Novel Zn-based alloys for biodegradable stent applications: Design, development and in vitro degradation.

The search for a degradable metal simultaneously showing mechanical properties equal or higher to that of stainless steel and uniform degradation is still an open challenge. Several magnesium-based alloys have been studied, but their degradation rate has proved to be too fast and rarely homogeneous. Fe-based alloys show appropriate mechanical properties but very low degradation rate. In the present work, four novel Zn-Mg and two Zn-Al binary alloys were investigated as potential biodegradable materials for stent applications. The alloys were developed by casting process and homogenized at 350°C for 48h followed by hot extrusion at 250°C. Tube extrusion was performed at 300°C to produce tubes with outer/inner diameter of 4/1.5mm as precursors for biodegradable stents. Corrosion tests were performed using Hanks׳ modified solution. Extruded alloys exhibited slightly superior corrosion resistance and slower degradation rate than those of their cast counterparts, but all had corrosion rates roughly half that of a standard purity Mg control. Hot extrusion of Zn-Mg alloys shifted the corrosion regime from localized pitting to more uniform erosion, mainly due to the refinement of second phase particles. Zn-0.5Mg is the most promising material for stent applications with a good combination of strength, ductility, strain hardening exponent and an appropriate rate of loss of mechanical integrity during degradation. An EBSD analysis in the vicinity of the laser cut Zn-0.5Mg tube found no grain coarsening or texture modification confirming that, after laser cutting, the grain size and texture orientation of the final stent remains unchanged. This work shows the potential for Zn alloys to be considered for stent applications.

Finite element shape optimization for biodegradable magnesium alloy stents.

Biodegradable magnesium alloy stents (MAS) are a promising solution for long-term adverse events caused by interactions between vessels and permanent stent platforms of drug eluting stents. However, the existing MAS showed severe lumen loss after a few months: too short degradation time may be the main reason for this drawback. In this study, a new design concept of MAS was proposed and a shape optimization method with finite element analysis was applied on two-dimensional (2D) stent models considering four different magnesium alloys: AZ80, AZ31, ZM21, and WE43. A morphing procedure was utilized to facilitate the optimization. Two experiments were carried out for a preliminary validation of the 2D models with good results. The optimized designs were compared to an existing MAS by means of three-dimensional finite element analysis. The results showed that the final optimized design with alloy WE43, compared to the existing MAS, has an increased strut width by approximately 48%, improved safety properties (decreased the maximum principal stress after recoil with tissue by 29%, and decreased the maximum principal strain during expansion by 14%) and improved scaffolding ability (increased by 24%). Accordingly, the degradation time can be expected to extend. The used methodology provides a convenient and practical way to develop novel MAS designs.

[Presentation of a consecutive series of 400 aortocoronary bypass patients without hospital mortality]. / Presentazione di una serie consecutiva di 400 pazienti operati di by-pass aorto-coronarico senza mortalità ospedaliera.

Four-hundred consecutive patients were operated of coronary artery bypass between July 1980 and November 1982 without any hospital mortality. Clinical and coronarographic characteristics and surgical techniques are presented. Eighteen cases were complicated by peri-operative myocardial infarction. Follow-up data, were available for 91% of the discharged patients, ranged between 5 and 33 months (mean 17,6). Two hundred and sixty-one patients were asymptomatic, 66 had improved clinical conditions, but angina was still present; 25 were unchanged while 5 had worsened. There were seven late deaths; 6 due to cardiac disease and 1 to a mesothelioma.

[Surgical treatment of aneurysms of the thoracic aorta. Presentation of personal cases]. / Il trattamento chirurgico degli aneurismi dell'aorta toracica. Presentazione di una casistica personale

Six cases of aneurysm of the thoracic aorta, four located in the 1st segment and two in the 3rd, are reported. The four cases in the ascending aorta presented a different aetiology: a) aneurysm on aortic stenosis (case 1); b) atheromatous aneurysm (case 2); c) aortic dissection (case 5); d) aneurysm due to dystrophy of the media in a patient with Marfan's disease (case 6). 3 tubular prosthetic substitutions of the ascending aorta were made (with a valvular substitution and commissural relocation associated with right aorto-coronary venous by-pass) and one plastic intervention on the aorta with valvular substitution. The aneurysms of the descending thoracic aorta presented traumatic aetiology and were treated with resection-dacron graft, using femoral artero-venous partial CEC.

[Aorto-coronary by-pass. Personal experience based on 342 cases operated on between April 1971 and December 1974 (author's transl)]. / Il by-pass aorto-coronarico. Esperienza personale su 342 casi operati sino al dicembre 1974

The authors report on the casuistry of aorto-coronary by-pass operations they performed between April 1971 and December 1974, discussing the criteria which indicate the necessity of operating, the principles of the operative techniques, and the results obtained. Out of a total of 342 operated cases, there was an operative mortality (within 30 days) of 3% in isolated by-pass cases, and 4% if one includes associated operations. In 3,5% of patients, postoperative necrosis was present. Almost the same values were found in the smaller group (66 cases) which underwent urgent by-pass operations. The authors consider that the aorto-coronary by-pass operation is a very useful treatment, both for stable and unstable angina, as long as the anatomo-functional conditions exist.