X-ray diffraction and polarizing optical microscopy investigation of the structural organization of rabbit tibia

New method for Raman investigation of the orientation of collagen fibrils and crystallites in the Haversian system of bone

Knowledge of the organization of the components of bone is of primary importance in understanding how this tissue responds to stresses and provides a starting point for the design and development of biomaterials. Bone structure has been the subject of numerous studies. The mineralized fiber arrangement in cortical bone is either a twisted or orthogonal plywood structure. Both mineral models coexist in compact bone. Raman polarized spectroscopy offers definite advantages in the study of biological samples, enabling the simultaneous analysis of mineral and organic components and the determination of molecular orientation through the polarization properties of the Raman scattering. In this study, we used the Raman polarization approach to simultaneously investigate the orientation of collagen fibrils and apatite crystals in human cortical bone. Raman bands ratios were monitored as a function of sample orientation. Specific ratios were chosen--such as nu(3) PO(4)/nu(1) PO(4), amide III (1271 cm(-1))/amide III (1243 cm(-1)), and amide I/amide III (1243 cm(-1))--due to their sensitivity to apatite-crystal and collagen-fibril orientation. Based on this original approach, spatial changes were monitored as a function of distance from the Haversian canal. The results revealed simultaneous tilting in intra-lamellar collagen-fibril and mineral crystal orientations. These results are consistent with a twisted plywood organization in the Haversian bone structure at the lamellar level. But at molecular level, the co-alignment of the collagen fibrils and the apatite crystal is observed in the innermost lamellae and becomes gradually less ordered as the distance from the Haversian canal increases. This work highlights the interest of Raman spectroscopy for the multiscale investigation of bone structure.

Biaxial mechanical evaluation of cholecyst-derived extracellular matrix: a weakly anisotropic potential tissue engineered biomaterial

A new acellular, natural, biodegradable matrix has been discovered in the cholecyst-derived extracellular matrix (CEM). This matrix is rich in collagen and contains several other macromolecules useful in tissue remodeling. In this study, the principal material axes, collagen fiber orientations, and biaxial mechanical properties in a physiological loading regime were characterized. Fiber direction was determined by polarized light microscopy, and the principal axes and degree of anisotropy were determined mechanically. Macroscopic equibiaxial strain tests were then conducted on preconditioned specimens. While 13% of the area of CEM contains collagen fibers oriented between 50 degrees and 60 degrees from the neck-fundus axis, the principal material axis was oriented 63 degrees +/- 13.7 degrees , with an aspect ratio of 0.11 +/- 0.06, indicating a weak anisotropy in that direction. Under biaxial loading, CEM exhibited a large toe region followed by an exponential rise in stress in both principal and perpendicular axis directions, similar to other materials currently under research. There was no significant difference between the biaxial stress-strain profile and the burst stress-strain profile. The results demonstrate that CEM is weakly anisotropic and it has the ability to support large strains across a physiological loading regime.

High-resolution imaging of proteins in human teeth by scanning probe microscopy

High-resolution studies of dental tissues are of considerable interest for biomedical engineering and clinical applications. In this paper, we demonstrate the application of piezoresponse force microscopy (PFM) to nanoscale imaging of internal structure of human teeth by monitoring the local mechanical response to an electrical bias applied via a conductive tip. It is shown that PFM is capable of detecting dissimilar components of dental tissues, namely, proteins and calcified matrix, which have resembling morphology but different piezoelectric properties. It is demonstrated that collagen fibrils revealed in chemically treated intertubular dentin exhibit high piezoelectric activity and can be visualized in PFM with spatial resolution of 10 nm. Evidence of the presence of protein inclusions of 100-200 nm wide and several micrometers long in tooth enamel has been obtained. Furthermore, it is found that the peritubular dentin and intertubular dentin exhibit different piezoelectric behavior suggesting different concentration of collagen fibrils. The obtained results demonstrate a high potential of PFM in providing an additional insight into the structure of dental tissues. It is suggested that the PFM approach can be used to study the structure of a wide range of biological materials by monitoring their electromechanical behavior at the nanoscale.

Enhanced osteobonding by negative surface charges of electrically polarized hydroxyapatite

Negative surface charges of electrically polarized hydroxyapatite ceramics have been proven to enhance osteobonding in canine bone tissues. Even in a wide gap of 0.2 mm between hydroxyapatite and bone, the negatively charged hydroxyapatite conducted formation of unidirectionally oriented bone layer into direct contact with the hydroxyapatite surface 7 days after implantation. By day 14, the gap was filled with maturing bones linked to each other while conventional hydroxyapatite required at least 28 days for direct bone-to-bone contact. The electrostatic force was deduced to have affected both the activation of bone formation by myeloid cells and the orientation of the bone domain on negatively charged surfaces.

Twisted plywood pattern of collagen fibrils in teleost scales: an X-ray diffraction investigation

The distribution and orientation of collagen fibrils, and apatite crystals, in the scales of a bony fish (Leuciscus cephalus) were investigated by X-ray diffraction. The small-angle diffraction patterns obtained with a microfocus scanning setup from most of the examined areas exhibit a distribution of intensity of the collagen reflections according to five preferential orientations, at 36 degrees from one another. It is suggested that the peculiar small-angle X-ray diffraction pattern is due to a plywood arrangement of collagen fibrils in successive layers parallel to the surface of the scale. The fibrils are strictly aligned in each layer and the alignment rotates by 36 degrees in successive layers, according to a discontinuous twist that generates a symmetric plywood pattern. The large spread of the wide-angle reflections does not allow one to distinguish the five directions of orientation in the intensity distribution of the 002 reflection of apatite. However, the patterns recorded from the less ordered regions of the scales display two different orientations of the 002 reflection and allow one to infer a preferential distribution of the apatite crystals with their c-axes parallel to the collagen fibrils. Although much electron microscopic evidence of plywood arrangements in calcified, as well as uncalcified, tissues has been reported, these are the very first diffraction data which unambiguously confirm the presence of these peculiar structures and suggest that this kind of investigation represents a powerful tool with which to study plywood arrangements in biological tissues.