Design parameters were chosen based on live urchin locomotory studies and were optimized to obtain the longest movement per actuation cycle, while easily and repeatably allowing adhesion and release from ferrous substrates. During the tube foot design optimization phase, the highly modular design of the Urchinbot provided an excellent experimental test bed for exploring the functionality and range of motion of these different preliminary tube foot geometries, which included 1) full asymmetrical bellows, 2) symmetrical bellows with a right angle attachment at the distal end, 3) bellows with a mix of asymmetrical and symmetrical segments, and 4) symmetrical bellows with a variable wall thickness. Based on the performance of these four different configurations, the final experimentally chosen design consisted of six symmetrical bellows which induced a linear extension, three asymmetrical bellows which enabled a tight curvature, and a permanent magnet embedded in a bi-stable domed tip. Figure 3A shows the cross-section of one of the high aspect ratio tube feet. The bi-stable domed tip with embedded magnet allowed for high force adhesion, low force retraction of the magnet, and was based on previous work on echinoderm-inspired tube feet [3]. Parameters related to the dome angle, thickness, and actuation length were experimentally modified in order to maintain a bi-stable architecture and ensure repeatability of attachment and release. A reasonable inflation pressure of 0.2 MPa was chosen based on available pumps that could operate with air or water, and the high aspect ratio tube foot was manufactured through silicone molding using a removable soft core [18]. The high aspect ratio tube foot and the soft core molds were 3D printed using an Objet30 inkjet-based 3D printer (Stratasys, Eden Prairie, MN, USA) from VeroClear (RGD810) material. Both the high aspect ratio tube feet, and the soft cores were produced in molds with appropriate gates and runners for material evacuation during the molding process.A 3 mm hexagonal aluminum rod was inserted in the soft core to lock its axial position and prevent rotation within the high aspect ratio tube foot mold. Figure 3B shows the top, bottom, and domed tip components of the three-part mold (light gray), the soft core (red) and its inserted aluminum rod (dark gray), as well as the resulting molded tube foot (green).