Bioabsorbable scaffolds for the treatment of obstructive coronary artery disease: the next revolution in coronary intervention?

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).

Emerging and Future Therapeutic Options for Femoropopliteal and Infrapopliteal Endovascular Intervention

Despite recent advances in endovascular therapy for peripheral artery disease, current technologies remain limited by rates of long-term restenosis and application to complex lesion subsets. This article presents data on upcoming therapies, including novel drug-coated balloons, drug-eluting stents, bioresorbable scaffolds, novel drug delivery therapies to target arteries, techniques to limit postangioplasty dissection, and treatment of severely calcified lesions.

Anti-thrombotic technologies for medical devices

Thrombosis associated with medical devices may lead to dramatic increases in morbidity, mortality and increased health care costs. Innovative strategies are being developed to reduce this complication and provide a safe biocompatible interface between device and blood. This article aims to describe the biological phenomena underlying device-associated thrombosis, and surveys the literature describing current and developing technologies designed to overcome this challenge. To reduce thrombosis, biomaterials with varying topographical properties and incorporating anti-thrombogenic substances on their surface have demonstrated potential. Overall, there is extensive literature describing technical solutions to reduce thrombosis associated with medical devices, but clinical results are required to demonstrate significant long-term benefits.

In Vitro Cytotoxicity, Adhesion, and Proliferation of Human Vascular Cells Exposed to Zinc

Zinc (Zn) and its alloys have recently been introduced as a new class of biodegradable metals with potential application in biodegradable vascular stents. Although an in vivo feasibility study pointed to outstanding biocompatibility of Zn-based implants in vascular environments, a thorough understanding of how Zn and Zn²⁺ affect surrounding cells is lacking. In this comparative study, three vascular cell types-human endothelial cells (HAEC), human aortic smooth muscle cells (AoSMC), and human dermal fibroblasts (hDF)-were studied to advance the understanding of Zn/Zn²⁺-cell interactions. Aqueous cytotoxicity using a Zn²⁺ insult assay resulted in LD₅₀ values of 50 µM for hDF, 70 µM for AoSMC, and 265 µM for HAEC. Direct cell contact with the metallic Zn surface resulted initially in cell attachment, but was quickly followed by cell death. After modification of the Zn surface using a layer of gelatin-intended to mimic a protein layer seen in vivo-the cells were able to attach and proliferate on the Zn surface. Further experiments demonstrated a Zn dose-dependent effect on cell spreading and migration, suggesting that both adhesion and cell mobility may be hindered by free Zn²⁺.

Bioresorbable vascular scaffold overlap evaluation with optical coherence tomography after implantation with or without enhanced stent visualization system (WOLFIE study): a two-centre prospective comparison

To assess if enhanced stent visualization (ESV)-guided implantation of overlapping bioresorbable vascular scaffold (BVS) is superior to angiography alone-guided implantation in the reduction of overlap length. WOLFIE is a two-centre prospective open study enrolling 30 patients treated with implantation of at least two overlapping BVS. In the first centre (London), BVS implantation was guided by conventional angiography, while in the second centre (Ferrara), an ESV system was systematically employed. The primary endpoint of the study was overlap length. Secondary endpoints were: stacked struts number, area, thickness, and amount of clusters. In the ESV-guided group, overlap length was significantly lower compared to angiography-guided group [0.9 (0.6-1.8) vs. 2.2 (1.3-3.2) mm, p = 0.02]. Similarly, all secondary endpoints were significantly reduced. ESV-guided implantation of overlapping BVS is safe and effective in minimizing both overlap length and number of stacked struts.

Metallic zinc exhibits optimal biocompatibility for bioabsorbable endovascular stents

Although corrosion resistant bare metal stents are considered generally effective, their permanent presence in a diseased artery is an increasingly recognized limitation due to the potential for long-term complications. We previously reported that metallic zinc exhibited an ideal biocorrosion rate within murine aortas, thus raising the possibility of zinc as a candidate base material for endovascular stenting applications. This study was undertaken to further assess the arterial biocompatibility of metallic zinc. Metallic zinc wires were punctured and advanced into the rat abdominal aorta lumen for up to 6.5months. This study demonstrated that metallic zinc did not provoke responses that often contribute to restenosis. Low cell densities and neointimal tissue thickness, along with tissue regeneration within the corroding implant, point to optimal biocompatibility of corroding zinc. Furthermore, the lack of progression in neointimal tissue thickness over 6.5months or the presence of smooth muscle cells near the zinc implant suggest that the products of zinc corrosion may suppress the activities of inflammatory and smooth muscle cells.

Update on percutaneous intervention for left main coronary artery stenosis

Percutaneous coronary intervention (PCI) using drug-eluting stents (DES) is currently considered as a viable alternative to coronary artery bypass graft surgery (CABG) for selected patients with left main coronary artery disease. The updated results of the landmark randomized trials comparing CABG versus PCI demonstrated comparable 5-year outcomes and are in line with the current guidelines that designate PCI as a reasonable treatment in this disease subset. Given that the completed randomized trials did not include contemporary DESs, the upcoming results of the ongoing trials evaluating the performance of new-generation DES compared with CABG (such as the EXCEL trial), may further help to clarify the current role and future recommendations of PCI for left main coronary artery disease. Apart from the recent stent technology, further improvements in outcomes after PCI may be possible when it is used with an integrated approach that combines functional concepts for decision-making, adjunctive imaging support and optimal pharmacotherapies.

Fully bioresorbable drug-eluting coronary scaffolds: A review

Following the development of stents, then drug-eluting stents (DES), bioresorbable scaffolds are proposed as a third evolution in coronary angioplasty, aiming to reduce the incidence of restenosis and stent thrombosis and to restore vascular physiology. At least 16 such devices are currently under development, but published clinical data were available for only three of them in September 2014. The first device is Abbott's BVS(®), a poly-L-lactic acid (PLLA)-based everolimus-eluting device, which has been tested in a registry and two non-randomized trials. Clinical results seem close to what is expected from a modern DES, but possibly with more post-procedural side-effects. Two randomized trials versus DES are underway. This device is already marketed in many European countries. The second device is Elixir's DESolve(®), a PLLA-based novolimus-eluting device, which has been evaluated in two single-arm trials. Results are not widely different from those expected from a DES. The third device is Biotronik's DREAMS(®), a metallic magnesium-based paclitaxel-eluting device, which has been assessed in an encouraging single-arm trial; its second version is currently undergoing evaluation in a single-arm trial. The available results suggest that the technological and clinical development of bioresorbable scaffolds is not yet complete: their possible clinical benefits are still unclear compared with third-generation DES; the impact of arterial physiology restoration has to be assessed over the long term; and their cost-effectiveness has to be established. From the perspective of a health technology assessment, there is no compelling reason to hasten the clinical use of these devices before the results of ongoing randomized controlled trials become available.

Bioresorbable scaffolds in peripheral arterial disease

The risk of in-stent restenosis has been dramatically reduced with the use of thin-strut nitinol and balloon-expandable drug-eluting stents in the peripheral arterial territory. However, the presence of a permanent endovascular device is linked to a series of events that can lead to restenosis and stent thrombosis. Significant advances in the technology of bioresorbable materials have delivered the potential for fully bioresorbable scaffolds (BRS), which are able to mechanically support the artery wall and elute an anti-restenotic drug for a predetermined time period after which the scaffold becomes fully absorbed into the vascular wall. Currently, several vascular BRS 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 current and potential future prospects of this innovative treatment option for peripheral arterial disease.

Current application and bioavailability of drug-eluting stents

INTRODUCTION

Drug-eluting stents (DES) were developed to reduce the restenosis rate of bare metal stents (BMS) and comprises three main components: i) a metallic scaffold; ii) an antiproliferative drug to reduce or abolish the formation of the neointima; and iii) the polymer, which both enables and controls drug elution into the vessel wall. Over the years, growing evidence has been reported on the safety and efficacy for different indications of DES.

AREAS COVERED

Since the introduction of first-generation DES, the technology has been refined, including changes in the alloy, stent design, polymer, drug and drug dose. In 2014, we will usher in a third generation of DES, which will include biodegradable polymers, polymer-free DES and bioabsorbable scaffolds.

EXPERT OPINION

In recent years, considerable progress has been made in DES development. The BMS platform set the groundwork for the development of metal scaffolds with drug-eluting capability to prevent restenosis. Importantly, extensive research has shown long-term safety and efficacy of the newer generation DES. Available data suggest that DES can be safely and effectively used to treat a complex subset of patients and lesions, including patients presenting with acute myocardial infarction, lesions in saphenous vein grafts, chronic total occlusions, multivessel disease, small vessels, long lesions and bifurcations. One of the safety targets is to eliminate stent thrombosis.

Short-term outcome of patients with ST-segment elevation myocardial infarction (STEMI) treated with an everolimus-eluting bioresorbable vascular scaffold

OBJECTIVES

To evaluate safety and efficacy of the everolimus-eluting bioresorbable scaffold (BVS) in patients with ST-segment elevation myocardial infarction (STEMI).

BACKGROUND

According to the current guidelines, drug-eluting stents are the treatment of choice in patients with STEMI. BVS represents a new technology capable to restore the native vessel vasomotion and potentially avoiding long-term limitations such as stent thrombosis.

METHODS

From October 2012 to May 2013, patients with evidence of STEMI eligible for BVS implantation were included in this study. Exclusion criteria were not defined.

RESULTS

A total of 25 patients, respectively 31 lesions, were treated. Procedural success was achieved in 97%. Two major adverse cardiac events occurred during hospitalization and follow-up: one patient with cardiogenic shock at the index procedure subsequently died. One patient suffered from instable angina with need for interventional revascularization of a previously untreated vessel. One target vessel failure as a consequence of an intra-procedural dissection was seen. However, no target lesion failure was noted. During 132.7 ± 68.7 days of follow-up none of the patients died.

CONCLUSION

Our findings suggest that implantation of BVS in STEMI patients is feasible in this small cohort of highly selected patients. Further evaluation in randomized-controlled trials is needed.