Why do some materials grow near-perfect crystals with mirror-smooth faces whereas others grow rough, bumpy crystals? Our group has recently gotten a glimpse of crystal growth in real time — not by watching individual atoms, but rather by freezing model atoms that can be observed directly with an optical microscope.

Colloidal suspensions – where micro-size or nano-size particles are suspended in a fluid – exhibit various equilibrium structures ranging from face-centered and cubic-centered crystals to binary ionic crystals, and even kagome lattices. When driven out-of-equilibrium by shear, even more diverse colloidal structures can be accessed. These structures lead to unique flow behaviors of suspensions.

Articular cartilage, the soft connective tissue that coats bones in joints, is a highly complex and inhomogeneous material. It is made up of a fluid-saturated, cross-linked network of collagen fibrils whose orientation and porosity vary with depth from the articular surface. Interspersed among the network are cells and highly charged molecules called proteoglycans. Cell shape, cell density and proteoglycan density are all also spatially dependent.  

Local mechanical properties in articular cartilage and other biological tissues are typically measured by tracking the displacement of cells, cell nuclei and other fiducial markers using particle image velocimetry (PIV) and other feature-tracking methods (see "Quasi-Static Shear Mechanical Properties of Articular Cartilage").  However, these techniques are limited in spatial resolution by the density of trackable markers.  In adult articular cartilage, intervertebral disk and other soft tissues, cells can be very sparse.  Therefore, we have developed grid-resolution automated tissue elastog

Our current work is focused on characterizing healthy breast tissue.  Stay tuned for more results...

As global climates change, agriculture and crop breeding programs must increase productivity to meet the demands of growing populations while simultaneously facing decreases in soil quality.

Articular cartilage (AC), a biological tissue that protects and lubricates joints, plays a critical role during healthy locomotion.  While much is known about this tissue's biochemistry and compressive mechanical properties, comparatively less attention has been given to its shear mechanical properties.  This represents a critical knowledge gap because cartilage tissue experiences significant shear under normal loading conditions, and may indeed most frequently fail in such circumstances.

Articular cartilage (AC), a biological tissue that protects and lubricates joints, plays a critical role during healthy locomotion.  Ongoing work in the Cohen lab has been examining the spatially heterogeneous mechanical properties of this tissue using confocal rheology.  This technique allows us to simultaneously deform the tissue with a known stress and measure the local strain field.  From this information, we can calculate the local shear properties.

In thermal equilibrium, particles suspended in a fluid randomly move about due to kicks from the fluid molecules, in what is known as Brownian motion or diffusion. Shear a fluid, however, and the particles' diffusion will be greatly enhanced. Why? Diffusion spreads some of the particles to regions of the fluid with different velocities. As the fluid then carries different particles with different speeds, the particles spread out faster, effectively increasing the diffusion. This mechanism, dubbed Taylor dispersion after its discoverer G. I.

Recently, Itai Cohen caught up with Ellen Ferrante  to discuss what it is like being a scientist. The interview is available on the LiveScience website, which has partnerships with MSNBC and Google News. ScienceLives is designed to showcase scientists and engineers who are
producing cutting-edge research in their fields.

http://www.livescience.com/culture/physics-motion-itai-cohen-sl-100610.html