Silicon addition to hydroxyapatite increases nanoscale electrostatic, van der Waals, and adhesive interactions

Abstract

The normal intersurface forces between nanosized probe tips functionalized with COO(-)-terminated alkanethiol self-assembling monolayers and dense, polycrystalline silicon-substituted synthetic hydroxyapatite (SiHA) and phase pure hydroxyapatite (HA) were measured via a nanomechanical technique called chemically specific high-resolution force spectroscopy. A significantly larger van der Waals interaction was observed for the SiHA compared to HA; Hamaker constants (A) were found to be A(SiHA) = 35 +/- 27 zJ and A(HA) = 13 +/- 12 zJ. Using the Derjaguin-Landau-Verwey-Overbeek approximation, which assumes linear additivity of the electrostatic double layer and van der Waals components, and the nonlinear Poisson-Boltzmann surface charge model for electrostatic double-layer forces, the surface charge per unit area, sigma (C/m(2)), was calculated as a function of position for specific nanosized areas within individual grains. SiHA was observed to be more negatively charged than HA with sigma(SiHA) = -0.024 +/- 0.013 C/m(2), two times greater than sigma(HA) = -0.011 +/- 0.006 C/m(2). Additionally, SiHA was found to have increased surface adhesion (0.7 +/- 0.3 nN) compared to HA (0.5 +/- 0.3 nN). The characterization of the nanoscale variations in surface forces of SiHA and HA will enable an improved understanding of the initial stages of bone-biomaterial bonding.

Atmospheric plasma sprayed silica–hydroxyapatite coatings on magnesium alloy substrates

“…This means that the implant is able to chemically join the bone through a strong "bioactive bond". HAP-Si was found to have increased surface adhesion compared to un-substituted HAP [6,7]. In this way, the osteointegration and the good performance of the implant are ensured [7].…”

Mechanochemical Synthesis of SiO44–‐Substituted Hydroxyapatite, Part I – Kinetics of Interaction between the Components

“…In other studies, the bioactivity of HA-Si is explained by its surface properties and, in particular, by a negative charge localized on the rough surfaces of ceramics and sharp corners of metallic implants. [18,[25][26][27] To date, the quantity of silicon that can enter the hydroxyapatite structure has not been reliably determined. Studies have shown that it may depend on the method and conditions of synthesis.…”

Silicon calcium phosphate ceramic as novel biomaterial to simulate the bone regenerative properties of autologous bone

“…[16][17][18] The bioactivity enhancement of Si-substituted calcium phosphates can be attributed to a number of factors that act synergistically. Si-substitution facilitates the precipitation of biological HA on implant surfaces [19][20][21] which promotes protein adsorption and osteoblast attachment and proliferation. This is added to the direct effect of Si either released to the extracellular matrix or present in the implant surface on osteoblasts, osteocalsts, and collagen synthesis.…”