Magmaris resorbable magnesium scaffold for the treatment of coronary heart disease: overview of its safety and efficacy

Drug-eluting resorbable coronary scaffolds: a review of recent advances

INTRODUCTION

Device-related persistent adverse events with current DES-use have refocused the attention on a 'leave-nothing-behind' philosophy, in which it is hypothesized that treating coronary stenosis without permanently caging the vessel with a metallic implant would lead to superior clinical outcomes. One of these uncaging technologies is bioresorbable scaffolds (BRS).

AREAS COVERED

In this article, we describe the technical specifications and clinical data of currently available BRS devices.

EXPERT OPINION

Newer BRS devices have thinner struts and more biocompatible scaffold backbones (either polymer-based or metal-based), resulting in improved radial strength, faster resorption times, and more antithrombogenic properties (e.g. magnesium-based scaffolds). Results of BRS in the treatment of simple coronary artery disease demonstrate favorable clinical efficacy and safety outcome data. It is probable that over the next 5 years more fourth-generation devices with ever-increasing biocompatibility and safety profiles will be investigated and released commercially, resulting in a much more prominent role for BRS, especially in the treatment of simple coronary artery disease in younger patients.

Current situation and overview of resorbable magnesium scaffolds: a perspective for overcoming the remaining issues of polymeric bioresorbable scaffold

Bioresorbable scaffolds (BRS) were developed as an innovative solution to overcome the limitations of metallic stents. While polymeric BRS initially demonstrated comparable clinical outcomes to drug-eluting stent (DES) in clinical trials, subsequent large-scale studies revealed that patients implanted with polymeric BRS experienced higher rates of scaffold thrombosis (ScT) and target lesion failure compared to those with metallic stents. Resorbable magnesium scaffolds (RMS) have emerged as a promising alternative owing to magnesium's natural degradability and favorable mechanical properties. Learning from the mechanism of polymeric BRS failure and through continuous improvements, recent clinical trials have shown promising clinical performance for RMS technology. However, comparative studies between RMS and DES have continued to highlight the remaining challenges with RMS, particularly in regard to late lumen loss. Recent advancements in third-generation RMS show improvements in strut thickness and homogeneous degradation, which enhances sustained structural integrity throughout the degradation process. Based on encouraging results from a first-in-human trial of the latest version of RMS, a randomized controlled trial has been initiated to compare the outcomes between metallic stents and the latest RMS, with patient enrollment already underway. This review aims to explore the limitations of polymeric BRS and provide an overview of the current developments and future potential of magnesium-based BRS.

Recent advances and perspectives in bioresorbable metal coronary drug-eluting stents

Intervention without implantation has become a requirement for developing percutaneous coronary intervention for coronary heart disease. In this paper, the recent advances of three representative types of bioresorbable metal coronary drug-eluting stents (DESs) are reviewed, and the material composition, structural design, mechanical properties and degradability of iron-based, magnesium-based and zinc-based bioresorbable metal coronary DES are analyzed. The methods of regulating the radial strength and degradation rate of the coronary stents are summarized, and thein vivo/in vitroperformance evaluation methods and ideal testing systems of the bioresorbable metal coronary DES are analyzed. Advances made in bioresorbable metal coronary DES, the existing shortcomings and optimization methods are proposed, and the future development direction is prospected.

Insight the long-term biodegradable Mg-RE-Sr alloy for orthopaedics implant via friction stir processing

Magnesium alloys, noted for their substantial mechanical strength and exceptional biocompatibility, are increasingly being considered for use in biodegradable implants. However, their rapid degradation and significant hydrogen release have limited their applications in orthopaedics. In this study, a novel Mg-RE-Sr alloy was created by friction stir processing to modify its microstructure and enhance its degradation performance. Through microstructural characterization, the friction stir processing effectively refined the grains, accelerated the re-dissolution of precipitates, and ensured a uniform distribution of these phases. The processed alloy demonstrated improved comprehensive properties, with an in vitro corrosion rate of approximately 0.4 mm/y and increases in ultimate tensile strength and elongation by 37 % and 166 %, respectively. Notably, in vivo experiments involving a rat subcutaneous implantation model revealed a slower degradation rate of 0.09 mm/y and a uniform degradation process, basically achieving the requirements for ideal performance in orthopaedic applications. The superior degradation characteristics were attributed to the synergistic effect of attenuated galvanic corrosion and the formation of a dense Y(OH)3/Y2O3 film induced by an exceptional microstructure with a highly solid-soluted matrix and uniformly refined precipitates. Meanwhile, the alloys exhibited excellent biocompatibility and did not cause undesirable inflammation or produce toxic degradation products. These improvements in biocompatibility and degradation characteristics indicate great promise for the use of this friction stir processed alloy in osteosynthesis systems in the clinical setting.

Long-term efficacy, safety and biocompatibility of a novel sirolimus eluting iron bioresorbable scaffold in a porcine model

Iron is considered as an attractive alternative material for bioresorbable scaffolds (BRS). The sirolimus eluting iron bioresorbable scaffold (IBS), developed by Biotyx Medical (Shenzhen, China), is the only iron-based BRS with an ultrathin-wall design. The study aims to investigate the long-term efficacy, safety, biocompatibility, and lumen changes during the biodegradation process of the IBS in a porcine model. A total of 90 IBSs and 70 cobalt-chromium everolimus eluting stents (EES) were randomly implanted into nonatherosclerotic coronary artery of healthy mini swine. The multimodality assessments including coronary angiography, optical coherence tomography, micro-computed tomography, magnetic resonance imaging, real-time polymerase chain reaction (PCR), and histopathological evaluations, were performed at different time points. There was no statistical difference in area stenosis between IBS group and EES group at 6 months, 1year, 2 years and 5 years. Although the scaffolded vessels narrowed at 9 months, expansive remodeling with increased mean lumen area was found at 3 and 5 years. The IBS struts remained intact at 6 months, and the corrosion was detectable at 9 months. At 5 years, the iron struts were completely degraded and absorbed in situ, without in-scaffold restenosis or thrombosis, lumen collapse, aneurysm formation, and chronic inflammation. No local or systemic toxicity and abnormal histopathologic manifestation were found in all experiments. Results from real-time PCR indicated that no sign of iron overload was reported in scaffolded segments. Therefore, the IBS shows comparable efficacy, safety, and biocompatibility with EES, and late lumen enlargement is considered as a unique feature in the IBS-implanted vessels.

Gd Added Mg Alloy for Biodegradable Implant Applications

Microstructure, mechanical, in vitro and in vivo behavior of extruded Mg alloys with varying Zn/Gd ratios, Mg-2Gd-2Zn-0.5Zr (Zn/Gd = 1), Mg-2Gd-6Zn-0.5Zr (Zn/Gd = 3), and Mg-10Gd-1Zn-0.5Zr (Zn/Gd = 0.1) were investigated. The results revealed that the major secondary phases such as W (Mg3Zn3Gd2), (Mg,Zn)3Gd, LPSO (Long period stacking order) and I (Mg3Zn6Gd) phase in alloys depended on Zn/Gd ratio. These second phases influenced the mechanical as well as biological characteristics of the alloys. Among studied alloys, Mg-10Gd-1Zn-0.5Zr alloy showed the highest yield strength and tensile strength of 270 (±9.29) and 330 MPa (±15.8), respectively, with a reasonably good elongation of 12% (±2.36). The presence of Gd2O3 in the degradation film of Mg-10Gd-1Zn-0.5Zr enhanced the resistance offered by the film, which resulted in its lowest biodegradation, better viability, and cell proliferation under in vitro condition. The short term (subcutaneous implantation in rats for 1 month) in vivo studies showed that the alloy Mg-10Gd-1Zn-0.5Zr degraded at a rate of 0.35 mm/y (±0.02) and did not induce any toxicity to the vital organs.

In vivo chronic scaffolding force of a resorbable magnesium scaffold

The aim of this study is to qualitatively characterize the in vivo chronic scaffolding force of the Magmaris® Resorbable Magnesium Scaffold (RMS). This important parameter of scaffolds must be balanced between sufficient radial support during the healing period of the vessel and avoidance of long-term vessel caging. A finite element model was established using preclinical animal data and used to predict the device diameter and scaffolding force up to 90 days after implantation. To account for scaffold resorption, it included backbone degradation as well as formation of discontinuities as observed in vivo. The predictions of the model regarding acute recoil and chronic development of the device diameter were in good agreement with the preclinical data, supporting the validity of the model. It was found that after 28 and 90 days, the Magmaris® RMS retained 90 % and 47 % of its initial scaffolding force, respectively. The reduction in scaffolding force was mainly driven by discontinuities in the meandering segments. Finite element analysis combined with preclinical data is a reliable method to characterize the chronic scaffolding force.

Cardiac Computed Tomography in Monitoring Revascularization

The use of coronary computed tomography angiography (CCTA) in the setting of stable coronary artery disease is highly recommended for low-risk patients. High-risk patients, such as symptomatic subjects with prior revascularization, are suggested to be investigated with noninvasive functional tests or invasive coronary angiography. CCTA is not considered for these patients because of some well-known CCTA artifacts, such as blooming and motion artifacts. However, new technology has allowed us to obtain images with high spatial resolution, overcoming these well-known limitations of CCTA. Furthermore, the introduction of CT-derived fractional flow reserve and stress CT perfusion has made CCTA a comprehensive examination, including anatomical and functional assessments of coronary plaques. Additionally, CCTA allows for plaque characterization, which has become a cornerstone for the optimization of medical therapy, which is not possible with functional tests. Recent evidence has suggested that CCTA could be used with the aim of monitoring revascularization, both after coronary bypass grafts and percutaneous coronary intervention. With this background information, CCTA can also be considered the exam of choice in subjects with a history of revascularization. The availability of a noninvasive anatomic test for patients with previous coronary revascularization and its possible association with functional assessments in a single exam could play a key role in the follow-up management of these subjects, especially considering the rate of false-positive and negative results of noninvasive functional tests. The present review summarizes the main evidence about CCTA and coronary artery bypass grafts, complex percutaneous coronary intervention, and bioresorbable stent implantation.

Efficacy and risks of drug-coated balloon treatment for coronary artery disease: A meta-analysis

Introduction

Coronary artery disease (CAD) often leads to myocardial ischemia and impaired cardiac function, significantly impacting the well-being and quality of life (QOL) of individuals. The use of drug-coated balloon (DCB) treatment has become a widespread approach in CAD management. However, currently, there is limited evidence available for the meta-analysis of DCB treatment in CAD.

Materials and methods

A systematic search was conducted across databases including PubMed, Cochrane Library, China National Knowledge Infrastructure (CNKI), Wanfang Database, and VIP Database, covering data from the inception of each database up to April 2023. Randomized controlled trials (RCTs) regarding DCB treatment were meticulously chosen based on independent assessment of eligibility and scope by three researchers. Literature screening and data extraction were independently performed by two researchers, while methodological quality of the enrolled studies was assessed using the risk of bias (ROB) tool developed by the Cochrane Collaboration. Meta-analysis was conducted using RevMan 5.3.

Results

Following the screening process, seven studies were included. Four studies demonstrated an odds ratio (OR) of 0.66 for target lesion revascularization (TLR), five reported an OR of 0.41 for postoperative myocardial infarction (MI), four indicated a mean difference (MD) of 6.03 in the degree of stenosis (DOS), five exhibited an MD of 0.13 for late lumen loss (LLL), five reported an OR of 0.33 for cardiac death, and two presented an OR of 1.01 for binary restenosis (BR).

Conclusion

DCB demonstrated a comparable efficacy to drug-eluting stents (DES) in treating CAD, with relatively lower associated risks.

In Vitro and In Vivo Applications of Magnesium-Enriched Biomaterials for Vascularized Osteogenesis in Bone Tissue Engineering: A Review of Literature

Bone is a highly vascularized tissue, and the ability of magnesium (Mg) to promote osteogenesis and angiogenesis has been widely studied. The aim of bone tissue engineering is to repair bone tissue defects and restore its normal function. Various Mg-enriched materials that can promote angiogenesis and osteogenesis have been made. Here, we introduce several types of orthopedic clinical uses of Mg; recent advances in the study of metal materials releasing Mg ions (pure Mg, Mg alloy, coated Mg, Mg-rich composite, ceramic, and hydrogel) are reviewed. Most studies suggest that Mg can enhance vascularized osteogenesis in bone defect areas. Additionally, we summarized some research on the mechanisms related to vascularized osteogenesis. In addition, the experimental strategies for the research of Mg-enriched materials in the future are put forward, in which clarifying the specific mechanism of promoting angiogenesis is the crux.

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

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.

Lithium-Induced Optimization Mechanism for an Ultrathin-Strut Biodegradable Zn-Based Vascular Scaffold

To reduce incidences of in-stent restenosis and thrombosis, the use of a thinner-strut stent has been clinically proven to be effective. Therefore, the contemporary trend is toward the use of ultrathin-strut (≤70 µm) designs for durable stents. However, stents made from biodegradable platforms have failed to achieve intergenerational breakthroughs due to their excessively thick struts. Here, microalloying is used to create an ultrathin-strut (65 µm) zinc (Zn) scaffold with modified biodegradation behavior and improved biofunction, by adding lithium (Li). The scaffold backbone consists of an ultrafine-grained Zn matrix (average grain diameter 2.28 µm) with uniformly distributed nanoscale Li-containing phases. Grain refinement and precipitation strengthening enable it to achieve twice the radial strength with only 40% of the strut thickness of the pure Zn scaffold. Adding Li alters the thermodynamic formation pathways of products during scaffold biodegradation, creating an alkaline microenvironment. Li₂ CO₃  may actively stabilize this microenvironment due to its higher solubility and better buffering capability than Zn products. The co-release of ionic zinc and lithium enhances the beneficial differential effects on activities of endothelial cells and smooth muscle cells, resulting in good endothelialization and limited intimal hyperplasia in porcine coronary arteries. The findings here may break the predicament of the next-generation biodegradable scaffolds.

Bioresorbable Magnesium-Based Stent: Real-World Clinical Experience and Feasibility of Follow-Up by Coronary Computed Tomography: A New Window to Look at New Scaffolds

(1) Background: The diagnostic accuracy of coronary computed tomography angiography (CCTA) for coronary artery disease (CAD) has greatly improved so CCTA represents a transition in the care of patients suffering from CAD. Magnesium-based bioresorbable stents (Mg-BRS) secure acute percutaneous coronary intervention (PCI) results without leaving, in the long term, a metallic caging effect. The purpose of this real-world study was to assess clinical and CCTA medium- and long-term follow-up of all our patients with implanted Mg-BRS. (2) Methods: The patency of 52 Mg-BRS implanted in 44 patients with de novo lesions (24 of which had acute coronary syndrome (ACS)) was evaluated by CCTA and compared to quantitative coronary angiography (QCA) post-implantation. (3) Results: ten events including four deaths occurred during a median follow-up of 48 months. CCTA was interpretable and in-stent measurements were successful at follow-up without being hindered by the stent strut's "blooming effect". Minimal in-stent diameters on CCTA were found to be 1.03 ± 0.60 mm smaller than the expected diameter after post-dilation on implantation (p < 0.05), a difference not found in comparing CCTA and QCA. (4) Conclusions: CCTA follow-up of implanted Mg-BRS is fully interpretable and we confirm the long-term Mg-BRS safety profile.

Challenges of the newer generation of resorbable magnesium scaffolds: Lessons from failure mechanisms of the past generation

Bioresorbable scaffolds (BRS) were developed to overcome the obstacles of metallic stents, mostly related to sustained presence of metallic foreign body in the coronary vessel. Following earlier success of single-arm BRS studies, randomized controlled trials of Absorb bioresorbable vascular scaffold (Abbott Vascular, Santa Clara, CA, USA) showed poor long-term clinical outcomes, particularly in terms of scaffold thrombosis. BRS made from magnesium alloy provide a promising alternative in terms of radial force, strut thickness and, potentially lower thrombogenicity. A recent clinical study demonstrated that magnesium-based BRS seems to be promising with regards to the risk of scaffold thrombosis. In this review, our aim is to describe the issues that prevented Absorb BVS from achieving favorable outcomes, provide current status of existing BRS technologies and the challenges that newer generation BRSs need to overcome, and the results of clinical studies for commercially available magnesium-based BRS, which remain the only BRS actively studied in clinical practice.

The bioresorbable magnesium scaffold (Magmaris)-State of the art: From basic concept to clinical application

Since its introduction to clinical practice, coronary artery stent implantation has become a crucial part of the therapy of coronary artery disease (CAD). Despite the undeniable evolution of percutaneous coronary revascularization procedures, drug-eluting stent (DES) technology shows some limitations. To overcome these limitations bioresorbable vascular scaffolds (BRS) were designed as a vessel-supporting technology allowing for anatomical and functional restoration of the vessel after the scaffold intended resorption. Various materials have been proposed as the basis of the scaffold backbone. In this narrative review, we present second-generation magnesium-alloy bioresorbable scaffold devices (Magmaris; Biotronik). Additionally, we discuss available preclinical and clinical data regarding this new magnesium BRS.

Drug-Eluting, Bioresorbable Cardiovascular Stents─Challenges and Perspectives

Globally, the leading causes of natural death are attributed to coronary heart disease and type 1 and type 2 diabetes. High blood pressure levels, high cholesterol levels, smoking, and poor eating habits lead to the agglomeration of plaque in the arteries, reducing the blood flow. The implantation of devices used to unclog vessels, known as stents, sometimes results in a lack of irrigation due to the excessive proliferation of endothelial tissue within the blood vessels and is known as restenosis. The use of drug-eluting stents (DESs) to deliver antiproliferative drugs has led to the development of different encapsulation techniques. However, due to the potency of the drugs used in the initial stent designs, a chronic inflammatory reaction of the arterial wall known as thrombosis can cause a myocardial infarction (MI). One of the most promising drugs to reduce this risk is everolimus, which can be encapsulated in lipid systems for controlled release directly into the artery. This review aims to discuss the current status of stent design, fabrication, and functionalization. Variables such as the mechanical properties, metals and their alloys, drug encapsulation and controlled elution, and stent degradation are also addressed. Additionally, this review covers the use of polymeric surface coatings on stents and the recent advances in layer-by-layer coating and drug delivery. The advances in nanoencapsulation techniques such as liposomes and micro- and nanoemulsions and their functionalization in bioresorbable, drug-eluting stents are also highlighted.

Improving the radiopacity of Fe–Mn biodegradable metals by magnetron-sputtered W–Fe–Mn–C coatings: Application for thinner stents

In this exploratory work, micrometric radiopaque W–Fe–Mn–C coatings were produced by magnetron sputtering plasma deposition, for the first time, with the aim to make very thin Fe–Mn stents trackable by fluoroscopy. The power of Fe–13Mn-1.2C target was kept constant at 400 W while that of W target varied from 100 to 400 W producing three different coatings referred to as P100, P200, P400. The effect of the increased W power on coatings thickness, roughness, structure, corrosion behavior and radiopacity was investigated. The coatings showed a power-dependent thickness and W concentration, different roughness values while a similar and uniform columnar structure. An amorphous phase was detected for both P100 and P200 coatings while γ-Fe, bcc-W and W₃C phases found for P400. Moreover, P200 and P400 showed a significantly higher corrosion rate (CR) compared to P100. The presence of W, W₃C as well as the Fe amount variation determined two different micro-galvanic corrosion mechanisms significantly changing the CR of coatings, 0.26 ± 0.02, 59.68 ± 1.21 and 59.06 ± 1.16 μm/year for P100, P200 and P400, respectively. Sample P200 with its most uniform morphology, lowest roughness (RMS = 3.9 ± 0.4 nm) and good radiopacity (∼6%) appeared the most suitable radiopaque biodegradable coating investigated in this study.

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Three W–Fe–Mn–C coatings (P100, P200, P400) were developed by magnetron sputtering.

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Coatings showed a columnar structure and power-dependent thickness and W concentration.

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Thicknesses from 0.9 ± 0.2 to 1.8 ± 0.2 μm and RMS from 3.9 ± 0.4 to 54.3 ± 8.1 nm were found for P100, P200, P400, resp.

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The amorphous phase of P100, P200 and γ-Fe, bcc-W and W₃C of P400 significantly affected the CR.

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The most uniform morphology, lowest roughness (3.9 ± 0.4 nm) and good radiopacity (∼6%) were found for P200.

Biodegradable Biomaterial Arterial Stent in the Treatment of Coronary Heart Disease

This study aims to evaluate the clinical application value of two materials, drug-eluting stent, and biodegradable stent, in the treatment of coronary heart disease. The results show that the therapeutic effects of drug-eluting stents and biodegradable stents are similar. Both treatment methods have high safety and effectiveness. The ideal coronary artery stent should have good biocompatibility, safety, and possibility.

The resorbable magnesium scaffold Magmaris in acute coronary syndrome: An appraisal of evidence and user group guidance

Bioresorbable scaffolds provide transient vessel support without the long-term limitations of permanent metallic drug-eluting stents. The sirolimus-eluting resorbable magnesium scaffold Magmaris is the only CE-marked metallic bioresorbable scaffold and provides short-term lumen support before being completely bioresorbed. To date, clinical trial results have demonstrated low adverse event rates in patients with simple coronary lesions. Seven European centers with large experience in Magmaris implantation, combined efforts in an informal collaboration to evaluate and appraise clinical data currently available regarding the performance of Magmaris in patients presenting with acute coronary syndromes, and to supply user-advice on patient selection and optimal implantation practice.

Degradation Analysis of Thin Mg-xAg Wires Using X-ray Near-Field Holotomography

Magnesium–silver alloys are of high interest for the use as temporary bone implants due to their antibacterial properties in addition to biocompatibility and biodegradability. Thin wires in particular can be used for scaffolding, but the determination of their degradation rate and homogeneity using traditional methods is difficult. Therefore, we have employed 3D imaging using X-ray near-field holotomography with sub-micrometer resolution to study the degradation of thin (250 μm diameter) Mg-2Ag and Mg-6Ag wires. The wires were studied in two states, recrystallized and solution annealed to assess the influence of Ag content and precipitates on the degradation. Imaging was employed after degradation in Dulbecco’s modified Eagle’s medium and 10% fetal bovine serum after 1 to 7 days. At 3 days of immersion the degradation rates of both alloys in both states were similar, but at 7 days higher silver content and solution annealing lead to decreased degradation rates. The opposite was observed for the pitting factor. Overall, the standard deviation of the determined parameters was high, owing to the relatively small field of view during imaging and high degradation inhomogeneity of the samples. Nevertheless, Mg-6Ag in the solution annealed state emerges as a potential material for thin wire manufacturing for implants.

Long-term clinical, angiographic, and optical coherence tomography findings of Mg-based bioresorbable scaffold in patients with acute coronary syndrome

BACKGROUND

This study sought to evaluate the clinical outcomes of patients treated with magnesium-based bioresorbable scaffolds (MgBRS) in the context of acute coronary syndromes (ACS) at long-term follow-up (24 months). The study also aims to investigate the MgBRS performance by angiography and the healing and bioresorption pattern by optical coherence tomography (OCT) at 18 months.

METHODS

Between December 2016 and December 2018, a total of 90 patients admitted for ACS and treated with MgBRS (Magmaris, Biotronik AG, Bülach, Switzerland) were enrolled in a multicenter prospective study. Clinical follow-up was performed in all patients at 24 months and angiographic and OCT follow-up in 51.5% of patients at 18 months. Serial OCT was available in 33 patients (36.7%).

RESULTS

At a 2-year follow-up, 88.8% were free of symptoms, no cardiac death was reported, and the device-oriented composite event (DOCE): consisting of cardiac death, target vessel myocardial infarction, and target lesion revascularization (TLR) was 13.3%. Stent thrombosis and TLR were observed in 2.2 and 11.1%, respectively. Binary restenosis was observed in 21.7% of cases and in-stent late lumen loss was 0.61 ± 0.75 mm. By serial OCT imaging, the minimal lumen area was significantly reduced greater than 40% (from 6.12 ± 1.59 to 3.5 ± 1.55 mm2, p < .001). At follow-up, area stenosis was 44.33 ± 23.07% and half of the patients presented indiscernible struts. The principal observed mechanism of restenosis was scaffold collapse.

CONCLUSIONS

At long-term follow-up, MgBRS implantation in ACS patients showed a high rate of DOCE, mainly caused by clinically driven TLR. MgBRS restenosis was caused by scaffold collapse in most of the cases.

The biological responses and mechanisms of endothelial cells to magnesium alloy

Due to its good biocompatibility and degradability, magnesium alloy (Mg alloy) has shown great promise in cardiovascular stent applications. Rapid stent re-endothelialization is derived from migrated and adhered endothelial cells (ECs), which is an effective way to reduce late thrombosis and inhibit hyperplasia. However, fundamental questions regarding Mg alloy affecting migration and adhesion of ECs are not fully understood. Here, we evaluated the effects of Mg alloy on the ECs proliferation, adhesion and migration. A global gene expression profiling of ECs co-culturing with Mg alloy was conducted, and the adhesion- and migration-related genes were examined. We found that Mg alloy had no adverse effects on ECs viability but significantly affected ECs migration and adhesion. Co-cultured with Mg alloy extract, ECs showed contractive adhesion morphology and decreased motility, which was supported by the down-regulation of adhesion-related genes (Paxillin and Vinculin) and migration-related genes (RAC 1, Rho A and CDC 42). Accordingly, the re-endothelialization of Mg alloy stent was inhibited in vivo. Our results may provide new inspiration for improving the broad application of Mg alloy stents.

Degradation behaviors and in-vivo biocompatibility of a rare earth- and aluminum-free magnesium-based stent

Biodegradable stents can provide scaffolding and anti-restenosis benefits in the short term and then gradually disappear over time to free the vessel, among which the Mg-based biodegradable metal stents have been prosperously developed. In the present study, a Mg-8.5Li (wt.%) alloy (RE- and Al-free) with high ductility (> 40%) was processed into mini-tubes, and further fabricated into finished stent through laser cutting and electropolishing. In-vitro degradation test was performed to evaluate the durability of this stent before and after balloon dilation. The influence of plastic deformation and residual stress (derived from the dilation process) on the degradation was checked with the assistance of finite element analysis. In addition, in-vivo degradation behaviors and biocompatibility of the stent were evaluated by performing implantation in iliac artery of minipigs. The balloon dilation process did not lead to deteriorated degradation, and this stent exhibited a decent degradation rate (0.15 mm/y) in vitro, but divergent result (> 0.6 mm/y) was found in vivo. The stent was almost completely degraded in 3 months, revealing an insufficient scaffolding time. Meanwhile, it did not induce possible thrombus, and it was tolerable by surrounding tissues in pigs. Besides, endothelial coverage in 1 month was achieved even under the severe degradation condition. In the end, the feasibility of this stent for treatment of benign vascular stenosis was generally discussed, and perspectives on future improvement of Mg-Li-based stents were proposed.

Introduction of Enzyme-Responsivity in Biomaterials to Achieve Dynamic Reciprocity in Cell-Material Interactions

Much effort has been made in the development of biomaterials that synthetically mimic the dynamics of the natural extracellular matrix in tissues. Most of these biomaterials specifically interact with cells, but lack the ability to adapt and truly communicate with the cellular environment. Communication between biomaterials and cells is achieved by the development of various materials with enzyme-responsive moieties in order to respond to cellular cues. In this perspective, we discuss different enzyme-responsive systems, from surfaces to supramolecular assemblies. Additionally, we highlight their further prospects in order to create, inspired by nature, fully autonomous adaptive biomaterials that display dynamic reciprocal behavior. This Perspective shows new strategies for the development of biomaterials that may find broad utility in regenerative medicine applications, from scaffolds for tissue engineering to systems for controlled drug delivery.

In vivo degradation and endothelialization of an iron bioresorbable scaffold

Detection of in vivo biodegradation is critical for development of next-generation medical devices such as bioresorbable stents or scaffolds (BRSs). In particular, it is urgent to establish a nondestructive approach to examine in vivo degradation of a new-generation coronary stent for interventional treatment based on mammal experiments; otherwise it is not available to semi-quantitatively monitor biodegradation in any clinical trial. Herein, we put forward a semi-quantitative approach to measure degradation of a sirolimus-eluting iron bioresorbable scaffold (IBS) based on optical coherence tomography (OCT) images; this approach was confirmed to be consistent with the present weight-loss measurements, which is, however, a destructive approach. The IBS was fabricated by a metal-polymer composite technique with a polylactide coating on an iron stent. The efficacy as a coronary stent of this new bioresorbable scaffold was compared with that of a permanent metal stent with the name of trade mark Xience, which has been widely used in clinic. The endothelial coverage on IBS was found to be greater than on Xience after implantation in a rabbit model; and our well-designed ultrathin stent exhibited less individual variation. We further examined degradation of the IBSs in both minipig coronary artery and rabbit abdominal aorta models. The present result indicated much faster iron degradation of IBS in the rabbit model than in the porcine model. The semi-quantitative approach to detect biodegradation of IBS and the finding of the species difference might be stimulating for fundamental investigation of biodegradable implants and clinical translation of the next-generation coronary stents.

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A semi-quantitative OCT method was suggested to evaluate in vivo biodegradation of an iron based coronary stent IBS in a nondestructive manner.

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The in vivo biodegradation of IBS exhibited dependence on animal species.

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The endothelial coverage on the biodegradable stent IBS was better than on the commercialized nonbiodegradable stent Xience in rabbits.

The coronary resorbable magnesium scaffold Magmaris®: what we have learnt (so far…)

Bioresorbable scaffold (BRS) technology provides transient vessel support with drug-delivery capability without the long-term limitations of the permanent metallic drug-eluting stents (DES). Numerous scaffolds have been developed and investigated by device manufacturers, many of which, due to device deficiencies, have fallen by the wayside. This short review will focus on the resorbable magnesium scaffold Magmaris^® the only metallic bioresorbable scaffold currently available, providing an evaluation of the most up to date clinical data whilst also briefly highlighting learning points regarding the ideal patient and lesion choice and optimal implantation technique.