Reduced Tissue-Level Stiffness and Mineralization in Osteoporotic Cancellous Bone

Osteoporosis alters bone mass and composition ultimately increasing the fragility of primarily cancellous skeletal sites; however, effects of osteoporosis on tissue-level mechanical properties of cancellous bone are unknown. Dual-energy x-ray absorptiometry (DXA) scans are the clinical standard for diagnosing osteoporosis though changes in cancellous bone mass and mineralization are difficult to separate using this method. The goal of this study was to investigate possible difference in tissue-level properties with osteoporosis as defined by donor T-scores. Spine segments from Caucasian female cadavers (58–92 yrs) were used. A T-score for each donor was calculated from DXA scans to determine osteoporotic status. Tissue level composition and mechanical properties of vertebrae adjacent to the scan region were measured using nanoindentation and Raman spectroscopy. Based on T-scores, six samples were in the Osteoporotic group (58–74 yrs) and four samples were in the Not Osteoporotic group (65–92 yrs). The indentation modulus and mineral to matrix ratio (mineral:matrix) were lower in the Osteoporotic group than the Not Osteoporotic group. Mineral:matrix ratio decreased with age (r2 = 0.35, p = 0.05), and the indentation modulus increased with a real bone mineral density (aBMD) (r2 = 0.41, p = 0.04)

Tuning hardness in calcite by incorporation of amino acids

Structural biominerals are inorganic/organic composites that exhibit remarkable mechanical properties. However, the structure–property relationships of even the simplest building unit—mineral single crystals containing embedded macromolecules—remain poorly understood. Here, by means of a model biomineral made from calcite single crystals containing glycine (0–7 mol%) or aspartic acid (0–4 mol%), we elucidate the origin of the superior hardness of biogenic calcite. We analysed lattice distortions in these model crystals by using X-ray diffraction and molecular dynamics simulations, and by means of solid-state nuclear magnetic resonance show that the amino acids are incorporated as individual molecules. We also demonstrate that nanoindentation hardness increased with amino acid content, reaching values equivalent to their biogenic counterparts. A dislocation pinning model reveals that the enhanced hardness is determined by the force required to cut covalent bonds in the molecules

Focused-Ion Beam and Electron Microscopy Analysis of Corrosion of Lead-Tin Alloys: Applications to Conservation of Organ Pipes

Across Europe, lead-tin alloy organ pipes are suffering from atmospheric corrosion. This deterioration can eventually lead to cracks and holes, preventing the pipes from producing sound. Organ pipes are found in compositions ranging from \u3e99% Pb to \u3e99% Sn. For very lead-rich (\u3e99% Pb) pipes, organic acids emitted from the wood of organ cases have previously been identified as significant corrosive agents. In order to study the role of alloy composition in the susceptibility of pipes to organic acid attack, lead-tin alloys containing 1.2-15 at.% Sn were exposed to acetic acid vapors in laboratory exposure studies. Corrosion rates were monitored gravimetrically, and corrosion product phases were identified using grazing incidence angle X-ray diffraction. In a new method, focused-ion beam (FIB) cross-sections were cut through corrosion sites, and SEM and WDX were used to obtain detailed information about the morphology and chemical composition of the corrosion layers. The combination of FIB and SEM has made it possible to obtain depth information about these micron-scale layers, providing insight into the influence of acetic acid on alloys in the 1.2-15 at.% Sn range

Mechanische Eigenschaften und Zuverlässigkeit von Materialien in Mikrodimensionen

Rapid developments in microtechnology place increasing demands on the mechanical properties of the materials involved as components are further miniaturized. The mechanical behavior of materials in small dimensions ("micromaterials") can be considerably different from the behavior of the same materials in bulk form. New mechanical test methods for micromaterials are presented and some of the special mechanical properties of these materials are discussed in order to continue the development of new micromaterials as well as to improve their reliability further fundamental research in this area is urgently needed

Mechanische Eigenschaften und Zuverlässigkeit von Materialien in Mikrodimensionen

Rapid developments in microtechnology place increasing demands on the mechanical properties of the materials involved as components are further miniaturized. The mechanical behavior of materials in small dimensions ("micromaterials") can be considerably different from the behavior of the same materials in bulk form. New mechanical test methods for micromaterials are presented and some of the special mechanical properties of these materials are discussed in order to continue the development of new micromaterials as well as to improve their reliability further fundamental research in this area is urgently needed