Mechanics and Geometry in Chiral Structures: From Helical Seed Pods to Twisted Embryonic Brain

Zi Chen, Research Scientist, Washington University in St. Louis

Friday, February 28, 2014, 3:30pm

Spanos Auditorium

This seminar is part of the Jones Seminars on Science, Technology, and Society series.

Mechanical forces play a key role in the shaping of versatile morphologies, especially chiral structures, in natural and synthetic systems.

First, an elasticity theory combining differential geometry and stationarity principles is developed for the spontaneous bending and twisting of ribbons with tunable geometries in the presence of mechanical anisotropy. Closed-form predictions are obtained from this theory with no adjustable parameters and validated with simple, table-top experiments that are in excellent agreement with the theoretical predictions. We then investigate the shape transition and multistability that also arise in a number of physical systems.

In embryos, chiral structures can also arise via mechanics. The embryonic chick brain, for example, undergoes rightward torsion, one of the earliest organ-level left-right asymmetry events in development. Here we studied the mechanical origin of brain torsion and the associated development of left-right asymmetry, through both experiments and modeling.

The study of mechanics and geometry in chiral structures will facilitate understanding of morphology generation in natural and synthetic systems, and benefit the ongoing efforts in developing programmable micro-fabrication techniques and novel functional devices such as NEMS devices, active materials, drug delivery agents, and bio-inspired robots. Studies of embryonic development can also benefit the future practices in preventing or treating some congenital defects.

About the Speaker

Zi Chen is currently a Society in Science – Branco Weiss Fellow and Research Scientist in the Department of Biomedical Engineering at Washington University. Dr. Chen received a bachelor’s and master’s degree in Materials Science and Engineering from Shanghai Jiaotong University, and a Ph.D. in Mechanical and Aerospace Engineering from Princeton under Dr. Mikko Haataja and David J. Srolovitz. He was also a visiting scholar in Dr. Clifford Brangwynne’s group at Princeton.

Dr. Chen’s research interests cover such diverse topics as mechanical instabilities of materials, energy harvesting devices, stretchable electronics, biomimetic materials/devices, nanofabrication, mechanics of morphogenesis in biological systems, mechanical feedback mechanisms in biology, DNA mechanics, dislocation dynamics, and phase transitions. Dr. Chen has received a number of awards including the Society in Science – Branco Weiss fellowship, Outstanding Paper Award at the ASME 2013 2nd Global Congress on NanoEngineering for Medicine and Biology (NEMB), American Academy of Mechanics Founder's Award, MRS Graduate Student Award Silver Award, etc. He is a founding co-Editor-in-Chief of the Journal of Postdoctoral Research, and an editorial board member of the Journal of Applied Mechanical Engineering and the Journal of Material Science & Engineering.