Soft tissue response to a new austenitic stainless steel with a negligible nickel content

Cytocompatibility of medical biomaterials containing nickel by osteoblasts: a systematic literature review

The present review is based on a survey of 21 studies on the cytocompatibility of medical biomaterials containing nickel, as assessed by cell culture of human and animal osteoblasts or osteoblast-like cells. Among the biomaterials evaluated were stainless steel, NiTi alloys, pure Ni, Ti, and other pure metals. The materials were either commercially available, prepared by the authors, or implanted by various techniques to generate a protective layer of oxides, nitrides, acetylides. The observation that the layers significantly reduced the initial release of metal ions and increased cytocompatibility was confirmed in cell culture experiments. Physical and chemical characterization of the materials was performed. This included, e.g., surface characterization (roughness, wettability, corrosion behavior, quantity of released ions, microhardness, and characterization of passivation layer). Cytocompatibility tests of the materials were conducted in the cultures of human or animal osteoblasts and osteoblast-like cells. The following assays were carried out: cell proliferation and viability test, adhesion test, morphology (by fluorescent microscopy or SEM). Also phenotypic and genotypic markers were investigated. In the majority of works, it was found that the most cytocompatible materials were stainless steel and NiTi alloy. Pure Ni was rendered and less cytocompatible. All the papers confirmed that the consequence of the formation of protective layers was in significant increase of cytocompatibility of the materials. This indicates the possible further modifications of the manufacturing process (formation of the passivation layer).

Nickel-free austenitic stainless steels for medical applications

The adverse effects of nickel ions being released into the human body have prompted the development of high-nitrogen nickel-free austenitic stainless steels for medical applications. Nitrogen not only replaces nickel for austenitic structure stability but also much improves steel properties. Here we review the harmful effects associated with nickel in medical stainless steels, the advantages of nitrogen in stainless steels, and emphatically, the development of high-nitrogen nickel-free stainless steels for medical applications. By combining the benefits of stable austenitic structure, high strength and good plasticity, better corrosion and wear resistances, and superior biocompatibility compared to the currently used 316L stainless steel, the newly developed high-nitrogen nickel-free stainless steel is a reliable substitute for the conventional medical stainless steels.

Uptake of nickel from 316L stainless steel into contacting osteoblastic cells and metal ion interference with BMP-2-induced alkaline phosphatase

Bone cells contacting nickel (Ni)-containing implant materials may be affected by Ni species via disturbed signaling pathways involved in bone cell development. Here we analyze effects of the Ni-containing steel 316L and major metal constituents thereof on bone morphogenetic protein-2 (BMP-2)-induced alkaline phosphatase (ALP) of MC3T3-E1 cells. While cells grew normally on 316L, cellular Ni content increased 10-fold vs. control within 4 days. With respect to the major components of 316L, Ni2+ (3-50 microM) was most inhibitory to BMP-2-induced ALP, whereas even 50 microM Fe3+, Cr3+, Mo5+, or Mn2+ had no such effect. In line with this, BMP-2-induced ALP was significantly reduced in cells on 316L. This effect was not prevented by the metal ion chelator diethylenetriaminepentaacetic acid (DTPA). Instead, DTPA abolished the stimulatory effect of BMP-2 on ALP, pointing to chelatable metal ions involved. Zn2+, as one possible candidate, antagonized the Ni2+ inhibition of BMP-2-induced ALP in both MC3T3-E1 and human bone marrow stromal cells. Results show that cells contacting 316L steel are exposed to increased concentrations of Ni which suffice to impair BMP-2-induced ALP activity. Zn2+, as a competitor of this inhibition, may help to restore normal osteoblastic function and bone development under these conditions.

Tribological characterization of surface-treated commercially pure titanium for femoral heads in total hip replacement: a feasibility study

Most noncemented total hip replacements combine a titanium alloy stem, a CoCrMo femoral head and an ultra-high molecular weight polyethylene (UHMWPE) acetabular cup. In spite of its nickel content of up to 1% and the resulting biocompatibility issues in some clinical situations, the higher cost and some difficulties in machining, CoCrMo alloy is preferred to titanium alloys thanks to its outstanding tribological properties, higher hardness and elastic modulus. Nowadays most of the heads of hip prostheses use CoCrMo as bearing material. The present study investigates the effect of various surface treatments and combinations of treatments, such as electrochemical oxidation (anodization), laser surface melting and barrel polishing, on the tribological properties of commercially pure grade 2 titanium. The aim of the study was to characterize surface treatments capable of improving the tribological properties of titanium surface to the same extent as CoCrMo. The tribological properties were characterized by multidirectional pin-on-flat screening wear tests, using UHMWPE pins as bearing surface. The experiments showed the possibility of improving the wear resistance of titanium to the degree of CoCrMo. Although further efforts will be required to optimize the treatments studied, the results are encouraging enough to warrant pursuing this direction of investigation.

Biocompatibility evaluation of surface-treated AISI 316L austenitic stainless steel in human cell cultures

The effects of AISI 316L austenitic stainless steel, tested in untreated state or subjected to glow-discharge nitriding (at 10 or 20 hPa) and nitriding + post-oxidizing treatments, on human umbilical vein endothelial cells (HUVEC) and on peripheral blood mononuclear cells (PBMC) were evaluated. All the treated samples showed a better corrosion resistance in PBS and higher surface hardness in comparison with the untreated alloy. In HUVEC put in contact for 72 h with the sample types, proliferation and apoptosis decreased and increased, respectively, in the presence of the nitrided + post-oxidized samples, while only slight differences in cytokine (TNF-alpha, IL-6, and TGF-beta1) release were registered. Intercellular adhesion molecule-1 (ICAM-1) increased in HUVEC incubated with all the treated samples, while vascular cell adhesion molecule-1 (VCAM-1) and E-selectin increased in the presence of all the sample types. PBMC incubated for 48 h with the samples showed a decrease in proliferation and an increase in apoptosis in the presence of the untreated samples and the nitrided + post-oxidized ones. All the sample types induced a remarkable increase in TNF-alpha and IL-6 release in PBMC culture medium, while only the untreated sample and the nitrided at 10 hPa induced an increase in ICAM-1 expression. In HUVEC cocultured with PBMC, previously put in contact with the treated AISI 316L samples, increased levels of ICAM-1 were detected. In HUVEC coincubated with the culture medium of PBMC, previously put in contact with the samples under study, a noteworthy increase in ICAM-1, VCAM-1, and E-selectin levels was always registered, with the exception of VCAM-1, which was not affected by the untreated sample. In conclusion, even if the treated samples do not show a marked increase in biocompatibility in comparison with the untreated alloy, their higher corrosion resistance may suggest a better performance as the contact with physiological environment becomes longer.