パラジウム合金鋳物の腐食と生体適合性試験

Corrosion and biocompatibility testing of palladium alloy castings.

抄録

目的:

パラジウム-銅合金の生体適合性については、文献的に疑問視されている。(a)銅を含む合金Option((R)) (79% Pd, 10% Cu, 9% Ga, 2% Au)と、銅を含まない合金IS85 (82% Pd, 6% Ga, 3.5% Sn, 3.5% In, 2.5% Ag, 2.5% Au)の浸漬試験におけるイオンの放出、(b)予備酸化によって生成された酸化皮膜が耐食性に及ぼす影響、(c)放出されたイオンによる生物学的相乗効果の可能性。

OBJECTIVE: The biocompatibility of palladium-copper alloys has been questioned in the literature. The intention of the present work was to study: (a) the release of ions in an immersion test from a copper-containing alloy, Option((R)) (79% Pd, 10% Cu, 9% Ga, 2% Au), compared with an alloy without Cu, IS85 (82% Pd, 6% Ga, 3.5% Sn, 3.5% In, 2.5% Ag, 2.5% Au); (b) the effect of oxide films produced by preoxidation on corrosion resistance; and (c) the possibility of biologically synergetic effects of ions released.

方法:

両方の合金の試験片を鋳造し、摩擦し、超音波洗浄した。(a)鋳造後、(b)約1000℃での予備酸化処理後に金属組織試験片を作製し、SEMとEDSで調べた。0.1mol/lのNaClと0.1mol/lの乳酸の溶液に37℃で7日間浸漬した。合金試料は以下の3段階で試験された：(1)酸化前、(2)その後研磨によって0.1mm厚の層を除去した後、(3)さらに研磨によって約0.1mm除去した後。試験溶液をICPで分析し、合金試料から溶出したイオンの量を記録した。生体適合性は、細胞培養試験とHET-CAM法によって調べた。試験溶液はPdCl(2)とCuCl(2)を適切な濃度に溶解して調製した。

METHODS: Specimens of both alloys were cast, rubbed and ultrasonically cleaned. Metallographic specimens were prepared after (a) casting and (b) preoxidizing treatment at approximately 1000 degrees C and studied by SEM and EDS. Immersion tests were carried out in a solution of 0.1mol/l of NaCl and 0.1mol/l of lactic acid at 37 degrees C for 7 days. The alloy specimens were tested in the following three steps: (1) as preoxidized; (2) after subsequent removal of a 0.1mm thick layer by grinding; and (3) after an additional removal of approximately 0.1mm by grinding. The test solutions were analyzed by means of ICP to record the amounts of ions that had leached out from the alloy specimens. The biocompatibility was studied by cell culture tests and the HET-CAM method. Test solutions were prepared by dissolving PdCl(2) and CuCl(2) to appropriate concentrations.

結果:

金属組織を調査した結果、樹枝間領域と粒界に中程度の偏析が見られた。空気中での予備酸化後、Optionでは厚さ25～200μm、IS85では5～10μmの酸化帯が見られた。酸化は両合金ともリムに沿って観察され、Optionでは樹枝間にも観察された。酸化物は、金属マトリックス中の1ミクロン以下の小さな黒い斑点として見られた。これらの結果は次のことを示している：(1)銅を含むパラジウム合金の酸化は、銅を含まない合金の酸化よりもはるかに激しい。細胞培養試験の結果、Cuが最も毒性が高く、次いでCu(2+)+Pd(2+)(1:2)であった。HET-CAM試験では、Cu(2+)+Pd(2+) (1:2)が最も高い刺激性スコアを示した。

RESULTS: The metallographic investigations revealed moderate segregations in interdendritic regions and grain boundaries. After preoxidation in air a zone of oxidation from 25 up to 200 microm thickness for Option and from 5 to 10 microm for IS85 was found. Oxidation was observed along a rim for both alloys and for Option also along interdendritic positions. The oxides were seen as small, dark spots <1 microm in a metallic matrix. These results indicate that: (1) the oxidation of the copper-containing palladium alloy is far more severe than that of the alloy with no copper; and (2) the elemental release from these oxides is substantially larger than that from the corrosion of the metallic structure. The results of the cell culture testing showed that Cu was most toxic, followed by Cu(2+)+Pd(2+) (1:2), based on the determination of the concentration that caused 50% cytotoxicity. The HET-CAM testing showed Cu(2+)+Pd(2+) (1:2) to have the highest irritation score.

意義:

銅含有Pd合金は、予備酸化中に金属マトリックス中に小さな酸化物粒子を含む厚さ0.1mmのリムを生じた。このリムが完全に除去されない場合、合金構造からよりも有意に多くのCu、Ga、Pdイオンが試験溶液中に溶出することが示されている。CuイオンとPdイオンの相乗効果は培養細胞では観察されなかったが、Pd(2+)+Cu(2+) (1:2)の混合物は、HET-CAM法で評価すると粘膜に対して最も刺激性があった。

SIGNIFICANCE: The copper-containing Pd alloy developed a 0.1mm thick rim with small oxide particles in a metallic matrix during preoxidation. If this rim is not completely removed, significantly more Cu, Ga and Pd ions have been shown to leach into the test solution than from the alloy structure. No synergetic effect of Cu and Pd ions was observed in cultured cells, while the mixture Pd(2+)+Cu(2+) (1:2) was most irritating to mucous membrane as evaluated by the HET-CAM method.