Control and Manipulation of Microfluidic Fluid Flow via Elastic Deformations   

We present a material with internal flexible valves that can control and direct fluid flow via external mechanical actuation for use in advanced materials for in situ mixing, chemical reactions, and rapid, portable chemical analysis. In particular, we microfabricate internal flexible valves so that macroscopic deformation leads to valve function that regulates fluid flow and so can direct flow from low to high regions of external stress. Creating a bio-inspired method for internal flow regulation will be useful for controlling fluid flow within multifunctional devices.

Mechanics of Surface Area Regulation of Cell Membranes   

We approach the complex problem of cell area regulation by using a model membrane system and a novel experimental setup, which couples a lipid bilayer to the controlled straining of an elastic sheet to study the response of pure lipid membranes to lateral stretch and compression.  We demonstrate that even a single component fluid lipid bilayer can controllably regulate its surface area upon straining by either the absorption of vesicles upon membrane dilation or through nanotube expulsion upon compression.  The processes of lipid membrane remodeling in our experiments closely resemble steps in the membrane traffic via exo- and endo-cytosis observed in biological cells.  Our results offer a simple insight into these complex cell processes as well as into the role of the lipid bilayer in their regulation and coordination.

Draping Films: A Wrinkle to Fold Transition    

Selected Press: Science News, Discovery News, Physics

A polymer film draping over a point of contact will wrinkle due to the strain imposed by the underlying substrate.  The wrinkle wavelength is dictated by a balance of material properties and geometry; most directly the thickness of the draping film.  At a critical strain, the stress in the film will localize, causing hundreds of wrinkles to collapse into several discrete folds.  In this paper, we examine the deformation of an axisymmetric sheet and quantify the force required to generate a fold. The onset of folding, in terms of a critical force or displacement, scales as the thickness to the four-ninth power, which we predict from the energy balance of the system.  The folds increase the tension in the remainder of the film causing the radial stress to increase, thereby decreasing the wavelength of the remaining wrinkles.  

Snapping Surfaces    

The responsive mechanism of the Venus flytrap has captured the interest of scientists for centuries.  Although a complete understanding of the mechanism controlling the Venus flytrap movement has yet to be determined, a recent publication highlights the importance of geometry and material properties for this fast, stimuli-responsive movement.  Specifically, the movement is attributed to a snap-through elastic instability whose sensitivity is dictated by the length scale, geometry, and materials properties of the features.  Here, we use lessons from the Venus flytrap to design surfaces that dynamically modify their topography.  We present a simple, biomimetic responsive surface based on an array of microlens shells that snap from one curvature to another when a critical stress develops in the shell structure.