The Stabilizing Effect of Silicate on Biogenic and Synthetic Amorphous Calcium Carbonate

Silicate ions increase the thermal stability of the unstable amorphous calcium carbonate (ACC). This effect was observed first by comparing ACC from two different species of cystoliths, small calcified bodies formed in the leaves of some plants. The temperature of crystallization to calcite in the silicate-rich cystoliths from M. alba is 100 °C higher than that of the silicate-poor cystoliths from F. microcarpa. The stabilizing effect is confirmed in vitro with synthetic samples differing in their silicate content. With increasing silicate concentration in ACC, the crystallization temperature to calcite also increases. A mechanism of geometric frustration is suggested, whereby the presence of the tetrahedral silicate ion in the flat carbonate lattice prevents organization into crystalline polymorphs

Mineral and Matrix Components of the Operculum and Shell of the Barnacle <i>Balanus amphitrite</i>: Calcite Crystal Growth in a Hydrogel

Sessile barnacles produce two types of mineralized exoskeletons: a cone-shaped shell and an operculum that is used to seal the shell opening. The mineral of both types is calcite. We show that the calcite crystals of the shell and the operculum (specifically the scutum) of the sessile barnacle <i>Balanus amphitrite</i> both fracture with conchoidal cleavage, have surfaces decorated with small rhombohedral shaped calcite crystals, and are poorly oriented. The scutum calcite is significantly more disordered at the atomic level than the shell calcite. We also show that a major component of the intercrystalline organic matrix of the shell and scutum is a nonproteinaceous sulfate-rich polymer that behaves as a hydrogel, and that the intracrystalline matrix contains highly acidic proteins. The crystal properties and microstructure are consistent with the calcite crystals forming in a hydrogel-like environment. The barnacle shell and operculum have many unique properties indicating that the crystal growth conditions are well controlled and possibly adapted to fulfill mechanical functions, which enable the barnacle to survive in the high energy environment of the intertidal zone

The Structural Basis for Enhanced Silver Reflectance in Koi Fish Scale and Skin

Fish have evolved biogenic multilayer reflectors composed of stacks of intracellular anhydrous guanine crystals separated by cytoplasm, to produce the silvery luster of their skin and scales. Here we compare two different variants of the Japanese Koi fish; one of them with enhanced reflectivity. Our aim is to determine how biology modulates reflectivity, and from this to obtain a mechanistic understanding of the structure and properties governing the intensity of silver reflectance. We measured the reflectance of individual scales with a custom-made microscope, and then for each individual scale we characterized the structure of the guanine crystal/cytoplasm layers using high-resolution cryo-SEM. The measured reflectance and the structural-geometrical parameters were used to calculate the reflectance of each scale, and the results were compared to the experimental measurements. We show that enhanced reflectivity is obtained with the same basic guanine crystal/cytoplasm stacks, but the structural arrangement between the stack, inside the stacks, and relative to the scale surface is varied when reflectivity is enhanced. Finally, we propose a model that incorporates the basic building block parameters, the crystal orientation inside the tissue, and the resulting reflectance and explains the mechanistic basis for reflectance enhancement

OL volume histograms from all the samples showing the OL volume distribution from 20 to 1200 μm³.

OL volume average and standard deviations are provided in Table 2. Note that the unusual distribution of T2 may be due to the poor resolution of the scan (see Methods).</p

2D representation of the temporal bone including a longitudinal cross section of the otic capsule.

(A) A slice from a low-resolution μ-CT tomogram obtained from the pig right temporal bone before extraction of the petrous bone showing the otic capsule in the grey rectangle. (B) SEM backscattered electron automated image map of a transverse section of a pig petrous bone after extraction, sectioning and polishing. The mastoid bone samples were collected from the same location (T) from two different pigs (Fig 2A). The locations of petrous bone samples from the outer and inner layers (OP and IP) are shown in Fig 2B. These samples were collected from the same locations in two different pigs.</p

Numbers of OL from all different samples.

Numbers of OL from all different samples.</p

The OL concentration using the two segmentation approaches.

Dark blue represents the MT segmentation with volumes from 10–2000μm3, light blue is the same segmentation method but with volumes from 20–2000 μm3, and grey represents the DLM segmentation for OL volumes between 10–2000μm3.</p

Flow chart of the pig samples in this study.

The animal used is indicated at the top row, and the samples extracted from each animal are indicated in the second row. The third row shows sample preparation and then the flow of analyses after each experiment.</p

Light-sheet fluorescent microscopy images of a cleared pig petrous bone.

All images are from the same Z-depth with (green) autofluorescence and (red) DRAQ5 signals. Low magnification images show the cleared bone tissue from the cochlear cavities towards the outer bone surface. High magnification images of areas indicated by the rectangles are shown. The local concentrations of DRAQ5 stained nuclei can best be seen in the high magnification image.</p

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