Mechanics of tunable helices and geometric frustration in biomimetic seashells Qiaohang Guo, Zi Chen, Wei Li, Pinqiang Dai, Kun Ren, Junjie Lin, Larry A. Taber and Wenzhe Chen EPL, 105 6 (2014) 64005 Published online: 31 March 2014 DOI: 10.1209/0295-5075/105/64005