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. 2023 Jun 5;19(2):e167-e175.
doi: 10.4244/EIJ-D-22-00718.

Preclinical evaluation of the degradation kinetics of third-generation resorbable magnesium scaffolds

Masaru Seguchi  1 , Philine Baumann-Zumstein  2 , Armin Fubel  2 , Ron Waksman  3 , Michael Haude  4 , Stefano Galli  5 , Michael Joner  1   6
Affiliations

Preclinical evaluation of the degradation kinetics of third-generation resorbable magnesium scaffolds

Masaru Seguchi et al. EuroIntervention. .

Abstract

Background: The novel sirolimus-eluting resorbable scaffold DREAMS 3G was designed as a third-generation development of its predecessor, the Magmaris scaffold.

Aims: This preclinical study aimed to examine the qualitative and temporal course of the degradation of the DREAMS 3G relative to the Magmaris scaffold.

Methods: Forty-nine DREAMS 3G and 24 Magmaris scaffolds were implanted into 48 mini swine for degradation kinetics analysis. Another DREAMS 3G was implanted into one mini swine for crystallinity analysis of the degradation end product after 730 days. Degradation kinetics were determined at 28, 90, 120, 180, and 365 days.

Results: Discontinuity density in DREAMS 3G was significantly lower than that in Magmaris scaffolds for the follow-up timepoints of 90 and 120 days. Planimetric analysis indicated 99.6% backbone degradation for DREAMS 3G at 12 months. Compared to the Magmaris scaffold, individual strut degradation in DREAMS 3G showed less variability and the remaining backbone core was more homogeneous. The degradation end product of DREAMS 3G manifested as calcium phosphate with a minor share of aluminium phosphate.

Conclusions: DREAMS 3G showed almost complete degradation after one year, with amorphous calcium and aluminium phosphate as the end products of degradation. Despite its thinner struts, scaffold discontinuity was significantly lower in the DREAMS 3G than in the Magmaris scaffold, likely providing a longer scaffolding time.

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Conflict of interest statement

P. Baumann-Zumstein is an employee of BIOTRONIK AG. A. Fubel is an employee of BIOTRONIK AG. M. Haude reports study grants and personal fees from BIOTRONIK, Cardiac Dimensions, and OrbusNeich. R Waksman reports serving on an advisory board for Abbott Vascular, Boston Scientific, Medtronic, Philips, and Pi-Cardia Ltd.; is a consultant for Abbott Vascular, BIOTRONIK, Boston Scientific, Cordis, Medtronic, Philips, Pi-Cardia Ltd., SIS Medical AG, Transmural Systems Inc., and Venous MedTech; has received grant support from BIOTRONIK, Boston Scientific, Chiesi, Medtronic, and Philips; and has investments in MedAlliance and Transmural Systems. M. Joner reports personal fees from Abbott, AstraZeneca, BIOTRONIK, OrbusNeich, ReCor, and Shockwave; grants and personal fees from Boston Scientific and Edwards Lifesciences; personal fees and a grant from Cardiac Dimensions; and a grant from Infraredx, outside the submitted work. S. Galli reports personal fees from BIOTRONIK. M. Seguchi has no conflicts of interest to declare.

Figures

Figure 1
Figure 1. Comparison of discontinuity density.
μCT images used for discontinuity density evaluation (indicated by arrowheads) of DREAMS 3G (A) and Magmaris RMS (B) at 90 days after implantation. C) Discontinuity density (1/mm) (without connectors) of individual scaffolds per follow-up timepoint and device group determined by μCT. The numbers represent the “mean±standard deviation” for each item. μCT: micro-computed tomography; d: days; n.a.: not available, n.s.: not significant; RMS: resorbable magnesium scaffold
Figure 2
Figure 2. Inhomogeneity index of backbone degradation of individual strut cross-section including mean value and 95 % confidence interval per follow-up timepoint and device group determined by optical microscopy planimetry.
d: days; n.a.: not available.
Figure 3
Figure 3. Overlaid XRD patterns of naïve artery without scaffold (blue), non-degraded DREAMS 3G prototype scaffold (red, characteristic crystalline peak positions for metallic magnesium are indicated with Mg), porcine bone sample (green, characteristic crystalline peak positions for mineral apatite are indicated with MA), and two-year in vivo degraded DREAMS 3G prototype scaffold (violet).
Figure 4
Figure 4. Qualitative elemental mappings by SEM/EDX of representative DREAMS 3G strut cross-sections for: A) 90 days; and B) 365 days.
Top line: Backscattered electron images. Bottom right of each column: Overlay images of selected constituents: Ca (red), P (green), Mg (blue). Qualitative data for illustrative purposes only; EDX mapping images are raw data without correction for matrix effects and each element’s intensity is scaled to its maximum for each image individually. It is to be noted, that in the non-degraded BIOmag alloy, the aluminium signal is erroneously low due to uncorrected absorption (different weight per volume of matrix and difficulty in quantification of the aluminium peak due to closeness of intense Mg peak as the main component of the alloy). Ca: calcium; EDX: energy dispersive X-ray analysis; Mg: magnesium; P: phosphorus; SEM: scanning electron microscopy
Figure 5
Figure 5. Simplified degradation mechanism and justifiably assumed degradation products for DREAMS 3G (reaction pathways).
Al: aluminium; Ca: calcium; HPO42- : hydrogen phosphate; Mg: magnesium
Figure 6
Figure 6. Schematic illustration of reduced discontinuity density of DREAMS 3G versus Magmaris RMS despite lower strut thickness and similar degradation kinetics.
More homogenous and uniform shapes of the remaining metallic magnesium core in DREAMS 3G (A) versus Magmaris RMS (B) plus overall decreased variability in strut degradation in DREAMS 3G (C) versus Magmaris RMS (D) plus inherently improved material properties of the BIOmag alloy versus the Magmaris RMS alloy (E) resulting in a reduced discontinuity density of DREAMS 3G (F) versus Magmaris RMS (G) as evaluated by μCT. μCT: micro-computed tomography; RMS: resorbable magnesium scaffold
See this image and copyright information in PMC

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