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Title:Effects of micro- and nano-scale surface geometry on behaviors of live cells and liquid droplets
Author(s):Grigola, Michael
Advisor(s):Hsia, K. Jimmy
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
cell alignment
Surface waviness
Abstract:As the scale of the surface texture responsible for superhydrophobicity becomes similar to the size of a droplet, simple models based on homogeneity assumptions begin to break down. In order to better understand these discrete phenomena, we first create a unique model with the finite element software, Surface Evolver, which simulates a droplet atop the individual features that comprise a superhydrophobic surface. We observe that the well-known Cassie-Baxter and spherical cap models give poor estimates of characteristics such as contact angle and wet area and also fail to capture the complex liquid surface geometry when features have discrete size. Further exploring this theme, we consider the influence of gravity on these theoretical models using analytical and simulation results, and we find that the impact of gravity on droplet shape becomes non-negligible as surfaces become very hydrophobic. Motion is also significantly affected by discrete features, for example increased hydrophobicity may actually hinder droplet motility due to pinning. In light of this, we analyze data collected with a novel method of measuring forces in moving droplets to better understand the dynamics of pinning. The results and methodology developed here will help other researchers better understand the relevant mechanics in micro-scale droplets. In a different setting, surface geometry also affects biological cells by altering their mechanical environment. In the case of cell mechanics we generally lack even a flawed model for describing the observed behavior, so we seek to identify parameters that might simplify these cellular systems. One method that allows us to investigate the effects of mechanics on cells is to expose the cells to uniform, periodic patterns. We first describe a unique procedure for generating approximately sinusoidal patterns at multiple length scales using thin-film buckling. These patterns are applied to study cells, first with muscle cells at the nano- to micro-scale where the patterns help identify a trend of muscle alignment as a function of surface characteristics. In the process we discover that cell-cell interaction also plays a role in the alignment. Next we investigate the effects of geometry on epithelial cells where the wavy patterns are used to ascertain the cause of unexpected ductal formations in a hydrogel culture. The cause is apparently mechanical and a result of variation in stiffness due to the underlying geometry. A final section also illustrates some of the techniques that were developed and used to investigate these phenomena, and which may be used by other researchers to further study these topics. These studies help better our understanding of mechanics at the micro- and nano-scale, while the methods used herein may be applied to a number of similar systems.
Issue Date:2014-05-30
Rights Information:Copyright 2014 Michael Grigola
Date Available in IDEALS:2014-05-30
Date Deposited:2014-05

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