Safety and performance of the second-generation drug-eluting absorbable metal scaffold in patients with de-novo coronary artery lesions (BIOSOLVE-II): 6 month results of a prospective, multicentre, non-randomised, first-in-man trial

Bioresorbable Scaffolds in Coronary Intervention: Unmet Needs and Evolution

Bioresorbable scaffolds (BRS) represent a novel paradigm in the 40-year history of interventional cardiology. Restoration of cyclic pulsatility and physiologic vasomotion, adaptive vascular remodeling, plaque regression, and removal of the trigger for late adverse events are expected BRS benefits over current metallic drug-eluting stents. However, first-generation BRS devices have significant manufacturing limitations and rely on optimal implantation technique to avoid experiencing an excess of clinical events. There are currently at least 22 BRS devices in different stages of development, including many trials of device iterations with thinner (<150 µm) struts than first-generation BRS. This article reviews the outcomes of commercially available and potentially upcoming BRS, focusing on the most recent stages of clinical development and future directions for each scaffold type.

Coronary Bioresorbable Vascular Scaffold Use in the Treatment of Coronary Artery Disease

Bioresorbable vascular scaffolds (BVS) represent a promising novel approach for the treatment of coronary artery disease. BVS promise to address some of the well-known limitations of current drug-eluting stents, while providing a transient scaffolding of the vessel to prevent acute vessel closure/recoil. Drug elution by BVS prevents neointimal proliferation in a similar fashion to drug-eluting stents, and complete bioresorption is associated with late vessel lumen enlargement, plaque regression, and restoration of vasomotion. Based on the pathophysiological reasons and on the results derived from clinical studies, BVS are increasingly being used in clinical practice. The aim of this review is to provide an overview of the current evidence supporting the use of BVS in clinical practice. In particular, we will discuss the randomized controlled trials and registries evaluating the clinical outcome of these devices, with a special focus on their application in patients with acute coronary syndrome and in specific lesion subsets (bifurcations, chronic total occlusions, and in-stent restenosis).

Delivery of Antioxidant and Anti-inflammatory Agents for Tissue Engineered Vascular Grafts

The treatment of patients with severe coronary and peripheral artery disease represents a significant clinical need, especially for those patients that require a bypass graft and do not have viable veins for autologous grafting. Tissue engineering is being investigated to generate an alternative graft. While tissue engineering requires surgical intervention, the release of pharmacological agents is also an important part of many tissue engineering strategies. Delivery of these agents offers the potential to overcome the major concerns for graft patency and viability. These concerns are related to an extended inflammatory response and its impact on vascular cells such as endothelial cells. This review discusses the drugs that have been released from vascular tissue engineering scaffolds and some of the non-traditional ways that the drugs are presented to the cells. The impact of antioxidant compounds and gasotransmitters, such as nitric oxide and carbon monoxide, are discussed in detail. The application of tissue engineering and drug delivery principles to biodegradable stents is also briefly discussed. Overall, there are scaffold-based drug delivery techniques that have shown promise for vascular tissue engineering, but much of this work is in the early stages and there are still opportunities to incorporate additional drugs to modulate the inflammatory process.

Drug-eluting stents versus bare-metal stents for acute coronary syndrome

BACKGROUND

Approximately 3.7 million people died from acute coronary syndrome worldwide in 2012. Acute coronary syndrome, also known as myocardial infarction or unstable angina pectoris, is caused by a sudden blockage of the blood supplied to the heart muscle. Percutaneous coronary intervention is often used for acute coronary syndrome, but previous systematic reviews on the effects of drug-eluting stents compared with bare-metal stents have shown conflicting results with regard to myocardial infarction; have not fully taken account of the risk of random and systematic errors; and have not included all relevant randomised clinical trials.

OBJECTIVES

To assess the benefits and harms of drug-eluting stents versus bare-metal stents in people with acute coronary syndrome.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, LILACS, SCI-EXPANDED, and BIOSIS from their inception to January 2017. We also searched two clinical trials registers, the European Medicines Agency and the US Food and Drug Administration databases, and pharmaceutical company websites. In addition, we searched the reference lists of review articles and relevant trials.

SELECTION CRITERIA

Randomised clinical trials assessing the effects of drug-eluting stents versus bare-metal stents for acute coronary syndrome. We included trials irrespective of publication type, status, date, or language.

DATA COLLECTION AND ANALYSIS

We followed our published protocol and the methodological recommendations of Cochrane. Two review authors independently extracted data. We assessed the risks of systematic error by bias domains. We conducted Trial Sequential Analyses to control the risks of random errors. Our primary outcomes were all-cause mortality, major cardiovascular events, serious adverse events, and quality of life. Our secondary outcomes were angina, cardiovascular mortality, and myocardial infarction. Our primary assessment time point was at maximum follow-up. We assessed the quality of the evidence by the GRADE approach.

MAIN RESULTS

We included 25 trials randomising a total of 12,503 participants. All trials were at high risk of bias, and the quality of evidence according to GRADE was low to very low. We included 22 trials where the participants presented with ST-elevation myocardial infarction, 1 trial where participants presented with non-ST-elevation myocardial infarction, and 2 trials where participants presented with a mix of acute coronary syndromes.Meta-analyses at maximum follow-up showed no evidence of a difference when comparing drug-eluting stents with bare-metal stents on the risk of all-cause mortality or major cardiovascular events. The absolute risk of death was 6.97% in the drug-eluting stents group compared with 7.74% in the bare-metal stents group based on the risk ratio (RR) of 0.90 (95% confidence interval (CI) 0.78 to 1.03, 11,250 participants, 21 trials/22 comparisons, low-quality evidence). The absolute risk of a major cardiovascular event was 6.36% in the drug-eluting stents group compared with 6.63% in the bare-metal stents group based on the RR of 0.96 (95% CI 0.83 to 1.11, 10,939 participants, 19 trials/20 comparisons, very low-quality evidence). The results of Trial Sequential Analysis showed that we did not have sufficient information to confirm or reject our anticipated risk ratio reduction of 10% on either all-cause mortality or major cardiovascular events at maximum follow-up.Meta-analyses at maximum follow-up showed evidence of a benefit when comparing drug-eluting stents with bare-metal stents on the risk of a serious adverse event. The absolute risk of a serious adverse event was 18.04% in the drug-eluting stents group compared with 23.01% in the bare-metal stents group based on the RR of 0.80 (95% CI 0.74 to 0.86, 11,724 participants, 22 trials/23 comparisons, low-quality evidence), and Trial Sequential Analysis confirmed this result. When assessing each specific type of adverse event included in the serious adverse event outcome separately, the majority of the events were target vessel revascularisation. When target vessel revascularisation was analysed separately, meta-analysis showed evidence of a benefit of drug-eluting stents, and Trial Sequential Analysis confirmed this result.Meta-analyses at maximum follow-up showed no evidence of a difference when comparing drug-eluting stents with bare-metal stents on the risk of cardiovascular mortality (RR 0.91, 95% CI 0.76 to 1.09, 9248 participants, 14 trials/15 comparisons, very low-quality evidence) or myocardial infarction (RR 0.98, 95% CI 0.82 to 1.18, 10,217 participants, 18 trials/19 comparisons, very low-quality evidence). The results of the Trial Sequential Analysis showed that we had insufficient information to confirm or reject our anticipated risk ratio reduction of 10% on cardiovascular mortality and myocardial infarction.No trials reported results on quality of life or angina.

AUTHORS' CONCLUSIONS

The current evidence suggests that drug-eluting stents may lead to fewer serious adverse events compared with bare-metal stents without increasing the risk of all-cause mortality or major cardiovascular events. However, our Trial Sequential Analysis showed that there currently was not enough information to assess a risk ratio reduction of 10% for all-cause mortality, major cardiovascular events, cardiovascular mortality, or myocardial infarction, and there were no data on quality of life or angina. The evidence in this review was of low to very low quality, and the true result may depart substantially from the results presented in this review.More randomised clinical trials with low risk of bias and low risks of random errors are needed if the benefits and harms of drug-eluting stents for acute coronary syndrome are to be assessed properly. More data are needed on the outcomes all-cause mortality, major cardiovascular events, quality of life, and angina to reduce the risk of random error.

Coronary balloon angioplasty, stents, and scaffolds

Since the first coronary angioplasty on Sept 16, 1977, the field of percutaneous coronary intervention has evolved rapidly. Now marking its 40th anniversary, percutaneous coronary intervention has become one of the most common medical procedures worldwide. Much of this progress has been due to the iteration and improvement of angioplasty technologies. Balloon angioplasty was limited by unpredictable procedural outcomes due to vessel dissection and recoil, and a high rate of restenosis. The introduction of stents resulted in more stable early results and lower rates of restenosis, although early stent thrombosis and neointimal hyperplasia causing vessel renarrowing were key limitations. Drug-eluting stents delivering antiproliferative agents significantly lowered the rates of restenosis, permitting widespread use of percutaneous coronary intervention in more advanced and complex disease. Although fully bioresorbable scaffolds have the potential to further improve long-term outcomes, they have not yet achieved results equivalent to those of conventional metallic drug-eluting stents in the early years after implantation. Progress in catheter technology did not occur in isolation, and the success of percutaneous coronary intervention is also due to important advances in intracoronary imaging, and adjunct pharmacotherapy-each of which is reviewed in other papers in this Series.

Evolution of the degradation mechanism of pure zinc stent in the one-year study of rabbit abdominal aorta model

In the present study, pure zinc stents were implanted into the abdominal aorta of rabbits for 12 months. Multiscale analysis including micro-CT, scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and histological stainings was performed to reveal the fundamental degradation mechanism of the pure zinc stent and its biocompatibility. The pure zinc stent was able to maintain mechanical integrity for 6 months and degraded 41.75 ± 29.72% of stent volume after 12 months implantation. No severe inflammation, platelet aggregation, thrombosis formation or obvious intimal hyperplasia was observed at all time points after implantation. The degradation of the zinc stent played a beneficial role in the artery remodeling and healing process. The evolution of the degradation mechanism of pure zinc stents with time was revealed as follows: Before endothelialization, dynamic blood flow dominated the degradation of pure zinc stent, creating a uniform corrosion mode; After endothelialization, the degradation of pure zinc stent depended on the diffusion of water molecules, hydrophilic solutes and ions which led to localized corrosion. Zinc phosphate generated in blood flow transformed into zinc oxide and small amounts of calcium phosphate during the conversion of degradation microenvironment. The favorable physiological degradation behavior makes zinc a promising candidate for future stent applications.

Magmaris preliminary recommendation upon commercial launch: a consensus from the expert panel on 14 April 2016

Bioresorbable scaffolds represent an exciting milestone in the development of coronary stent technology with the potential to substantially improve the management of patients with coronary artery disease. In an attempt to provide first recommendations for the technology, experienced experts involved in the first-in-man studies met in Zurich on the 14 April 2016 in order to reach consensus on a responsible market introduction. This document will be updated regularly as new information from clinical trials becomes available and should be understood as a review of current data, opportunities, expectations, advice, and recommendations for future investigations.

Magmaris: a new generation metallic sirolimus-eluting fully bioresorbable scaffold: present status and future perspectives

Drug-eluting stents (DES) have reached a high safety and efficacy profile, becoming the best option for percutaneous coronary interventions (PCI) based revascularization. However, despite their optimal performance, a few concerns remain regarding their use, mainly due to permanent caging of the vessels and its consequences, first of all late stent thrombosis (ST). Bioresorbable scaffolds (BRS) aim to overcome these issues. The results achieved in randomized controlled trials (RCT) by the first generation of poly-L-lactic acid (PLLA) based scaffolds were promising at 1 year, but the first long term reports (albeit flawed by non-optimal implantation technique) have been disappointing, showing, for instance, an increased risk of ST and target vessel myocardial infarction (TV-MI). In such a scenario the advent of a newer generation magnesium (Mg) based BRS is welcome, mainly because of its innovative mechanical and chemical features coupled with well proven biocompatibility. Despite being in its infancy, this technology seems to promise a great potential. In our article, we review the Magmaris (Biotronik AG, Bülach, Switzerland) Mg BRS development from animal models to human use, underscore its best qualities and weaknesses, and provide hints of its possible future perspectives.

Mechanical behavior of polymer-based vs. metallic-based bioresorbable stents

Bioresorbable scaffolds (BRS) were developed to overcome the drawbacks of current metallic drug-eluting stents (DES), such as late in-stent restenosis and caging of the vessel permanently. The concept of the BRS is to provide transient support to the vessel during healing before being degraded and resorbed by the body, freeing the vessel and restoring vasomotion. The mechanical properties of the BRS are influenced by the choice of the material and processing methods. Due to insufficient radial strength of the bioresorbable material, BRS often required large strut profile as compared to conventional metallic DES. Having thick struts will in turn affect the deliverability of the device and may cause flow disturbance, thereby increasing the incidence of acute thrombotic events. Currently, the bioresorbable poly-l-lactic acid (PLLA) polymer and magnesium (Mg) alloys are being investigated as materials in BRS technologies. The bioresorption process, mechanical properties, in vitro observations and clinical outcomes of PLLA-based and Mg-based BRS will be examined in this review.

Long-term surveillance of zinc implant in murine artery: Surprisingly steady biocorrosion rate

Metallic zinc implanted into the abdominal aorta of rats out to 6months has been demonstrated to degrade while avoiding responses commonly associated with the restenosis of vascular implants. However, major questions remain regarding whether a zinc implant would ultimately passivate through the production of stable corrosion products or via a cell mediated fibrous encapsulation process that prevents the diffusion of critical reactants and products at the metal surface. Here, we have conducted clinically relevant long term in vivo studies in order to characterize late stage zinc implant biocorrosion behavior and products to address these critical questions. We found that zinc wires implanted in the murine artery exhibit steady corrosion without local toxicity for up to at least 20months post-implantation, despite a steady buildup of passivating corrosion products and intense fibrous encapsulation of the wire. Although fibrous encapsulation was not able to prevent continued implant corrosion, it may be related to the reduced chronic inflammation observed between 10 and 20months post-implantation. X-ray elemental and infrared spectroscopy analyses confirmed zinc oxide, zinc carbonate, and zinc phosphate as the main components of corrosion products surrounding the Zn implant. These products coincide with stable phases concluded from Pourbaix diagrams of a physiological solution and in vitro electrochemical impedance tests. The results support earlier predictions that zinc stents could become successfully bio-integrated into the arterial environment and safely degrade within a time frame of approximately 1-2years.

STAEMENT OF SIGNIFICANCE

Previous studies have shown zinc to be a promising candidate material for bioresorbable endovascular stenting applications. An outstanding question, however, is whether a zinc implant would ultimately passivate through the production of stable corrosion products or via a cell mediated tissue encapsulation process that prevented the diffusion of critical reactants and products at the metal surface. We found that zinc wires implanted in the murine artery exhibit steady corrosion for up to at least 20months post-implantation. The results confirm earlier predictions that zinc stents could safely degrade within a time frame of approximately 1-2years.

Safety and performance of the DRug-Eluting Absorbable Metal Scaffold (DREAMS) in patients with de novo coronary lesions: 3-year results of the prospective, multicentre, first-in-man BIOSOLVE-I trial

AIMS

Bioresorbable scaffolds were designed to overcome the limitations of permanent stents. In the BIOSOLVE-I study we aimed to assess the long-term safety and performance of a drug-eluting absorbable metal scaffold (DREAMS) at three years.

METHODS AND RESULTS

In this prospective, multicentre first-in-man study, 46 patients with 47 de novo lesions were enrolled. We report the final results at three-year follow-up. Mean age was 65.3±9.7 years, lesions were 2.73±0.48 mm in diameter and 10.99±4.59 mm long. Follow-up at three years was available for 44 patients (one patient died of a non-cardiac cause and one patient withdrew consent). Three target lesion failures (TLF) occurred (6.6%), consisting of two clinically driven target lesion revascularisations at scheduled six-month angiography (4.3%) and one myocardial infarction after drug-eluting balloon treatment in a non-target lesion but target vessel at 12-month angiography (2.2%). No cardiac death or scaffold thrombosis occurred. Seven patients had additional angiographic follow-up at 28±4 months: in-scaffold late lumen loss had improved from 0.51±0.46 mm (median 0.28 mm) at 12 months to 0.32±0.32 mm (median 0.20 mm).

CONCLUSIONS

The BIOSOLVE-I study showed excellent long-term outcomes at three years with a low TLF rate and no cardiac death or scaffold thrombosis. No TLF event was observed beyond 377 days.

Bioresorbable Scaffolds: Clinical Outcomes and Considerations

Bioresorbable scaffolds (BRS) have been engineered to eliminate the theoretic stimulus to late coronary events, a caveat of conventional metallic drug-eluting stents (DESs). Outcome benefits of BRSs over current-generation DESs are expected to accrue after complete bioresorption. Before this timeframe, BRSs need to prove at least similarly safe and effective compared with DESs. Several randomized studies of the Absorb BRS have been made available. Several manufacturers are at the beginning of their line of clinical development of competing BRSs. This article reviews the contemporary clinical outcomes of the Absorb scaffold, and provides an updated state of the art on the other players in the BRS arena.

In vitro and in vivo degradation of rapamycin-eluting Mg-Nd-Zn-Zr alloy stents in porcine coronary arteries

In this work, rapamycin-eluting poly (d, l-lactic acid) coating (PDLLA/RAPA) was prepared on biodegradable Mg-Nd-Zn-Zr alloy (JDBM) for both in vitro and in vivo investigation of the degradation behaviors of the magnesium alloy stent platform. Electrochemical tests and hydrogen evolution test demonstrated significant in vitro protection of the polymeric coating against magnesium degradation both in short and long term. The 3-month in vivo study on the RAPA-eluting JDBM stent implanted into porcine coronary arteries confirmed its favorable safety, and in the meanwhile revealed similar neointima proliferation compared to the second generation DES Firebird 2 with no occurrence of adverse complications. Moreover, Micro-CT examination combined with IVUS and OCT detection indicated a remarkably lower degradation rate and prolonged radial supporting duration of the drug-eluting JDBM stent as compared to the bare, attributable to the protection of the coating in vivo. Hence, rapamycin-eluting JDBM stents exhibit great potential for clinical application.

Neointimal Healing Evaluated by Optical Coherence Tomography after Drug-Eluting Absorbable Metal Scaffold Implantation in de novo Native Coronary Lesions: Rationale and Design of the Magmaris-OCT Study

Objectives: We sought to explore neointimal healing assessed by optical coherence tomography (OCT) following implantation of the Magmaris sirolimus-eluting absorbable metal scaffold. Methods: The Magmaris-OCT is a prospective, multicenter, single-arm observational clinical study, intended to enrol 60 consecutive patients with up to 2 de novo native coronary lesions, each located in different major epicardial vessels, with a reference vessel diameter of 2.5-3.5 mm, and a maximum lesion length of 20 mm. Patients will undergo Magmaris scaffold implantation in the target lesion, according to the standard practice. Clinical follow-up will take place at 30 days, and at 3, 6, 9, and 12 months. For invasive-imaging follow-up, patients will be classified into 3 groups: cohort A will be scheduled for follow-up at 3 months, cohort B at 6 months, and cohort C at 12 months. Invasive imaging will include quantitative coronary angiography, OCT evaluation, and coronary flow reserve measurement. The primary end point will be the percentage of uncovered scaffold struts assessed by OCT at the prespecified follow-up. Conclusions: This study will provide insight into the short- and mid-term healing properties following Magmaris scaffold implantation, with special emphasis on the neointimal coverage of scaffold struts.

Computational Modeling of the Mechanical Performance of a Magnesium Stent Undergoing Uniform and Pitting Corrosion in a Remodeling Artery

Coronary stents made from degradable biomaterials such as magnesium alloy are an emerging technology in the treatment of coronary artery disease. Biodegradable stents provide mechanical support to the artery during the initial scaffolding period after which the artery will have remodeled. The subsequent resorption of the stent biomaterial by the body has potential to reduce the risk associated with long-term placement of these devices, such as in-stent restenosis, late stent thrombosis, and fatigue fracture. Computational modeling such as finite-element analysis has proven to be an extremely useful tool in the continued design and development of these medical devices. What is lacking in computational modeling literature is the representation of the active response of the arterial tissue in the weeks and months following stent implantation, i.e., neointimal remodeling. The phenomenon of neointimal remodeling is particularly interesting and significant in the case of biodegradable stents, when both stent degradation and neointimal remodeling can occur simultaneously, presenting the possibility of a mechanical interaction and transfer of load between the degrading stent and the remodeling artery. In this paper, a computational modeling framework is developed that combines magnesium alloy degradation and neointimal remodeling, which is capable of simulating both uniform (best case) and localized pitting (realistic) stent corrosion in a remodeling artery. The framework is used to evaluate the effects of the neointima on the mechanics of the stent, when the stent is undergoing uniform or pitting corrosion, and to assess the effects of the neointimal formation rate relative to the overall stent degradation rate (for both uniform and pitting conditions).

Bioresorbable Scaffold: The Emerging Reality and Future Directions

In the era of drug-eluting stents, large-scale randomized trials and all-comer registries have shown excellent clinical results. However, even the latest-generation drug-eluting stent has not managed to address all the limitations of permanent metallic coronary stents, such as the risks of target lesion revascularization, neoatherosclerosis, preclusion of late lumen enlargement, and the lack of reactive vasomotion. Furthermore, the risk of very late stent, although substantially reduced with newer-generation drug-eluting stent, still remains. These problems were anticipated to be solved with the advent of fully biodegradable devices. Fully bioresorbable coronary scaffolds have been designed to function transiently to prevent acute recoil, but have retained the capability to inhibit neointimal proliferation by eluting immunosuppressive drugs. Nevertheless, long-term follow-up data of the leading bioresorbable scaffold (Absorb) are becoming available and have raised a concern about the relatively higher incidence of scaffold thrombosis. To reduce the rate of clinical events, improvements in the device, as well as implantation procedure, are being evaluated. This review will focus on the current CE-mark approved bioresorbable scaffolds, their basic characteristics, and clinical results. In addition, we summarize the current limitations of bioresorbable scaffold and their possible solutions.

Three-Year Clinical Outcome of Patients with Coronary Disease and Increased Event Risk Treated with Newer-Generation Drug-Eluting Stents: From the Randomized DUTCH PEERS Trial

OBJECTIVE

Limited data is available on the long-term outcome of patients with increased cardiovascular event risk, treated with newer-generation durable polymer drug-eluting stents (DES).

METHODS

We therefore assessed 3-year follow-up data of high-risk versus low- to intermediate-risk patients of the randomized DUTCH PEERS trial (NCT01331707). In both risk groups we also compared patients treated with Resolute Integrity versus Promus Element DES. Patients were categorized as "high-risk" if they met ≥1 of the following criteria: (1) diabetes (17.9%); (2) previous myocardial infarction (21.9%); (3) previous coronary revascularization (25.8%); (4) chronic renal failure (3.5%); (5) left ventricular ejection fraction ≤30% (1.5%); and (6) age ≥75 years (17.3%).

RESULTS

At the 3-year follow-up, the incidence of the composite endpoint target vessel failure (TVF) (13.2 vs. 7.5%; logrank p < 0.001) and 2 of its components - cardiac death (4.7 vs. 1.5%; logrank p < 0.001) and target vessel revascularization (7.3 vs. 4.7%; logrank p = 0.03) - was higher in high-risk (n = 957) versus low- to intermediate-risk patients (n = 854). Among high-risk patients, treatment with Resolute Integrity (n = 481) and Promus Element stents (n = 476) was similarly safe and efficacious (TVF: 13.3 vs. 13.1%; logrank p = 0.95; definite-or-probable stent thrombosis: 1.7 vs. 1.7%; logrank p = 1.00).

CONCLUSIONS

The newer-generation Resolute Integrity and Promus Element stents showed similar results in terms of safety and efficacy for treating high-risk patients, who had significantly higher event rates than patients with low-to-intermediate risk.

Expandable Mg-based Helical Stent Assessment using Static, Dynamic, and Porcine Ex Vivo Models

A bioresorbable metallic helical stent was explored as a new device opportunity (magnesium scaffold), which can be absorbed by the body without leaving a trace and simultaneously allowing restoration of vasoreactivity with the potential for vessel remodeling. In this study, developed Mg-based helical stent was inserted and expanded in vessels with subsequent degradation in various environments including static, dynamic, and porcine ex vivo models. By assessing stent degradation in three different environments, we observed: (1) stress- and flow-induced degradation; (2) a high degradation rate in the dynamic reactor; (3) production of intermediate products (MgO/Mg(OH)₂ and Ca/P) during degradation; and (4) intermediate micro-gas pocket formation in the neighboring tissue ex vivo model. Overall, the expandable Mg-based helical stent employed as a scaffold performed well, with expansion rate (>100%) in porcine ex vivo model.

Bioresorbable Polymers and Stent Devices

OPINION STATEMENT

Percutaneous coronary interventions will never become obsolete, as evolution is inherent to interventional cardiology. Current drug-eluting platforms have appreciably improved their safety and efficacy profiles in different clinical settings compared to first-generation devices such that it is difficult to consider other alternatives. However, there is definite biological plausibility to consider devices with bioabsorbable polymers and/or scaffolds. It is also an undeniable fact that many patients, based on variety of belief systems, would prefer not to have a permanently implanted device. BP DES with or without bioresorbable scaffolds offer advantages over durable polymer DES in restoring normal coronary physiology and vascular adaptive responses, resulting in late lumen gain and plaque regression. They will likely allow flexibility in treating complex CAD. However, so far, we have been able to prove non-inferiority in a selected population of patients without long-term data. Is "as good as" good enough? Are we ready to reach for the BRS or a BP DES in our catheterization laboratory based on preclinical and mechanistic data (endothelialization, OCT imaging, vasomotion) with limited human experience? I am not. While I will maximize my efforts to recruit patients in related randomized controlled trials, the technology is not ready for prime time. Randomized controlled trials are needed to determine whether any or all of these devices improve long-term outcome compared to best in class DP DES. Most definitive evidence is likely about a decade away. Until then, we can learn to be disciplined implanters not only in selecting the appropriate patient but also in perfecting implantation techniques.

Macrophage phagocytosis of biomedical Mg alloy degradation products prepared by electrochemical method

Biomedical Mg alloy is promising for its widespread use clinically. In vitro and in vivo studies showed that the degradation products of biomedical Mg alloy were composed of O, P, Ca, Mg and other alloying elements. However, little is known about the metabolism of the degradation products. In this study, the in vitro macrophage phagocytosis of the degradation products of a biomedical Mg-Nd-Zn-Zr alloy was directly observed. This result affirms the necessity to investigate the long-term fate of Mg alloy degradation products in physiological environments. Besides, an electrochemical method was proposed to prepare enough amount of degradation products in vitro efficiently.

In vivo response of AZ31 alloy as biliary stents: a 6 months evaluation in rabbits

Mg-based metallic materials have been making continuing progress as vascular stents. However, the research of Mg-based materials as non-vascular stents is still at its primary stage. AZ31 stents hereby were implanted into the common bile duct of rabbits for 6 months. The results revealed an existence of 93.82 ± 1.36% and 30.89 ± 2.46% of the original volume after 1 and 3 month, respectively. Whole blood tests indicated an inflammation decreasing to normal level after 3 month implantation. A benign host response was observed via H&E staining. Nonuniform corrosion at the two ends of the stents was observed and considered the results of flow or local inflammation. Moreover, the application of Mg-based materials for different stenting treatment were reviewed and compared. Esophagus was hypothesized most destructive, whilst blood vessel and bile duct considered similar and less destructive. Trachea and nasal cavity were thought to be mildest.

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Zusammenfassung. Die perkutane Ballonangioplastie revolutionierte die Behandlung der koronaren Herzkrankheit. Der Einsatz von Gefässstützen (Stents) setzte diese Revolution fort. Nach den reinen Metallstents (Bare metal stents, BMS) und den Medikamenten-beschichteten Stents (drug-eluting stents, DES) folgen nun bioresorbierbare Stents (bioresorbable vascular scaffolds, BVS). Im Gegensatz zu den ersten zwei Stent-Generationen werden die BVS nach einer bestimmten Zeit vollständig abgebaut und versprechen eine Antwort für bisher ungelöste Probleme von BMS und DES.

Bioresorbable Vascular Scaffolds for Coronary Revascularization

Contemporary metallic drug-eluting stents are associated with very good 1-year outcomes but an ongoing risk of stent-related adverse events (thrombosis, myocardial infarction, restenosis) after 1 year. The pathogenesis of these very late events is likely related to the permanent presence of the metal stent frame or polymer. Bioresorbable scaffolds have been developed to provide drug delivery and mechanical support functions similar to metallic drug-eluting stents, followed by complete resorption with recovery of more normal vascular structure and function, potentially improving very late clinical outcomes. A first-generation bioresorbable scaffold has been demonstrated to be noninferior to a contemporary metallic drug-eluting stents for overall 1-year patient-oriented and device-oriented outcomes. Increased rates of scaffold thrombosis and target vessel-related myocardial infarction were noted that may be mitigated by improved patient and lesion selection, procedural technique, and device iteration. Large-scale, randomized, clinical trials are ongoing to determine the long-term relative efficacy and safety of bioresorbable scaffolds compared with current metallic drug-eluting stents.

Reduced antibacterial property of metallic magnesium in vivo

Magnesium and its alloys have drawn interest as antibacterial biomaterials, owing to their ability to alkalize the surrounding medium during degradation. The antibacterial effect of pure Mg and Mg alloys in vitro has previously been reported. However, the antibacterial property of Mg in vivo might be different because of the apparently dissimilar corrosion characteristics. In this study, pure Mg rods were implanted and bacterial suspension were injected into rat femurs to investigate the antibacterial property of Mg in vivo. The results showed that contrary to the high antibacterial rate in vitro, Mg exhibited a dramatic drop in antibacterial effect in vivo. Bacteria proliferated on the surface of the Mg rods as well as in the femur. Inflammatory cells filled cavities in the cortical bone of the femur, which was demonstrated by histological and micro-CT examination after 2 and 4 weeks of implantation. It is suggested that a reduced corrosion rate in vivo would result in insufficient pH value. In addition, the deposition layer would prevent further corrosion of Mg and provide a favorite site for bacteria adhesion. Hence, the dramatically reduced antibacterial property of Mg needs to be noticed when it is used as a biomaterial.

Magnesium alloys: A stony pathway from intensive research to clinical reality. Different test methods and approval-related considerations

The first degradable implant made of a magnesium alloy, a compression screw, was launched to the clinical market in March 2013. Many different complex considerations are required for the marketing authorization of degradable implant materials. This review gives an overview of existing and proposed standards for implant testing for marketing approval. Furthermore, different common in vitro and in vivo testing methods are discussed. In some cases, animal tests are inevitable to investigate the biological safety of a novel medical material. The choice of an appropriate animal model is as important as subsequent histological examination. Furthermore, this review focuses on the results of various mechanical tests to investigate the stability of implants for temporary use. All the above aspects are examined in the context of development and testing of magnesium-based biomaterials and their progress them from bench to bedside. A brief history of the first market launch of a magnesium-based degradable implant is given. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 329-347, 2017.

Bioresorbable vascular scaffolds - basic concepts and clinical outcome

The introduction of percutaneous treatment of coronary artery stenosis with balloon angioplasty was the first revolution in interventional cardiology; the advent of metallic coronary stents (bare and drug-eluting) marked the second and third revolutions. However, the latest generation of drug-eluting stents is limited by several factors. Permanent vessel caging impairs arterial physiology, and the incidence of very late stent thrombosis - although lower with the second generation than with the first generation of drug-eluting stents - remains a major concern. This complication is mainly related to the presence of permanent metallic implants, chronic degeneration triggered by an inflammatory response to the coating polymer, and/or adverse effects of antiproliferative drugs on endothelial regeneration. In 2011, self-degrading coronary stents - the bioresorbable vascular scaffolds (BVS) - were introduced into clinical practice, showing good short-term results owing to their adequate strength. The advantage of these devices is the transient nature of vascular scaffolding, which avoids permanent vessel caging. In this Review, we summarize the latest research on BVS, with a particular emphasis on the implantation technique (which is different from that used with metallic stents) to outline the concept that BVS deployment methods have a major effect on procedural success and prognosis of patients with coronary artery stenosis. Furthermore, the clinical outcome of BVS in randomized clinical trials and in phase IV studies are discussed in different pathophysiological settings, such as stable or acute coronary disease. Finally, all the available data on the safety profile of BVS regarding scaffold thrombosis are discussed.

Bioresorbable vascular scaffolds-what does the future bring?

Bioresorbable vascular scaffolds (BVS) have emerged as an interesting alternative since the presence of the prosthesis in the coronary artery is transient. This technology enables to restore the normal vasomotor tone and allows positive remodeling, simultaneously reducing the trigger for persistent inflammation and facilitating further interventions by percutaneous or surgical means. Absorb BVS(®) is the first generation everolimus-eluting poly-L-lactide (PLLA) bioresorbable scaffold. In recent meta-analyses Absorb BVS(®) was definitely proved to be safe and effective device in the treatment of symptomatic coronary artery disease. This was recently confirmed by FDA advisory panel of experts who recommended approval of the device based on an analysis of its risks and rewards. Nevertheless, still there are some concerns regarding stent thrombosis, and the real vessel functionality restoration at long-term observation. Worth mentioning is the fact that apart from stable coronary disease Absorb BVS(®) is used successfully in a series of off-label clinical settings such as acute coronary syndromes including STEMI, in-stent restenosis, coronary bifurcations, left main stenting or chronic total occlusions. Moreover, new bioresorbable scaffolds are under development with DEsolve(®) and DREAM 2G(®), which are the most advanced.

Fatigue behaviors of HP-Mg, Mg-Ca and Mg-Zn-Ca biodegradable metals in air and simulated body fluid

The dynamic loading in human body, along with the corrosive body fluid, presents a great challenge for the practical use of biodegradable magnesium implants. In this study, a high purity magnesium (99.99wt.%) and two typical promising biodegradable magnesium alloys (binary Mg-1Ca and ternary Mg-2Zn-0.2Ca) were chosen as the experimental materials. Their dynamic mechanical performances were comparatively evaluated by carrying out fatigue tests in air and in simulated body fluid (SBF). The fatigue strengths of HP-Mg, Mg-1Ca and Mg-2Zn-0.2Ca were all around 90MPa in air, however, they decreased to 52MPa, 70MPa and 68MPa in SBF at 4×10(6)cycles, respectively. The fatigue cracks initiated from the microstructural defects when tested in air, but nucleated from surface corrosion pits when tested in SBF. Cyclic loading significantly increased the corrosion rates of all the experimental materials compared to that in static SBF. Moreover, based on our findings, the fatigue failure processes and interactions between material, corrosion and cyclic loading were systematically discussed.

STATEMENT OF SIGNIFICANCE

Fatigue strength and life are vital parameters to the design of metallic implant devices. For the corrosion fatigue of biomedical magnesium alloys, we reported the corrosion fatigue behavior of AZ91D and WE43 in SBF (Acta Biomaterialia, 6 (2010) 4605-4613), and till now there is no other reports to our knowledge. We spent 3years to finish the fatigue testing and get S-N curves for three more magnesium biomaterials, and our significant finding is that the fatigue strengths of HP-Mg, Mg-1Ca and Mg-2Zn-0.2Ca are all around 90MPa in air but 52MPa, 70MPa and 68MPa in SBF at 4×10(6)cycles, which will provide the first-hand data for the future magnesium implants design.

Treatment of the femoropopliteal artery with the bioresorbable REMEDY stent

OBJECTIVE

Bioresorbable stents are an emerging technology in the endovascular treatment of femoropopliteal lesions. They address the issue of leaving permanent stents in the treated arterial segment that are only temporarily needed to treat dissection or recoil. The REMEDY stent (Kyoto Medical Planning Co, Kyoto, Japan) was the first commercially available biodegradable scaffold for peripheral use. We evaluated its performance and safety in the treatment of short femoropopliteal stenosis or occlusion.

METHODS

A prospective, multicenter, observational registry was set up of patients in Rutherford-Becker categories 2 to 5 with femoropopliteal lesions that could be treated with one REMEDY stent. Clinical examination and duplex ultrasound imaging were performed at 1, 6, and 12 months. The primary end point was absence of clinically driven target lesion revascularization at 12 months. Secondary end points were technical and clinical success, primary and secondary patency rate, clinically driven target vessel revascularization, major complications, and Rutherford-Becker classification at 6 and 12 months.

RESULTS

The registry enrolled 99 patients between January 2011 and July 2013 in 12 centers in Belgium. Most lesions were determined as TransAtlantic Inter-Society Consensus for the Management of Peripheral Arterial Disease (TASC II) A (n = 80) and located in the superficial femoral artery (n = 91). There were 19 total occlusions (mean length, 41.3 mm) and 80 stenoses (mean length, 37.5 mm). Technical success was achieved in 96 patients, and clinical success was obtained in 95. Target lesion revascularization, which equalled target vessel revascularization, was 19% at 6 months and rose to 33% at 12 months. Primary patency was 68% at 6 months and 58% at 12 months. Secondary patency was 85% at 6 months and 86% at 12 months. After 12 months, two patients had undergone an amputation.

CONCLUSIONS

The 1-year follow-up results of the REMEDY stent do not meet current standards set by nitinol stents. Given the significant issues concerning bioresorbable stents in femoropopliteal arteries, their use outside clinical trials should be withheld until improvements are made and better data are available.

Antiproliferative Drugs for Restenosis Prevention

Cardiovascular disease is a leading cause of death and disability worldwide. Current treatment strategies aimed at treating the symptoms and consequences of obstructive vascular disease have embraced both optimal medical therapy and catheter-based percutaneous coronary intervention with drug-eluting stents. Drug-eluting stents elute antiproliferative drugs inhibiting vascular smooth muscle cell proliferation, which occurs in response to injury and thus prevents restenosis. However, all drugs currently approved for use in drug-eluting stents do not discriminate between proliferating vascular smooth muscle cells and endothelial cells, thus delaying re-endothelialization and subsequent vascular healing.