The authors have proposed a fabrication process of "4D printer" for magnetic soft actuators. In this paper, we applied this 4D printer to bio-mimic field and show some examples using a gel material dispersed with magnetic powder. 4D printer is a recently developed process that can print out not only a 3-dimensional structure but also print deformations of the printed structure at the same time. We employed a UV-curable gel material. The material could be used in the same manner as the conventional 3D-printing process. We applied a magnetic field to set magnetic anisotropy in the curing portion during the building step. This anisotropy is set in each portion of the structure so that the printed structures could deform under an applied magnetic field. Using this technique, we demonstrated 2 kinds of biomimetic examples; one is a worm-type soft actuator and the other is an array of artificial cilia. The first example could crawl in a narrow gap. The second one could reproduce a metachronal wave, which is a phase propagation wave found on natural small organisms. We will also show a computational method to design the deformation of the structure.

In this paper, we developed a new 3D-printing system for magnetic elastomer, and demonstrated to fabricate artificial cilia. Natural cilia are hair-like organ found in nature. They are effective fluidic system in the natural world that are widely observed on surfaces of microorganisms of creatures, such as Paramecium and throat surface of mammals. Recently, the motion of cilia has been analyzed and mimicked for developing soft actuator, for example, some studies on artificial cilia driven magnetically have been reported. They are small soft actuators, and there are various manufacturing methods for these actuators depending on materials and products. Among them, authors have already developed the concept of a printing system that not only forms a three-dimensional object but also prints out the deformation of the structure. This system can fabricate various shapes of soft actuators without any assembly. In this report, we utilized UV-curable urethane acrylate as a more flexible material than that used in the previous reports, and fabricated artificial cilia by the printer. We set magnetic anisotropy to each cilium and mimicked a metachronal wave, sequential action of plural cilia that causes effective flow.

Recently, many researches on biomimetics have been reported, in which soft motions of natural creatures have also been targeted. Among them, cilia are attracting natural soft organ, which is an effective fluidic system in the natural world. Cilium is a simple hair-like organ; however, it works in a non-simple way. For example, beating pattern of natural cilium consists of 2 types of different stroke patterns; effective stroke and recovery stroke. We focused on a cilium as our target as a simple cantilever of a soft elastic material. We have already developed artificial cilia with magnetic elastomers. In this research, we compared cantilever beams with soft-and hard-magnetic particles. In this paper, we performed 2 experiments to compare the characteristics of cantilevers with 2 types of magnetic powders. In the first experiment, we utilized neodymium magnets that could be controlled the angle in order to observe the motion of beams in the static state. The latter one, we actuated beams in rotating magnetic fields to obtain dynamic behavior of an artificial cilium. As a result, we showed some differences between soft-and hard-magnetic materials.

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The authors proposed a fabricating process for soft actuators, named 4D printing system for magnetic gel materials. 4D printer is a recently developed process that can print out not only a 3-dimensional structure but also deformations in the printed structure at the same time. Our proposing process utilizes a gel material dispersed with magnetic particles as a starting material. We can design magnetic anisotropy in each portion of the printed object during additive manufacturing so that the printed structures could deform under an applied magnetic field. In this paper, we demonstrated 2 kinds of biomimetic examples by this printing system, a worm-type soft actuator and an array of artificial cilia. The first example could crawl in a narrow gap. The second one could reproduce a metachronal wave, which is a phase propagation wave found on natural small organisms. These demonstrations show that the proposed printing system could output variable bio-mimic soft actuators.