Soft actuators—materials that change shape in response to stimuli—are considered the foundation of the next generation of robots. These materials, which can bend, twist, contract, and expand, promise robots that move like living things, not like machines made up of gears and motors. Despite its promise for robotics, soft actuation has not progressed as rapidly as expected. The limiting factor is not engineering or control, but rather the chemistry—especially polymer chemistry.
For decades, polymer actuation has been touted as being “almost ready” to move into practical applications, but the gap between laboratory demonstration and practical implementation remains large. In recent years, electroactive polymers, liquid crystal elastomers, hydrogels, and ionic polymer–metal composites have all been touted as the next big thing in actuation, but few have made the leap to widespread real-world application. The reason for the lack of progress is simple: the materials are not good enough, and to make them better, a greater connection between polymer chemists and the larger soft actuation community is required.
The core of every actuator lies in its molecular mechanism, with performance fundamentally dictated by the chemistry of the polymer material. While mechanical design, electronics, and control algorithms can be optimized, intrinsic material limitations, such as responsiveness, durability, voltage requirements, or speed cannot be engineered away. Failures such as limited cycle life, drying out, high voltage demands, or slow response are rooted in the material’s chemistry, not in engineering shortcomings, making material selection and development crucial for actuator success.
Nevertheless, the prevailing culture in soft robotics research is that materials are secondary considerations rather than the main innovation. Many roboticists design systems using polymers selected from catalogs or prior studies. In contrast, a more effective approach is to design polymers specifically for the application and then engineer systems around these custom materials.
Let’s look at electroactive polymers (EAPs), one of the most popular classes of soft actuators. Dielectric elastomers can be made to deform significantly; however, this can be achieved only with extremely high electric fields, often exceeding 100 MV/m. This is not a minor problem; this is a fundamental materials limitation. Lowering the voltage requirement requires polymers with higher dielectric constants and higher breakdown voltage; these are materials challenges that fall squarely in the domain of polymer chemists. Likewise, ionic polymer actuators, such as hydrogels and ionomer-based polymers, suffer from long response times, dehydration, and low force output. These are all chemical limitations on the material’s performance. The performance limit is low; without new materials that can retain water or operate in a solventless fashion, this limit will never be overcome.
Liquid crystal elastomers are notable for their reversible shape-changing abilities, but their synthesis is complex, alignment is difficult to scale, and their mechanical properties are limited. Progress in actuation with these materials relies on chemists simplifying synthesis, stabilizing mesogenic units, and developing scalable alignment methods. The robotics community cannot solve these challenges alone.
The field requires a shift in perspective: moving from adapting existing materials to designing new ones specifically for actuation. This necessitates involving chemists early in device development. Researchers should ask, “What polymer must we invent to make this actuator possible?” rather than “Which polymer can we use for this actuator?”
Polymer chemistry offers significant opportunities for innovation. Dynamic covalent networks could enable self-healing materials. Sequence-controlled polymers may regulate ion transport or dipole orientation. Supramolecular materials can provide hierarchical responses. Polymer informatics is emerging as a predictive tool, revolutionizing materials discovery by informing researchers about properties beyond those found through empirical testing.
Soft robotics reveals a key challenge: while we create advanced machines, polymers are still viewed as passive rather than programmable materials. The future of the field depends on whether polymer chemists take a leading role or continue as supporting contributors. Funding agencies in the US and other countries need to take a more proactive role in promoting collaboration among researchers, particularly those working on polymer design, functional materials, and soft robotics technologies, where interdisciplinary efforts are essential. Journals need to promote materials-based innovations rather than simply device-based innovations. And finally, a set of standard testing procedures needs to be developed so that chemists can start comparing materials.
Ganesh Shimoga Credit:
Courtesy of Ganesh Shimoga
Sang-Youn Kim Credit:
Courtesy of Sang-Youn Kim
The future of soft actuation will not be found by researchers making incremental improvements to existing materials. Instead, it will be found by chemists designing polymers with actuation in mind from the beginning, polymers that are faster and longer lasting, that require lower voltages, and that work well in complex robots. And the future of robots will not be found in clever mechanisms or control algorithms. Instead, it will be found in the chemistry of materials.
To fully realize the potential of soft robotics, it is essential for polymer chemists to take a leading role. The most significant advancements in this field are likely to originate from innovations in polymer science, rather than from the robotics domain itself.
Ganesh Shimoga is a research scientist in the Polymer Chemistry Research Group of the Biotechnology and Nanomedicine Department at SINTEF Industry.
Sang-Youn Kim is a professor in the Department of Computer Science and Engineering at the Korea University of Technology and Education.
Views expressed are those of the authors and not necessarily those of C&EN or ACS.
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