Comparative study of the corrosion behavior of peripheral stents in an accelerated corrosion model: experimental in vitro study of 28 metallic vascular endoprostheses

PURPOSE

Clinical cases of stent-fractures show that corrosion behavior might play a role in these fractures. Implanted in vivo, especially in combination with other implanted foreign materials, these metallic products are exposed to special conditions, which can cause a process of corrosion. Here, we aimed to test the corrosion potential of stents made of different materials in an in vitro setting.

METHODS

A total of 28 peripheral stents of different materials (nitinol, cobalt-chromium-nickel, tantalum, V4A) and surface treatments (electropolish, mechanical polish, no polish) were tested in vitro. Corrosion was accelerated by applying a constant voltage of 3.5 V and amperage of 1.16 mA in 0.9% NaCl.

RESULTS

Nitinol stents showed the lowest susceptibility to corrosion and the longest period without damage. The Memotherm II^® (BARD Angiomed^®) was the only stent that showed neither macroscopic nor microscopic damages. The worst performing material was cobalt-chromium-nickel, which showed corrosion damages about ten times earlier compared to nitinol. Considering the reasons for termination of the test, nitinol stents primarily showed length deficits, while V4A and tantalum stents showed fractures. Cobalt-chromium-nickel stents had multiple fractures or a complete lysis in equal proportions. When placed in direct contact, nitinol stents showed best corrosion resistance, regardless of what material they were combined with. In terms of polishing treatments, electropolished stents performed the best, mechanical-polished stents and those without polishing treatment followed.

CONCLUSION

The analysis of corrosion behavior may be useful to select the right stent fulfilling the individual needs of the patient within a large number of different stents.Congenital stenosis or volume decreasing processes due to accumulation of tissues or by outside pressures are the most common indications for vascular interventional therapies. After the initial “cardiac catheterization” by Forssmann et al. (1) in 1929, percutaneous interventional techniques for treatment of vasoconstricting processes was continued constantly, whereby the use of permanent mechanical stents has gained an increasingly important role.Stents used in clinical practice should fulfill certain conditions to achieve an un-problematic application as well as an optimal result. The following properties apply to this ideal: good biocompatibility, low shortening, high-density in X-ray, high patency rates, low thrombogenicity, rapid endothelialization without excessive intimal hyperplasia, high flexibility and longitudinal elasticity, sufficient pressure stability at high centrifugal force, technical ability to secure application and exact positioning, and good expansion ratio for safe percutaneous application also with larger prostheses (2, 3). With the approval of stents for clinical use in 1986, the use of stents in peripheral vessels was also practiced on human patients. Palmaz et al. (4) published the first results of the clinical use in 1988 in one of the first multicenter trials on the use of stents in stenosed atherosclerotic iliac arteries. After the successful development of Palmaz^® stents and Wallstents^® as prototypes of balloon-expandable and self-expanding stents, a variety of new stents have been developed.The stents used today are made of different materials. These include nickel titanium alloys (nitinol), surgical stainless steel (V4A), tantalum, and cobalt compounds. Implanted in the human body, especially in combination with other implanted foreign materials, these metallic products are exposed to special conditions causing a process of corrosion. The higher the ionic conductivity of a liquid is, the faster the reaction. For this reason, liquids that contain a high proportion of electrolytes, such as blood with its high proportion of NaCl, cause much faster corrosion of materials (5).We aimed to perform a comparative study regarding the corrosion behavior of peripheral stents, to reffect the behavior of implanted stents in patients and contribute to find a safer indication in the selection of vascular prostheses. Likewise, we tested the hypothesis that the polishing process influences their corrosion behavior.     

A high-resolution physical map of human chromosome 11.

The development of a highly reliable physical map with landmark sites spaced an average of 100 kbp apart has been a central goal of the Human Genome Project. We have approached the physical mapping of human chromosome 11 with this goal as a primary target. We have focused on strategies that would utilize yeast artificial chromosome (YAC) technology, thus permitting long-range coverage of hundreds of kilobases of genomic DNA, yet we sought to minimize the ambiguities inherent in the use of this technology, particularly the occurrence of chimeric genomic DNA clones. This was achieved through the development of a chromosome 11-specific YAC library from a human somatic cell hybrid line that has retained chromosome 11 as its sole human component.To maximize the efficiency of YAC contig assembly and extension, we have employed an Alu-PCR-based hybridization screening system. This system eliminates many of the more costly and time-consuming steps associated with sequence tagged site content mapping such as sequencing, primer production, and hierarchical screening, resulting in greater efficiency with increased throughput and reduced cost. Using these approaches, we have achieved YAC coverage for >90% of human chromosome 11, with an average intermarker distance of <100 kbp. Cytogenetic localization has been determined for each contig by fluorescent in situ hybridization and/or sequence tagged site content. The YAC contigs that we have generated should provide a robust framework to move forward to sequence-ready templates for the sequencing efforts of the Human Genome Project as well as more focused positional cloning on chromosome 11.     

Electrocardiogram signal variance analysis in the diagnosis of coronary artery disease—A comparison with exercise stress test in an angiographically documented high prevalence population

Variance electrocardiography (variance ECG) is a new resting procedure for detection of coronary artery disease (CAD). The method measures variability in the electrical expression of the depolarization phase induced by this disease. The time-domain analysis is performed on 220 cardiac cycles using high-fidelity ECG signals from 24 leads, and the phase-locked temporal electrical heterogeneity is expressed as a nondimensional CAD index (CAD-I) with the values of 0–150. This study compares the diagnostic efficiency of variance ECG and exercise stress test in a high prevalence population. A total of 199 symptomatic patients evaluated with coronary angiography was subjected to variance ECG and exercise test on a bicycle ergometer as a continuous ramp. The discriminant accuracy of the two methods was assessed employing the receiver operating characteristic curves constructed by successive consideration of several CAD-I cutpoint values and various threshold criteria based on ST-segment depression exclusively or in combination with exertional chest pain. Of these patients, 175 with CAD (≥ 50% luminal stenosis in 1 + major epicardial arteries) presented a mean CAD-I of 88 ± 22, compared with 70 ± 21 in 24 nonaffected patients (p < 0.01). Variance ECG provided a stochastically significant discrimination (p < 0.01) which was matched by exercise test only when chest pain variable was added to ST-segment depression as a discriminating criterion. Even then, the exercise test diagnosed single-vessel disease with a significantly lower sensitivity. At a cutpoint of CAD-I ≥ 70, compared with ST-segment depression ≥ 1 mm combined with exertional chest pain, the overall sensitivity of variance ECG was significantly higher (p < 0.01) than that of exercise test (79 vs. 48 %). When combined, the two methods identified 93% of coronary angiography positive cases. Variance ECG is an efficient diagnostic method which compares favorably with exercise test for detection of CAD in high prevalence population.     

C-reactive protein in relation to early atherosclerosis and periodontitis

Periodontitis may affect atherosclerosis via the chronic inflammation. We investigated high-sensitivity C-reactive protein (hsCRP) in relation to early vascular atherosclerotic changes in non-symptomatic subjects with and without long-term periodontitis. Carotid ultrasonography with calculation of common carotid artery intima-media area (cIMA) was performed, and hsCRP and atherosclerosis risk factors were analysed in randomly chosen 93 patients with periodontitis and 41 controls. The relationship between hsCRP, cIMA and atherosclerosis risk factors was evaluated with multiple logistic regression analysis. Women displayed lower hsCRP (p < 0.05) and higher serum HDL (p < 0.001) than men. In all patients with periodontitis, cIMA values were higher than in controls. Periodontitis appeared to be a major predictor for increased cIMA (odds ratio, 3.82; 95% confidence interval, 1.19–12.26). Neither of these factors was significantly associated with hsCRP which thus appeared not sensitive enough to be a marker for periodontitis or atherosclerosis. Hence, irrespective of low hsCRP levels, periodontitis appeared to increase the risk for atherosclerosis.     

Quantitative spatially resolved post-mortem analysis of lithium distribution and transition metal depositions on cycled electrodes via a laser ablation-inductively coupled plasma-optical emission spectrometry method

Diminishing the loss of performance of lithium ion batteries (LIBs) is a challenge that is yet to be fulfilled. Understanding of deterioration processes and mechanisms (i.e., so-called aging) requires analytically accurate examination of aged cells. Changes in the distribution of lithium or transition metals in the LIB cells can influence their cycle and calendar life significantly. As electrochemically treated cells and especially their electrodes do not age homogeneously and the local electrochemistry (e.g. deposition patterns) is strongly dependent on surface properties, bulk analysis is not a satisfactory investigation method. Therefore, a surface sensitive method, namely laser ablation-inductively coupled plasma-optical emission spectrometry (LA-ICP-OES) is presented. LIB cells with lithium metal oxide LiNi_1/3Co_1/3Mn_1/3O₂ (NCM111) as cathode material and graphite as anode material are investigated using a 213 nm Nd:YAG laser.

An LA-ICP-OES method was developed and applied to investigate the transition metal dissolution in lithium batteries as well as lithium deposition e.g. in case of short circuits.