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.
The in vitro biocompatibility of the nickel‐free austenitic steel (brand name P2000) characterized by extreme strength, high ductility and superior corrosion resistance was tested. As the material appears promising for hard tissue implant development we employed osteoblastic cells (MC3T3‐E1) as test specimens. Cells growing directly on this metal were undistinguishable from control cells on cell culture tested plastic material with respect to morphology and growth parameters. P2000 can, therefore, be classified as a biocompatible material. In line with that application of bone morphogentic protein 2 (BMP‐2) increased expression of alkaline phosphatase as it does under control conditions. However, the slope of the dose response curve was diminished, indicating partially impaired BMP‐2 signaling on P2000. Since P2000 contains nitrogen and may release alkalizing amounts of NH3 we compared steady state intracellular pH (pHi) of cells on P2000 vs. controls, but were unable to find any differences. Further studies are needed to understand how P2000 can influence cellular functions of directly contacting cells.
Austenitic stainless steels generally have a favorable combination of strength and ductility as well as a sufficient resistance against corrosion. This and the reported biocompatibility lead to the use of 304- and later 316 L-type steels in medical applications. Especially in orthopedics these steels were applied as implants for e.g. fracture fixation as bone plates, intermedullary nails, and screws. But these steels contain a high amount of Ni, which was attributed to cause Ni-allergies for an growing amount of patients. Thus, alternatives were needed and — beside the already known CoCrMo-alloys — implants of Ti and its alloys emerged increasingly into the medical market. The aim of this paper is to introduce a new austenitic Ni-free CrMnMo-steel X13CrMnMoN18-14-3 (Material No.: 1.4452, brand name: P2000), which makes use of about 1 % N in order to gain a combination of high strength, high ductility, and a superior corrosion resistance. In a first step the cyclic fatigue behavior in air and in Ringer solution in the solution annealed state is investigated. This is accompanied by electrochemical testing in Ringer solution as well as in-vitro cytotoxicity tests against MC3T3 cells in bovine serum. The tests revealed that the solution annealed X13CrMnMoN18-14-3 at 5 Hz has an 50 % endurance limit of 346 MPa in air and of 302 MPa in Ringer solution, which is markedly higher compared to solution annealed CrNiMo-steels. In addition it was found that the CrMnMoN-steel shows no distinct susceptibility to stress-corrosion cracking in the entire region of finite life between stress amplitudes of 400 to 550 MPa. The pitting potential in Ringer solution was measured to be 1.1 V, which is in the range of common Ni-containing high-Nitrogen steels as well as of CoCr20Mo6 alloys. No reduction of MC3T3 cell adhesion could be observed. Thus, the Ni-free CrMnMoN-steels might be a promising alternative to the CrNiMo- steels in medical applications.
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