Dissolution Kinetics of Hydroxyapatite

Defect Induced Asymmetric Pit Formation on Hydroxyapatite

“…To overcome these issues, dissolution of biological apatites as well as hydroxyapatite 9,10 (HAP), a close synthetic analog of biological apatite, have been studied under simplified acidic conditions in vitro. [11][12][13] Several dissolution mechanisms have been proposed based on solution phase kinetic data by measuring transient calcium and phosphate ion concentrations from bulk solutions. [14][15][16] However, bone resorption occurs on the apatite surfaces.…”

“…The dissolution of bone mineral, known as biological apatite, has been difficult to characterize due to the complexity of the system (structurally diverse mixture of inorganic apatite mineral, organic macromolecules, , extracellular matrix, cells, and ions) and the technological limitations associated with attaining a well-defined system for gathering precise measurements. To overcome these issues, dissolution of biological apatites as well as hydroxyapatite , (HAP), a close synthetic analog of biological apatite, have been studied under simplified acidic conditions in vitro. − Several dissolution mechanisms have been proposed based on solution phase kinetic data by measuring transient calcium and phosphate ion concentrations from bulk solutions. − However, bone resorption occurs on the apatite surfaces. Recent microscopic kinetic studies based on scanning probe microscopes have shown that the reactions taking place at the solid/liquid (or gas) interface, such as dissolution, nucleation, diffusion and catalytic reactions are significantly affected by local surface structural and stoichiometric environments. − Therefore, the direct observation of atomically well-defined apatite surfaces can provide a fundamental understanding of how the inorganic components of bone and tooth resorb, which cannot be obtained from bulk solution experiments.…”

Chemical and Mathematical Simulation of Caries

“…This product was shown to contain impurities which reduce the rate of dissolu tion of enamel or apatite [Francis el al., 1973], Brady et al [1966] found a reduc tion in the rate of dissolution of hydroxy apatite by phytate of a factor 5. Assuming this to be indicative for the effect of compa rable products, we introduced a gradient of a factor 5 in the k,lis for the simulations of these caries experiments too.…”

Characterization of the Dominant Molecular Step Orientations on Hydroxyapatite (100) Surfaces

“…There are a number of factors that influence the relative step retraction velocity. Because the dissolution rate increases as the solution pH decreases, − two factors in particular are expected to play important roles in determining relative step velocities: (i) how easily a step is attacked by protons and (ii) how much the protonation of specific steps can lower the activation energy of calcium phosphate bond breaking. Regardless of these plausible kinetic variables affecting step velocity during dissolution, we found that the step orientations that evolve during dissolution are the same as the dominant step orientations found on HAP crystal surfaces prepared under thermodynamic control.…”