Autonomous Soft Robotic Machines by Kinetic Asymmetry in Hydrogel Engines

• Applicant: Professor Dr. Andreas Walther
• Subject Area: Polymer Materials
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 543779550

Classical hydrogel soft robotics are based on bilayer actuators that follow reciprocal motion and cannot accumulate work or propel themselves in cyclic operation of agonist/antagonist triggers. By taking inspiration from kinetic asymmetry of molecular machines, this proposal aims to develop generic concepts for hydrogel engine systems in which the built-in kinetic asymmetry in swelling/deswelling transitions allows continuous extraction of mechanical work through cyclic operation of uniformly applied agonist/antagonist stimuli. The key element is the achievement of non-reciprocal motion through a material-embodied ratcheting mechanism combining chemically identical hydrogels with different porosities. A thorough understanding of the physicochemical principles for achieving kinetic asymmetry in swelling/deswelling kinetics (by engineering porosity) will therefore be the foundation. Via Finite Element Modeling, spatial asymmetry in compartmentalized hydrogel devices under kinetic actuation asymmetry will be predicted, maximized by geometric design, and then transferred to soft robotic engines by which energy of an external stimulus is converted into hydraulic or kinetic energy for the accumulation of work. The hydrogel engine system will be implemented into soft robotic machines with various configurations that act as artificial flagella for breaststroke motion and artificial cilia that generate metachronal waves for pumping fluids. A crucial aspect is to go beyond external agonist/antagonist switching, and in the final steps, the soft robotic engines will be coupled with photoacids and chemical oscillators to achieve remote-controlled operation and truly autonomous and automotive soft robotic machines. Overall, this project will introduce the concept of kinetic asymmetry - largely known from the field of molecular machines - to the world of soft robotics materials by demonstrating autonomous soft robotic hydrogel engines and their machines capable of accumulating work and performing functions. In combination with chemical controllers and photochemical manipulators, we will show how autonomous and remote operation can be possible. In a more abstract way, we hope to inspire material scientists to think about simplicity in material selection, since our kinetic asymmetry will not use multiple orthogonal stimuli requiring multiple materials, but we will simply use the physics of swelling/deswelling kinetics through porosity engineering of the kinetic asymmetry of the same material. This could help in a technological translation.

• DFG Programme: Research Grants