Showing papers by "J. Christopher Love published in 2004"

Mechanical anisotropy of adherent cells probed by a three-dimensional magnetic twisting device.

Abstract: We describe a three-dimensional magnetic twisting device that is useful in characterizing the mechanical properties of cells. With the use of three pairs of orthogonally aligned coils, oscillatory mechanical torque was applied to magnetic beads about any chosen axis. Frequencies up to 1 kHz could be attained. Cell deformation was measured in response to torque applied via an RGD-coated, surface-bound magnetic bead. In both unpatterned and micropatterned elongated cells on extracellular matrix, the mechanical stiffness transverse to the long axis of the cell was less than half that parallel to the long axis. Elongated cells on poly-L-lysine lost stress fibers and exhibited little mechanical anisotropy; disrupting the actin cytoskeleton or decreasing cytoskeletal tension substantially decreased the anisotropy. These results suggest that mechanical anisotropy originates from intrinsic cytoskeletal tension within the stress fibers. Deformation patterns of the cytoskeleton and the nucleolus were sensitive to loading direction, suggesting anisotropic mechanical signaling. This technology may be useful for elucidating the structural basis of mechanotransduction.

Fabrication of Free-Standing Metallic Pyramidal Shells

Abstract: This paper describes a technique for fabricating three-dimensional, metallic, pyramidal microstructures with base dimensions of 1−2 μm, wall thicknesses of ∼100−200 nm, and tip-curvature radius of ∼50 nm. The procedure begins with the fabrication of pyramidal pits in the surface of an n-doped silicon substrate. An electrically insulating surface layer of SiO2 covers the regions outside the pits. These pits are patterned using either conventional photolithography or soft lithography and formed by selective anisotropic etching. The resulting topographically patterned silicon serves as the cathode for the selective electrodeposition of metal in the pyramidal pits. Removing the silicon template by etching generates free-standing, pyramidal, metallic microstructures.

Nanostructures Replicated by Polymer Molding

Abstract: This article discusses materials and techniques used to generate polymer replicas of nanostructures by molding, embossing, and printing. Nanostructures are defined as those that have lateral dimensions of less than 100 nm. The effect of spatially confining materials to these dimensions gives rise to physical, electronic, mechanical, magnetic, and optical properties, e.g., quantum behavior, superparamagnetism, depressed melting point, and increased hardness, that differ, at times significantly, from those of microstructures and macrostructures. The fabrication and characterization of nanostructures are important for applications in optics, computation, data storage, specialty materials, and biology. Most processes for producing electrically, magnetically, and optically functional devices containing nanostructures include four basic steps: 1) fabrication of a ‘‘master’’ (i.e., a substrate from which replicas are formed); 2) replication of the master; 3) transfer of the replica into a functional material (e.g., semiconductor or metal); and 4) registration of the pattern of a master (the same as or different than the one used originally) with that of the replica for multilayer structures. This article focuses on the polymers and the molding techniques useful for the second step of this process.