title: 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.
authors.affiliation: Department of Materials Science and Engineering, RM 13-4022, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, 02139, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Vandiver
authors.forename: Delphine
authors.initials: D
authors.lastname: Dean
authors.forename: Nelesh
authors.initials: N
authors.lastname: Patel
authors.forename: Claudia
authors.initials: C
authors.lastname: Botelho
authors.forename: Serena
authors.initials: S
authors.lastname: Best
authors.forename: José D
authors.initials: JD
authors.lastname: Santos
authors.forename: Maria A
authors.initials: MA
authors.lastname: Lopes
authors.forename: William
authors.initials: W
authors.lastname: Bonfield
authors.forename: Christine
authors.initials: C
authors.lastname: Ortiz
mesh_terms: D001672:Biocompatible Materials; D002448:Cell Adhesion / Q000187:drug effects; D017886:Durapatite / Q000494:pharmacology*; D008855:Microscopy, Electron, Scanning; D049329:Nanostructures; D012825:Silicon / Q000494:pharmacology*; D013053:Spectrophotometry; D017550:Spectroscopy, Fourier Transform Infrared; D055672:Static Electricity; D013314:Stress, Mechanical
chemical_list: D001672:Biocompatible Materials; D017886:Durapatite; D012825:Silicon