Ingenious Architecture and Coloration Generation in Enamel of Rodent Teeth.

Teeth exemplify architectures comprising an interplay of inorganic and organic constituents, resulting in sophisticated natural composites. Rodents (Rodentia) showcase extraordinary adaptations, with their continuously growing incisors surpassing human teeth in functional and structural optimizations. In this study, employing state-of-the-art direct atomic-scale imaging and nanoscale spectroscopies, we present compelling evidence that the release of material from ameloblasts and the subsequent formation of iron-rich enamel and surface layers in the constantly growing incisors of rodents are complex orchestrated processes, intricately regulated and independent of environmental factors. The synergistic fusion of three-dimensional tomography and imaging techniques of etched rodent́s enamel unveils a direct correlation between the presence of pockets infused with ferrihydrite-like material and the acid resistant properties exhibited by the iron-rich enamel, fortifying it as an efficient protective shield. Moreover, observations using optical microscopy shed light on the role of iron-rich enamel as a microstructural element that acts as a path for color transmission, although the native color remains indistinguishable from that of regular enamel, challenging the prevailing paradigms. The redefinition of "pigmented enamel" to encompass ferrihydrite-like infusion in rodent incisors reshapes our perception of incisor microstructure and color generation. The functional significance of acid-resistant iron-rich enamel and the understanding of the underlying coloration mechanism in rodent incisors have far-reaching implications for human health, development of potentially groundbreaking dental materials, and restorative dentistry. These findings enable the creation of an entirely different class of dental biomaterials with enhanced properties, inspired by the ingenious designs found in nature.

Design and Differentiation of Quantum States at Subnanometer Scale in La2CuO4-Sr2CuO4-δ Superlattices.

We present a study on the properties of superlattices made of ultrathin Sr2CuO4-δ layers sandwiched between La2CuO4 layers beyond the antiferromagnetic insulating nature of the individual layers of choice. Using molecular beam epitaxy, we synthesized these superlattices and observed superconductivity and metallicity at the interfaces. We probed the hole distribution to determine the discernible quantum states and found that the high-quality epitaxy, combined with mapping the electronic fine structure by electron energy-loss spectroscopy, allowed for the differentiation of insulating, metallic, and superconducting layers at the atomic-column scale. Our results demonstrate the possibility of exploring specific electronic properties at the subnanometer scale and highlight the potential of utilizing metastable Sr2CuO4-δ slabs.

Correcting the linear and nonlinear distortions for atomically resolved STEM spectrum and diffraction imaging.

Specimen and stage drift as well as scan distortions can lead to a mismatch between true and desired electron probe positions in scanning transmission electron microscopy (STEM) which can result in both linear and nonlinear distortions in the subsequent experimental images. This problem is intensified in STEM spectrum and diffraction imaging techniques owing to the extended dwell times (pixel exposure time) as compared to conventional STEM imaging. As a consequence, these image distortions become more severe in STEM spectrum/diffraction imaging. This becomes visible as expansion, compression and/or shearing of the crystal lattice, and can even prohibit atomic resolution and thus limits the interpretability of the results. Here, we report a software tool for post-correcting the linear and nonlinear image distortions of atomically resolved 3D spectrum imaging as well as 4D diffraction imaging. This tool improves the interpretability of distorted STEM spectrum/diffraction imaging data.

Towards atomically resolved EELS elemental and fine structure mapping via multi-frame and energy-offset correction spectroscopy.

Electron energy-loss spectroscopy and energy-dispersive X-ray spectroscopy are two of the most common means for chemical analysis in the scanning transmission electron microscope. The marked progress of the instrumentation hardware has made chemical analysis at atomic resolution readily possible nowadays. However, the acquisition and interpretation of atomically resolved spectra can still be problematic due to image distortions and poor signal-to-noise ratio of the spectra, especially for investigation of energy-loss near-edge fine structures. By combining multi-frame spectrum imaging and automatic energy-offset correction, we developed a spectrum imaging technique implemented into customized DigitalMicrograph scripts for suppressing image distortions and improving the signal-to-noise ratio. With practical examples, i.e. SrTiO3 bulk material and Sr-doped La2CuO4 superlattices, we demonstrate the improvement of elemental mapping and the EELS spectrum quality, which opens up new possibilities for atomically resolved EELS fine structure mapping.

Magnesium-Assisted Continuous Growth of Strongly Iron-Enriched Incisors.

Teeth are an excellent example where optimally designed nanoarchitectures with precisely constructed components consist of simple compounds. Typically, these simple constituent phases with insignificant properties show mechanical property amplifications when formed into composite architectures. Material properties of functional composites are generally regulated on the nanoscale, which makes their characterization particularly demanding. Using advanced analytical and imaging transmission electron microscopy techniques, we identified innovative microstructural adjustments combined with astonishing compositional adaptations in incisors of coypu. Unique constituents, recognized as an additional amorphous Fe-rich surface layer followed by a transition zone covering pigmented enamel, provide the required structural stability to withstand repeated mechanical load. The chemically diverse Fe-rich surface layer, including ferrihydrite and iron-calcium phosphates, gives the typical orange-brown coloration to the incisors. Within the spaces between elongated hydroxyapatite crystals in the pigmented enamel, only ferrihydrite was found, implying that enamel pigmentation is a very strictly controlled process. Most significantly, an unprecedentedly high amount of Mg was measured in the amorphous flake-like material within the dentinal tubules of the incisors, suggesting the presence of a (Mg,Ca) phosphate phase. This unusually high influx of Mg into the dentin of incisors, but not molars, suggests a substantial functionality of Mg in the initial formation stages and constant growth of incisors. The present results emphasize the strong mutual correlation among the microstructure, chemical composition, and mechanical properties of mineralized dental tissues.

Oxygen octahedra picker: A software tool to extract quantitative information from STEM images.

In perovskite oxide based materials and hetero-structures there are often strong correlations between oxygen octahedral distortions and functionality. Thus, atomistic understanding of the octahedral distortion, which requires accurate measurements of atomic column positions, will greatly help to engineer their properties. Here, we report the development of a software tool to extract quantitative information of the lattice and of BO6 octahedral distortions from STEM images. Center-of-mass and 2D Gaussian fitting methods are implemented to locate positions of individual atom columns. The precision of atomic column distance measurements is evaluated on both simulated and experimental images. The application of the software tool is demonstrated using practical examples.

Atomic-Scale Quantitative Analysis of Lattice Distortions at Interfaces of Two-Dimensionally Sr-Doped La2CuO4 Superlattices.

Using spherical aberration corrected high-resolution and analytical scanning transmission electron microscopy, we have quantitatively studied the lattice distortion and the redistribution of charges in two-dimensionally strontium (Sr)-doped La2CuO4 superlattices, in which single LaO planes are periodically replaced by SrO planes. As shown previously, such structures show Tc up to 35 K as a consequence of local charge accumulation on both sides of the nominal SrO planes position. This is caused by two distinct mechanisms of doping: heterogeneous doping at the downward side of the interface (space-charge effect) and "classical" homogeneous doping at the upward side. The comparative chemical and atomic-structural analyses reveal an interrelation between local CuO6 octahedron distortions, hole spatial distribution, and chemical composition. In particular we observe an anomalous expansion of the apical oxygen-oxygen distance in the heterogeneously doped (space-charge) region, and a substantial shrinkage of the apical oxygen-oxygen distance in the homogeneously doped region. Such findings are interpreted in terms of different Jahn-Teller effects occurring at the two interface sides (downward and upward).

Microstructure, chemistry, and electronic structure of natural hybrid composites in abalone shell.

The crystal structure and chemical composition at the inorganic/inorganic and inorganic/organic interfaces in abalone shell (genus Haliotis) were investigated using advanced analytical transmission electron microscopy (TEM) methods. Electron energy-loss near-edge structures (ELNES) of Ca-M2,3, C-K, Ca-L2,3, O-K and low-loss EEL spectra acquired from aragonite and calcite are distinctly different. When comparing biogenic with inorganic material for aragonite, only minor differences in C-K fine structures could be detected. The crystal structure of the mineral bridges was confirmed by ELNES experiments. ELNES and energy-filtered TEM (EFTEM) experiments of regular and self-healed interfaces between nacreous aragonite and prismatic calcite reveal relatively rough transitions. In this work, the importance of TEM specimen preparation and specimen damage on structural features is discussed.

Linking microstructure and nanochemistry in human dental tissues.

Mineralized dental tissues and dental pulp were characterized using advanced analytical transmission electron microscopy (TEM) methods. Quantitative X-ray energy dispersive spectroscopy was employed to determine the Ca/P and Mg/P concentration ratios. Significantly lower Ca/P concentration ratios were measured in peritubular dentine compared to intertubular dentine, which is accompanied by higher and variable Mg/P concentration ratios. There is strong evidence that magnesium is partially substituting calcium in the hydroxyapatite structure. Electron energy-loss near-edge structures (ELNES) of C-K and O-K from enamel and dentine are noticeably different. We observe a strong influence of beam damage on mineralized dental tissues and dental pulp, causing changes of the composition and consequently also differences in the ELNES. In this article, the importance of TEM sample preparation and specimen damage through electron irradiation is demonstrated.