Inspired by the rolling behavior of oosperm through smooth muscle contraction of fallopian tube, a simple biomimetic experiment is devised in order to disclose the possibly mechanical transport mechanism. An interesting experimental observation demonstrates that an elastic strain gradient can be utilized to transport a soft latex bubble on a stretchable substrate by rolling. A corresponding theoretical model is established, in which an elastically three-dimensional bubble contacts adhesively on an elastic substrate subject to strain gradient. The initiation and steady-state energy release rates for such a rolling motion are achieved and analyzed. The influencing factors of rolling are found. The finding may have general implications on designing active transport systems with strain gradient.
Support from the National Natural Science Foundation of China (Grant Nos. 11372317, 11125211), the 973 Nano-project (2012CB937500), and the CAS/SAFEA International Partnership Program for Creative Research Teams are gratefully acknowledged. The work of HG has been supported by the Center for Mechanics and Materials at Tsinghua University.