Many studies have been conducted to determine the most reliable technique for evaluating the position of the endotracheal tube in patients receiving mechanical ventilation support. In this study, we aimed to determine the endotracheal tube position by ultrasonography in intubated patients with a diagnosis of critical CHD followed in the neonatal ICU.

In nature, the molecular-recognition ability of peptides and, consequently, their functions are evolved through successive cycles of mutation and selection. Using biology as a guide, it is now possible to select, tailor, and control peptide–solid interactions and exploit them in novel ways. Combinatorial mutagenesis provides a protocol to genetically select short peptides with specific affinity to the surfaces of a variety of materials including metals, ceramics, and semiconductors. In the articles of this issue, we describe molecular characterization of inorganic-binding peptides; explain their further tailoring using post-selection genetic engineering and bioinformatics; and finally demonstrate their utility as molecular synthesizers, erectors, and assemblers. The peptides become fundamental building blocks of functional materials, each uniquely designed for an application in areas ranging from practical engineering to medicine.

The characteristic of combining liquid behavior with and magnetic properties makes ferrofluids unique and it provides them a variety of applications, in particular in the medial field. For medical application ferrofluids are required to be stable at neutral pH and against high salt concentration. Here we present a new approach to stabilize water-based ferrofluids by using genetically engineered peptides for inorganics (GEPI's). Such GEPI's selected for specific and strong binding to the surface of nanoparticles not only increase colloidal stability by acting as a thin surfactant, but they also enable an efficient route for rendering the ferrofluid bio-functional and bio-compatible. The stability of a ferrofluid was characterized by the ac-susceptibility and by using it in a ferro-microfluidic device. This chip actuates the ferrofluid directly via magnetic fields alone, and the pumping spectrum as a function of frequency reveals information about the size of the magnetic nanoparticles. An ideal ferrofluid with monodisperse particles displays a single and clear pumping peak. Agglomeration can directly be observed as a broadening of the pumping spectrum.

Dental enamel is the most durable bioceramics produced by a vertebrate as it is designed to perform masticatory functions throughout its lifetime. The understanding of the mechanism of enamel formation and effects of proteins during the biomineralization process are fundamental issues, essential for both potential enamel regeneration and as a base for synthesis, via self-assembly, of biomimetic composites.

The biomineralization process of enamel is carried out by ameloblast cells that line the inner enamel epithelium and secrete an extracellular protein matrix onto a mineralized dentin surface at the dentin-enamel junction (DEJ). A major matrix protein, amelogenin, is believed to regulate the mineralization of hydroxyapatite (HAP) in the enamel tissue. It has been shown to undergo self-assembly in vitro and in vivo to form nanospheres of ∼20nm in diameter. Previous TEM studies have shown that the nanospheres align along the length (c-axis) of hydroxyapatite (HA) crystals. There are two domains, namely A (residues 1-42) and B (residues 157-173), that control the self-assembly behavior of the nanospheres.

Nacre is a segmented layered composite containing both nanoscale-thick organic and sub- micrometer thick scale inorganic phases. In addition to controlling the formation of the intricate architecture, the organic plays a significant role in the mechanical properties of the biocomposite. In our previous work, three dimensional finite element models of nacre were constructed to design “brick and mortar” micro-architecture to study effects of nonlinear response of the organic component. Recently, nanomechanical properties such as hardness and elastic moduli of the individual components of nacre have been determined using nanoindentation techniques. In this work, we used these actual properties of the components to perform mesoscale finite element models to quantitatively evaluate nanoscale effects. Specifically, we studied the effect of the solid contacts between the platelets through the organic layer on bulk properties under tensile and compressive loading. In the new 3D finite element model, we also incorporated the pseudo-hexagonal platelet morphology to more accurately represent the nacre microstructure. The multiscale approach in our study involves incorporation of experimentally obtained nanoscale parameters into meso-macroscale numerical models. Our simulations imply that mineral contacts in the aragonitic platelets have marginal impact both on bulk elastic behavior of nacre and yielding. Stress concentration in contact regions were high enough for the contacts to break long before yield started in nacre. These results have important implications in the design of biomimetic segmented-layered composites for improved mechanical properties.

The understanding of detailed structures and properties of enamel is essentia for designing new implant materials that faithfully resemble enamel structure or to regenerate enamel through biomimetics using proteins as templates. As part of a greater effort in enamel biomimetics, this work focused on nanostructures and mechanical properties of individual enamel rods using the mause as a test animal.

A mature mouse incisor consists of two layers - dentin and enamel. In order to perform its normal masticatory function, the incisor must have sufficiently high flexural strength, toughness, and wear resistance. Enamel, which is highly mineralized (∼100%) with a knitted micro-architecture, satisfies the mechanical property requirements. It is known that elongated hydroxyapatite (HAP) crystals mineralize in bundles, i.e., enamel rods, and organize in a 3-D cross pattern. [1,2] However the organizations of HAP crystals within and between rods are not well understood.

Previous work on microstructural characterization has shown variations in terms of defects and organization of nanostructures in the two polymorphs of calcium carbonate, calcite, and aragonite in mollusc shells. Large variations in mechanical properties are observed between these sections which have been attributed to variations in composite microstructure as well as intrinsic properties of the inorganic phases. Here we present local low-loss electron energy-loss spectroscopic (EELS) study of calcitic and aragonitic regions of abalone shell that were compared to geological (single-crystal) counterpart polymorphs to reveal intrinsic differences that could be related to organismal effects in biomineralization. In both sets of samples, local dielectric function is computed using Kramer-Kronig analysis. The electronic structures of biogenic and geological calcitic materials are not significantly different. On the other hand, electronic structure of biogenic aragonite is remarkably different from that of geological aragonite. This difference is attributed to the increased contribution from single electron excitations in biogenic aragonite as compared to that of geological aragonite. Implications of these changes are discussed in the context of macromolecular involvement in the making of the microstructures and properties in biogenic phases.

Mechanical properties were determined from the organic matrix of a mollusc hard tissue using a nanomechanical testing instrument attached to an atomic force microscope (AFM). Shells of molluscs are two-tier functionally-gradient ceramic/polymer biocomposites used by organisms as impact resistant materials. The inner section of the red abalone (Haliotis refuscens)shell, nacre (mother-ofpearl), has a brick and mortar microarchitecture with pseudo-hexagonal-shaped bricks made of aragonitic (orthorhombic) CaCO3 platelets (0.25 μn thick, and 5 μm edge length) surrounded by a thin (10-25 nm thick) proteinaceous organic matrix (Fig. 1). This higly ordered biocomposite has submicron-layered structure that result in excellent bulk mechanical properties, not achieved by manmade composites with similar phase compositions and, therefore, offers biomimetic lessons for novel materials design. In this model biomimetic composite, mechanical properties of its constituents need to be evaluated in addition to the details of the microstructure. We previously determined nanomechanical properties (hardness and modulus) of individual (twinned, single crystalline) aragonitic platelets.

The enamel of human teeth is composed of parallel rods (bundles) of long, closely-packed, ribbonlike hydroxyapatite (HAP) Ca10(PO4)6(OH)2 crystallites oriented normal to the tooth surface. Both the unique structure of the crystallites and the higher order arrangement of the crystallites are believed to be a consequence of interactions between proteins secreted by the enamel forming tissues and the growing crystallites. A better understanding of the precise molecular mechanism that controls enamel crystallite formation could potentially lead to both novel enamel repair strategies and crystal growth control systems. It has been previously reported that the unidirectional flow of calcium ions across a membrane can be used to form ribbon-like structures of a related form of calcium phosphate. We have created a similar model system which utilizes the unidirectional flow of calcium ions to generate ribbon-like HAP crystallites. Ultimately, this system will be modified so that enamel proteins can be introduced into the crystallization milieu to better characterize their role in enamel formation.

SEM and TEM samples were prepared using the experimental setup shown in Fig. 1. Several tubes containing a 50mM HAP solution dissolved in 0.1M HC1 were placed upside down into a 50mM MOPS pH buffering solution at pH 7.0.

Enamel, which covers the anatomical crown of the tooth, is the hardest tissue in human body. Supported by a soft but tough dentin structure, the tooth is an advanced nanocomposite that can endure mastication stresses throughout a lifetime. A detail understanding the structure of the tooth, and sepecifically detin-enamel junction (DEJ), not only provides a sound basis for a model for synthetic dental restoration, but also provides lessons from nature on biomimetic regeneration with mechanical integrity. Enamel is a non-growing mineralized tissue and is subjected to most mechanical abuse. Dentin-enamel junction plays a critical role of distributing load between two very dissimilar materials - enamel and dentin. Bulk scale mechanical tests have shown that induced cracks on enamel tend to be arrested DEJ. Furthermore, nanoindentation measurements have also shown that there is a gradual decrease in hardness from enamel to dentin in the DEJ zone suggests a strong mechanical coupling in both deciduous and adult incisors. The objective of this investigation, through microscopical study, is to understand how these two dental hard tissues structurally couple through their junction zone.

This paper focuses on the differences of physical properties, specifically local dielectric function, of biogenic and geological mineral CaCO3. The goal is to assess the role of organism in forming biogenic inorganic materials. Local dielectric functions of biogenic and geological minerals were determined by transmission electron energy loss spectroscopy using a previously developed strategy.

Previous work on microstructural characterization of biological hard tissues, e.g., abalone shells, has shown variations in terms of defects, morphology, crystallography, and organization of nano- and microstructures in two biological polymorphs of calcium carbonate, calcite and aragonite, in the prismatic and nacreous regions, respectively. In the abalone, the outer (1-5 mm thick) region of the shell is composed of calcite crystallites (1-5 μm diameter) with columnar organization perpendicular to shell plane. On the inner region, 1-10 mm thick nacre is composed of aragonite crystallites (0.5 μm thick and 5 -10 μm edge-length) forming flat platelets, parallel to the shell plane.

The human tooth is a functionally-gradient structural composite material composed of collagen and hydroxyapatite (HAP). The outer most region is a hard enamel layer consisting primarily of HAP. Underneath is dentin region, which is composed of HAP with a significant fraction of collagen fibers. It has been demonstrated that it is possible to perform nano-indentation on sub-micron regions of tooth using either a standard nanoindentor or modified cantilever type atomic force microscope tip (AFM). In this study, we report nano-mechanical properties of dentin and enamel regions of a human tooth, measured with a nanoindentor attached to an AFM using a vertical force, in correlation with the microstructures observed with TEM.

TEM and nano-indentation samples were prepared from a juvenile human incisor tooth. The tooth was first sectioned into 1 mm thick slices along its length, each containing both dentin and enamel regions. A slice was taken to prepare a TEM sample and an adjacent slice was used for nano-indentation measurements.

The research in biological hard tissues offers lessons for biomimetic (structure and processing) strategies, such as for the synthesis of hierarchical architectures tailored for specific engineering applications. These biocomposites, i.e., biogenic materials in which the major phase is an inorganic component associated with macromolecules (proteins and polysaccharides), include bones, dentin, sea-urchin skeletal units, bacterial and algal particles and molluscan shells. Here, a summary is given from a recent TEM study of the interfacial region of nacreous and prismatic sections of red abalone shell to understand the morphological and crystallographic correlations across this transition region.

Many mollusk species have shells made of CaCO3 in various architectures that have evolved under different ecological conditions to produce structures that best protect the organism. The shells of many species contain both aragonite (orthorhombic, Pmnc) and calcite (Rhombohedral, R3m). In red abalone (Haliotis rufescens), the outer section, prismatic (P), is composed of columnar crystallites of calcite (1-5 μm base, 5-10 μm height), and the inner section, nacre (N), is composed of pseudo-hexagonal platelets of aragonite (side 2-5 μm), stacked as 0.25 μm layers, separated by a few nm-thick organic layer (Fig. 1).

ELFS (energy loss fine structure), similar to XAFS (x-ray absorption fine structure) provides short-range order atomic structural information of crystalline and amorphous materials. Although known quite sometime, ELFS spectroscopy only until recently has gained importance, mainly due new developments in spectrometer and TEM designs, spectra acquisition and interpretation techniques. This paper focuses on some new developments in the acquisition, interpretation, and the use of the extended regime of the ELFS spectroscopy.

Although fine structure spectroscopy in EELS and its similarity to XAFS were recognized sometime ago, ELFS has only seen limited use mainly because of insufficient spectral statistics, various systematic errors and drifts, and the absence of sophisticated software that faithfully uses the XAFS software and incorporates the latest advances in modeling theory. We have systematically improved the data acquisition technique and developed ELFS data analysis procedure which utilizes the sophisticated UWXAFS data analysis software package8 after correction of the differences between ELFS and XAFS data.

Formation and growth mechanisms of biological hard tissues are relevant in biomimetics for obtaining lessons in the assembly of complex and ordered microstructures for engineering applications. Shells of mollusks offer examples of organic/inorganic hybrid structures with nanoscale order that produce functionally-gradient macroarchitectures. Here, the nacre/prismatic interface of red abalone (Haliotis rufescens) was topographically profiled with an atomic force microscope (Park Scientific PC) using contact mode in air to elucidate growth characteristics of the shell. The results give a quantitative (spatial and temporal) measure of how nacre (N) grows over the prismatic (P) section of the shell.

Nine regions, with a length of 350 µm parallel to the growing edge and a width of 120 µm, were scanned (e.g., Figs 1 & 2). Raster scanning from N to the P sections revealed that the rms roughness of the surface tends to increase from N to P region with the latter having topographical height variations of up to 5 µm at the growing edge.

Transmission electron energy loss spectroscopy was used to obtain local dielectric properties in barium titanate. The high frequency dielectric function of the material was studied dynamically during the cubic-to-tetragonal (c → t) phase transformation in conjunction with the effect of a small amount (0.9%) of donor dopant (niobium). In order to obtain the local dielectric function during the phase transformation, Kramers–Kronig relations were applied to the energy loss measurements. The optical excitations in the energy loss spectra were consistent with band structure results from the literature. The Re (1/∈), real part of the inverse dielectric function, obtained from the energy loss data indicated a change at the phase transformation. Specifically, a broadening of the valence plasmon excitation is observed which is attributed to the order-disorder nature of the t → c transformation. A 0.4 eV shift in the volume plasmon was observed in the Nb-doped sample in all regions (within grains as well as at grain boundaries), indicating a uniform incorporation of the dopant in the lattice. In this paper, the changes in the dielectric function, such as shifts in collective excitations, are attributed to a large contribution from loosely bound Nb electrons. Furthermore, it is demonstrated that it is possible to obtain local (≈10 nm) physical property of a complex material dynamically at relatively high temperature.

Nanocrystalline powders with an average particle size of 50 nm has been synthesized in two materials systems under hydrothermal conditions below 100°C. Processing variables, such as temperature, concentration and molar ratio of reactants and reaction time were optimized to obtain particles of reduced size and stoichiometric compositions. Hydrothermal reaction takes place between Ba(OH)2 solution and titanium/iron precursors in sealed polyethylene bottles in the BaTiO3 and BaFe12O19 systems, respectively. While crystalline BaTiO3 forms relatively fast within a few hours, formation of fully crystalline and stoichiometric BaFei20i9 require considerably longer reaction times up to several weeks and strongly dependent on the Ba:Fe ratio of the precursors. The structural and compositional evaluation of the nanophase powders were studied by XRD and TEM techniques.