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Biodegradable magnesium alloys are advantageous in various implant applications, as they reduce the risks associated with permanent metallic implants. However, a rapid corrosion rate is usually a hindrance in biomedical applications. Here we report a facile two step procedure to introduce multifunctional, anti-corrosive coatings on Mg alloys, such as AZ31. The first step involves treating the NaOH-activated Mg with bistriethoxysilylethane to immobilize a layer of densely crosslinked silane coating with good corrosion resistance; the second step is to impart amine functionality to the surface by treating the modified Mg with 3-amino-propyltrimethoxysilane. We characterized the two-layer anticorrosive coating of Mg alloy AZ31 by Fourier transform infrared spectroscopy, static contact angle measurement and optical profilometry, potentiodynamic polarization and AC impedance measurements. Furthermore, heparin was covalently conjugated onto the silane-treated AZ31 to render the coating haemocompatible, as demonstrated by reduced platelet adhesion on the heparinized surface. The method reported here is also applicable to the preparation of other types of biofunctional, anti-corrosive coatings and thus of significant interest in biodegradable implant applications.

Subacute stent thrombosis, caused by undesired interactions between blood and the stent surface, is a major concern in the first few weeks following coronary artery stent implantation. The aim of this study was to establish a novel in vitro model for hemocompatibility testing of coronary artery stents according to ISO 10993-4. The model consists of a modified Chandler-Loop design with closed heparin-coated PVC Loops and a thermostated water bath. The tests were performed with anticoagulated human whole blood. After incubation in the loop, blood was analyzed for coagulation and inflammatory activation markers (TAT, β-TG, sP-selectin, SC5b-9 and PMN-elastase). Three different stent types with varying thrombogenicity were tested; statistically significant differences were found between the three stent types in measures of coagulation and platelet activation. The new Chandler-Loop model can be used as an alternative to animal and current in vitro models, especially for the determination of early events after stent implantation.

Background: Stent implantation is the predominant therapy for non-surgical myocardial revascularization in patients with coronary artery disease. However, despite substantial advances in multidetector computed tomography (MDCT) coronary imaging, a reliable detection of coronary in-stent restenosis is currently not possible. Purpose: To examine the ability of 64-detector-row CT to detect and to grade in-stent stenosis in coronary stents using a newly developed ex-vivo vessel phantom with a realistic CT density pattern, artificial stenosis, and a thorax phantom. Material and Methods: Four different stents (Liberté and Lunar ROX, Boston Scientific; Driver, Medtronic; Multi-Link Vision, Guidant) were examined. The stents were placed on a polymer tube with a diameter of 2.5, 3.0, 3.5, or 4.0 mm. Different degrees of stenosis (0%, 30%, 50%, 70–80%) were created inside the tube. For quantitative analysis, attenuation values were measured in the non-stenotic vessel outside the stent, in the non-stenotic vessel inside the stent, and in the stenotic area inside the stent. The grade of stenosis was visually assessed by two observers. Results: All stents led to artificial reduction of attenuation, the least degree of which was found in the Liberté stent (11.3±10.2 HU) and the Multi-Link Vision stent (17.6±17.9 HU; P = 0.25). Overall, the non-stenotic vessel was correctly diagnosed in 55.5%, the low-grade stenosis in 58.3%, the intermediate stenosis in 63.8%, and the high-grade stenosis in 80.5%. In the 3.0-, 3.5-, and 4.0-mm vessels, in none of the cases was a non-stenotic or low-grade stenotic vessel misdiagnosed as intermediate or high-grade stenosis. The average deviation from the real grade of stenosis was 0.40 for the Liberté stent, 0.46 for the Lunar ROX stent, 0.45 for the Driver stent, and 0.58 for the Multi-Link Vision stent. Conclusion: Our ex-vivo data show that non-stenotic stents and low-grade in-stent stenosis can be reliably differentiated from intermediate and high-grade in-stent stenosis in vessels with a diameter of 3 to 4 mm. With regard to artifacts and the grading of stenoses, the Liberté stent was best suited for CT coronary angiography.

The aim of the study was to examine the ability of a 64-slice MDCT to detect in-stent stenoses in an ex vivo model of coronary stents. Five different stents (Liberte™, Boston Scientific; Driver®, Medtronic; Multi-Link Vision®, Guidant; Taxus® Express®, Boston Scientific; Cypher®, Cordis) were examined using a dynamic cardiac phantom. The stents were pulled over a vessel model that consists of a polymer tube with diameters of 3.0, 3.5, and 4.0 mm and four different degrees of stenoses (0%; 30%; 50%; 70–80%). This model was moved with a rate of 60 bpm to mimic cardiac motion. To assess the degree of artificial signal reduction (artificial reduction of attenuation (ARA)) by the different stents, attenuation values were measured in the vessel outside the stent, and in the non-stenotic vessel inside the stent. Furthermore the grade of stenosis was assessed by two clinical observers. Highest ARA was found for the Cypher® Stent (35 HU), whereas the Liberte™ Stent presented the lowest ARA (16 HU). Depending on the stent and the vessel diameter, up to 87.5% of the stenoses were correctly diagnosed. In the 3.0 and 3.5 mm vessels, a nonstenotic or low-grade stenotic vessel was diagnosed as intermediate or high-grade stenosis in 22.5%, whereas in the 4.0 mm vessels, this kind of overestimation did not occur. A 50% stenosis was diagnosed as a 30% stenosis in 30%. On the other hand, highgrade stenoses were underestimated in only 10%. On a fourpoint scale, the average deviation from the real grade of stenosis was 0.21 for the Liberte™ stent, 0.54 for the Taxus® Express® stent, 0.29 for Driver® stent, 0.62 for the Multi-Link Vision® stent, and 0.37 for the Cypher™ stent. In a dynamic cardiac phantom model, high grade stenoses in vessels with a diameter of 4 mm could be reliably detected irrespective of the stent type used in this study. Vice versa, high grade stenoses (≥50%) could only be ruled out with certainty in vessels with a diameter of 4 mm. In smaller vessels, the ability to correctly diagnose high-grade stenoses was dependent on the type of stent and the imaging artifacts associated with it.

Today, stent designs consist of permanent metal alloy scaffolds which hold arteries open after percutaneous coronary intervention (PCI) to maintain arterial blood flow. Bioabsorbable stents are being investigated as an alternate for permanent stents, that disintegrate and dissolve in the body. In this article, we profile magnesium (Mg) alloy as a candidate for bioabsorbable stent material, and discuss aspects of its properties and challenges. Experimental data are generated in effort to draw correlations between in vivo vessel absorption and in vitro degradation, and to provide an overview of alloy mechanical properties, stent designs, and electrochemical behaviors. Preclinical porcine coronary model test results exhibit early on-set and rapid corrosion presenting a challenge to researchers to establish material design concepts that balance degradation time, duration for need of scaffolding, and healing.