Bone microstructure

FIGURE 8.1 The four levels of bone microstructure, from the level of mineralized collagen fibrils to cortical and trabecular bone. It is generally assumed that at the former level, all bone is equal, although there may be subtle differences in the nature of the lamellar architecture and degree of mineralization between cortical and trabecular bone. Adaptedfrom Ref. 145.)... 

Hildebrand, T., Laib, A., Mtiller, R., Dequeker,., and RUegsegger, P. (1999), Direct three-dimensional morphometric analysis of human cancellous bone microstructural data from spine, femur, iliac crest, and calcaneus, J. Bone Miner. Res. 14(7) 1167-1174. 

A first example of application of microtomography is taken from life sciences. Here X-ray microscopy and microtomography allows to reconstruct the internal three-dimensional microstructure without any preparation and sometimes even of living objects. Fig. la shows an X-ray transmission microscopical image of bone (femoral head). Several reconstructed cross-sections are shown in Fig.lb. Fig.lc shows the three-dimensional reconstruction of this bone. 

This outcome was consistent with a hypothesis that structural deterioration could have been a byproduct of microorganism activity. The higher lipid content in the poorly preserved tissue suggests that those lipids are primarily extrinsic, that is, that they were produced by bacteria and/or fungi. As the food source for such microorganisms, the protein within the bone may have been substantially altered in concert with the microstructure deterioration. The quantification of the changes to the organic fraction became our next focus of research. 

Akkus O, Polyakova-Akkus A, Adar F, Schaffler MB (2003) Aging of microstructural compartments in human compact bone. J Bone Miner Res 18 1012-1019... 

Fluorine is an essential element involved in several enzymatic reactions in various organs, it is present as a trace element in bone mineral, dentine and tooth enamel and is considered as one of the most efficient elements for the prophylaxis and treatment of dental caries. In addition to their direct effect on cell biology, fluoride ions can also modify the physico-chemical properties of materials (solubility, structure and microstructure, surface properties), resulting in indirect biological effects. The biological and physico-chemical roles of fluoride ions are the main reasons for their incorporation in biomaterials, with a pre-eminence for the biological role and often both in conjunction. This chapter focuses on fluoridated bioceramics and related materials, including cements. The specific role of fluorinated polymers and molecules will not be reviewed here. 

The microstructure of bread and other microporous foods can be conveniently studied by applying synchrotron radiation X-ray microtomography (X-MT) (Falcone et al., 2004a Maire et al., 2003) to centimeter- or millimeter-sized samples (Lim and Barigou, 2004). X-MT application only requires the presence of areas of morphological or mass density heterogeneity in the sample materials. The use of this technique for food microstructure detection is of recent date. It was traditionally used for the analysis of bone quality (Peyrin et al., 1998, 2000 Ritman et al., 2002). 

Harrigan, T.P. and Hamilton, J.J. (1993) Bone strain sensation via transmembrane potential changes in surface osteoblasts loading rate and microstructural implications. Journal of Biomechanics 26 183-200... 

Hert, J., Pribylova, E. and Liskova, M. (1972) Reaction of bone to mechanical stimuli. Part 3. Microstructure of compact bone of rabbit tibia after intermittent loading. Acta anatomica 82 218-230... 

Natural and man-made porous media usually possess formidably complex microstructure, often hierarchical. In this paper we shall not discuss hierarchical microstructures revealed, for instance by fractured porous media and biological tissues like bone and soft tissue. However, recently developed stochastic reiterated homogenisation enables one to determine macroscopic properties of random porous media with hierarchical architecture, cf. [11],... 

In one report, kidney cells of Xenopus laevis (A6) were cultured in a 96-well Si microphysiometer sensor array [897], Mouse fibroblasts (3T3-J2) were cultured in stacked PU microstructures that mimic the bone architecture. PU is used because it is biocompatible [160],... 

A. Fritsch, C. Universal microstructural patterns in bone Micromechanics-based prediction of anisotropic material behavior. Matls. Rsrch. Soc. Sym. Pro.-Mech. of Bio. Bio-Inspired Matls. 975, 128-134 (2006)... 

Chemical characterisation of F uptake in archaeological bone has already been developed in the 19th century [1,2] and is now well established [60], However, relatively few studies use a combined multianalytical approach using trace elemental and microstructure analytical techniques (PIXE/PIGE, TEM-EDX) for evidencing modifications on different microscopic and nanoscopic levels (Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), SEM, TEM) and enabling an objective evaluation of the F uptake mechanisms [32-34,51],... 

Considerable development has occurred on sintered ceramics as bone substitutes. Sintered ceramics, such as alumina-based ones, are uru eactive materials as compared to CBPCs. CBPCs, because they are chemically synthesized, should perform much better as biomaterials. Sintered ceramics are fabricated by heat treatment, which makes it difficult to manipulate their microstructure, size, and shape as compared to CBPCs. Sintered ceramics may be implanted in place but cannot be used as an adhesive that will set in situ and form a joint, or as a material to fill cavities of complicated shapes. CBPCs, on the other hand, are formed out of a paste by chemical reaction and thus have distinct advantages, such as easy delivery of the CBPC paste that fills cavities. Because CBPCs expand during hardening, albeit slightly, they take the shape of those cavities. Furthermore, some CBPCs may be resorbed by the body, due to their high solubility in the biological environment, which can be useful in some applications. CBPCs are more easily manufactured and have a relatively low cost compared to sintered ceramics such as alumina and zirconia. Of the dental cements reviewed in Chapter 2 and Ref. [1], plaster of paris and zinc phosphate... 

The biocompatible CBPC development has occurred only in the last few years, and the recent trend has been to evaluate them as biocompatible ceramics. After all, biological systems form bone and dentine at room temperature, and it is natural to expect that biocompatible ceramics should also be formed at ambient temperature, preferably in a biological environment when placed in a body as a paste. CBPCs allow such placement. We have discussed such calcium phosphate-based cements in Chapter 13. Calcium-based CBPCs, especially those constituting hydroxyapatite (HAP), are a natural choice. HAP is a primary mineral in bone [3], and hence calcium phosphate cements can mimic natural bone. Some of these ceramics with tailored composition and microstructure are already in use, yet there is ample room for improvement. This Chapter focuses on the most recent biocompatible CBPCs and their testing in a biological environment. To understand biocompatible material and its biological environment, it is first necessary to understand the structure of bone and how it is formed. 

Fig. 1 Microstructure of bone, showing staggered structure of collagen molecules, which creates hole zones in which HAp is nucleated (a) [1]. The lowest level of hierarchical structure of bone, showing alignment and elongation of HAp crystals as a function of underlying aligned collagen fibrils (b) [2] (Reproduced by permission of The Royal Society of Chemistry)...

This information provides a more complete characterization of bone development, microstructure and aging because the chemical spatial variations contribute greatly to the structural integrity and ultimate biological function of bone. 

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