My lab studies matter in motion. In many cases we are fascinated with emergent physical phenomena that arise from interactions between the individual constituents be they colloidal particles, polymeric strands, neurons, or individuals. Often, these complex phenomena involve materials driven out-of-equilibrium and beyond their linear response regime. Understanding their behavior often requires the development of new experimental techniques, analysis tools, and theoretical models.
We focus on a number of areas at the forefront of this broad field: I) Colloidal suspensions – where the interactions between microscopic particles suspended in a fluid control material properties; II) Biological tissues – where the organization of cells and biopolymer networks controls tissue properties; III) Biolocomotion – where emergent properties of neural networks control mechanisms needed to maintain flapping flight; IV) Origami materials – where folding tailors the shape, mechanics, and transformations of the resulting materials. Understanding the nested physical principles that act on different length scales in such systems remains one of the most challenging and interesting problems in the field of Soft Condensed Matter Physics.
Moreover, in each case, working towards a fundamental understanding of the phenomena we study has the potential to profoundly affect society. Our colloidal studies are uncovering new methods for tuning the flow properties of thickening suspensions that will be used to create the next generation flexible spacesuits, 3D printing pastes, and fluids for vehicle traction control. Our work on cartilage is elucidating the location dependent mechanical properties needed for 3D printing replacement tissues. Our work on the flight of insects is shedding light on methods used by animals to distribute control throughout their bodies as well as the neural circuits used in these controllers. Finally, learning how to self-fold graphene may ultimately serve as a pathway to self-assembly of nanoscale machines.
One of our main goals is to develop instruments and techniques for simultaneous imaging of the material structure and measurement of its flow properties. To this end, we have built shear, compression, and indentation devices that can be loaded onto a confocal microscope. These devices allow us to simultaneously image the 3-D structure of materials such as a colloidal suspension or biological tissue while measuring the amount of force necessary to deform them. In this way, the link between material structure at the microscopic scale and the material properties at the macroscopic scale can be investigated quantitatively.
To study insect flight, we developed 3D image analysis techniques for extracting insect flight kinematic data from high speed videos and the motion of humans in a crowd. Our main goal has been to automate our image extraction so that significantly larger data sets can be attained and analyzed.
To study dense suspensions of colloidal particles we often use 3D confocal microscopy. Using these images we invented techniques for measuring forces at the single particle scale as well as methods for locating particle positions and determining their radii down with nm scale precision.
This research is inherently interdisciplinary in nature. Our group freely traverses past what would be considered the traditional boundaries of Physics in pursuit of the most interesting and highest impact scientific questions. To this end, we collaborate with numerous other groups on campus with the aim of producing research results that are greater in scope than the simple cumulative contributions of each individual research group. Nevertheless, my group's ability to design and build table top experiments that combine custom built force measuring devices with techniques in photolithography, confocal microscopy, light scattering, high speed imaging, and image analysis, allows us to develop novel approaches for investigating these materials and make unique contributions to these studies.
Cheng, Xiang, Jonathan H. McCoy, Jacob N. Israelachvili, and Itai Cohen. Imaging the microscopic structure of shear thinning and thickening colloidal suspensions. Science 333, no. 6047 (2011): 1276-1279.
Lin, Neil YC, Matthew Bierbaum, Peter Schall, James P. Sethna, and Itai Cohen. Measuring nonlinear stresses generated by defects in 3D colloidal crystals. Nature Materials (2016).
Silverberg, Jesse L., Aliyah R. Barrett, Moumita Das, Poul B. Petersen, Lawrence J. Bonassar, and Itai Cohen. Structure-function relations and rigidity percolation in the shear properties of articular cartilage. Biophysical journal 107, no. 7 (2014): 1721-1730.
Ristroph, Leif, Gunnar Ristroph, Svetlana Morozova, Attila J. Bergou, Song Chang, John Guckenheimer, Z. Jane Wang, and Itai Cohen. Active and passive stabilization of body pitch in insect flight. Journal of The Royal Society Interface 10, no. 85 (2013): 20130237.
Silverberg, Jesse L., Arthur A. Evans, Lauren McLeod, Ryan C. Hayward, Thomas Hull, Christian D. Santangelo, and Itai Cohen. Using origami design principles to fold reprogrammable mechanical metamaterials. Science 345, no. 6197 (2014): 647-650.