Bistable Metal Strip Characterization: Bistable metal strips were purchased from Amazon (Seattle, Washington, USA), originally sold as slap/snap bracelets. We removed the plastic covers to obtain the metal strips with 21 cm in length, 2.5 cm in width and 0.15 mm in thickness. The metal strip has curvature on both long and short directions. The curvature for the long side is 1.5 cm and 2.4 cm for the short side. A pair of tin snips was used to cut the metal strips into different shapes with different taper ratios. A small hole was punctured on the tip of the metal strip to allow us to fix a piece of commercially available fishing thread (Beadalon Supplemax JNX0.25W-F, Coatesville, Pennsylvania, USA) with 0.01 inch diameter. We then screw a nail in the middle of the metal strip which acts as a pivot and allow its fixture on the clamp. The other end of the thread was fixed onto a force sensor (Vernier Dual-Range Force Sensor, Beaverton, Oregon, USA). A pulley was used to adjust and fix the force angles. Pull the thread until the metal strip snaps or resets and the forces are recorded in the Logger Pro software for later analysis.