To avoid nickel ion release from SUS317L as an implant amount of iron ion or colloidal fine particles released from material, a new type of nickel, commercially free, of high FJ was about a quarter of that from SUS317L, although the purity, and high chromium ferritic stainless steel, was devel-weight loss of a pin of FJ was almost 5/3 that of SUS317L. oped. The new stainless steel (FJ) was studied for aspects
The artifical physiologic solution used for SUS317L fretting of fretting corrosion and cytocompatibility compared with was more harmful to the growth of L929 and MC3T3-E1 cells SUS317L. A pin-on-plate fretting corrosion test in an artificial than that used for FJ fretting. FJ was therefore superior to physiologic solution, and cell culture in media with the addi-SUS317L as a biomaterial, judging from the resistance to tion of the artificial physiologic solution used for fretting fretting-induced crevice corrosion, electrochemical stability, was conducted. Resistance to the fretting induced crevice and the cytocompatibility of fretting corrosion products. corrosion of FJ was higher than that of SUS317L because of
the favorable electrochemical stability of the FJ alloy. The
Introduction
difficult to demonstrate an advantage of Ti or Co-Cr alloy over stainless steel of this type for in vivo application. 8 The advantages of stainless steel compared to Ti Although austenitic stainless steels containing nickel and Co-Cr alloys include good hot-and cold-working are used for metallic implants, the fretting corrosion mechanical properties, good machinability, and low product of steel can cause adverse reactions, both locost. 9 Ti alloy is known to be more susceptible to wear cally and systemically. The fretting corrosion products than stainless steel, thus generating greater amounts include metallic and fine particles of metal hydroxide of metallic particles for loose functional implants. 10 Alplus ions generated by mechanical wear, and these though in general Co-Cr alloys are known to have products can influence wear-accelerating dissolution.
excellent wear and corrosion resistance in vivo, they Studies on retrieved stainless-steel orthopedic imdo occasionally generate particles and release ions to plants have shown significant amounts of metallic their surroundings by the mechanism of fretting corroproducts transferred to tissues with an associated resion and wear. Also some Co-Cr particles prepared lease of nickel ions from a fretting corrosion mechafrom in vitro wear tests were found to be very toxic to nism. [1][2][3] Histologic analysis revealed a nickel concenmacrophages, 11 and the intramuscular injection of these tration as high as 2% in tissues around some stainlessparticles induced local sarcomas in animals. 12 In some steel implants. 4 Nickel ions released from implants revision operations, extensive local tissue reactions were found in the lungs, spleen, and kidneys in aniwere found associated with corroded Co-Cr implants. 13 mals. 5 The incidence of nickel hypersensitivity has been Cobalt can be carcinogenic based on animal experiestimated to be as much as 15%, 6 and nickel ion may ments and may cause inheritable damage in exposed lead to carcinogenesis. 7 humans. 14,15 Therefore, it may be difficult completely Stainless steel is still preferred by many surgeons as to substitute Ti or Co-Cr alloy for stainless steel as a bone plate material, with this preference based, in implant materials, especially as a bone plate material. part, on millions of satisfactory clinical cases. It is also To avoid nickel ion release from the currently available stainless steel, a new type of nickel-free, highpurity, and high-chromium ferritic stainless steel was *To whom correspondence should be addressed.