Woodruff School of Mechanical Engineering
Mechanical Engineering Seminar
Soft and Wet Materials: From Fundamental Mechanics to Bio-inspired Device
Dr. Yuhang Hu
University of Illinois at Urbana-Champaign
Thursday, April 13, 2017 at 2:00:00 PM
MRDC Building, Room 4211
Soft and hydrated materials that consist of polymeric network and solvent are ubiquitous in nature from cells, tissues to organs. They are also important engineering materials. For instance, various hydrogels have been widely used as cell culture scaffold, drug carrier, microfluidic device, sensors, actuators, soft robots, fuel cell membrane, and many others. Defying the classical definitions of solid and fluid, these materials are both solid-like and fluid-like. The coupling between liquid flow and network deformation makes the response sufficiently complex so that current mathematical models still cannot match experimental observations in many cases. Despite the importance, the experiments that promote these fundamental studies are still rare due to many practical challenges in material characterization. Our work explores this important frontier by developing an oscillation indentation method that can be easily carried out using Atomic Force Microscope (AFM). Within the theory of poroelasticity, we showed that a unified solution could be obtained for cylindrical punch, spherical indenter and conical indenter. The solutions were summarized in remarkably simple forms allowing the material parameters including shear modulus, Poisson's ratio and the diffusivity to be extracted with ease. The method was demonstrated on various gels using AFM. Besides material characterization, we also explore the bio-inspired designs of new materials based on the liquid-solid composite system. Its hybrid nature offers tremendous combinatorial potential for mixing and matching a broad range of inputs and outputs. Building upon this platform, we recently constructed a dynamically actuated skin that can change surface properties rapidly in response to programmable voltage signals. Such a dynamic skin demonstrated its ability to precisely control droplet dynamics from being completely pinned, to fast sliding, to bursting and jetting, and at the mean time allows for repeated and seamless switch among these different manipulations. These could be the desired properties in many applications such as microfluidics, anti-icing, anti-bacteria coatings, water harvesting, heat transfer and others.
Dr. Yuhang Hu received her B.S. degree in Engineering Mechanics from Shanghai Jiao Tong University, P. R. China in 2005, M.S. degree in Civil and Environmental Engineering from Nanyang Technological University, Singapore in 2007, and PhD degree in Solid Mechanics area from Harvard in 2011. She was a Postdoctoral Fellow at Harvard from 2011-2014 studying Bio-inspired Materials. In 2015, she joined the faculty of Mechanical Science and Engineering at University of Illinois at Urbana Champaign as an assistant professor. Dr. Hu's research focuses on mechanics of soft materials and bioinspired materials. Her study involves both theory and experiments. In 2016, she received the NSF CARRER award, and AFOSR YIP award.