Adhesion of bioactive glass coating to Ti6A14V oral implant.

Bioactive glass (BAG) is a bioactive material with a high potential as implant material. Reactive plasma spraying produces an economically feasible BAG-coating for Ti6A14V oral implants. This coating is only functional if it adheres well to the metal substrate and if it is strong enough to transfer all loads. To examine these two properties an appropriate mechanical adhesion test, the moment test, is developed. This test quantifies under a realistic loading condition the corresponding functional adhesion strength to be >84 MPa in tensile. To get a qualitative insight in the BAG-coating behavior during loading the mechanical test was combined with finite element analysis, acoustic emission and microscopic analysis. These analyses showed that the coating withstands without any damage an externally generated tensile stress of 47 MPa. Not only the initial adhesion is determining for the implant quality, but more important is the coating functionality after reaction of the BAG. Adhesion testing after two months of in vitro reaction in a simulated body fluid showed that coating adhesion strength decreased with 10%, but the implant system was still adequate for load-bearing applications.

Adhesion of new bioactive glass coating.

A valuable alternative to the existing biomedical implant coatings is a bioactive glass (BAG) coating that is produced by reactive plasma spraying. A mechanical performance requirement that is of the utmost importance is the adhesion strength of the coating. Considering the application as dental implant, a new adhesion test (shear test), which was close to the service conditions, was designed. A Ti6Al4V rod (3 mm) with a sprayed BAG coating of 50 microm was glued with an epoxy glue to a hollow cylindrical counterpart and was used as such in the tensile machine. This test was evaluated by finite element analysis (FEA). Preliminary experiments showed that a conversion from shear to tensile adhesion strength is possible by using the Von Mises criterion (sigma = 3(1/2)tau), indicating that thin coatings of brittle materials can behave as a ductile material. The new coating technique was proved to produce a high quality coating with an adhesion strength of 40.1 +/- 4.8 MPa in shear and 69.4 +/- 8.4 MPa in tension. The FEA revealed that no one homogeneously distributed shear stress is present but several nonhomogeneously distributed stress components (shear and tensile) are present in the coating. This analysis indicated that real service conditions are much more complicated than standard adhesion tests.

Comparison of the cytotoxicity of molybdenum as powder and as alloying element in a niobium-molybdenum alloy.

Commercially pure metal niobium (c.p. Nb) as well as niobium-molybdenum (Nb-Mo) alloys were produced following several powder metallurgical routes. In brief, niobium and molybdenum powders were blended and milled in order to form Nb-Mo alloys. The alloy powders and the c.p. Nb were then either pressed and sintered, or cold isostatically pressed followed by hot isostatically pressing. In order to assess the cytotoxicity of the c.p. Nb and c.p. Mo powders, a 72 h minimal essential medium-extraction test was performed according to ISO/EN 10993-5. The cytotoxicity of the c.p. Nb metal and the Nb-Mo alloys was tested in a 72 h direct contact test. Compared to a negative control (UHMWPE), c.p. Nb was non-toxic, but c.p. Mo was moderately toxic. None of the powder metallurgically produced materials were toxic. Neither differences in molybdenum concentration, nor in porosity of the samples, due to different production routes, had any influence on the toxicity of the materials. Rat bone marrow cultures showed that only on c.p. Nb was a mineralized extracellular matrix formed, while on the more porous Nb-Mo alloys, cell growth was observed, but no mineralization. In conclusion, c.p. Mo powder is moderately toxic, however, as an alloying element it is non-toxic. Material porosity seems to influence differentiation of bone tissue in vitro.

In vitro simulation of biocompatibility of Ti-Al-V.

The presented data are the result of a reappraisal of the biocompatibility properties of titanium alloys. An in vitro study has been conducted using Hanks' solution with four different additional compounds (EDTA, l-leucine, Na-citrate, and 8-hydroxyquinoline). A measurable dissolution rate was observed for Ti and Al in a solution containing EDTA and for Ti, Al, and V for a solution containing Na-citrate. The dissolution kinetics are discussed and explained in terms of the composition of the surface layers. The results contain useful introductory information for an extended study of media allowing representative in vitro simulation of the in vivo behavior of titanium alloys.