A Novel Approach to the Growth of Polycrystalline Hydroxyapatite Thin Films for Biomedical Applicati

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A Novel Approach to the Growth of Polycrystalline
Hydroxyapatite Thin Films for Biomedical
Applications
What is HA?
Why is HA important?

• Biocompatible strong bond with bone

Hydroxyapatite(HA) Ca10(PO4)6(OH)2 main
inorganic constituent of natural bone
What is the problem?

• Poor bulk mechanical properties ?
• hence used to coat implant metals
• adhesion then critical!

Ca2
PO43 -
OH-
HA Coating Techniques

• Plasma spraying
• commercially available
• high throughput
• non-stoichiometric coatings
• poor adhesion

• Right angle RF magnetron sputtering
• our approach
• better adhesion
• stoichiometric coatings
• polycrystalline coatings NO post
• deposition heat treatment required

• RF planar magnetron sputtering
• research labs
• better adhesion
• non-stoichiometric coatings
• post deposition heat treatment needed

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Characterization of NU HA coatings

• Atomic Force Microscopy (AFM)
• Inductively Coupled Plasma-Optical Emission
  Spectroscopy (ICP-OES)
• Fourier Transform Infrared Spectroscopy (FTIR)
• Nanoindentation (Mechanical properties)
• Raman Spectroscopy
• Scanning Electron Microscopy (SEM)
• Conventional X-ray Diffraction (XRD)
• Grazing Incidence Synchrotron X-ray Diffraction
  (GISXRD)
• Stylus Profilometry
• X-ray Photoelectron Spectroscopy (XPS)
• Cell Culture

Characterization tools
Atomic Force Microscopy (AFM)
X-ray Reflectivity (XRR)
Scanning Electron Microscopy (SEM)
All measurements show as-deposited coatings to be
very smooth. Post deposition heat treatment
roughens surface (severe crack formation due to
thermal mismatch, as noted by other workers).
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X-ray Diffraction (XRD)
Mechanical Properties
Nanoindentation yields modulus comparable to
conventional magnetron sputtered, but superior to
plasma sprayed films however,
hardness enhanced by a factor of 4.
As-sputtered coatings highly crystalline. Post
deposition heat treatment yields no further
improvement in crystallinity.
Cell Culture Studies
Scanning electron micrograph of in vitro murine
osteoblast growth (in collaboration with Rio de
Janeiro partners) demonstrates osteoblast cells
attach and grow well on as-sputtered coatings.
NU HA coatings show large improvements in cell
proliferation rate over plain titanium and plasma
sprayed HA coatings (performed by fluorescence
microcopy in collaboration with Prof. Webster at
Brown University).
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The accompanying theory program aims at
describing the chemical and structural properties
of metal impurities like Fe, Zn, Pb, Sr, which
play a critical role in biological processes. We
need to understand details of adsorption at the
HA surface, diffusion to the interior of
particles and films, and exchange with the native
Ca ions. Since biologically active surfaces have
interesting topology as well as interesting
chemistry, we develop Kinetic Monte Carlo methods
for constructing textured surfaces used in
simulations.
Columnar HA surface
With Ions in Aqueous Environment
With Attached Peptide/Protein Fragments