Active-Cells for the Construction of Redundant and Configurable Articulated Structures

This paper describes preliminary design and analysis of “active cells” used for the construction of homogeneous actuated electromechanical composite structures made from many of these electromechanical active cells. Each cell consists of a simple rapid-prototyped outer shell containing both a contractile Nitinol element and a return spring, such that these tiny, self-contained contractile engineered cells can serve as the building blocks for larger articulated structures. Each cell occupies approximately 3.0 cm³ in volume. Design considerations are explored that will affect the packing of a number of cells in a mold with a highly elastic binding agent to constrain them. The structures made from these cells can be easily fabricated in a nearly arbitrary shape — by producing an appropriate mold to contain the cells — and can be highly redundant and robust to localized cell failures. The composite structure is actuated via the application of an electrical potential across each of the individual cells, causing the cells to activate through resistive heating. The material properties of the ensemble structure can be varied by changing the properties of the binding material and the return springs of the cells, thus enabling the design of a wide range of stiffness and damping properties.