Gymnarchus niloticus. Credit: Wikimedia Commons

Fish fins inspire soft material

30 December 2022

Researchers have developed a new soft material which can be magnetically manipulated and has potential in multiple fields including biosensing, microfluidics and robotics.

The material, a ferromagnetic silicone elastomer attached to a hard substrate, was created by a team led by Professor Zhang Li from the Chinese University of Hong Kong. According to Li the rippling movement of knifefish fins was the inspiration, “Natural organisms often exhibit highly controllable morphological transformations to enhance their adaptability to the physical environment. For example, a variety of plants with wrinkled surfaces can modulate their hydration by changing their surface areas, while the knifefish ensures its locomotion is manoeuvrable and stable by regulating its wavy ribbon fins. Inspired by the wavy fins of knifefish that can buckle freely, we have developed a magnetic elastomer that can freely deform to achieve the multimodal transformation of 3D structures at different dimensional scales.”

Ribbon fin-based propulsions have been achieved at the centimeter scale (20–50 cm) by using electromechanical systems to control the locomotion of multiple nodes on the ribbon. At smaller scales, because of limited space, electromagnetic propulsion is more difficult. To solve this problem Li and his colleagues attached two 16mm strips of the magneto-elastomer to a polylactic acid flat plate and activated the strips using three-axis Helmholtz coils. The resulting swimming device moves efficiently in four directions.

To achieve the wavy effect, the team used geometric constraints and an organic solvent to encode 3D heterogeneous magnetisation profiles into the material. The resulting structures generate diverse buckling transformations across different scales with tunable geometric parameters. Changing the direction of the magnetic stimuli and field gradient produces reversible multimodal anisotropic transformations of the structure. External magnetic stimulation is used to determine the stable state of soft structure during buckling process. Prolonged magnetic stimulation is not needed.

Using different configurations of elastomer, substrate, magnetic field and solvent, Li and his colleagues have demonstrated additional potential uses for the material including in fluidics, selective object trapping and biomedical analysis.

The image shows the geometric transformation of cellular structures and simulation results with different magnetic field inputs. Credit: Chinese University of Hong Kong

The collaborative team includes Dr Jin Dongdong from the Chinese University of Hong Kong, Professor Zhang Jiachen from the City University of Hong Kong, and Professor Wang Liu from the University of Science and Technology of China. Their research results have been published in Nature Communications.