Blog posts

Ting Y. Tsui, Andrew J. McKerrow, and Joost J. Vlassak

Published in the Journal of The Mechanics and Physics of Solids, 54 (5), 887-903 (2006)

Abstract – Organosilicate glass (OSG) is a material that is used as a dielectric in advanced integrated circuits. It has a network structure similar to that of amorphous silica where a fraction of the Si-O bonds has been replaced by organic groups. It is well known from prior work that OSG is sensitive to subcritical crack growth as water molecules in the environment are transported to the crack tip and assist in rupturing Si-O bonds at the crack tip. In this study, we demonstrate that exposure of an OSG containing film stack to water prior to fracture results in degradation of the adhesion of the film stack. This degradation is the result of the diffusion of water into the film stack. We propose a quantitative model to predict adhesion degradation as a function of exposure time by coupling the results of independent subcritical crack growth measurements with diffusion concentration profiles. The model agrees well with experimental data and provides a novel method for measuring the water diffusion coefficient in film stacks that contain OSG. This study has important implications for the reliability of advanced integrated circuits.

Computational models of the cell nucleus, along with experimental observations, can help in understanding the biomechanics of force-induced nuclear deformation and mechanisms of stress transition throughout the nucleus. Here, we develop a computational model for an isolated nucleus undergoing indentation, which includes separate components representing the nucleoplasm and the nuclear envelope. The nuclear envelope itself is composed of three separate layers: two thin elastic layers representing the inner and outer nuclear membranes and one thicker layer representing the nuclear lamina. The proposed model is capable of separating the structural role of major nuclear components in the force-induced biological response of the nucleus (and ultimately the cell). A systematic analysis is carried out to explore the role of major individual nuclear elements, namely inner and outer membranes, nuclear lamina, and nucleoplasm, as well as the loading and experimental factors such as indentation rate and probe angle, on the biomechanical response of an isolated nucleus in atomic force microscopy indentation experiment.

Microcantilevers have taken much attention as devices for label-free detection of molecules and/or their conformations in solutions and air. Recently, microcantilevers have allowed the nanomechanical mass detection of thin film [1-3], small molecules [4, 5], and biological components such as viruses [6] and vesicles [7] in the order of a pico-gram to a zepto-gram. The great potential of microcantilevers is the sensitive, reliable, fast label-free detection of proteins and/or protein conformations. Specifically, microcantilevers are capable of label-free detection of marker proteins related to diseases, even at a low concentration in solution [8-17]. Microcantilevers, operated in a viscous fluid, have also enabled the real-time monitoring of protein-protein interactions [8, 12-15]. Furthermore, microcantilevers are able to recognize the specific protein conformations [18] and/or reversible conformation changes of proteins/polymers [19, 20].

The Department of Mechanical Engineering at the University of Wyoming invites applications for a tenure-track faculty position. Applicants are sought at the Associate or Assistant Professor level with expertise in experimental mechanics and particularly in emerging areas of science and technology. Such areas include but are not limited to the study of biomaterials, tissue engineering, nanomechanics of engineering materials, as well as thin films and multilayers, fracture, fatigue and damage.

The successful applicant will be expected to establish a strong, funded research program, as well as teach at the graduate and undergraduate levels. She/He will be expected to participate in interdisciplinary research efforts both within and outside the College of Engineering. Minimum qualifications include an earned doctorate in mechanical engineering, materials science/engineering, or a closely related field.

Cellular and Molecular Mechanics

I was invited by Dr. Zhigang Suo to write a short piece on “Cellular and Molecular Mechanics”. I am writing this informally to introduce this subject matter rather than talk in vernacular such as mechanotransduction, phosphorylation, etc. I have more formal papers if someone is interested in more detailed discussions on this subject area. This is a field in which I have been working for over a decade now and I find it more exciting every day. The question always is how does mechanics affect biological processes. This is a very interdisciplinary subject matter as mechanists, engineers, physicists, chemists, and biologists have been investigating this process from various perspectives. I am obviously not the first to study this process. For most of us, it is realized from an empirical perspective that mechanics matters to biology, but exactly how mechanics specifically alters biochemistry continues to be highly debated today. Mechanics of course matters in many physiological areas. Your blood flows, your heart pumps, your bone and muscle feel mechanics. Not only does the body experience mechanical stimulation, but it reacts biochemically to it. A wonderful example is when people go into space (NASA) for long periods of time. The bone in one’s body begins to resorb in a similar response mode to what one experiences in aging (osteoporosis). This is primarily due to just the change in the gravity (mechanics). Other diseases are related to these issues including the two biggest killers: heart disease and cancer. While biomechanics on this scale has been studied for awhile (Leonardo Da Vinci, who was interested in mechanics, also wrote one of the first texts on anatomy), the movement to the cellular and molecular scales has brought a tremendous amount of excitement. I consider the cell as one of the ultimate smart materials exhibiting these characteristics. The cell has evolved over millions of years and is designed better than almost any system that we can personally build. Just as the biological eye provides a beautiful template for optics based lenses, much can be learned about building technology (“nanotechnology” and “microtechnology”) through examining the behavior of cells and molecules.