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

Abstract

Hydroxyapatite (HAP) is the major inorganic component of bones and teeth. The characterization of HAP surfaces on the molecular level is important for achieving a fundamental understanding of bone remodeling and dental caries processes. On the microscopic level, hydroxyapatite growth and dissolution reactions mainly occur at steps. Therefore, this study focuses on individual molecular steps on HAP (100) facets under both static conditions and dynamic dissolution conditions using atomic force microscopy (AFM). We found that molecular steps parallel to the elongated axes of HAP crystals and those angled approximately 54 degrees against the elongated axis are not only energetically favorable but also kinetically dominant under dissolution conditions.

Surface modification of hydroxyapatite for hydrogen generation

“…2a, represent the elongated HAP whiskers. Examination of the XRD results shows that HAP whiskers have a crystalline phase consistent with the typical single-crystal HAP patterns [25]. Additionally, the XRD results show that the synthesis was carried out without the occurrence of thermal decomposition by-product impurities.…”

Synthesis and characterisation of large chlorapatite single-crystals with controlled morphology and surface roughness

“…Single crystals can be used to perform careful studies to reveal the dissolution mechanisms of apatite that could be involved in bone remodeling [5, 6]. The use of single crystals could offer insights on the role of defects and crystallography that cannot be obtained with polycrystalline bulk samples.…”

“…For example, large apatite crystals can be used to determine intrinsic properties and analyse basic surface chemical and biological processes that play a critical role in the resorption and remodelling of bone and bioactive implants [4]. In this respect, apatite crystals can be used to study dissolution [5, 6], protein adsorption [7, 8], or mechanical response and their dependence with crystal orientation [9–11]. …”

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

“…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. The steps with θ = 54° can be divided into two pairs of crystallographically equivalent steps; the step velocities on one side are almost twice as fast as their counterparts on the other side, suggesting the formation of asymmetric pits [51]. Moreover, the addition of NaCl to the same dissolution reaction solutions (10 mmol L −1 citrate, pH 6) strongly suppressed HAP (100) face dissolution kinetics [52].…”