Local electronic structure and nanolevel hierarchical organization of bone tissue: theory and NEXAFS study.

Theoretical and experimental investigations of native bone are carried out to understand relationships between its hierarchical organization and local electronic and atomic structure of the mineralized phase. The 3D superlattice model of a coplanar assembly of the hydroxyapatite (HAP) nanocrystallites separated by the hydrated nanolayers is introduced to account the interplay of short-, long- and super-range order parameters in bone tissue. The model is applied to (i) predict and rationalize the HAP-to-bone spectral changes in the electronic structure and (ii) describe the mechanisms ensuring the link of the hierarchical organization with the electronic structure of the mineralized phase in bone.

[CHARACTERISTICS OF OSTEOCYTE CELL LINES FROM BONES FORMED AS A RESULT OF MEMBRANOUS (SKULL BONES) AND CHONDRAL (LONG BONES) OSSIFICATION].

The aim of this work was to analyze the literature data and the results of authors' own research, to answer the question--if the osteocytes of bone tissues resulting from membranous and chondral ossification, belong to one or to different cell lines. The differences between the cells of osteocyte lines derived from bones resulting from membranous and chondral ossification were established in: 1) the magnitude of the mechanical signal, initiating the development of the process of mechanotransduction; 2) the nature of the relationship between the magnitude of the mechanical signal that initiates the reorganization of the architecture of bone structures and the resource of their strength; in membranous bones significantly lower mechanical signal caused a substantially greater increment of bone strength resource; 3) the biological activity of bone structures, bone fragments formed from membranous tissue were more optimal for transplantation; 4) the characteristics of expression of functional markers of bone cells at different stages of their differentiation; 5) the nature of the reaction of bone cells to mechanical stress; 6) the sensitivity of bone cells to one of the factors controlling the process of mechanotransduction (PGI2); 7) the functioning of osteocytes during lactation. These differences reflect the functional requirements to the bones of the skeleton--the supporting function in the bones of the limbs and the shaping and protection in the bones of the cranial vault.

[Hierarchically organized model of interconnected cellular and tissue mechanisms of calcium exchange between bone and blood].

The objective of this study was to propose, on the basis of the results of authors' own research and literature data, the hierarchically organized model of the interrelation of morphological mechanisms with the participation of biochemical bases of Ca2+ exchange between bone and blood. It is shown that osteocytes control the activity of main known mechanism of skeleton architecture remodeling (osteoclast-osteoblast remodeling, modeling, osteocyte remodeling etc.), that is the destruction and formation of mineral matrix component, thus influencing calcium turnover between bone and blood.

[Precision error minimization algorithm for dual-energy X-ray absorptiometry to clinically insignificant values].

Objective: To propose an algorithm for using dual-energy X-ray absorptiometry (DEXA) on the basis of the authors' findings and the data available in the literature on the estimation of the projectional bone mineral density (PBMD), which can minimize the precision error (PE) to clinically insignificant values while solving the problems of diagnosis, prognosis, and therapeutic effectiveness monitoring in a specific patient.

Material And Methods: The results of the authors' ex vivo studies and literature data on PE during DEXA in a densitometry room were systematized.

Results: The performed analysis allowed the elaboration of a PE minimizing algorithm in the individual control in terms of clinical problems to be solved.

[Osteocytes and the pathways of mechanical homeostasis optimization from the point of view of functional osteology].

The aim of this work was to determine, on the basis of the results of authors' own research and literature data, the main pathways of osteocyte (OC) influence on the mechanical homeostasis of the skeleton. The following pathways of reorganization of the architecture of bone structures are postulated: at the ultrastructural level without direct cell participation, through the bone matrix synthesis by osteoblasts and OC, through bone matrix resorption by osteoclasts and OC, the latter being able to resorb the surrounding mineral and organic matrix both separately, and conjointly. This reorganization results in local changes of the mechanical characteristics of bones due to changes in: porosity of interstitial spaces, transport ability of the lacunar-canalicular system, porosity of the area of osteoblastic-osteoclastic remodeling, modeling of bone structures.