title: Suspension thermal spraying of hydroxyapatite: microstructure and in vitro behaviour.
abstract: In cementless fixation of metallic prostheses, bony ingrowth onto the implant surface is often promoted by osteoconductive plasma-sprayed hydroxyapatite coatings. The present work explores the use of the innovative High Velocity Suspension Flame Spraying (HVSFS) process to coat Ti substrates with thin homogeneous hydroxyapatite coatings. The HVSFS hydroxyapatite coatings studied were dense, 27-37μm thick, with some transverse microcracks. Lamellae were sintered together and nearly unidentifiable, unlike conventional plasma-sprayed hydroxyapatite. Crystallinities of 10%-70% were obtained, depending on the deposition parameters and the use of a TiO2 bond coat. The average hardness of layers with low (<24%) and high (70%) crystallinity was ≈3.5GPa and ≈4.5GPa respectively. The distributions of hardness values, all characterised by Weibull modulus in the 5-7 range, were narrower than that of conventional plasma-sprayed hydroxyapatite, with a Weibull modulus of ≈3.3. During soaking in simulated body fluid, glassy coatings were progressively resorbed and replaced by a new, precipitated hydroxyapatite layer, whereas coatings with 70% crystallinity were stable up to 14days of immersion. The interpretation of the precipitation behaviour was also assisted by surface charge assessments, performed through Z-potential measurements. During in vitro tests, HA coatings showed no cytotoxicity towards the SAOS-2 osteoblast cell line, and surface cell proliferation was comparable with proliferation on reference polystyrene culture plates.
authors.affiliation: Department of Engineering "Enzo Ferrari", Università di Modena e Reggio Emilia, Via Vignolese 905, 41125 Modena, MO, Italy. Electronic address: giovanni.bolelli@unimore.it.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Bolelli
authors.forename: Devis
authors.initials: D
authors.lastname: Bellucci
authors.forename: Valeria
authors.initials: V
authors.lastname: Cannillo
authors.forename: Luca
authors.initials: L
authors.lastname: Lusvarghi
authors.forename: Antonella
authors.initials: A
authors.lastname: Sola
authors.forename: Nico
authors.initials: N
authors.lastname: Stiegler
authors.forename: Philipp
authors.initials: P
authors.lastname: Müller
authors.forename: Andreas
authors.initials: A
authors.lastname: Killinger
authors.forename: Rainer
authors.initials: R
authors.lastname: Gadow
authors.forename: Lina
authors.initials: L
authors.lastname: Altomare
authors.forename: Luigi
authors.initials: L
authors.lastname: De Nardo
mesh_terms: D001826:Body Fluids / Q000737:chemistry; D002450:Cell Communication / Q000187:drug effects; D016923:Cell Death / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D020099:Coated Materials, Biocompatible / Q000737:chemistry / Q000494:pharmacology; D003460:Crystallization; D004055:Differential Thermal Analysis; D017886:Durapatite / Q000737:chemistry* / Q000494:pharmacology; D055119:Elastic Modulus / Q000187:drug effects; D006244:Hardness / Q000187:drug effects; D006801:Humans; D008422:Materials Testing / Q000379:methods*; D008855:Microscopy, Electron, Scanning; D058626:Plasma Gases / Q000737:chemistry; D011208:Powders; D013059:Spectrum Analysis, Raman; D055672:Static Electricity; D013535:Suspensions; D013696:Temperature; D013718:Tensile Strength / Q000187:drug effects; D013818:Thermogravimetry; D014961:X-Ray Diffraction
chemical_list: D020099:Coated Materials, Biocompatible; D058626:Plasma Gases; D011208:Powders; D013535:Suspensions; D017886:Durapatite
keywords: Bioactive coating; Cytocompatibility; Cytotoxicity; High Velocity Suspension Flame Spraying (HVSFS); Hydroxyapatite; Simulated body fluid (SBF)