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Connective tissues are biological composites comprising of collagen fibrils embedded in (and reinforcing) the hydrated proteoglycan-rich (PG) gel within the extracellular matrices (ECMs). Age-related changes to the mechanical properties of tissues are often associated with changes to the structure of the ECM, namely, fibril diameter. However, quantitative attempts to correlate fibril diameter to mechanical properties have yielded inconclusive evidence. Here, we described a novel approach that was based on the rule of mixtures for fiber composites to evaluate the dependence of age-related changes in tendon tensile strength ([sigma]) and stiffness (E) on the collagen fibril cross-sectional area fraction ([rho]), which is related to the fibril volume fraction. Tail tendons from C57BL6 mice from age groups 1.6-35.3 months old were stretched to failure to determine [sigma] and E. Parallel measurements of p as a function of age were made using transmission electron microscopy. Mathematical models (rule of mixtures) of fibrils reinforcing a PG gel in tendons were used to investigate the influence of p on ageing changes in [sigma] and E. The magnitudes of [sigma], E, and p increased rapidly from 1.6 months to 4.0 months (P-values 0.05); this trend continued for E and [rho] (P-values >0.05) from 29.0 months to 35.3 months, but not for [sigma], which decreased gradually (P-values Keywords: stiffness, strength, area fraction, collagen, rule of mixtures

The influence of Ca2+ ions on the structural organization of microfibrillar arrays was studied using electron and biochemical analyses of isolated microfibrils and x-ray diffraction data for tissue microfibrils. The observed Ca2+-stimulated reversible change in the intensities of the meridional Bragg peaks was attributed to the varied distributions of free Ca2+. When exposed to Ca2+, the dominant diffracting subspecies were found to be microfibrils axially aligned in a 0.33 periodicity stagger. On the other hand, removal of Ca2+ resulted in regular molecular spacing.

A potential solution to the important questions of modern human evolution and dispersal lies in the use of genetic information from Pleistocene fossil humans, but the retrieval of authentic biomolecular material from these fossils has only rarely proved successful. The extraction of mitochondrial DNA from the Neanderthal individuals from Feldhofer and Mezmaiskaya has been encouraging, however these are isolated results and failure to recover biomolecular material from fossil human remains is much more common. What makes the successful bones special? The answer lies in several factors affecting diagenesis, principally the biological processes of decay, the burial environment and the cumulative climatic history of the site. We have examined a series of Pleistocene and Holocene skeletal samples in an attempt to establish the unique attributes of specimens that contain well-preserved DNA. Thermal models based on the theoretical rates of decay of DNA provide a baseline for predicting which geographical regions and localities are more favorable for biomolecular survival. The samples themselves have been subjected to a suite of well-established tests to determine the porosity, crystallinity, histological alteration and collagen content of the bone. The phenomenon of better preservation in caves compared with open sites is being investigated through careful sample selection and thermal monitoring of cave sites. Our results indicate that DNA survival exceeds predictions from theoretical models in particular burial environments. This research is supported by the Wellcome Trust, CVCP, NERC, ESRF, CNRS and the EC.

If bone is considered as a composite of collagen (protein) and bioapatite (mineral), then three pathways of diagenesis are identified: (1) chemical deterioration of the organic phase; (2) chemical deterioration of the mineral phase; and (3) (micro) biological attack of the composite. The first of these three pathways is relatively unusual and will only occur in environments that are geochemically stable for bone mineral. However, because rates of biomolecular deterioration in the burial environment are slow, such bones would yield useful biomolecular information. In most environments, bones are not in thermodynamic equilibrium with the soil solution, and undergo chemical deterioration (path 2). Dissolution of the mineral exposes collagen to biodeterioration, and in most cases the initial phase of dissolution will be followed by microbial attack (path 3). Biological attack (3) also proceeds by initial demineralization; therefore paths 2 and 3 are functionally equivalent. However,in a bone that follows path 3 the damage is more localized than in path 2, and regions equivalent to path 1 may therefore exist outside these zones of destruction. Other biomolecules, such as blood proteins, cellular lipids and DNA, exist within the physiological spaces within bone.For these biomolecules, death history may be particularly important for their survival. [ABSTRACT FROM AUTHOR]