Defect Induced Asymmetric Pit Formation on Hydroxyapatite

Abstract

Defect sites on bone minerals play a critical role in bone remodeling processes. We investigated single crystal hydroxyapatite (100) surfaces bearing crystal defects under acidic dissolution conditions using real-time in situ atomic force microscopy. At defect sites, surface structure-dependent asymmetric hexagonal etch pits were formed, which dominated the overall dissolution rate. Meanwhile, dissolution from the flat terraces proceeded by stochastic formation of flat bottom etch pits. The resulting pit shapes were intrinsically dictated by the HAP crystal structure. Computational modeling also predicted different step energies associated with different facets of the asymmetric etch pits. Our microscopic observations of HAP dissolution are significant for understanding the effects of local surface structure on the bone mineral remodeling process and provide useful insights for the design of novel therapies for treating osteoporosis and dental caries.

Dynamics of crystallization and dissolution of calcium orthophosphates at the near-molecular level

“…For an HAP (100) surface exposed to deionized water, the average height of each step was 0.84 ± 0.1 nm, which is close to the interlayer distance of the (100) , respectively, suggesting that steps with (110) facets were energetically less stable than steps with (010) facets, and that the (110) face could be more susceptible to dissolution [50]. Molecular steps parallel to the elongated axes of HAP crystals, and those angled at approximately 54° to the elongated axis, are not only energetically favorable but also kinetically dominant under dissolution conditions.…”

Effect of Salinity on Hydroxyapatite Dissolution Studied by Atomic Force Microscopy

“…However, previously, we showed that pits with hexagonal shape formed on the (100) surface when dissolution experiments were performed in the same acidic buffer in the absence of NaCl. 7 In addition, hexagonal pit shapes were observed previously in both synthetic and biological apatites in various acidic solution environments without NaCl.…”

“…Previously, to address this challenging problem, we investigated HAP dissolution processes by directly observing atomically well defined (100) HAP surfaces under acidic dissolution conditions using in situ atomic force microscopy (AFM). 7 We found that dissolution originating from small local structural defects (e.g., screw and edge dislocations) embedded on atomically flat terraces came to dominate the overall dissolution process by formation of hexagonal deep etch pits. Here, using the same technique, we report the effects of NaCl concentration on the HAP dissolution process.…”

“…Previously, we showed that HAP dissolution rate is dominated by local defects which become major sources of steps. 7 In addition, many groups reported that dissolution rate can be significantly modified by changes of step velocities through interactions between additives (ranging from small inorganic ions to large peptides) and molecular steps. 14 Particularly, selective interactions between additives and specific molecular steps caused the change of steps' orientations and even the bulk shapes of crystals.…”

Preparation of Ruthenium Incorporated Heterogeneous Catalysts Using Hydroxyapatite as Catalytic Supports for Aerobic Oxidation of Alcohols

“…4 Because of its biocompatibility, HAP has been used as the model compounds for the study of biominerals. [5][6][7] One important chemical characteristic of HAP is its high ion exchange capability. It is well known that various anions such as carbonate, fluoride and chloride ions can be incorporated onto HAP surface via anion exchange with hydroxyl group in aqueous solution.…”