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In this paper, a comprehensive framework is proposed to estimate the anisotropic permeability matrix in trabecular bone specimens based on micro-computed tomography (microCT) imaging combined with pore-scale fluid dynamics simulations. Two essential steps in the proposed methodology are the selection of (i) a representative volume element (RVE) for calculation of trabecular bone permeability and (ii) a converged mesh for accurate calculation of pore fluid flow properties. Accurate estimates of trabecular bone porosities are obtained using a microCT image resolution of approximately 10μm. We show that a trabecular bone RVE in the order of 2×2×2mm3is most suitable. Mesh convergence studies show that accurate fluid flow properties are obtained for a mesh size above 125,000 elements. Volume averaging of the pore-scale fluid flow properties allows calculation of the apparent permeability matrix of trabecular bone specimens.

Diatoms are single‐celled micro‐algae that possess an exoskeleton (called frustule) comprised of diverse and highly ordered 3D porous silica structures and that hold considerable promise for biological or biomimetic fabrication of nanostructured materials and devices. We have used, for the first time, a soft lithographic approach of replica molding to replicate porous diatom structures into polymers. Two centric diatom species, Coscinodiscus sp.,Thalassiosira eccentricacultured in our laboratory were used as masters for replication. In the first step, replica molding onto soft and elastic polymer using poly(dimethylsiloxane) PDMS produced a negative replica of the diatom frustule. These PDMS replicas were then used as a mold to fabricate the positive polymer replicas of diatoms using a mercaptol ester type UV curable polymer (NOA 60). Fabricated polymer replicas were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). In all cases, diatom micro‐ and nanoscale porous structures were successfully transferred with high precision into polymer replicas. Such an accomplishment effectively demonstrates the potential for using diatoms as blueprints for rapid and simple fabrication of polymer nanostructures. The prepared replicas were used as diffraction gratings and as nanowells to hold polymeric nanoparticles effectively demonstrating the functional properties of these biomimetic structures.

Three immobilization methods have been used for scanning tunneling microscopy (STM) studies of glucose oxidase (GOD) on gold. They are based on (a) physical adsorption from solution, (b) microcontact printing, and (c) covalent bonding onto self-assembled monolayers (SAMs) of 3-mercaptopropionic acid (MPA). The STM images are used to provide information about the organization of individual GOD molecules and more densely packed monolayers of GOD on electrode surfaces, thus providing information on the role of interfacial structure on biosensor performance. The use of atomically flat gold substrates enables easy distinction of deposited enzyme features from the flat gold substrate. Microcontact printing is found to be a more reliable method than adsorption from solution for preparing individual GOD molecules on the gold surface. STM images of printed samples reveal two different shapes of native GOD molecules. One is a butterfly shape with dimensions of 10 ± 1 nm × 6 ± 1 nm, assigned to the lying position of the molecule, while the second is an approximately spherical shape with dimensions of 6.5 ± 1 nm × 5 ± 1 nm assigned to a standing position. Isolated clusters of five to six GOD molecules are also observed. With monolayer coverages, GOD molecules exhibit a tendency to organize themselves into a two-dimensional array with adequate sample stability to obtain high-resolution STM images. Within these two-dimensional arrays repeating clusters of five to six enzyme molecules in a unit are clearly seen. Cluster structures are observed at both high and low coverages despite the fact that native GOD is a negatively charged molecule under physiological conditions. GOD monolayers covalently immobilized onto SAMs (MPA) are considerably more difficult to image than when the enzyme is adsorbed directly onto the metal.

The influence of the underlying gold surface topography on the response of enzyme electrodes fabricated by covalent attachment of glucose oxidase to a 3‐mercaptopropionic acid self‐assembled monolayer was assessed. Six different gold substrates were prepared. The bare substrates were evaluated for roughness and defects using atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Despite large variations in surface roughness, the shapes of the enzyme electrode calibration plots indicate that approximately the same amount of MPA was adsorbed on the surface and from electrochemical stripping experiments the same number of active enzyme molecules were attached. However, compared with the smoother surfaces, enzyme electrodes fabricated on surfaces with high microscopic roughness had a smaller linear range but a similar current sensitivity in the linear portion of the calibration plot. Tapping‐mode AFM images of the enzyme modified surfaces showed that the enzyme adsorbed onto the surface as clusters of five or six enzyme molecules. The formation of these clusters did not appear to be influenced by the surface roughness.

The influence of the topography of the underlying gold surface on the integrity of self-assembled monolayers (SAMs) of hexadecanethiol (HDT) prepared by solution assembly and microcontact printing was assessed using six different gold substrates. The bare substrates were evaluated for roughness and defects using scanning tunneling microscopy (STM). The structural integrity of self-assembled monolayers on these substrates has been evaluated using both surface methods (STM) and electrochemical measurements. Perhaps not surprisingly, the flattest substrates seem to produce the highest quality monolayer. It is surprising to note, however, that the layer quality is not necessarily traceable to a variation in coverage. Despite both the solution-formed and printed SAMs appearing similar in STM images, electrochemical assessment of the SAM integrity indicated the printed SAMs were inferior, forming a less effective passivating barrier with many more pinholes. The quality of printed SAMs could be improved considerably by rolling the inked stamp across the gold surface rather than placing the stamp horizontally onto the substrate. This second printing technique of rolling the stamp across the surface produced SAMs which were still marginally inferior to those formed from solution but were assembled in less than a minute rather than 24 h.

Emerging as a promising candidate for grid-scale energy storage, aqueous zinc-ion batteries are challenged by both sluggish Zn2+migration kinetics and poor cyclic stability of cathode materials. Herein, a maximized crystal water content of 14.8 wt% is reported for layered Na5V12O32·11.9H2O as the new cathode material. Such a content has enlarged the lattice space up to 12.75 Å providing spacious channels for rapid Zn2+migration. The charge-shielding effect of crystal water alleviates the electrostatic interactions between Zn2+and the cathode framework, enhancing ionic conductivity. The density functional theory calculation reveals that the high crystal water content facilitates the electrical conductivity. These should promote the Zn2+migration kinetics and cyclic stability. Through characterizations by ex situX-ray photoelectron spectroscopy and near edge X-ray absorption fine structure analysis, the high crystal water content is found to associate with two-electron redox reactions during Zn2+(de)intercalation. As a result, the Na5V12O32·11.9H2O cathode presents a reversible capacity of 430.52 mA h/g at 0.1 A/g with 103.7% retention of initial capacity over 3,862 cycles at 1 A/g.