Initial evidence for the return of coronary vasoreactivity following the absorption of bioabsorbable magnesium alloy coronary stents

Challenges and Pitfalls of Research Designs Involving Magnesium-Based Biomaterials: An Overview

Magnesium-based biomaterials hold remarkable promise for various clinical applications, offering advantages such as reduced stress-shielding and enhanced bone strengthening and vascular remodeling compared to traditional materials. However, ensuring the quality of preclinical research is crucial for the development of these implants. To achieve implant success, an understanding of the cellular responses post-implantation, proper model selection, and good study design are crucial. There are several challenges to reaching a safe and effective translation of laboratory findings into clinical practice. The utilization of Mg-based biomedical devices eliminates the need for biomaterial removal surgery post-healing and mitigates adverse effects associated with permanent biomaterial implantation. However, the high corrosion rate of Mg-based implants poses challenges such as unexpected degradation, structural failure, hydrogen evolution, alkalization, and cytotoxicity. The biocompatibility and degradability of materials based on magnesium have been studied by many researchers in vitro; however, evaluations addressing the impact of the material in vivo still need to be improved. Several animal models, including rats, rabbits, dogs, and pigs, have been explored to assess the potential of magnesium-based materials. Moreover, strategies such as alloying and coating have been identified to enhance the degradation rate of magnesium-based materials in vivo to transform these challenges into opportunities. This review aims to explore the utilization of Mg implants across various biomedical applications within cellular (in vitro) and animal (in vivo) models.

Adaptation of Vascular Smooth Muscle Cell to Degradable Metal Stent Implantation

Iron-, magnesium-, or zinc-based metal vessel stents support vessel expansion at the period early after implantation and degrade away after vascular reconstruction, eliminating the side effects due to the long stay of stent implants in the body and the risks of restenosis and neoatherosclerosis. However, emerging evidence has indicated that their degradation alters the vascular microenvironment and induces adaptive responses of surrounding vessel cells, especially vascular smooth muscle cells (VSMCs). VSMCs are highly flexible cells that actively alter their phenotype in response to the stenting, similarly to what they do during all stages of atherosclerosis pathology, which significantly influences stent performance. This Review discusses how biodegradable metal stents modify vascular conditions and how VSMCs respond to various chemical, biological, and physical signals attributable to stent implantation. The focus is placed on the phenotypic adaptation of VSMCs and the clinical complications, which highlight the importance of VSMC transformation in future stent design.

Advances in coatings on magnesium alloys for cardiovascular stents - A review

Magnesium (Mg) and its alloys, as potential biodegradable materials, have drawn wide attention in the cardiovascular stent field because of their appropriate mechanical properties and biocompatibility. Nevertheless, the occurrence of thrombosis, inflammation, and restenosis of implanted Mg alloy stents caused by their poor corrosion resistance and insufficient endothelialization restrains their anticipated clinical applications. Numerous surface treatment tactics have mainly striven to modify the Mg alloy for inhibiting its degradation rate and enduing it with biological functionality. This review focuses on highlighting and summarizing the latest research progress in functionalized coatings on Mg alloys for cardiovascular stents over the last decade, regarding preparation strategies for metal oxide, metal hydroxide, inorganic nonmetallic, polymer, and their composite coatings; and the performance of these strategies in regulating degradation behavior and biofunction. Potential research direction is also concisely discussed to help guide biological functionalized strategies and inspire further innovations. It is hoped that this review can give assistance to the surface modification of cardiovascular Mg-based stents and promote future advancements in this emerging research field.

Recent advances and directions in the development of bioresorbable metallic cardiovascular stents: Insights from recent human and in vivo studies

Over the past two decades, significant advancements have been made regarding the material formulation, iterative design, and clinical translation of metallic bioresorbable stents. Currently, magnesium-based (Mg) stent devices have remained at the forefront of bioresorbable stent material development and use. Despite substantial advances, the process of developing novel absorbable stents and their clinical translation is time-consuming, expensive, and challenging. These challenges, coupled with the continuous refinement of alternative bioresorbable metallic bulk materials such as iron (Fe) and zinc (Zn), have intensified the search for an ideal absorbable metallic stent material. Here, we discuss the most recent pre-clinical and clinical evidence for the efficacy of bioresorbable metallic stents and material candidates. From this perspective, strategies to improve the clinical performance of bioresorbable metallic stents are considered and critically discussed, spanning material alloy development, surface manipulations, material processing techniques, and preclinical/biological testing considerations. STATEMENT OF SIGNIFICANCE: Recent efforts in using Mg, Fe, and Zn based materials for bioresorbable stents include elemental profile changes as well as surface modifications to improve each of the three classes of materials.  Although a variety of alloys for absorbable metallic stents have been developed, the ideal absorbable stent material has not yet been discovered. This review focuses on the state of the art for bioresorbable metallic stent development. It covers the three bulk materials used for degradable stents (Mg, Fe, and Zn), and discusses their advances from a translational perspective. Strategies to improve the clinical performance of bioresorbable metallic stents are considered and critically discussed, spanning material alloy development, surface manipulations, material processing techniques, and preclinical/biological testing considerations.

Layered hydroxide/polydopamine/hyaluronic acid functionalized magnesium alloys for enhanced anticorrosion, biocompatibility and antithrombogenicity in vascular stents

Magnesium alloys are promising cardiovascular stent materials due to the favourable physical properties and complete biodegradability in vivo. However, the rapid degradation, poor cytocompatibility and tendency of thrombogenesis hinder practical clinical applications. In order to solve these problems, a facile and highly efficient strategy of alkali treatment combined with subsequent layer-by-layer assembly was used to fabricate a multifunctional coating. A bottom layer hydroxyl (–OH) with negative charge after alkali treatment first formed a solid bond with magnesium matrix to provide a rough outer surface for the further immobilization of functional biomolecules. Afterwards, polydopamine and hyaluronic acid were successively immobilized on alkali-treated magnesium surface via strong electrostatic adsorption and covalent bonding between carboxyl group of hyaluronic acid and amine or hydroxyl of polydopamine to form magnesium/OH/polydopamine/hyaluronic acid. Hydroxyl significantly improves the corrosion resistance while polydopamine and hyaluronic acid layers act as a further barrier to provide better anticorrosion. A balance between biocompatibility and antithrombogenicity has been achieved by adjusting the content of hyaluronic acid on polydopamine surface. The multifunctional magnesium/OH/polydopamine/hyaluronic acid coating with lower hyaluronic acid concentrations expose more active sites of polydopamine molecules to promote endothelial cell proliferation while retaining the intrinsic antithrombogenic function of hyaluronic acid to offer a potential application for vascular stents.

Bioresorbable Vascular Scaffolds-Dead End or Still a Rough Diamond?

Percutaneous coronary interventions with stent-based restorations of vessel patency have become the gold standard in the treatment of acute coronary states. Bioresorbable vascular scaffolds (BVS) have been designed to combine the efficiency of drug-eluting stents (DES) at the time of implantation and the advantages of a lack of foreign body afterwards. Complete resolution of the scaffold was intended to enable the restoration of vasomotor function and reduce the risk of device thrombosis. While early reports demonstrated superiority of BVS over DES, larger-scale application and longer observation exposed major concerns about their use, including lower radial strength and higher risk of thrombosis resulting in higher rate of major adverse cardiac events. Further focus on procedural details and research on the second generation of BVS with novel properties did not allow to unequivocally challenge position of DES. Nevertheless, BVS still have a chance to present superiority in distinctive indications. This review presents an outlook on the available first and second generation BVS and a summary of results of clinical trials on their use. It discusses explanations for unfavorable outcomes, proposed enhancement techniques and a potential niche for the use of BVS.

Analysis of Vascular Mechanical Characteristics after Coronary Degradable Stent Implantation

PURPOSE

To explore the effect of vascular stress changes on endothelial function recovery and vascular restenosis inhibition, under the condition of dynamic degradation process of the degradable stent.

METHODS

Fitting the material parameters of the hyperelastic vascular constitutive relationship, the stress distribution of the intima of the blood vessel before the stent was implanted and during the dynamic degradation was calculated by numerical simulation. In vitro culture experiments were carried out, and the stretch ratios of the silicone chamber were set to 0%, 5%, 10%, and 15%, respectively, to simulate the effects of different degradation stages on the growth state of endothelial cells.

RESULTS

After the stent was completely degraded, the circumferential intimal stress (strain) of the vessel was recovered to 0.137 MPa, 5.5%, which was close to the physiological parameters (0.122 MPa, 4.8%) before stent implantation. In vitro experiments showed that the endothelial cell survival rate was the highest under the condition of circumferential stress (strain) of 0.1 MPa, 5%, and all adhesion growth could be achieved.

CONCLUSIONS

With the occurrence of degradation process of the stent, the circumferential stress (strain) of the intima was recovered to a range close to physiological parameters, which promotes the growth of endothelial cells. The recovery of intimal function can effectively inhibit the process of vascular restenosis. The results can provide a theoretical basis and experimental platform for the study of coronary intervention for the treatment of vascular restenosis.

Biodegradable Magnesium Alloy Stents as a Treatment for Vein Graft Restenosis

PURPOSE

To explore the effects of biodegradable magnesium alloy stents (BMAS) on remodeling of vein graft (VG) anastomotic restenosis.

MATERIALS AND METHODS

To establish a VG restenosis model, seventy two New Zealand rabbits were randomly divided into three groups according to whether a stent was implanted in the graft vein or not. BMASs and 316L stainless steel stents were implanted in BMAS and 316L groups, respectively, while no stent was implanted in the no-treatment control group (NC group). Loss of lumen diameter in the graft vein was measured in all three groups. Upon harvesting VG segments to evaluate intimal proliferation and re-endothelization, the degradation and biological safety of the stents were observed to explore the effects of BMAS on VG remodeling.

RESULTS

Model establishment and stent implantation were successful. The BMAS reduced lumen loss, compared with the control group (0.05±0.34 mm vs. 0.90±0.39 mm, p=0.001), in the early stage. The neointimal area was smaller in the BMAS group than the 316L group after 4 months (4.96±0.66 mm² vs. 6.80±0.69 mm², p=0.017). Re-endothelialization in the BMAS group was better than that in the 316L group (p=0.001). Within 4 months, the BMAS had degraded, and the magnesium was converted to phosphorus and calcium. The support force of the BMAS began to reduce at 2-3 months after implantation, without significant toxic effects.

CONCLUSION

BMAS promotes positive remodeling of VG anastomosis and has advantages over the conventional 316L stents in the treatment of venous diseases.

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.

Current Status and Future Potential of Transcatheter Interventions in Congenital Heart Disease

Percutaneous therapies for congenital heart disease have evolved rapidly in the past 3 decades. This has occurred despite limited investment from industry and support from regulatory bodies resulting in a lack of specific device development. Indeed, many devices remain off-label with a best-fit approach often required, spurning an innovative culture within the subspecialty, which had arguably laid the foundation for many of the current and evolving structural heart interventions. Challenges remain, not least encouraging device design focused on smaller infants and the inevitable consequences of somatic growth. Data collection tools are emerging but remain behind adult cardiology and cardiac surgery and leading to partial blindness as to the longer-term consequences of our interventions. Tail coating on the back of developments in other fields of adult intervention will soon fail to meet the expanding needs for more precise interventions and biological materials. Increasing collaboration with surgical colleagues will require development of dedicated equipment for hybrid interventions aimed at minimizing the longer-term consequences of scar to the heart. Therefore, great challenges remain to ensure that children and adults with congenital heart disease continue to benefit from an exponential growth in minimally invasive interventions and technology. This can only be achieved through a concerted collaborative approach from physicians, industry, academia, and regulatory bodies supporting great innovators to continue the philosophy of thinking beyond the limits that has been the foundation of our specialty for the past 50 years.

Intermediate analysis of magnesium alloy covered stent for a lateral aneurysm model in the rabbit common carotid artery

OBJECTIVE

To analyze the outcomes of a magnesium alloy covered stent (MACS) for a lateral aneurysm model in common carotid artery (CCA).

METHODS

In 32 rabbits, a MACS (group A, n = 17) or a Willis covered stent (WCS; group B, n = 15) was inserted and the rabbits were sacrificed 1, 3, 6, or 12 months after stenting. Angiography and intravascular ultrasound (IVUS) were performed at 3, 6, and 12 months. Scanning electron microscopy was performed for six stents in each group at 1, 3, and 6 months, and histopathology and histomorphology were conducted at 3 (n = 4), 6 (n = 4), and 12 (n = 12) months.

RESULTS

Final angiography showed complete occlusion of the aneurysms in 12 cases. IVUS at 6 and 12 months revealed a significant increase in mean lumen area of the stented CCA in group A and also showed greater mean lumen area in group A than in group B. The endothelialization process was quicker in group A than in group B.

CONCLUSION

MACS is effective for occlusion of lateral aneurysms and is superior to WCS in growth of the stented CCA and endothelialization. Further work is needed to make this device available for human use.

KEY POINTS

• The MACS is an effective approach for occlusion of a lateral aneurysm. • IVUS showed that the CCA could grow following degradation of the MACS. • The lumen area of the stented CCA was excellent in MACS. • HE staining displayed the degradation of the magnesium alloy stent. • Combination of IVUS and DSA were applied in this study.

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.

Bioresorbable Scaffolds: Current Evidences in the Treatment of Coronary Artery Disease

Percutaneous coronary revascularization strategies have gradually progressed over a period of last few decades. The advent of newer generation drug-eluting stents has significantly improved the outcomes of Percutaneous Coronary Intervention (PCI) by substantially reducing in-stent restenosis and stent thrombosis. However, vascular inflammation, restenosis, thrombosis, and neoatherosclerosis due to the permanent presence of a metallic foreign body within the artery limit their usage in complex Coronary Artery Disease (CAD). Bioresorbable Scaffolds (BRS) represent a novel approach in coronary stent technology. Complete resorption of the scaffold liberates the treated vessel from its cage and restores pulsatility, cyclical strain, physiological shear stress, and mechanotransduction. In this review article, we describe the advances in this rapidly evolving technology, present the evidence from the pre-clinical and clinical evaluation of these devices, and provide an overview of the ongoing clinical trials that were designed to examine the effectiveness of BRS in the clinical setting.

Bioresorbable scaffolds: a new paradigm in percutaneous coronary intervention

Numerous advances and innovative therapies have been introduced in interventional cardiology over the recent years, since the first introduction of balloon angioplasty, but bioresorbable scaffold is certainly one of the most exciting and attracting one. Despite the fact that the metallic drug-eluting stents have significantly diminished the re-stenosis ratio, they have considerable limitations including the hypersensitivity reaction to the polymer that can cause local inflammation, the risk of neo-atherosclerotic lesion formation which can lead to late stent failure as well as the fact that they may preclude surgical revascularization and distort vessel physiology. Bioresorbable scaffolds overcome these limitations as they have the ability to dissolve after providing temporary scaffolding which safeguards vessel patency. In this article we review the recent developments in the field and provide an overview of the devices and the evidence that support their efficacy in the treatment of CAD. Currently 3 devices are CE marked and in clinical use. Additional 24 companies are developing these kind of coronary devices. Most frequently used material is PLLA followed by magnesium.

Biphasic responses of human vascular smooth muscle cells to magnesium ion

Magnesium-based alloys are promising in biodegradable cardiovascular stent applications. The degradation products of magnesium stents may have significant impacts on the surrounding vascular cells. However, knowledge on the interactions between magnesium ion and vascular cells at the molecular and cellular levels is still largely missing. Vascular smooth muscle cell (SMC) plays an important role in the pathogenesis of restenosis and wound healing after stent implantation. This study evaluated the short-term effects of extracellular magnesium ion (Mg(2+)) on the cellular behaviors of SMCs. Cellular responses to Mg(2+) were biphasic and in a concentration-dependent manner. Low concentrations (10 mM) of Mg(2+) increased cell viability, cell proliferation rate, cell adhesion, cell spreading, cell migration rate, and actin expression. In contrast, higher concentrations (40-60 mM) of Mg(2+) had deleterious effects on cells. Gene expression analysis revealed that Mg(2+) altered the expressions of genes mostly related to cell adhesion, cell injury, angiogenesis, inflammation, coagulation, and cell growth. Finding from this study provides some valuable information on SMC responses toward magnesium ions at the cellular and molecular levels, and guidance for future controlled release of magnesium from the stent material.

Current and future perspectives on drug-eluting bioresorbable coronary scaffolds

Despite improvements in stent platform, polymer and drug elution, the permanent metallic stents have significant limitations as they distort vessel physiology, predispose to late thrombosis and may preclude surgical revascularization. Bioresorbable scaffold (BRS) technology has evolved over the last few years to overcome these drawbacks. Actually, different BRS are either available or under clinical and preclinical investigation. However, the use of BRS has largely been restricted to patients recruited into clinical trials with a relatively small number of 'real world' patients treated with these devices. Here, we highlight the potentialities of these devices, describe the evidence from the recent clinical trials and discuss the potential advantages, as well as challenges, that this novel technology may face in routine clinical practice.

The effects of novel, bioresorbable scaffolds on coronary vascular pathophysiology

Percutaneous coronary intervention (PCI) has rapidly evolved over the past 30 years as technology has sought to improve clinical outcomes by addressing pathophysiologic complications arising from the intervention. Stents were designed to resolve the drawbacks of balloon angioplasty by providing radial support to prevent vessel recoil, by sealing coronary dissections, and by preventing abrupt vessel closure. The conceptualization of an ideal drug-eluting fully bioresorbable scaffold (BRS), whether metallic or polymeric, would theoretically address the adverse aspects of permanent metallic stents. In this review of the literature, we will discuss the impact these novel fully BRS platforms have on vascular pathophysiology following PCI.

Bioresorbable metal scaffold for cardiovascular application: current knowledge and future perspectives

Over the last decade, the introduction of drug-eluting stents has dramatically reduced restenosis and the need for repeat revascularization after implantation of metallic stents. Numerous concerns still remain, however, because of their permanent nature. Thus, the concept of bioresorbable temporary scaffolds composed of biocompatible materials has emerged as a potential alternative to permanent metal stents. Here we focus on metal alloys & discuss preclinical and clinical experiences with bioresorbable metal scaffolds.

Bioresorbable scaffolds: rationale, current status, challenges, and future

Current generation of drug-eluting stents has significantly improved the outcomes of percutaneous coronary intervention by substantially reducing in-stent restenosis and stent thrombosis. However, a potential limitation of these stents is the permanent presence of a metallic foreign body within the artery, which may cause vascular inflammation, restenosis, thrombosis, and neoatherosclerosis. The permanent stents also indefinitely impair the physiological vasomotor function of the vessel and future potential of grafting the stented segment. Bioresorbable scaffolds (BRSs) have the potential to overcome these limitations as they provide temporary scaffolding and then disappear, liberating the treated vessel from its cage and restoring pulsatility, cyclical strain, physiological shear stress, and mechanotransduction. While a number of BRSs are under development, two devices with substantial clinical data have already received a Conformité Européenne marking. This review article presents the current status of these devices and evaluates the challenges that need to be overcome before BRSs can become the workhorse device in coronary intervention.

Bioresorbable drug-eluting magnesium-alloy scaffold: design and feasibility in a porcine coronary model

AIMS

Among three versions of bioresorbable magnesium scaffolds featuring different paclitaxel-elution kinetics, we determined the best-performing scaffold and compared it with established, paclitaxel-eluting, permanent stents TAXUS Liberté and eucaTAX.

METHODS AND RESULTS

Drug-elution kinetics in magnesium scaffolds were modulated by varying the composition of their bioresorbable poly(lactide-co-glycolide) coating loaded with paclitaxel. A 50:50 ratio of lactide to glycolide, or an 85:15 ratio and either high- or low-molecular-weight polymer was applied in the "50/50", "85/15H", and "85/15L" scaffolds, respectively. Seventy-three magnesium scaffolds (25 50/50, 24 85/15H, 24 85/15L) and 36 control stents (18 TAXUS Liberté, 18 eucaTAX) were implanted in coronary arteries of 50 Yucatan mini-pigs. Angiography, histomorphometry, and histopathology data were acquired at 28, 90 and 180 days. The best-performing magnesium scaffold, 85/15H, was equivalent to TAXUS Liberté and superior to eucaTAX regarding late luminal loss, intimal area, fibrin score, and endothelialisation. Intimal inflammation score was higher in 85/15H than in the control stents at 28 days, but this effect disappeared at later time points.

CONCLUSIONS

By selecting suitable paclitaxel-elution kinetics, it was feasible to develop a bioresorbable magnesium scaffold whose efficacy and healing characteristics in a porcine coronary model are comparable with those of established paclitaxel-eluting permanent metallic stents.

Progress in treatment by percutaneous coronary intervention: the stent of the future

First generation drug-eluting stents have considerably reduced in-stent restenosis and broadened the applications of percutaneous coronary interventions for the treatment of coronary artery disease. The polymer is an integral part of drug-eluting stents in that, it controls the release of an antiproliferative drug. The main safety concern of first generation drug-eluting stents with permanent polymers--stent thrombosis--has been caused by local hypersensitivity, delayed vessel healing, and endothelial dysfunction. This has prompted the development of newer generation drug-eluting stents with biodegradable polymers or even polymer-free drug-eluting stents. Recent clinical trials have shown the safety and efficacy of drug-eluting stents with biodegradable polymer, with proven reductions in very late stent thrombosis as compared to first generation drug-eluting stents. However, the concept of using a permanent metallic prosthesis implies major drawbacks, such as the presence of a foreign material within the native coronary artery that causes vascular inflammation and neoatherosclerosis, and also impedes the restoration of the vasomotor function of the stented segment. Bioresorbable scaffolds have been introduced to overcome these limitations, since they provide temporary scaffolding and then disappear, liberating the treated vessel from its cage. This update article presents the current status of these new technologies and highlights their future perspectives in interventional cardiology.

Biodegradable vascular scaffold ABSORB BVS™ - scientific evidence and methods of implantation

Since 2006, over 600 biodegradable vascular scaffolds (BVS) have been implanted worldwide in clinical trials such as ABSORB cohort A and B, ABSORB Extend and ABSORB II RCT. Due to completely changed construction and mechanical properties of BVS, the choice of proper scaffold diameter and its implantation differ significantly from those used in the case of metal stents (bare metal stent (BMS) or drug eluting stent (DES)). Furthermore, all data concerning BVS efficacy and safety come from clinical trials, conducted in a selected group of patients. In 2012 BVS ABSORB™ was approved as the first biodegradable scaffold for the treatment of coronary artery disease in EU and other countries, with a limitation of use only for experienced and trained interventional cardiologists. As one of the most experienced clinical centers in Europe and the first one that in 2006 implanted BVS ABSORB™ in Poland we have a great pleasure and honor to share our experience with interventional cardiologists who would like to prepare for BVS ABSORB™ implantation in their centers. In this article we wanted to summarize the clinical data from already finished and ongoing trials, give a short overview of patient selection, and provide a detailed description of the implantation process with tips which could be helpful during BVS use.

Bioresorbable scaffolds in the treatment of coronary artery disease

Drug-eluting stents have reduced the risk of in-stent restenosis and have broadened the application in percutaneous coronary intervention in coronary artery disease. However, the concept of using a permanent metallic endovascular device to restore the patency of a stenotic artery has inherited pitfalls, namely the presence of a foreign body within the artery causing vascular inflammation, late complications such as restenosis and stent thrombosis, and impeding the restoration of the physiologic function of the stented segment. Bioresorbable scaffolds (BRS) were introduced to potentially overcome these limitations, as they provide temporary scaffolding and then disappear, liberating the treated vessel from its cage. Currently, several BRSs are available, undergoing evaluation either in clinical trials or in preclinical settings. The aim of this review is to present the new developments in BRS technology, describe the mechanisms involved in the resorption process, and discuss the potential future prospects of this innovative therapy.

Bioresorbable scaffolds: current evidence and ongoing clinical trials

Bioresorbable scaffolds (BRS) represent a novel approach in coronary stent technology. In contrast to the metallic stents, they provide transient scaffolding, thereby safeguarding early vessel patency and acute gain. Subsequently a process of “decomposition” occurs, that results in the complete absorption of the scaffold. This reduces the risk of late complications, allowing the vessel to maintain its integrity and physiological function. This unique ability has attracted interest and nowadays several BRS are available. The aim of this review article is to describe the advances in the field, present the evidence from the preclinical and clinical evaluation of these devices, and provide an overview of the ongoing clinical trials that were designed to examine the effectiveness of BRS in the clinical setting.

Everolimus-eluting ABSORB bioresorbable vascular scaffold: present and future perspectives

Everolimus-eluting ABSORB bioresorbable vascular scaffolds represent a novel approach that provides transient vessel support with drug-delivery capability without the long-term limitations of the metallic drug-eluting stents (DESs). The technology has the potential to overcome many of the safety concerns associated with metallic DESs and possibly even convey further clinical benefit. In particular the scaffold is designed for providing a short-term lumen support (up to 6-12 months) and for thereafter being completely bioresorbed, eliminating the permanent caging typical of the metallic DES. The first clinical studies testing this device in a small number of patients have shown very promising results with good clinical outcome up to 5 years' follow-up, highlighting important morphological and functional modifications at the scaffolded segment level, such as late lumen enlargement and recuperation of a normal vasoreactivity. A randomized trial, comparing ABSORB with the Xience Prime stent, will evaluate the efficacy and safety of this device in a wide population.

Absorbable stent: focus on clinical applications and benefits

Coronary stents have improved very significantly the immediate and long-term results of percutaneous coronary interventions. However, once the vessel has healed, the scaffolding function of the stent is no longer needed, and the presence of a permanent metallic prosthesis poses important disadvantages. This has led to the idea of creating new devices that are able to provide mechanical support for a determined period and then disappear from the vessel, allowing its natural healing and avoiding the risks associated with having a permanent metallic cage, such as stent thrombosis. Absorbable stents currently appear as one of the most promising fields in interventional cardiology. The present article will review the available clinical evidence regarding these devices at present and their future perspectives.

Evaluation of the second generation of a bioresorbable everolimus-eluting vascular scaffold for the treatment of de novo coronary artery stenosis: 12-month clinical and imaging outcomes

OBJECTIVES

The aim of this study was to demonstrate that the prevention of early scaffold area shrinkage of the ABSORB BVS (Rev.1.1, Abbott Vascular, Santa Clara, California) was sustained and not simply delayed by a few months.

BACKGROUND

With improved scaffold design and modified manufacturing process of its polymer, the second iteration of ABSORB (BVS 1.1) has improved performance to prevent a scaffold area reduction at 6 months.

METHODS

Fifty-six patients were enrolled and received 57 ABSORB scaffolds. Quantitative coronary angiography, intravascular ultrasound (IVUS), analysis of radiofrequency backscattering, echogenicity and optical coherence tomography (OCT) were performed at baseline and at 12-month follow-up.

RESULTS

Overall the scaffold area remained unchanged with IVUS as well as with OCT, whereas the radiofrequency backscattering and the echogenicity of the struts decreased by 16.8% (p < 0.001) and 20% (p < 0.001), respectively; more specifically, the strut core area on OCT decreased by 11.4% (p = 0.003). Despite the absence of scaffold area loss, pharmacological vasomotion was restored. On an intention-to-treat basis, the angiographic late lumen loss amounted to 0.27 ± 0.32 mm with an IVUS relative decrease in minimal lumen area of 1.94% (p = 0.12), without significant changes in mean lumen area. The OCT at follow-up showed that 96.69% of the struts were covered and that malapposition, initially observed in 18 scaffolds was only detected at follow-up in 4 scaffolds. Two patients experienced peri-procedural and iatrogenic myocardial infarction, respectively, whereas 2 underwent repeat intervention, resulting in the major adverse cardiac event rate of 7.1% (4 of 56).

CONCLUSIONS

The 12-month performance of the second-generation ABSORB bioresorbable everolimus-eluting scaffold justifies the conduct of a randomized trial against current best standards. (A Clinical Evaluation of the Bioabsorbable Everolimus Eluting Coronary Stent System [BVS EECSS] in the Treatment of Patients With de Novo Native Coronary Artery Lesions; NCT00856856).

Mechanical properties and in vivo performance of a novel sliding-lock bioabsorbable poly-p-dioxanone stent

A bioabsorbable poly-p-dioxanone (PPDO) stent with a novel sliding-lock structure was fabricated to treat stenotic peripheral vessels. The sliding-lock PPDO stents have greater radial strength (107 kPa) than PPDO stents with conventional net-tube structure (32 kPa). The sliding-lock PPDO stents were implanted into the iliac arteries of pigs, and implantation success rate was 90% indicating the feasibility of this design. Additionally, we found that sliding-lock PPDO stents kept vessels patent, although by 3 and 6 months post implantation, luminal diameter decreased slightly due to intimal hyperplasia. At 1 month post implantation, the stents were sparsely covered with endothelial cells, and by 6 months, the stents were mostly absorbed and inflammatory reaction gradually decreased as the stents were absorbed. This study shows favorable mechanical strength, degradability and efficacy for the sliding-lock PPDO stents, and supports further research and development of this unique design of polymer stents for applications in vascular devices.

Controllable biodegradability, drug release behavior and hemocompatibility of PTX-eluting magnesium stents

Cardiovascular magnesium-based stents have been already applied in patients. However, their high corrosion rate hinders their clinical application. In this study, we adopt a new approach in the design of a Mg-based stent to improve the biodegradation rate and the drug release rate. By fabricating a micro-arc oxidation/poly-l-lactic acid (MAO/PLLA) composite coating on the magnesium alloy AZ81 substrate, the corrosion resistance decreased and the biodegradation rate became controllable. The drug release coating was composed of one Poly(dl-lactide-co-glycolide)/paclitaxel (PLGA/PTX) layer and one pure PLGA blank layer without paclitaxel, and this coating also functions to provide controlled biodegradation rate of the stent. The drug release rate was controlled by controlling the ratio of the LA:GA of the PLGA without PTX. The scanning electron microscopy (SEM) images were used to demonstrate the morphology of the samples before and after this modification. The blood compatibility of the samples was demonstrated by the platelet adhesion test. The drug release was determined by ultraviolet-visible (UV-visible) spectrophotometer. The result showed that the PLLA effectively sealed the micro-cracks and micro-holes on the surface of the MAO coating to give controllable biodegradation of the AZ81. The drug release rate of PTX exhibited a nearly linear sustained-release profile with no significant burst releases that would come from the uncontrolled oxidation/corrosion of AZ81. The samples modified had better hemocompatibility than 316L stainless steel.