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Calcium phosphate coatings on coronary stents by electrochemical deposition Tsui, Manus Pui-Hung

Abstract

Calcium phosphate ceramic coatings, especially hydroxyapatite (HA), have attracted much attention in the orthopedics and dentistry due to their excellent biocompatibility and bioactivity. Among the different methods of calcium phosphate coatings processing, electrochemical deposition (ECD) is a relatively low cost and flexible process technology. In this study, electrochemical deposition was used to deposit uniform calcium phosphate coatings on 316L stainless steel coronary stents. The influence of the ECD process parameters (deposition time, current density, electrolyte temperature, pH, and Ca/P ratio) on the resulting deposition morphology was investigated. Scanning electron microscopy (SEM) and X-Ray diffractometry (XRD) were used to analyze the coatings. The results demonstrated that both dicalcium phosphate dihydrate (CaHP0₄·2H₂0, DCPD) and hydroxyapatite (Ca₁₀(P0₄)(OH)₂, HA) were present in the uniform [tilde]0.5 [micro sign]m thick as-deposited coating. However, a post-treatment process, including a O.1N NaOH(aq) phase conversion at 75°C and a 500°C heat treatment produced a pure phase HA coating. The final deposit revealed a highly porous surface morphology which could be useful for drug encapsulation. With the application of the substrate surface modification and the post-treatment processes, sufficient coating adhesion was achieved as demonstrated by the in-vitro stent deployment tests without visible damage to the coating. Commercial in-vitro 40 million cycles fatigue tests demonstrated that the coatings exhibit good adhesion to the stent substrate, with no coating cracking or delamination. It was confirmed that the ECD-HA coating process for coronary stents is reliable and reproducible.

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