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Plasma-sprayed hydroxylapatite coatings on metals such as titanium have been investigated for many years and have shown a good biocompatibility when implanted in bony tissues. Radiofrequency magnetron sputtering was used as an alternative method to deposit thin films of hydroxylapatite on titanium substrates. X-ray diffraction demonstrated that the sputtered layer was crystalline with a preferred (001) crystallographic orientation with the C-axis perpendicular to the substrate surface. Scanning electron microscopy showed that the deposited films had a uniform and dense structure. The calcium phosphate ratio varied between 1.5 and 2.0, as determined by energy-dispersive X-ray analysis. The in vitro dissolution appeared to be determined by the degree of the coating's crystallinity.

The effects of discharge radio frequency (RF) power and film thickness were studied on the characteristics of Ca5(P04)30 H (hydroxyapatite) thin films fabricated by RF magnetron sputtering. The structure and chemical compo sition were investigated with a-step (thickness), scanning electron microscopy (SEM), X-ray diffraction (XRD), Ruth erford backscattering spectrometry (RBS), and infrared ab sorption spectrometry (FTIR). The films were analyzed assputtered and after annealing at 550°C under argon flow. SEM showed that the film surfaces had no cracks or other defects. X-ray diffraction showed that the deposited films were amorphous with low-discharge RF power, and crystalline with high-discharge RF power. After annealing, all the films had the same crystalline structure as apatite. However, the RBS measurements revealed that all films had a higher calcium-phosphate ratio than standard syn thetic hydroxyapatite. Furthermore, statistical testing of the RBS data revealed the existence of only a weak correlation between the Ca/P ratio and the discharge power level* Al though all sputtered films showed phosphate bonds in the infrared spectrum, only after annealing did the O H bonds of hydroxyapatite become visible.

A rat bone marrow cell culture was used to evaluate the osteogenic potential of amorphous and crystalline thin calcium phosphate (Ca/P) coatings. The coatings were deposited on titanium discs using a radiofrequency magnetron sputter procedure. Amorphous and crystalline plasma spray Ca/P coated and noncoated titanium discs served as reference material. The cellular behavior was analyzed with quantitative (attachment and proliferation rates) and qualitative (scanning electron microscopy) techniques. No significant differences were found in cell attachment and proliferation rates between the various materials. Scanning electron microscopy showed extracellular matrix formation after 18 days of culture on amorphous plasma-sprayed and the two types of magnetron sputtered coatings. Furthermore, no severe degradation of the magnetron sputtered coatings was observed. They even appeared to induce apatite formation. On basis of the results, we conclude that magnetron sputtering appears to be a promising method to manufacture bioactive ceramic coatings.

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In previous studies we developed a RF magnetron sputter technique for the production of thin Ca-P coatings. With this technique coatings can be produced that vary in Ca/P ratio as well as in structural appearance. The aim of this investigation was to obtain more understanding of the biological behavior of these coatings by way of in vitro experiments. The effect of noncoated titanium (Ti) and three different Ca-P-sputtered surfaces on the proliferation and differentiation (morphology and matrix production) of osteoblast-like cells was studied. Proliferation was determined using counting procedures; morphology was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Fluorescent markers and energy-dispersive X-ray microanalysis (EDX) were used to obtain quantitative and compositional information about the resultant calcified extracellular matrix (ECM). Results demonstrated that proliferation of the osteoblast-like cells was significantly (p < 0.05) higher on noncoated than on Ca-P-coated samples. On the other hand, more mineralized ECM was formed on the coated surfaces. In addition, TEM confirmed that the cells on the coated substrates were surrounded by ECM with collagen fibers embedded in crystallized, needle-shaped structures. On the basis of these findings, we concluded that: (1) the investigated Ca-P sputter coatings possess the capacity to activate the differentiation and expression of osteogenic cells, and (2) bone formation proceeds faster on Ca-P surfaces than on Ti substrates. Further, this bone-inductive effect appeared to be dependent on the Ca-P ratio of the deposited coatings.

The aim of this study was to investigate the bone response to calcium phosphate (Ca-P) plasm a-spray and radiofrequency m agnetron sputter-coated im plants with comparable rough ness. Therefore, tapered conical screw designed im plants were installed in the trabecular bone of the femurs of nine goats. They were provided w ith two types of coatings, a plasm a-spray dual coating of fluorapatite and hydroxyapatite (FA/HA-PS) and a titanium plasm a-spray coating, cov ered w ith an am orphous Ca-P m agnetron sputtercoating (TPS/Ca-P-a). These implants were evaluated histologically and mechanically after 3 months of implantation. A wellcontrolled m ethod to apply and measure a torsional force to load die screw-type implants to the point of failure was introduced. All im plants healed uneventful and w ere well fixed. N o significant difference (Student t Lest, p > 0.05) for the torsional failure force w as m easured for both type of coatings. N evertheless, SEM revealed differently situated fracture planes. Light m icroscopy show ed intimate boneim plant contact for both types of coatings; original drill m ar gins w ere still visible. A lam ellar type of bone w ith some rem odeling lacunae w as show n. H istoniorphom etry re vealed a higher percentage of bone contact for the F A /H A -PS-coated im plants (student t test, p <0.05). M easurem ent of the am ount of bone revealed more bone mass around T PS/ C a-P-a-coated im plants (analysis of variance and Tukey m ultiple com parison, p < 0.05).

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