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Here, 3D printable auxetic tubular springs from thermoplastic polyurethane (TPU) for rapid and sustainable hopping are developed. Because the springs have negative Poisson's ratios, they become stiffer as compression proceeds and theoretically stores 35.2% more energy than a linear spring with the same stiffness. As the stress concentrates on the hinges, it is revealed through experimental, numerical, and analytical investigations that hinge geometries, for example, the lattice angle and hinge radius, governs the global stiffness and robustness of the springs. The hopping robot leg composed of three auxetic tubular springs in parallel sustains more than 1,000 cycles of repeated, one\u2010degree\u2010of\u2010freedom (1\u2010DOF) vertical hopping and two\u2010degree\u2010of\u2010freedom (2\u2010DOF) forward hopping. The 2.5\u2009kg\u2010robot system requires minimum 420\u2009mJ of elastic energy for repeated hopping. The springs are pre\u2010compressed by tendon\u2010driven actuators and stores 1.08\u2009J during jumping and release the springs when touching the ground. The power stroke is calculated as 15\u201318\u2009W. The average velocity of the hopping robot reaches 0.06\u2009m\u2009s<jats:sup>\u22121<\/jats:sup> with the increase of touchdown angle to 0.125\u2009rad. The cost of transport is calculated as 6.7, similar to those of the living organisms.<\/jats:p><\/jats:sec>","DOI":"10.1002\/aisy.202100152","type":"journal-article","created":{"date-parts":[[2021,12,19]],"date-time":"2021-12-19T05:24:40Z","timestamp":1639891480000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":24,"title":["Tendon\u2010Driven Auxetic Tubular Springs for Resilient Hopping Robots"],"prefix":"10.1002","volume":"4","author":[{"given":"Young-Joo","family":"Lee","sequence":"first","affiliation":[{"name":"Department of Materials Science and Engineering University of Pennsylvania  3231 Walnut Street Philadelphia PA 19104 USA"}]},{"given":"Shivangi","family":"Misra","sequence":"additional","affiliation":[{"name":"Department of Mechanical Engineering and Applied Mechanics University of Pennsylvania  220 South 33rd Street Philadelphia PA 19104 USA"}]},{"given":"Wei-Hsi","family":"Chen","sequence":"additional","affiliation":[{"name":"Department of Electrical and Systems Engineering University of Pennsylvania  200 South 33rd Street Philadelphia PA 19104 USA"}]},{"given":"Daniel E.","family":"Koditschek","sequence":"additional","affiliation":[{"name":"Department of Electrical and Systems Engineering University of Pennsylvania  200 South 33rd Street Philadelphia PA 19104 USA"}]},{"given":"Cynthia","family":"Sung","sequence":"additional","affiliation":[{"name":"Department of Mechanical Engineering and Applied Mechanics University of Pennsylvania  220 South 33rd Street Philadelphia PA 19104 USA"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8834-3320","authenticated-orcid":false,"given":"Shu","family":"Yang","sequence":"additional","affiliation":[{"name":"Department of Materials Science and Engineering University of Pennsylvania  3231 Walnut Street Philadelphia PA 19104 USA"}]}],"member":"311","published-online":{"date-parts":[[2021,12,19]]},"reference":[{"key":"e_1_2_8_2_1","doi-asserted-by":"publisher","DOI":"10.1002\/aisy.201900163"},{"key":"e_1_2_8_3_1","doi-asserted-by":"publisher","DOI":"10.1242\/jeb.004226"},{"key":"e_1_2_8_4_1","doi-asserted-by":"publisher","DOI":"10.1242\/jeb.02146"},{"key":"e_1_2_8_5_1","unstructured":"R.Van Ham B.Vanderborght M.Van Damme B.Verrelst D.Lefeber inProc. 2006 IEEE Int. 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