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 press ed and sintered, or cold isostatically pressed followed by hot isostaticall y 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 acco rding to ISO/EN 10993-5. The cytotoxicity of the c.p. Nb metal and the Nb-M o alloys was tested in a 72 h direct contact test. Com pa red 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, du e 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 miner alized extracellular matrix formed, while on the more porous Nb-Mo alloys, cell growth was observed, but no mineralization. In conclusion, c.p. Mo pow der is moderately toxic, however, as an alloying element it is non-toxic. M aterial porosity seems to influence differentiation of bone tissue in vitro . (C) 1998 Kluwer Academic Publishers.