PubMed · 12652661
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En Ma. 2003. Controlling plastic instability.. https://doi.org/10.1038/nmat797
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We have found that the concentration of titanium (Ti) in the blood of patients with loosened Ti-alloy prostheses is elevated. An increase in the levels of elemental Ti in the blood and lung tissues of rats with an alloyed-Ti implant also has been found. The cellular reaction to elevated elemental Ti in the circulation remains unclear. We further performed experiments to examine the changes of inducible nitric oxide synthase (iNOS) expression in alveolar macrophages from alloyed-Ti-implanted rats. The elevation of nitrite and iNOS expression induced by lipopolysaccharide (LPS) was suppressed. The in vitro effect of a soluble form of Ti was further investigated. Ti (0.01-0.06 mM) inhibited the LPS-induced nitrite production and iNOS expression in alveolar macrophages from normal rats without any cytotoxic effects. LPS induced protein tyrosine phosphorylation, tyrosine-phosphorylation of lyn (a CD14-receptor-associated-tyrosine kinase), and degradation of IkappaB-alpha protein (inhibitor of NF-kappaB) in alveolar macrophages. These events were inhibited by co-incubation with Ti. These results indicate that elemental Ti may impair iNOS expression in alveolar macrophages through the alteration of protein tyrosine phosphorylation and NF-kappaB activation. The inhibitory action of Ti on cellular responses of alveolar macrophages may be anti-inflammatory and thus may depress local defense mechanisms related to microbial killing.
Our aims in this study were (1) to develop an electrochemical method of depositing adherent octacalciumphosphate (OCP) and other calcium phosphate coatings on titanium alloy (Ti6Al4V) substrates of different shapes and surface preparations, (2) to determine the properties of the coating (composition, morphology, thickness, dissolution), and (3) to observe transformation of OCP to carbonatehydroxyapatite (CHA) in simulated body fluid (SBF). Titanium (Ti)-alloy plates, tensile bars with four types of surfaces (grit-blasted with apatitic abrasive, chemically textured, arc-deposited, and Co-Cr-beaded) and dissolution cylinders were electrochemically coated with the use of modulated pulse time electric fields programmed with a custom-made dual microprocessor. Modulated electrochemical deposition (MECD) was carried out with pH and temperature conditions favorable for OCP formation. Coatings were characterized using X-ray diffraction, FT-IR, scanning electron microscopy, tensile strength tests, and solubility tests. XRD and FT-IR analyses showed that pure, uniform OCP coatings were produced on Ti6Al4V surfaces with coating-to-substrate tensile strengths greater than 7,000 psi. Coatings on Ti arc-deposited surfaces, chemically textured surfaces, and Co-Cr-beaded surfaces all gave tensile strengths ranging from 5,000 to 7,000 psi, with no coating shadows in the crevices. Dissolution of OCP coating in 100 mL of 0.1 M Tris buffer solution was determined from the amount of calcium (Ca) released onto the buffer, which was 7.7 +/- 1.0 ppm Ca at pH 7.3 after 4 h, and 22 -/+ 1.4 ppm Ca at pH 3 after 2 h. We found that OCP crystal size can be controlled by the current density and relative pulse time modulation. Our study demonstrated the following: (1) Highly adherent calcium phosphate (e.g., OCP) coating of uniform compositions (e.g., OCP) on Ti-alloy substrates can be obtained at low temperatures with the use of MECD by optimizing pulse time modulation of the electric field, reaction pH, temperature, and electrolyte composition; and (2) OCP readily transforms to CHA when exposed to SBF.
Nitinol (nickel-titanium) alloys exhibit a combination of properties which make these alloys particularly suited for self-expanding stents. Some of these properties cannot be found in engineering materials used for stents presently. This article explains the fundamental mechanism of shape memory and superelasticity, and how they relate to the characteristic performance of self-expanding stents. Nitinol stents are manufactured to a size slightly larger than the target vessel size and delivered constrained in a delivery system. After deployment, they position themselves against the vessel wall with a low, "chronic" outward force. They resist outside forces with a significantly higher radial resistive force. Despite the high nickel content of Nitinol, its corrosion resistance and biocompatibility is equal to that of other implant materials. The most common Nitinol stents are listed and described.