Collagen type I is the most abundant structural protein in tendon, skin and bone, and largely determines the mechanical behaviour of these connective tissues. To obtain a better understanding of the relationship between structure and mechanical properties, tensile tests and synchrotron X–ray scattering have been carried out simultaneously, correlating the mechanical behaviour with changes in the microstructure. Because intermolecular cross–links are thought to have a great influence on the mechanical behaviour of collagen, we also carried out experiments using cross–link–deficient tail–tendon collagen from rats fed with β–APN, in addition to normal controls. The load–elongation curve of tendon collagen has a characteristic shape with, initially, an increasing slope, corresponding to an increasing stiffness, followed by yielding and then fracture. Cross–link–deficient collagen produces a quite different curve with a marked plateau appearing in some cases, where the length of the tendon increases at constant stress. With the use of in situ X–ray diffraction, it was possible to measure simultaneously the elongation of the collagen fibrils inside the tendon and of the tendon as a whole. The overall strain of the tendon was always larger than the strain in the individual fibrils, which demonstrates that some deformation is taking place in the matrix between fibrils. Moreover, the ratio of fibril strain to tendon strain was dependent on the applied strain rate. When the speed of deformation was increased, this ratio increased in normal collagen but generally decreased in cross–link–deficient collagen, correlating to the appearance of a plateau in the force–elongation curve indicating creep. We proposed a simple structural model, which describes the tendon at a hierarchical level, where fibrils and interfibrillar matrix act as coupled viscoelastic systems. All qualitative features of the strain–rate dependence of both normal and cross–link–deficient collagen can be reproduced within this model. This complements earlier models that considered the next smallest level of hierarchy, describing the deformation of collagen fibrils in terms of changes in their molecular packing.

The continuously forming fin bony rays of zebrafish represent a simple bone model system in which mineralization is temporally and spatially resolved. The mineralized collagen fibrils of the fin bones are identical in structure to those found in all known bone materials. We study the continuous mineralization process within the tissue by using synchrotron microbeam x-ray diffraction and small-angle scattering, combined with cryo-scanning electron microscopy. The former provides information on the mineral phase and the mineral particles size and shape, whereas the latter allows high-resolution imaging of native hydrated tissues. The integration of the two techniques demonstrates that new mineral is delivered and deposited as packages of amorphous calcium phosphate nanospheres, which transform into platelets of crystalline apatite within the collagen matrix.

X-ray scattering experiments at synchrotron sources are characterized by large and constantly increasing amounts of data. The great number of files generated during a synchrotron experiment is often a limiting factor in the analysis of the data, since appropriate software is rarely available to perform fast and tailored data processing. Furthermore, it is often necessary to perform online data reduction and analysis during the experiment in order to interactively optimize experimental design. This article presents an open-source software package developed to process large amounts of data from synchrotron scattering experiments. These data reduction processes involve calibration and correction of raw data, one- or two-dimensional integration, as well as fitting and further analysis of the data, including the extraction of certain parameters. The software,DPDAK(directly programmable data analysis kit), is based on a plug-in structure and allows individual extension in accordance with the requirements of the user. The article demonstrates the use ofDPDAKfor on- and offline analysis of scanning small-angle X-ray scattering (SAXS) data on biological samples and microfluidic systems, as well as for a comprehensive analysis of grazing-incidence SAXS data. In addition to a comparison with existing software packages, the structure ofDPDAKand the possibilities and limitations are discussed.