Elsevier

Thrombosis Research

Volume 99, Issue 6, 15 September 2000, Pages 577-585
Thrombosis Research

Original article
In Vitro Analyses of Diamond-like Carbon Coated Stents: Reduction of Metal Ion Release, Platelet Activation, and Thrombogenicity

https://doi.org/10.1016/S0049-3848(00)00295-4Get rights and content

Abstract

Coronary artery stents can induce platelet activation by shear forces, contact to the biomaterial, and release of metal ions. This activation is one important trigger for thrombosis. Coating of stents is a possible approach to prevent this side effect. The purpose of this study was to evaluate in vitro the biocompatibility of stents coated with diamond-like carbon (DLC). Semiquantitative energy-dispersive X-ray microanalyses showed a complete coverage of the DLC stents. Flow cytometric analyses revealed a significantly higher increase of mean channel fluorescence intensity for the activation-dependent antigens CD62p and CD63 in non-coated compared to DLC-coated stents (p<0.05). Atomic adsorption spectrophotometry analyses revealed a significant release of nickel and chromium metal ions by non-coated stents over a storage period of 96 hours in human plasma (p<0.05). In contrast, only minimal concentrations of released ions could be detected in the case of DLC-coated stents. Similar observations were made with inductively coupled plasma mass spectrometry analyses. Here, high concentrations of molybdenum and manganese ions were released from non-coated stents (p<0.05), while release of these ions from DLC-coated stents was virtually undetectable (p=0.1 for molybdenum and p=0.4 for manganese). Coating of intracoronary stents with diamond-like carbon significantly improves biocompatibility. This biocompatible coating may therefore contribute to a reduction in thrombogenicity.

Section snippets

Diamond-like Carbon Coated Stents

316 L stainless steel stents were coated on the inside and outside surfaces with diamond-like carbon (DLC) by a plasma-induced cold deposition technique (BioDiamond 9, Plasmachem, Mainz, FRG). Undeployed stents were 8.6 mm in length and were composed of four segments of DLC-coated 316L steel loops connected by a central bridging strut. The thickness of the stent wall (measured at both ends) was 60 μm±10%.

Sample Collection and Preparation of Platelet-rich Plasma and Plasma

The study was approved by the Institutional Review Board and the Local Ethical Committee.

Energy-Dispersive X-ray Microanalyses (EDX)

Semiquantitative energy-dispersive X-ray microanalyses showed the percentage elemental composition of the metal alloy to be 65.1% iron (Fe), 19.8% chromium (Cr), 12.0% nickel (Ni), and 0.003% sulfur (S). This elemental composition is characteristic of 316L stainless steel. The results of EDX were identical in coated and non-coated stent areas, because the process cannot detect carbon with atomic number six.

Atomic Adsorption Spectrophotometry (AAS) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

The interassay precision for nickel and chromium analyses was 12.9% and 4.7%,

Discussion

In spite of considerable progress in antithrombotic therapy and implantation techniques, interventional cardiological therapy and the use of stents in coronary arteries is still complicated by a substantial rate of thrombotic occlusions and restenoses 1, 6, 38, 39. Both conditions are associated with an increase in platelet activation, a non-physiological state that can be induced by metal ions 9, 10.

In this study, two intracoronay stent types (316L-stainless steel±DLC-coating) which only

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