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Page 20 of 35 Kulkarni et al. Soft Sci. 2025, 5, 12 https://dx.doi.org/10.20517/ss.2023.51

Design and topology optimization
Design approaches for soft robots are primarily based heuristically and empirically on bioinspiration and
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intuitive perspectives . Although traditional biomimetic and intuitive approaches have documented
utility , their outcomes are based on initial assumptions about the structure and are greatly dependent on
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anthropogenic factors, such as the designers’ experience, and professional knowledge . The design of soft
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actuators presents challenges due to the hyper-elastic and viscoelastic properties of low-modulus materials
that produce highly dimensional design spaces . Optimization algorithms, simulation, and analysis tools
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targeting more efficient design methods have been explored . Topology optimization is one such method
for form-finding of high-performance, lightweight, multifunctional structural designs and has been widely
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used in aerospace , automotive , and architecture industries .
Topology optimization works to identify numerically optimal structural forms by allocating material
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distribution that satisfies prescribed constraints within a specified design domain . That domain,
predefined by the user, supplies the loading and support configuration and a geometric region on which the
material distribution is determined by individual design variables. For compliant mechanisms, such as
grippers, the objective function typically maximizes mutual potential energy, geometric advantage, or
mechanical advantage . For example, a soft, cable-driven compliant gripper uses topology optimization to
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model interactions between grippers and objects in the form of pressure loading and friction . This
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method has been demonstrated to design flexible thermoelectric devices with increasing output voltage and
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a corresponding improvement in power generation efficiency . It allows for the design of multiple
microstructural materials within a macrostructure geometry that has spatial variation and hierarchical
structures . Using these methods, nonlinear viscoelastic and even hyperelastic properties of materials used
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in soft robots can be considered . Topology optimization techniques allow designers to improve the
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efficiency and performance of robot design, beneficial when developing devices to function in complex
environments.

The human body is a challenging environment due to its susceptibility to tissue damage. With the
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increasing use of soft robots in healthcare services and their interaction with fragile materials such as
human tissue becoming more common , the safety of these robots is a growing concern . In such cases,
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reducing the mass and inertia of these robots minimizes the risk of injury to humans during interactions.
Thus, structural topology optimization is beneficial for designing lightweight medical devices . The
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medical industry has proposed topology optimization techniques to design prosthetics and implants such as
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soft compliant finger prosthetics , soft finger-like devices , and bioinspired quadruped compliant
legs . These biomedical soft devices can mimic the stiffness, density, and structure of the body part such
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that they can avoid causing injury .
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In challenging environments such as confined spaces, topology optimization can be advantageous in
creating efficient designs for effective locomotion. One study developed a framework specifically for moving
objects using a topology optimization method incorporating a material point method that can simulate the
motion of objects . Similarly, topology optimization methods have been used in aerospace and marine
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environments where the weight of the craft, ship, and other devices is an important consideration.
Expanding the use of topology optimization in soft robot design should broaden the application space and
enable rapid optimization of soft devices capable of withstanding these complex environments.

Control systems that enable soft robot use in extreme environments
Developing control systems for soft systems is a challenge as soft robots have continuous flexible structures
as opposed to discrete degrees of freedom. Therefore, implementing control systems that consider the
mechanical structure or properties of these devices is crucial to developing reliable and efficient systems.