al. presented a vacuum-driven soft gripper grip but also improves the structural rigidity of the robot,
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based on an origami “magic-ball” structure. The gripper enabling it to handle heavier objects and operate in more
used negative pneumatic pressure (vacuum) to achieve demanding environments. This dual functionality of
significant grasping force while maintaining compliance. LMPA providing both flexibility and rigidity opens new
The vacuum-driven approach provides an effective method possibilities for the design and application of soft robots.
for locking the gripper’s shape. Faber et al. investigated 2. Materials and methods
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the folding mechanism of the earwig wing, which remained
open through a bistable locking mechanism and rapidly 2.1. Design of soft grippers
self-folds without muscular actuation. Inspired by this To facilitate a comprehensive evaluation, two types of soft
biological system, they developed a spring origami model grippers were designed: A pure thermoplastic polyurethane
that enables programmable morphing functionalities (TPU) soft gripper and an LMPA-integrated TPU soft
through precise design and fabrication. However, the gripper. Both grippers were engineered to possess identical
fabrication processes involved in these studies are complex. dimensions and functional characteristics, enabling a direct
In this paper, we propose an innovative solution that comparison of their performance. The design process was
aligns with sustainability and energy-efficiency principles, meticulously executed using SolidWorks 2022.

Volume 3 Issue 3 (2024) 2 doi: 10.36922/msam.4144