Mechanics of the Small

Whale A pigmy shrew consumes much more food than a whale per unit volume of their body weights. The shrew looses lot more energy through its large body surface compared to its volume - a consequence of scaling. pygmy shrew

Our primary focus is the mechanics of the small. We have two objects of study: a living cell and a material sample, both at micro to sub-micro meter scale. We are interested at the fundamental mechanisms that arise from the small size. We use both theory and experiment to explore the mechanisms. We develop micro and nano-machines to explore the world of small. Currently we are exploring the questions: How small size of material samples (such as thin films or nano wires) or their microstructures determine their properties? Does the mechanical stiffness of cancer tumors play a role in initiating metastasis, and if so, how? Do memory and learning in animals depend on mechanical forces in neurons?

How small

For a material sample, the smallness may appear in various forms, e.g., the physical size, the layer thickness of a multilayer system, or the grain size in a polycrystalline metal. Size brings interfaces. Smaller the size, higher the interface to volume ratio. At nano scale, interfaces are abundant, and they play important roles in defining macroscopic properties of materials such as mechanical strength, energy dissipation and conductivity. Interfaces interfere with the mechanisms by which macroscopic materials behave, and may generate new mechanisms.

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One of our central goals is to explore and understand the interaction between the macroscopic mechanisms and the interfaces, and the new mechanisms that interfaces may generate (structure-property relation, a fancier way of saying). For example, when the grains of a crystalline metal is large, dislocations (crystal defect) can move through the crystal when sheared to accommodate deformation. When the grain size is small, grain boundaries impede the dynamics of dislocation (deformation mechanism of the macro), and changes the deformation characteristics and strength of the metal.

Single cells are basic units of life. There is increasing experimental evidence suggesting that extracellular and intracellular mechanical forces have a profound influence on a wide range of cell behavior such as growth, differentiation, apoptosis (programmed cell death), gene expression, adhesion and signal transduction. Study of cell mechanics has drawn considerable attention from diverse fields, including biology, physics, biochemistry, and bioengineering.

Our studies of cell mechanics are motivated by three primary reasons: (1) understanding mechanotransduction - how cells transduce mechanical stimuli into biochemical processes and vice versa, (2) disease detection: is there a mechanical signature for a disease state in cell mechanical behavior, and (3) functionality change - can cell behavior be tuned by mechanical stimuli, such as expedite growth for tissue engineering, or differentiate cells to a preferred type. A deeper understanding of these issues may have a revolutionary impact on biological and health sciences of the 21st century. Recent advancements in micro-nano technology will catalyze this revolution through the unique capabilities of probing biological phenomena at a cellular and sub-cellular scale. Our current projects involve neurons, cancer cells and interactions between clusters of cells to form biological machines. We seek to address: What is the role of tension in neurons for memory and learning? Does mechanical microenvironment influence the onset of metastasis during cancer development? Can clusters of cells be guided so that they evolve into biological machines?