Ageing bone fractures: The case of a ductile to brittle transition that shifts with age.

Human bone becomes increasingly brittle with ageing. Bones also fracture differently under slow and fast loadings, being ductile and brittle, respectively. The effects of a combination of these two factors have never been examined before.

Thermal decomposition of the amino acids glycine, cysteine, aspartic acid, asparagine, glutamic acid, glutamine, arginine and histidine.

Background: The pathways of thermal instability of amino acids have been unknown. New mass spectrometric data allow unequivocal quantitative identification of the decomposition products.

Results: Calorimetry, thermogravimetry and mass spectrometry were used to follow the thermal decomposition of the eight amino acids G, C, D, N, E, Q, R and H between 185 °C and 280 °C.

Plasticity of two structural proteins: alpha-collagen and beta-keratin.

Although the microstructures of Type-I collagen in bone and F-keratin in avian feathers are very different, their plastic behaviour is similar. In both plasticity is thermally activated, with the activation enthalpy H=1.1 eV in bone and 1.

The peacock's train (Pavo cristatus and Pavo cristatus mut. alba) II. The molecular parameters of feather keratin plasticity.

Thermal activation analysis of plastic deformation of peacock tail feathers, by temperature changes and stress relaxation, gave for the keratin cortex an activation enthalpy of 1.78 ± 0.89 eV and an activation volume of 0.

The peacock's train (Pavo cristatus and Pavo cristatus mut. alba) I. structure, mechanics, and chemistry of the tail feather coverts.

The feathers in the train of the peacock serve not for flying but for sexual display. They are long, slender beams loaded in bending by their own weight. An outer circular conical shell, the cortex, is filled by a closed foam of 7.

The thermodynamic driving force for bone growth and remodelling: a hypothesis.

The Eshelby stress (static energy momentum) tensor is derived for bone modelled as an inhomogeneous piezoelectric and piezomagnetic Cosserat (micropolar) medium. The divergence of this tensor is the configurational force felt by material gradients and defects in the medium. Just as in inhomogeneous elastic media, this force is identified with the thermodynamic force for phase transformations, in bone it is the thermodynamic cause of structural transformations, i.

Evidence for an elementary process in bone plasticity with an activation enthalpy of 1 eV.

The molecular mechanisms for plastic deformation of bone tissue are not well understood. We analysed temperature and strain-rate dependence of the tensile deformation behaviour in fibrolamellar bone, using a technique originally developed for studying plastic deformation in metals. We show that, beyond the elastic regime, bone is highly strain-rate sensitive, with an activation volume of ca 0.