Analyses of biopolymer/calcium carbonate composites grown on inorganic abiotic substrates implanted between the shell and the shell-secreting epithelium of live red abalones (Haliotis rufescens) provide detailed spatial and temporal data on the in vivo assembly process that generates the shell. X-ray diffraction and scanning electron microscopy analyses of the growth of these flat pearl composites reveal that biomineralization is initiated by the deposition of an organic sheet on the implanted substrate, followed by the growth of a calcite layer with preferred {10.4} orientation and, finally, by the growth of nacreous aragonite. The calcite layer is structurally similar to the green organic/calcite heterolayer of native shell nacre. It comprises 0.2−2.0-μm-diameter elongated crystallites of typical geological habits in various aggregate arrangements. The shell also contains an external layer of (00.1)-oriented prismatic calcite, which is deposited on one edge of a flat pearl and has a morphology similar to that of the {10.4}-oriented calcite layer. The transition from {10.4}-oriented calcite to aragonite in both the shell and the flat pearl is abrupt. In vitro calcium carbonate growth experiments reveal that a similar calcite-to-aragonite transition is induced by the addition of soluble proteins isolated from the aragonitic nacre. The growth of flat pearls is highly sensitive to physical and chemical properties of the abiotic substrate. Either roughened or hydrophobic substrates result in abnormal arrangements of the basal calcite layer, which are corrected for by a reinitiation of the biomineralization process, beginning with the deposition of an organic sheet. Insertion of flat pearls as substrates, however, results in continued nacre growth without the deposition of an organic sheet and a calcite layer.

We describe a distinct type of spontaneous hierarchical self-assembly of cytoskeletal filamentous actin (F-actin), a highly charged polyelectrolyte, and cationic lipid membranes. On the mesoscopic length scale, confocal microscopy reveals ribbonlike tubule structures that connect to form a network of tubules on the macroscopic scale (more than 100 micrometers). Within the tubules, on the 0.5- to 50-nanometer length scale, x-ray diffraction reveals an unusual structure consisting of osmotically swollen stacks of composite membranes with no direct analog in simple amphiphilic systems. The composite membrane is composed of three layers, a lipid bilayer sandwiched between two layers of actin, and is reminiscent of multilayered bacterial cell walls that exist far from equilibrium. Electron microscopy reveals that the actin layer consists of laterally locked F-actin filaments forming an anisotropic two-dimensional tethered crystal that appears to be the origin of the tubule formation.

A versatile strategy is reported for the multi-gram synthesis of discrete oligomers from commercially available monomer families, e.g., acrylates, styrenics, siloxanes. Central to this strategy is the identification of reproducible procedures for the separation of oligomer mixtures using automated flash chromatography systems with the effectiveness of this approach demonstrated through the multi-gram preparation of discrete oligomer libraries (Đ = 1.0). Synthetic availability, coupled with accurate structural control, allows these functional building blocks to be harnessed for both fundamental studies as well as targeted technological applications.

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A simple hybrid design has been developed to produce practically scatterless aperture slits for small‐angle X‐ray scattering and high‐resolution X‐ray diffraction. The hybrid slit consists of a rectangular single‐crystal substrate (e.g. Si or Ge) bonded to a high‐density metal base with a large taper angle (> 10°). The beam‐defining single‐crystal tip is oriented far from any Bragg peak position with respect to the incident beam and hence produces none of the slit scattering commonly associated with conventional metal slits. It has been demonstrated that the incorporation of the scatterless slits leads to a much simplified design in small‐angle X‐ray scattering instruments employing only one or two apertures, with dramatically increased intensity (a threefold increase observed in the test setup) and improved low‐angle resolution.

In this article we present experimental results demonstrating an approach to controlling the size and spatial patterning of defect domains in a smectic liquid crystal (LC) by geometric confinement in surface-modified microchannels. By confining the LC 4-octyl-4-cyanobiphenyl in m-sized rectangular channels with controlled surface polarity, we were able to generate defect domains that are not only nearly uniform in size but also arranged in quasi-2D ordered patterns. Atomic force microscopy measurements revealed that the defects have a toroidal topology, which we argue is dictated by the boundary conditions imposed by the walls of the microchannel. We show that the defects can be considered to be colloidal objects, which interact with each other to form ordered patterns. This method opens the possibility for exploiting the unique optical and rheological properties associated with LC defects to making new materials. For example, the control of the shape, size, and spatial arrangement of the defects at the mesoscale suggests applications in patterning, templating, and when extended to lyotropic LCs, a process leading to uniform-sized spherical particles for chemical encapsulation and delivery. S mectic (Sm) liquid crystals (LCs) are composed of elongated molecules that are aligned and arranged in layers. Local disruptions in the orientational, positional (layering), or morphological (bending) order in a Sm LC result in defects, which, when observed under crossed polarizers, exhibit complex textural patterns. The texture, which results from the highly anisotropic polarization of the molecules, has been extensively characterized and categorized based on the type of the LC structure (1-5). Understanding and controlling defects in LCs are important to many technological applications (e.g., displays and optical switches). Because the defects are considered to be anomalies in the LC structure, general efforts have been directed at minimizing or annealing the defects, including by using microstructures (grooves and gratings) (6-8). However, defect domains possess unique rheological and optical properties, which could potentially be exploited to make novel materials. The prerequisite for doing so would be the control of the type, size, and spatial distribution of the defects, which had not been well addressed in previous studies.In this article we present experimental results demonstrating the control of the size and spatial distribution of toroidal defects in the Sm LC 4Ј-octyl-4-cyanobiphenyl (8CB) by using surfacemodified microchannels. By changing the depth and width of the m-scale channels with a controlled surface polarity, we were able to generate focal conic defects that are not only nearly uniform in size but also arranged in 2D ordered patterns. This process is analogous to colloidal crystallization, except here the ''colloids'' are the ''soft'' m-sized defects within the LC. In addition, whereas the ordering in colloids is caused by interparticle interactions, here the defect ordering results from the competitio...

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Intermolecular interactions between charged membranes and biological polyelectrolytes, tuned by physical parameters, which include the membrane charge density and bending rigidity, the membrane spontaneous curvature, the biopolymer curvature, and the overall charge of the complex, lead to distinct structures and morphologies. The self-assembly of cationic liposome-microtubule (MT) complexes was studied, using synchrotron x-ray scattering and electron microscopy. Vesicles were found to either adsorb onto MTs, forming a ''beads on a rod'' structure, or undergo a wetting transition and coating the MT. Tubulin oligomers then coat the external lipid layer, forming a tunable lipid-protein nanotube. The beads on a rod structure is a kinetically trapped state. The energy barrier between the states depends on the membrane bending rigidity and charge density. By controlling the cationic lipid͞tubulin stoichiometry it is possible to switch between two states of nanotubes with either open ends or closed ends with lipid caps, a process that forms the basis for controlled chemical and drug encapsulation and release.polyelectrolyte lipid complexes ͉ small angle x-ray scattering ͉ nanotubebased drug delivery ͉ membrane ͉ tubulin