Structural and Chemical Hierarchy in Hydroxyapatite Coatings

Hydroxyapatite coatings need similarly shaped splats as building blocks and then a homogeneous microstructure to unravel the structural and chemical hierarchy for more refined improvements to implant surfaces. Coatings were thermally sprayed with differently sized powders (20–40, 40–63 and 63–80 µm)...

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Bibliographic Details
Published in:Materials 2020-10, Vol.13 (19), p.4447
Main Authors: Gross, Karlis A., Petzold, Christiane, Pluduma-LaFarge, Liene, Kumermanis, Maris, Haugen, Håvard J.
Format: Article
Language:English
Subjects:
Atomic force microscopy
Chemical composition
Chemistry
Coatings
Crystal structure
Electric potential
Hydroxyapatite
Microscopy
Particle size
Raman spectroscopy
Structural hierarchy
Surface layers
Topography
Transplants & implants
X-ray diffraction
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Summary:Hydroxyapatite coatings need similarly shaped splats as building blocks and then a homogeneous microstructure to unravel the structural and chemical hierarchy for more refined improvements to implant surfaces. Coatings were thermally sprayed with differently sized powders (20–40, 40–63 and 63–80 µm) to produce flattened homogeneous splats. The surface was characterized for splat shape by profilometry and Atomic force microscopy (AFM), crystal size by AFM, crystal orientation by X-ray diffraction (XRD) and structural variations by XRD. Chemical composition was assessed by phase analysis, but variations in chemistry were detected by XRD and Raman spectroscopy. The resulting surface electrical potential was measured by Kelvin probe AFM. Five levels of structural hierarchy were suggested: the coating, the splat, oriented crystals, alternate layers of oxyapatite and hydroxyapatite (HAp) and the suggested anion orientation. Chemical hierarchy was present over a lower range of order for smaller splats. Coatings made from smaller splats exhibited a greater electrical potential, inferred to arise from oxyapatite, and supplemented by ordered OH− ions in a rehydroxylated surface layer. A model has been proposed to show the influence of structural hierarchy on the electrical surface potential. Structural hierarchy is proposed as a means to further refine the properties of implant surfaces.
ISSN:1996-1944
1996-1944
DOI:10.3390/ma13194447