Mechanical behavior of in vivo degraded second generation resorbable magnesium scaffolds (RMS).

Resorbable magnesium scaffolds are used for the treatment of atherosclerotic coronary vascular disease and furthermore, for vascular restoration therapy. Recently, the first-in-man clinical studies with Magmaris showed promising results regarding the target lesion failure as well as vasomotion properties after 12 and 24 month. The consistency of in vivo degraded magnesium alloys in a cardiovascular environment is qualitatively described in literature, but only little has been disclosed about the actual change in mechanical properties and the behavior of the magnesium alloy degradation products. In the present study, uncoated magnesium scaffolds 3.0 × 20 mm were implanted in coronary arteries of two healthy Goetinnger mini-swine. The scaffolds were explanted to evaluate the mechanical properties of the degraded magnesium scaffolds after 180 days in vivo. Ex vivo sample preparation and test conditions were adapted to a customized compression test setup which was developed to investigate the micro-scale scaffold fragments (width 225 ±â€¯75 µm, thickness 150 µm). As reference bare undegraded magnesium scaffold fragments were tested. Mechanical parameters relating to force as a function of displacement were determined for both sample groups. The undegraded samples showed no fracturing at the maximum applied force of 8 N, whereas the in vivo degraded test samples showed forces of 0.411 ±â€¯0.197 N at the first fracturing and a maximum force of 0.956 ±â€¯0.525 N. The deformation work, calculated as area beneath the force-displacement curve, of the in vivo degraded test samples was reduced by approximately 87-88% compared to the undegraded samples (5.20 mN mm and 40.79 mN mm, both at 7.5% deformation). The indication for a complete loss of structural integrity through a reduction of mechanical properties after a certain degradation time increases the chance to restore vascular function and physiological vasomotion in the stented vessel compartment.

Preclinical evaluation of degradation kinetics and elemental mapping of first- and second-generation bioresorbable magnesium scaffolds.

AIMS: Because vascular restoration therapy using bioresorbable vascular scaffolds (BRS) remains an appealing concept to restore vasoreactivity, an understanding of biodegradation remains paramount during preclinical testing. We therefore aimed to investigate the qualitative and temporal course of degradation of magnesium alloy-based bioresorbable vascular scaffolds in juvenile swine. METHODS AND RESULTS: Qualitative characterisation of biodegradation was performed in 41 DREAMS 1G up to three years, while degradation kinetics were acquired in 54 DREAMS 2G implanted into porcine coronary arteries for 28, 90 and 180 days, one and two years. Assessment of end product composition was achieved in DREAMS 2G at 180 days. Myocardium was examined, while an OCT attenuation score was derived at strut level from 180 days to two years in DREAMS 2G. Degradation of DREAMS entails two corrosive phases. At one year, 94.8% of the magnesium was bioabsorbed in DREAMS 2G and, at two years, magnesium was completely replaced by amorphous calcium phosphate. Von Kossa staining revealed variable peri-strut mineralisation at all time points and only small focal myocardial emboli observed in one animal in the 180 days cohort. Strut discontinuity density was low at 28 days (0.5±0.57 per mm) and increased to a density above 7.5 per mm up to one year. OCT attenuation score correlated well with strut-based degradation analysis up to two years. CONCLUSIONS: While the current set of data supports vascular safety, clinical trials are warranted to prove the concept of vascular restoration following DREAMS implantation.