Calcium biological variability

Calcium-idiosphate-based bioceramics have also been used as coatings on dense implants and porous surface layers to accelerate and enhance fixation of a substrate biomaterial to tissue (Kohn and Ducheyne, 1992 Cook et al 1992 Ducheyne et al., 1980 Oonishi et al., 1994). Results of these smdies vary with respect to bond strength, solubility, and overall in vivo function, suggesting a window of material variability in parallel with a window of biologic variability (Kohn and Ducheyne, 1992). 

To see if monitoring these variables acmally yields any useful information on the folding pathway, multiple simulated annealing runs with all parameter monitoring facihties implemented were carried out on a family of vitamin D molecules (Figure 4) [23]. The classical biological responses for l,25(OH)2-vitamin D3 are now well established. The vitamin D hormone is known to mediate intestinal calcium absorption and bone calcium metabolism via its receptor. More recently, non-traditional activities have been discovered including cell differentiation and prohferation. 

About 20-35% of magnesium is bound to proteins and other anions at pH 7.4, less in acidosis and more in alkalosis as discussed for calcium. As a variable amount of magnesium is bound, total magnesium concentration (Table 1) is only a poor estimate of free magnesium concentration, which is considered to be the biologically active fraction. 

The stoichiometric HAP, characterized by an atomic ratio Ca/P = 1.67 and a hexagonal structure, is the nearest relative of biologic apatite ciystals. Moreover, the HAP is the least soluble and the least resorbable calciirm phosphate. When an HAP ceramic is implanted in a bone site, the bone tissue formation is observed on its contact (osteoconduction) (see Figure 12.1). Besides, in certain conditions, calcium phosphate ceramics can induce the formation of bone tissue in ectopic sites. HAP implants appear in the form of dense ceramics or with variable porosity or again, in the case of prostheses, as thin coatings deposited by plasma sprayed on a metal. 

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