Biomedical subjects

R B Heimann

Publications and source records attributed to R B Heimann.

5 recordsLinked to original sources

PubMed2004

In vitro and in vivo performance of Ti6Al4V implants with plasma-sprayed osteoconductive hydroxylapatite-bioinert titania bond coat "duplex" systems: an experimental study in sheep.

To evaluate the in vivo performance of "duplex" hydroxylapatite top coat/TiO(2) bond coat systems, cylindrical Ti6Al4V rods of 130 mm in length and 11-13 mm in diameter were coated by atmospheric plasma spray (APS) technique with both a standard hydroxylapatite (HAp) layer and a HAp+TiO(2) bond coat "duplex" layer. In this pilot study coated and uncoated rods serving as controls were implanted into the femur of sheep so that their distal ends were freely suspended in the medulla of the femur. After an observation time of six months it was found that bone apposition and bone ingrowth were considerably increased in the presence of a osteoconductive coating. In particular, in vivo spalling and delamination frequently observed with HAp coatings was virtually absent in duplex coatings owing to the strong adhesion of the bond coat to the HAp top coat that anchored the latter solidly to the metallic surface of the implant. Some tentative mechanisms leading to this improved coating adhesion will be discussed.

Alloys↗

PubMed2000

Compositional and microstructural changes of engineered plasma-sprayed hydroxyapatite coatings on Ti6Al4V substrates during incubation in protein-free simulated body fluid.

Hydroxyapatite (HAp) coatings engineered for maximum surface roughness (coating type I), porosity (coating type II), and tensile adhesion strength (coating type III) were deposited by atmospheric plasma spraying (APS) onto Ti6Al4V substrates and characterized for their microstructure, phase composition, and design properties. The composition of the as-sprayed coatings changed during treatment with protein-free simulated body fluid (Hank's Balanced Salt Solution, HBSS) for up to 12 weeks by preferential dissolution of thermal decomposition products, and amorphous calcium phosphate (ACP). From solutions supersaturated with respect to calcium and phosphorus ions, a thin, very porous layer precipitated onto the leached surfaces of coating type II samples after an incubation time of 8 weeks, consisting of spherical agglomerates of a poorly crystallized bone-like Ca-deficient defect hydroxyapatite that is thought to accelerate in vivo bone apposition rates and, hence, may induce favorable osseoconductive conditions.

Adhesiveness↗

PubMed1998

Microstructural and in vitro chemical investigations into plasma-sprayed bioceramic coatings.

Hydroxyapatite (HA) coatings plasma sprayed without and with bond coats (titania, zirconia) onto titanium alloy (Ti6A14V) substrates under both atmospheric and low pressure plasma spray conditions were investigated in terms of their microstructure and their resorption resistance during immersion in simulated body fluid (Hank's balanced salt solution). The microstructures of test samples were characterized using SEM on as-sprayed and leached surfaces and on the corresponding cross sections. Selected coating systems were studied by 2-dimensional secondary ion mass spectroscopy imaging to obtain information on plasma spray induced diffusional processes at the coating interfaces, as well as the spatial distribution of minor and trace elements. Coatings consisting of thin (10-15 microm) titania/zirconia (eutectic ratio) and titania bond coats, combined with a 150- to 180-microm thick HA top coat, yielded peel strengths in excess of 32 N/m, as well as sufficient resorption resistance.

Ceramics↗

PubMed1998

Development of plasma-sprayed bioceramic coatings with bond coats based on titania and zirconia.

Bond coats for plasma-sprayed hydroxyapatite (HAp) coatings on Ti-6A1-4V hip endoprotheses are being developed for improved in vivo performance. Bond coat powders consisting of (i) CaO-stabilized zirconia, (ii) a eutectic composition of titania and non-stabilized zirconia, and (iii) titania were applied by atmospheric plasma spraying (APS) to Ti-6A1-4V-coupons and 100 microm-thick Ti-6A1-4V foils. Subsequently, a thick layer of HAp was sprayed onto the thin bond coats. Peel tests on Ti-6A1-4V foil/bond coat/HAp top coat assemblies revealed that titania and titania/ zirconia bond coats increased the peel adhesion strength in a statistically significant way from 22 N m(-1) (HAp without a bond coat) to >42 and 32 N m(-1), respectively. Microstructural investigations by SEM on cross-sections of coatings leached in simulated body fluid for up to 28 days led to the conclusion that the chemically very stable bond coats act as an improved chemical barrier against in vivo release of metal ions from the implant, as well as an improved adhesive bond by development of very thin well-adhering reaction layers, presumbly composed of perovskite, calcium dititanate, and/or calcium zirconate.

Alloys↗

PubMed1998

Adhesion of thermally sprayed hydroxyapatite-bond-coat systems measured by a novel peel test.

Ti6Al4V foils, 100 microm thick, were coated with thin (10-15 microm) bond coats based on titania and zirconia, and subsequently coated with a thick (100-120 microm) hydroxyapatite layer, using atmospheric plasma spraying. Peel adhesion tests of the coating systems performed on the foils showed that titania, and mixed titania/non-stabilized zirconia bond coats improved the adhesion of the ceramic layers to the metallic substrate in a statistically significant way, while a partially CaO-stabilized zirconia bond coat led to a decrease of the peel adhesion strength when compared to hydroxyapatite coatings without a bond coat.

Journal Article↗