Inhibition of Neointima Formation by a Novel Drug-Eluting Stent System That Allows for Dose-Adjustable, Multiple, and On-Site Stent Coating

Small-Diameter Stents in Cardiovascular Applications

Small-diameter stents play a crucial role in treating congenital heart diseases and variety of vascular conditions that have application from paediatrics to geriatric conditions, and a comprehensive review in this direction is lacking. This review explores historical development, design innovations, material compositions and mechanistic insights into functions of small-diameter stents, with a specific emphasis on biodegradable options. The necessity for stents that can adapt to growth of paediatric patients is discussed, highlighting the transition from durable polymers to bioresorbable materials such as polylactic acid (PLA) and magnesium alloys. While acknowledging the advancements made in reducing complications like restenosis and thrombosis, the review addresses the challenges that persist, including the need for improved biocompatibility and minimization of late adverse cardiac events associated with certain stent technologies. A detailed examination of various stent generations emphasizes the importance of drug release kinetics, structural integrity and potential for personalized interventions based on patient-specific factors. The exploration of novel therapeutic compounds, including nanoparticles and interfering RNA, illustrates the ongoing research aimed at enhancing stent efficacy. Ultimately, the review seeks to provide a comprehensive understanding of current landscape while identifying the gaps that future research must address to develop the ideal stent for diverse patient populations.

Endovascular Drug Delivery

Drug-eluting stents (DES) and balloons revolutionize atherosclerosis treatment by targeting hyperplastic tissue responses through effective local drug delivery strategies. This review examines approved and emerging endovascular devices, discussing drug release mechanisms and their impacts on arterial drug distribution. It emphasizes the crucial role of drug delivery in modern cardiovascular care and highlights how device technologies influence vascular behavior based on lesion morphology. The future holds promise for lesion-specific treatments, particularly in the superficial femoral artery, with recent CE-marked devices showing encouraging results. Exciting strategies and new patents focus on local drug delivery to prevent restenosis, shaping the future of interventional outcomes. In summary, as we navigate the ever-evolving landscape of cardiovascular intervention, it becomes increasingly evident that the future lies in tailoring treatments to the specific characteristics of each lesion. By leveraging cutting-edge technologies and harnessing the potential of localized drug delivery, we stand poised to usher in a new era of precision medicine in vascular intervention.

Perturbed post-translational modification (PTM) network atlas of collagen I during stent-induced neointima formation

Myocardial infarction (MI) leading to heart failure contributes to almost 85% of deaths associated with CVDs. MI results from plaque formation in the coronary artery which leads to a lack of oxygen and nutrients in the myocardium. To date, stenting is a widely used gold-standard technique to maintain the proper blood flow through coronary circulation in the myocardium. Bare metal stents (BMS) and drug-eluting stents (DES) are majorly used in implantation. However, BMS and DES both can induce neointima formation by depositing excessive collagens in the coronary arteries leading to restenosis. Identification and quantitative analysis of site-specific post-translational modifications (PTMs) of deposited COL1A1 from neointima ECM are not known. Applying our in-house workflow, we re-analyzed a previously published mass-spectrometry data set to comprehensively map site-specific prolyl-hydroxylation, lysyl hydroxylation, and O-glycosylation sites in COL1A1 from neointima ECM. Furthermore, we quantitated the occupancy level of 9 3-hydroxyproline (3-HyP) sites, 2 hydroxylysine sites, and glycosylation microheterogeneity on 6 lysine sites of COL1A1. Although the total level of COL1A1 was decreased in DES-induced neointima, the occupancy levels of 2 3-HyP sites (P⁸⁷², and P⁸⁸¹) and 2 HyK (K⁴³⁵ and K⁷⁶⁸) sites of COL1A1 were significantly (p < 0.05) elevated in DES-induced neointima compared to BMS-induced neointima. We also found O-glycosylation to be significantly elevated on 3 lysine sites (K⁵⁷³, K³³⁹, and K and K⁸⁴⁹) of COL1A1 in DES-induced neointima compared to BMS-induced neointima. Taken together, our first comprehensive PTM analysis of COL1A1 reflected significant site-specific alterations that may play a very important role in the ECM remodeling during stent-induced neointima formation in MI patients. SIGNIFICANCE: The knowledge about site-specific post-translational modifications (PTMs) of collagen 1 deposited in the neointima ECM during the post-stenting restenosis process is absent. Here for the first time, we report the altered levels of COL1A1 PTMs during metal stent and drug-eluting stent-induced neointima formation. Our study showcases a novel ECM remodeling through site-specific collagen PTMs during stent-induced restenosis.

Surface engineering and the application of laser-based processes to stents - A review of the latest development

Late in-stent thrombus and restenosis still represent two major challenges in stents’ design. Surface treatment of stent is attracting attention due to the increasing importance of stenting intervention for coronary artery diseases. Several surface engineering techniques have been utilised to improve the biological response in vivo on a wide range of biomedical devices. As a tailorable, precise, and ultra-fast process, laser surface engineering offers the potential to treat stent materials and fabricate various 3D textures, including grooves, pillars, nanowires, porous and freeform structures, while also modifying surface chemistry through nitridation, oxidation and coatings. Laser-based processes can reduce the biodegradable materials' degradation rate, offering many advantages to improve stents’ performance, such as increased endothelialisation rate, prohibition of SMC proliferation, reduced platelet adhesion and controlled corrosion and degradation. Nowadays, adequate research has been conducted on laser surface texturing and surface chemistry modification. Laser texturing on commercial stents has been also investigated and a promotion of performance of laser-textured stents has been proved.

In this critical review, the influence of surface texture and surface chemistry on stents performance is firstly reviewed to understand the surface characteristics of stents required to facilitate cellular response. This is followed by the explicit illustration of laser surface engineering of stents and/or related materials. Laser induced periodic surface structure (LIPSS) on stent materials is then explored, and finally the application of laser surface modification techniques on latest generation of stent devices is highlighted to provide future trends and research direction on laser surface engineering of stents.

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Compared conventional surface engineering with laser-based methods for biomedical devices.

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Explained the influence of texture geometry and surface chemistry on stents biological response.

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Reviewed state of the art in laser surface engineering of stents for improved biological response.

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Reviewed state of the art in laser surface engineering to control degradation of bioresorbable stents.

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Highlighted novel laser surface engineering designs for improved stents'performance.

Long term safety and efficacy of the Yukon Choice Flex sirolimus-eluting coronary stent-a real-world data from India

In-stent restenosis and stent thrombosis are the major concerns while choosing a coronary stent. This single-centre, retrospective study evaluated the one and three-year clinical outcomes following implantation of Yukon Choice Flex (YCF) sirolimus-eluting stent. A total of 168 consecutive patients with 217 lesions underwent stenting with YCF stent. The presentation was with acute coronary syndrome in 158 (94%) patients. At 3 years, 9 (5.3%) patients died due to cardiac cause. Myocardial infarction, and definite stent thrombosis occurred in 10 (6%) and 4 (2.4%) patients respectively. Redo stenting and coronary artery bypass surgery was performed in 3 (1.8%) and 1 (0.6%) patient respectively. The use of YCF sirolimus eluting stent was associated with a favourable safety and efficacy profile at one and three-years of follow-up in a high-risk population.

Ten-year clinical outcomes of polymer-free versus durable polymer new-generation drug-eluting stent in patients with coronary artery disease with and without diabetes mellitus : Results of the Intracoronary Stenting and Angiographic Results: Test Efficacy of Sirolimus- and Probucol- and Zotarolimus-Eluting Stents (ISAR-TEST 5) trial

BACKGROUND

Very long-term outcomes according to diabetic status of patients with coronary artery disease (CAD) undergoing percutaneous coronary intervention (PCI) with new-generation drug-eluting stents (DES) are scant. Both, the durable polymer zotarolimus-eluting stent (DP-ZES), the first DES to gain FDA-approval for specific use in patients with diabetes mellitus, and the polymer-free sirolimus- and probucol-eluting stent (PF-SES), with a unique design that enables effective drug release without the need of a polymer offer the potential to enhance clinical long-term outcomes especially in patients with diabetes mellitus.

METHODS

We investigate 10-year clinical outcomes of the prespecified subgroups of patients with and without diabetes mellitus, randomly assigned to treatment with PF-SES versus DP-ZES in the ISAR-TEST 5 trial. The primary endpoint of interest was major adverse cardiac events (MACE), defined as the composite of all-cause death, any myocardial infarction or any revascularization. Further endpoints of interest were cardiac death, myocardial infarction related to the target vessel and target lesion revascularization as well as the individual components of the primary composite endpoint and the incidence of definite or probable stent thrombosis at 10 years.

RESULTS

This analysis includes a total of 3002 patients randomly assigned to PF-SES (n = 2002) or DP-ZES (n = 1000). Prevalence of diabetes mellitus was high and comparable, 575 Patients (28.7%) in PF-SES group and 295 patients (29.5%) in DP-ZES group (P = 0.66). At 10 years 53.5% of patients with diabetes mellitus and 68.5% of patients without diabetes mellitus were alive. Regarding major adverse cardiac events, PF-SES as compared to DP-ZES showed comparable event rates in patients with diabetes mellitus (74.8% vs. 79.6%; hazard ratio 0.86; 95% CI 0.73-1.02; P = 0.08) and in patients without diabetes (PF-SES 62.5% vs. DP-ZES 62.2%; hazard ratio 0.99; 95% CI 0.88-1.11; P = 0.88).

CONCLUSION

At 10 years, both new-generation DES show comparable clinical outcome irrespective of diabetic status or polymer strategy. Event rates after PCI in patients with diabetes mellitus are considerable higher than in patients without diabetes mellitus and continue to accrue over time.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT00598533, Registered 10 January 2008, https://clinicaltrials.gov/ct2/show/NCT00598533?term=NCT00598533 Kaplan-Meier estimates of endpoints of interest for patients with vs. without diabetes mellitus treated with PF-SES vs. DP-ZES. Bar graphs: Kaplan-Meier estimates as percentages. PF-SES: polymer-free sirolimus-eluting stent; DP-ZES: durable polymer zotarolimus-eluting stent; DM: diabetes mellitus. Comparison of event rates of individual endpoints in patients with and without diabetes mellitus treated with PF-SES vs. DP-ZES all without statistically significant differences. Comparison of event rates of individual endpoints in overall patients with vs. without diabetes mellitus significantly different (P ≤ 0.01 for all comparisons).

Drug-Eluting Stents and Balloons-Materials, Structure Designs, and Coating Techniques: A Review

Controlled drug delivery is a matter of interest to numerous scientists from various domains, as well as an essential issue for society as a whole. In the treatment of many diseases, it is crucial to control the dosing of a drug for a long time and thus maintain its optimal concentration in the tissue. Heart diseases are particularly important in this aspect. One such disease is an obstructive arterial disease affecting millions of people around the world. In recent years, stents and balloon catheters have reached a significant position in the treatment of this condition. Balloon catheters are also successfully used to manage tear ducts, paranasal sinuses, or salivary glands disorders. Modern technology is continually striving to improve the results of previous generations of stents and balloon catheters by refining their design, structure, and constituent materials. These advances result in the development of both successive models of drug-eluting stents (DES) and drug-eluting balloons (DEB). This paper presents milestones in the development of DES and DEB, which are a significant option in the treatment of coronary artery diseases. This report reviews the works related to achievements in construction designs and materials, as well as preparation technologies, of DES and DEB. Special attention was paid to the polymeric biodegradable materials used in the production of the above-mentioned devices. Information was also collected on the various methods of producing drug release coatings and their effectiveness in releasing the active substance.

Evaluation of the suitability of a fluidized bed process for the coating of drug-eluting stents

Drug-eluting stents are often coated using single-stent coating techniques. In pharmaceutical industry, single-tablet coating is unthinkable. Instead large batches of tablets are coated in fluidized bed apparatuses or pan coaters. Therefore, it was the aim of this work to evaluate whether stents can be coated using a fluidized bed process. For this purpose stents were coated with the model fluorescent drug triamterene embedded in ammonium methacrylate copolymer. Different stent lengths as well as different coating yields were assessed and also a drug-free topcoat was evaluated. The coated stents were analysed regarded coating layer mass, drug content, surface structure, coating thickness and drug release. Furthermore, coating yield and stent defect rate were examined. Except for one stent configuration good results were obtained without optimization of process parameters which indicates the suitability of the method to coat large amounts of stents simultaneously in principle. Drug release was tuneable over a wide range of time spans and a wide range of drug loadings was produced. Further work will be necessary to transform the results of this study from a model stent to a clinically relevant product.

Non-polymer drug-eluting coronary stents

Cardiovascular complications are leading causes of most fatalities. Coronary artery disease and surgical failures contribute to the death of the majority of patients. Advanced research in the field of medical devices like stents has efficiently resolved these problems. Clinically, drug-eluting stents have proven their efficacy and safety compared to bare metal stents, which have problems of in-stent restenosis. However, drug-loaded stents coated with polymers have shown adverse effects related to the stability and deterioration of the polymer coating over time. This results in late stent thrombosis and immunogenicity. These reasons laid the foundation for the development of non-polymeric drug-eluting stents. This review focuses on non-polymer drug-eluting stents loaded with different drugs like anti-inflammatory agents, anti-thrombotic, anti-platelet agents, immune suppressants and others. Surface modification techniques on stents like crystalline coating; microporous, macroporous, and nanoporous coatings; and chemically modified self-assembled monolayers are described in detail. There is also an update on clinically approved products and those under development.

Cardiovascular stents: overview, evolution, and next generation

Compared to bare-metal stents (BMSs), drug-eluting stents (DESs) have been regarded as a revolutionary change in coronary artery diseases (CADs). Releasing pharmaceutical agents from the stent surface was a promising progress in the realm of cardiovascular stents. Despite supreme advantages over BMSs, in-stent restenosis (ISR) and long-term safety of DESs are still deemed ongoing concerns over clinically application of DESs. The failure of DESs for long-term clinical use is associated with following factors including permanent polymeric coating materials, metallic stent platforms, non-optimal drug releasing condition, and factors that have recently been supposed as contributory factors such as degradation products of polymers, metal ions due to erosion and degradation of metals and their alloys utilizing in some stents as metal frameworks. Discovering the direct relation between stent materials and associating adverse effects is a complicated process, and yet it has not been resolved. For clinical success it is of significant importance to optimize DES design and explore novel strategies to overcome all problems including inflammatory response, delay endothelialization, and sub-acute stent thrombosis (ST) simultaneously. In this work, scientific reports are reviewed particularly focusing on recent advancements in DES design which covers both potential improvements of existing and recently novel prototype stent fabrications. Covering a wide range of information from the BMSs to recent advancement, this study mostly sheds light on DES's concepts, namely stent composition, drug release mechanism, and coating techniques. This review further reports different forms of DES including fully biodegradable DESs, shape-memory ones, and polymer-free DESs.

Percutaneous coronary intervention: balloons, stents and scaffolds

In this review, major achievements in the field of percutaneous coronary interventions are delineated with particular focus on Germany's contribution. The review deals with important developments, including the first heart catheterization and coronary angiography, first coronary balloon angioplasty and refinement of the technique, coronary stenting and optimization of adjunctive antithrombotic treatment, drug-eluting stents and balloons, as well as bioresorbable polymeric and metallic drug-eluting scaffolds.

Modelling drug release from polymer-free coronary stents with microporous surfaces

Traditional coronary drug-eluting stents (DES) are made from metal and are coated with a permanent polymer film containing an anti-proliferative drug. Subsequent to stent deployment in a diseased coronary artery, the drug releases into the artery wall and helps prevent restenosis by inhibiting the proliferation of smooth muscle cells. Although this technology has proven to be remarkably successful, there are ongoing concerns that the presence of a polymer in the artery can lead to deleterious medical complications, such as late stent thrombosis. Polymer-free DES may help overcome such shortcomings. However, the absence of a rate-controlling polymer layer makes optimisation of the drug release profile a particular challenge. The use of microporous stent surfaces to modulate the drug release rate is an approach that has recently shown particularly promising clinical results. In this study, we develop a mathematical model to describe drug release from such stents. In particular, we develop a mathematical model to describe drug release from microporous surfaces. The model predicts a two-stage release profile, with a relatively rapid initial release of most of the drug, followed by a slower release of the remaining drug. In the model, the slow release phase is accounted for by an adsorption/desorption mechanism close to the stent surface. The theoretical predictions are compared with experimental release data obtained in our laboratory, and good agreement is found. The valuable insights provided by our model will serve as a useful guide for designing the enhanced polymer-free stents of the future.

Study protocol for a randomised controlled trial: harmonising optimal strategy for treatment of coronary artery stenosis - coronary intervention with next-generation drug-eluting stent platforms and abbreviated dual antiplatelet therapy (HOST-IDEA) trial

INTRODUCTION

We have recently seen the introduction of newer generation drug-eluting stents with ultrathin struts that use advanced polymer technologies. However, the efficacy and safety of these newest stents have not yet been fully explored. In addition, there are still controversies over the optimal duration of dual antiplatelet therapy (DAPT) after stent implantation, particularly for ultrathin stents with the newest polymer technologies.

METHODS AND ANALYSIS

The HOST-IDEA trial is a randomised, open-label, multicentre, non-inferiority trial and the first study to directly compare two of these ultrathin sirolimus-eluting stents: Orsiro stent with biodegradable polymer, and polymer-free Coroflex ISAR (CX-ISAR) stent. This study has a scheme of 2×2 factorial design according to the stent type and DAPT duration (3 vs 12 months). A total of 2152 patients will be randomised and stratified to demonstrate the non-inferiority of CX-ISAR to Orsiro, or of the abbreviated DAPT duration to the conventional 12 months (both in 1:1 ratio). For the comparison of stent type, the primary endpoint is target lesion failure (TLF), which is a composite of cardiac death, target vessel-related myocardial infarction and clinically driven target lesion revascularisation. For the comparison of DAPT duration, the net adverse clinical event is the coprimary endpoint, which is defined as a composite of TLF, definite/probable stent thrombosis and major bleeding.

ETHIC APPROVAL AND DISSEMINATION

All the institutions involved in this study are required to have ethical approval prior to patient enrolment. This multicentre study will recruit patients through competitive registration, but institutions that have not yet obtained ethical approvals have made it impossible to enrol patients in a centralised web database. The final results will be presented at relevant international conferences and will be materialised in the form of papers.

TRIAL REGISTRATION NUMBER

NCT02601157; Pre-results.

Enhancing Stent Effectiveness with Nanofeatures

Drug-eluting stents are an effective therapy for symptomatic arterial obstructions, substantially reducing the incidence of restenosis by suppressing the migration and proliferation of vascular smooth muscle cells into the intima. However, current drug-eluting stents also inhibit the growth of endothelial cells, which are required to cover the vascular stent to reduce an excessive inflammatory response. As a result, the endothelial lining of the lumen is not regenerated. Since the loss of this homeostatic monolayer increases the risk of thrombosis, patients with drug-eluting stents require long-term antithrombotic therapy. Thus, there is a need for improved devices with enhanced effectiveness and physiological compatibility towards endothelial cells. Current developments in nanomaterials may enhance the function of commercially available vascular devices. In particular, modified design schemes might incorporate nanopatterns or nanoparticle-eluting features that reduce restenosis and enhance re-endothelialization. The intent of this review is to discuss emerging nanotechnologies that will improve the performance of vascular stents.

Endovascular Drug Delivery and Drug Elution Systems: First Principles

Endovascular drug delivery continues to revolutionize the treatment of atherosclerosis in coronary and peripheral vasculature. The key has been to identify biologic agents that can counter the hyperplastic tissue responses to device expansion/implantation and to develop effective local delivery strategies that can maintain efficacious drug levels across the artery wall over the course of device effects. This article reviews the evolution of endovascular drug delivery technology, explains the mechanisms they use for drug release, and provides a quantitative mechanistic framework for relating drug release mode to arterial drug distribution and effect.

Long-term clinical impact of polymer-free sirolimus-eluting stents in unselected patients

OBJECTIVES

The long-term clinical impact of polymer-free sirolimus-eluting stents (PF-SES) in unselected patients undergoing percutaneous coronary intervention (PCI) still remains poorly investigated. We studied the long-term clinical impact of PF-SES in a large cohort of unselected patients receiving PCI therapy at two tertiary care centers in India.

METHODS

A total of 3213 patients received PCI with drug-eluting stents during the period from December 2004 to September 2011. Among these, those receiving PF-SES implantation were retrospectively included in this registry. The primary endpoint in our study was the occurrence of major adverse cardiac events (MACE), defined as the composite of death/myocardial infarction (MI) and target lesion revascularization, whereas the main secondary endpoints were cardiac death/MI and definite/probable stent thrombosis.

RESULTS

A total of 1213 patients (83.8% men, 31.8% diabetics) with 1658 lesions (52.5% B2/C, according to the American College of Cardiology/American Heart Association classification) were studied. After a median follow-up of 1160 days, MACE occurred in 10.0% of patients, whereas the rates of cardiac death/MI and definite/probable ST were found to be 5.4 and 1.9%, respectively. The incidence of MACE was more common in patients aged at least 65 years [hazard ratio (HR)=1.69, 95% confidence interval (CI)=1.13-2.52, P=0.01] and diabetics (HR=1.71, 95% CI=1.18-2.47, P=0.004). The incidence of cardiac death/MI was more common in patients aged at least 65 years (HR=2.21, 95% CI=1.32-3.70, P=0.003). The baseline risk profile did not impact the occurrence of target lesion revascularization.

CONCLUSION

In this large cohort of unselected PCI patients treated in India, PF-SES shows a sustained safety and efficacy at long-term follow-up.

Safety and efficacy of the Yukon Choice Flex sirolimus-eluting coronary stent in an all-comers population cohort

AIMS

The use of biodegradable-polymer drug-eluting stents has been shown to provide favorable results when compared with durable polymer drug-eluting stents and long-term follow up data have recently shown significant reductions in terms of very late stent thrombosis. Aim of the present study was to assess the safety and efficacy profile of a novel biodegradable polymer DES, the Yukon Choice Flex sirolimus-eluting stent.

METHODS

We report here the one-year clinical outcomes associated with the use of the Yukon Choice Flex sirolimus-eluting stent in an all-comers patient population. The present stent represents a further refinement of the stent platform tested in the ISAR TEST 3 and 4 randomized clinical trials. A total of 778 consecutive patients undergoing implantation of this stent were enrolled in the present observational study and prospectively followed for one year.

RESULTS

The use of the Yukon Choice Flex stent in a patient population with complex coronary lesion morphology was associated with optimal immediate angiographic results. At one year follow up the rates of death, myocardial infarction, definite stent thrombosis and ischemia-driven target lesion revascularization were respectively 2.4%, 1.9%, 0.3% and 11.3%.

CONCLUSIONS

The use of the sirolimus-eluting biodegradable polymer Yukon Choice Flex stent in an all-comers population of patients with complex coronary artery disease is associated with a favorable safety and efficacy profile up to one year follow up.

Inhalable, large porous PLGA microparticles loaded with paclitaxel: preparation, in vitro and in vivo characterization

Large porous particles (LPPs) could be used as a useful carrier for non-invasive delivery to the deep lung. Pulmonary delivery of paclitaxel-loaded LPPs (PTX-LPPs) can help to eliminate the highly complicated and harmful solvent used in PTX parenteral formulations. PTX-LPPs with mass median aerodynamic diameter (MMAD) of 5.74 ± 0.09 μm, high encapsulation efficiency and good aerosolisation properties were produced using ammonium bicarbonate as porogen. Cytotoxicity of PTX-LPPs on A549 and Calu-6 cell lines was comparable with Free-PTX. Endotracheal administration of PTX-LPPs in rats exhibited PTX plasma concentration in the therapeutic range which lasted 4-fold longer than i.v. injection. The bioavailability was measured as 51 ± 7.1%. The lung targeting efficiency (Te) of PTX-LPPs was 11.9-fold higher than i.v. administration. PTX-LPPs could deliver a higher PTX to lung with a non-toxic plasma level in a longer duration which shows their pulmonary delivery suitability.

Controlling drug delivery from coronary stents: are we aiming for the right targets?

In this review article, the currently employed or explored delivery concepts for local intravascular drug delivery with drug-eluting stents (DES) are discussed with a special emphasis on clinical evidence regarding the desired release profiles. Traditional concepts to control drug release from DES include diffusion through polymers, polymer degradation and erosion as well as dissolution of particulate drug. Published clinical studies do not always reveal fine mechanistic details. The long duration of release favored for DES and the short duration of release favored for drug-eluting balloons require further investigation in experimental studies and clinical trials.

Polymer-Free Drug-Eluting Stents: An Overview of Coating Strategies and Comparison with Polymer-Coated Drug-Eluting Stents

Clinical evaluations have proven the efficacy of drug-elution stents (DES) in reduction of in-stent restenosis rates as compared to drug-free bare metal stents (BMS). Typically, DES are metal stents that are covered with a polymer film loaded with anti-inflammatory or antiproliferative drugs that are released in a sustained manner. However, although favorable effects of the released drugs have been observed, the polymer coating as such has been associated with several adverse clinical effects, such as late stent thrombosis. Elimination of the polymeric carrier of DES may therefore potentially lead to safer DES. Several technologies have been developed to design polymer-free DES, such as the use of microporous stents and inorganic coatings that can be drug loaded. Several drugs, including sirolimus, tacrolimus, paclitaxel, and probucol have been used in the design of carrier-free stents. Due to the function of the polymeric coating to control the release kinetics of a drug, polymer-free stents are expected to have a faster drug elution rate, which may affect the therapeutic efficacy. However, several polymer-free stents have shown similar efficacy and safety as the first-generation DES, although the superiority of polymer-free DES has not been established in clinical trials.

Controlled Slow-Release Drug-Eluting Stents for the Prevention of Coronary Restenosis: Recent Progress and Future Prospects

Drug-eluting stents (DES) have become more widely used by cardiologists than bare metal stents (BMS) because of their better ability to control restenosis. However, recognized negative events, particularly including delayed or incomplete endothelialization and late stent thrombosis, have caused concerns over the long-term safety of DES. Although stent-based drug delivery can facilitate a drug's release directly to the restenosis site, a burst of drug release can seriously affect the pharmacological action and is a major factor accounting for adverse effects. Therefore, the drug release rate has become an important criterion in evaluating DES. The factors affecting the drug release rate include the drug carrier, drug, coating methods, drug storage, elution direction, coating thickness, pore size in the coating, release conditions (release medium, pH value, temperature), and hemodynamics after the stent implantation. A better understanding of how these factors influence drug release is particularly important for the reasonable use of efficient control strategies for drug release. This review summarizes the factors influencing the drug release from DES and presents strategies for enhancing the control of the drug's release, including the stent design, the application of absorbable stents, the development of new polymers, and the application of nanocarriers and improvements in the coating technology. Therefore, this paper provides a reference for the preparation of novel controlled slow-release DES.

Macromolecular approaches to prevent thrombosis and intimal hyperplasia following percutaneous coronary intervention

Cardiovascular disease remains one of the largest contributors to death worldwide. Improvements in cardiovascular technology leading to the current generation of drug-eluting stents, bioresorbable stents, and drug-eluting balloons, coupled with advances in antirestenotic therapeutics developed by pharmaceutical community, have had a profound impact on quality of life and longevity. However, these procedures and devices contribute to both short- and long-term complications. Thus, room for improvement and development of new, alternative strategies exists. Two major approaches have been investigated to improve outcomes following percutaneous coronary intervention including perivascular delivery and luminal paving. For both approaches, polymers play a major role as controlled research vehicles, carriers for cells, and antithrombotic coatings. With improvements in catheter delivery devices and increases in our understanding of the biology of healthy and diseased vessels, the time is ripe for development of novel macromolecular coatings that can protect the vessel lumen following balloon angioplasty and promote healthy vascular healing.

Vitamin-C delivery from CoCr alloy surfaces using polymer-free and polymer-based platforms for cardiovascular stent applications

Antiproliferative drugs such as paclitaxel and sirolimus are delivered from stents to inhibit the growth of smooth muscle cells (SMCs) for preventing neointimal hyperplasia. However, these drugs delay the growth of endothelial cells (ECs) as well and cause late stent thrombosis. We recently demonstrated the use of Vitamin-C (l-ascorbic acid, l-AA) over paclitaxel and sirolimus for inhibiting SMCs growth and promoting EC growth simultaneously. In this study, we have investigated the delivery of l-AA from CoCr alloy surfaces for potential use in stents. A polymer-free phosphoric acid (PA) platform and a polymer-based poly(lactic-co-glycolic acid) (PLGA) platform were used for coating l-AA onto CoCr surfaces. For the PA platform, FTIR confirmed that the PA was coated on CoCr, while the AFM showed that the PA coating on the CoCr surface was homogeneous. The successful deposition of l-AA on PA-coated CoCr was also confirmed by FTIR. The uniform distribution of l-AA crystals on PA-coated CoCr was shown by SEM, optical profilometer, and AFM. The drug release studies showed that l-AA (276 μg/cm(2)) was burst released from the PA platform by 1 h. For the PLGA platform, SEM showed that the l-AA incorporated polymer films were smoothly and uniformly coated on CoCr. FTIR showed that l-AA was incorporated into the bulk of the PLGA film. DSC showed that the l-AA was present in an amorphous form and formed an intermolecular bonding interaction with PLGA. The drug release studies showed that l-AA was sustained released from the PLGA coated CoCr for up to 24 h. The SEM, FTIR, and DSC characterizations of samples collected post drug release shed light on the mechanism of l-AA release from PLGA coated CoCr. Thus, this study demonstrated the delivery of l-AA from biomaterial surfaces for potential applications in stents and other implantable medical devices.

Polymer-free sirolimus-eluting versus polymer-based paclitaxel-eluting stents: an individual patient data analysis of randomized trials

INTRODUCTION AND OBJECTIVES

The angiographic and clinical efficacy of polymer-free sirolimus-eluting stents vs polymer-based paclitaxel-eluting stents remain a matter of debate. We sought to investigate angiographic and clinical measures of efficacy of polymer-free sirolimus-eluting stents vs polymer-based paclitaxel-eluting stents.

METHODS

Patient data from the randomized intracoronary stenting and angiographic restenosis-test equivalence between the 2 drug-eluting stents (ISAR-TEST) clinical trial and the LIPSIA Yukon clinical trial (randomized comparison of a polymer-free sirolimus-eluting stent vs a polymer-based paclitaxel-eluting stent in patients with diabetes mellitus) were pooled. The angiographic (primary) endpoint was in-stent late lumen loss at 6 months to 9 months. The clinical (secondary) endpoints were death or myocardial infarction, cardiac death or myocardial infarction, target lesion revascularization, and myocardial infarction.

RESULTS

A total of 686 patients (polymer-free sirolimus-eluting stents, n=345 vs polymer-based paclitaxel-eluting stents, n=341) and 751 lesions (polymer-free sirolimus-eluting stents, n=383 vs polymer-based paclitaxel-eluting stents, n=368) were included in the study. Control angiography (606 lesions, 80.6%) showed comparable in-stent late lumen loss for polymer-free sirolimus-eluting stents vs polymer-based paclitaxel-eluting stents (0.53 [0.59] mm vs 0.46 [0.57] mm; P=.15). Median follow-up was 34.8 months. Polymer-free sirolimus-eluting stents and polymer-based paclitaxel-eluting stents were associated with comparable risk of death or myocardial infarction (relative risk=1.17; 95% confidence interval, 0.49-2.80; P=.71), cardiac death or myocardial infarction (relative risk=1.17; 95% confidence interval, 0.72-1.89; P=.50), target lesion revascularization (relative risk=0.98; 95% confidence interval, 0.65-1.47; P=.93), and myocardial infarction (relative risk=1.79; 95% confidence interval, 0.85-3.76; P=.12).

CONCLUSIONS

In this pooled analysis, polymer-free sirolimus-eluting stents were comparable to polymer-based paclitaxel-eluting stents with respect to both angiographic and clinical efficacy.

Fabrication of a novel polymer-free nanostructured drug-eluting coating for cardiovascular stents

Angioplasty with stents is the most important method for the treatment of coronary artery disease (CAD). However, the drug-eluting stents (DES) that are widely used have the increased risks of inflammatory reactions and late stent thrombosis (LST) because of the persistence of the polymer coatings. To improve the biosafety, a novel polymer-free-composite drug-eluting coating composed of magnetic mesoporous silica nanoparticles (MMSNs) and carbon nanotubes (CNTs) was constructed using the electrophoretic deposition (EPD) method in this study. A crack-free two-layered coating with impressive network nanotopologies was successfully obtained by regulating the composition and structures. This nanostructured coating exhibits excellent mechanical flexibility and blood compatibility in vitro, and the drug-loading and release performance is satisfactory as well. The in vivo study shows that this composite coating has the obvious advantage of rapid endothelialization because of its unique 3D nanostructured topology in comparison with the commercial polymer-coated DES. This study aims to provide new ideas and reliable data to design novel functional coatings that could accelerate the re-endothelialization process and avoid inflammatory reactions, thus improving the in vivo biosafety of DES.

Five-year clinical follow-up of a randomized comparison of a polymer-free sirolimus-eluting stent versus a polymer-based paclitaxel-eluting stent in patients with diabetes mellitus (LIPSIA Yukon trial)

OBJECTIVES

The long-term performance of polymer-free stent systems in patients with diabetes mellitus has not been investigated extensively. This study reports long-term results of the LIPSIA Yukon trial which compared the polymer-free sirolimus-eluting Yukon Choice stent with the polymer-based paclitaxel-eluting Taxus Liberté stent in this subpopulation. At 9 months, the Yukon Choice stent failed to show non-inferiority in terms of the primary end point late lumen loss, while no significant difference in clinical outcome was detected.

METHODS AND RESULTS

The LIPSIA Yukon trial randomized 240 patients with diabetes mellitus to a polymer-free sirolimus eluting stent (Yukon Choice, Translumina) versus a polymer-based paclitaxel-eluting stent (Taxus Liberté, Boston Scientific). Clinical follow-up was conducted with a standardized telephone follow-up and all events were centrally adjudicated. Follow-up was available for 98.3% of patients after a median of 5.0 years. The incidence of all-cause death (16.9% versus 14.0%, P = 0.67), respectively definite or presumed cardiovascular death (7.6% versus 8.8%, P = 0.94) were similar in the Yukon Choice and the Taxus Liberté group. There were no significant differences in the rates of myocardial infarction (9.3% versus 7.9%, P = 0.88), definite stent thrombosis (0.8% versus 0.9%, P = 1.0), target lesion revascularization (15.3% versus 15.8%, P = 1.0), target vessel revascularization (18.6% versus 23.7%, P = 0.44), non-target vessel revascularization (18.6% versus 26.3%, P = 0.21), and stroke (3.4% versus 4.4%, P = 0.96) between patients assigned to the Yukon Choice and the Taxus Liberté stent.

CONCLUSION

At 5 years of follow-up, clinical outcome was similar between the polymer-free sirolimus-eluting Yukon Choice stent and the polymer-based paclitaxel-eluting Taxus Liberté stent.

Systematic review of infrapopliteal drug-eluting stents: a meta-analysis of randomized controlled trials

INTRODUCTION

Drug-eluting stents (DES) have been proposed for the treatment of infrapopliteal arterial disease. We performed a systematic review to provide a qualitative analysis and quantitative data synthesis of randomized controlled trials (RCTs) assessing infrapopliteal DES.

MATERIALS AND METHODS

PubMed (Medline), EMBASE (Excerpta Medical Database), AMED (Allied and Complementary medicine Database), Scopus, CENTRAL (Cochrane Central Register of Controlled Trials), online content, and abstract meetings were searched in September 2012 for eligible RCTs according to the preferred reporting items for systematic reviews and meta-analyses selection process. Risk of bias was assessed using the Cochrane Collaboration's tool. Primary endpoint was primary patency defined as absence of ≥50 % vessel restenosis at 1 year. Secondary outcome measures included patient survival, limb amputations, change of Rutherford-Becker class, target lesion revascularization (TLR) events, complete wound healing, and event-free survival at 1 year. Risk ratio (RRs) were calculated using the Mantel-Haenszel fixed effects model, and number-needed-to-treat values are reported.

RESULTS

Three RCTs involving 501 patients with focal infrapopliteal lesions were analyzed (YUKON-BTX, DESTINY, and ACHILLES trials). All three RCTs included relatively short and focal infrapopliteal lesions. At 1 year, there was clear superiority of infrapopliteal DES compared with control treatments in terms of significantly higher primary patency (80.0 vs. 58.5 %; pooled RR = 1.37, 95 % confidence interval [CI] = 1.18-1.58, p < 0.0001; number-needed-to-treat (NNT) value = 4.8), improvement of Rutherford-Becker class (79.0 vs. 69.6 %; pooled RR = 1.13, 95 % CI = 1.002-1.275, p = 0.045; NNT = 11.1), decreased TLR events (9.9 vs. 22.0 %; pooled RR = 0.45, 95 % CI = 0.28-0.73, p = 0.001; NNT = 8.3), improved wound healing (76.8 vs. 59.7 %; pooled RR = 1.29, 95 % CI = 1.02-1.62, p = 0.04; NNT = 5.9), and better overall event-free survival (72.2 vs. 57.3 %; pooled RR = 1.26, 95 % CI = 1.10-1.44, p = 0.0006; NNT = 6.7).

CONCLUSION

DES for focal infrapopliteal lesions significantly inhibit vascular restenosis and thereby improve primary patency, decrease repeat procedures, improve wound healing, and prolong overall event-free survival.

Balloon coating with rapamycin using an on-site coating device

PURPOSE

The efficacy of drug-eluting balloons has been demonstrated in clinical trials. The drug predominantly used is paclitaxel because of its lipophilic properties and the rapid onset of action. The aim of the investigation was to evaluate the feasibility and efficacy of an alternative balloon coating with rapamycin that can be applied on site.

METHODS

The balloon coating (3.0/18 and 3.0/12 mm, Cathy No. 4, Translumina GmbH) with rapamycin was conducted with a coating machine (Translumina GmbH). Concentrations were 2, 2 × 2, 3, and 4 %. Measurements regarding the amount of substance released to the vessel wall were carried out on explanted porcine coronaries by means of ultraviolet and visible-light spectroscopy. Inflation time varied between 30 and 120 s. The biological effect of the coating was evaluated in a porcine peripheral overstretch and stent implantation model.

RESULTS

The amount of rapamycin on the balloon surface ranged from 558 ± 108 μg for the 2 % solution to 1,441 ± 228 μg in the 4 % solution. An amount of 95 ± 63-193 ± 113 μg was released into the vessel wall. The quantitative measurements of the angiographic examinations 4 weeks after treatment revealed a reduction of diameter stenosis from 20.6 ± 17.4 % in the control group to 11.6 ± 5.5 % in the drug-eluting balloon group.

CONCLUSION

A balloon coating with rapamycin omitting an excipient is possible with a dose-adjustable coating machine. However, the biological effects are moderate, which make further optimization of the coating process and evaluation of appropriate excipients necessary.

Succinobucol-eluting stents increase neointimal thickening and peri-strut inflammation in a porcine coronary model

Objective

The aim of this study was to assess the efficacy of stent-based delivery of succinobucol alone and in combination with rapamycin in a porcine coronary model. Background: Current drugs and polymers used to coat coronary stents remain suboptimal in terms of long term efficacy and safety. Succinobucol is a novel derivative of probucol with improved antioxidant and anti-inflammatory properties.

Methods

Polymer-free Yukon stents were coated with 1% succinobucol (SucES), 2% rapamycin (RES), or 1% succinobucol plus 2% rapamycin solutions (SucRES) and compared with a bare metal stent (BMS).

Results

The in vivo release profile of SucES indicated drug release up to 28 days (60% drug released at 7 days); 41 stents (BMS, n = 11; SucES, n =10; RES, n = 10; SucRES, n = 10) were implanted in the coronary arteries of 17 pigs. After 28 days, mean neointimal thickness was 0.31 ± 0.14 mm for BMS, 0.51 ± 0.14 mm for SucES, 0.19 ± 0.11 mm for RES, and 0.36 ± 0.17 mm for SucRES (P < 0.05 for SucES vs. BMS). SucES increased inflammation and fibrin deposition compared with BMS (P < 0.05), whereas RES reduced inflammation compared with BMS (P < 0.05).

Conclusion

In this model, stent-based delivery of 1% succinobucol using a polymer-free stent platform increased neointimal formation and inflammation following coronary stenting. © 2012 Wiley Periodicals, Inc.

Microrough cobalt-chromium alloy surfaces for paclitaxel delivery: preparation, characterization, and in vitro drug release studies

Cobalt-chromium (Co-Cr) alloys have extensive biomedical applications including drug-eluting stents (DES). This study investigates the use of eight different microrough Co-Cr alloy surfaces for delivering paclitaxel (PAT) for potential use in DES. The eight different surfaces include four bare microrough and four self-assembled monolayer (SAM) coated microrough surfaces. The bare microrough surfaces were prepared by grit blasting Co-Cr with glass beads (50 and 100 μm in size) and Al(2)O(3) (50 and 110 μm). The SAM coated surfaces were prepared by depositing a -COOH terminated phosphonic acid monolayer on the different microrough surfaces. PAT was then deposited on all the bare and SAM coated microrough surfaces. The surfaces were characterized using scanning electron microscopy (SEM), 3D optical profilometry, and Fourier transform infrared spectroscopy (FTIR). SEM showed the different morphologies of microrough surfaces without and with PAT coating. An optical profiler showed the 3D topography of the different surfaces and the changes in surface roughness and surface area after SAM and PAT deposition. FTIR showed ordered SAMs were formed on glass bead grit blasted surfaces, while the molecules were disordered on Al(2)O(3) grit blasted surfaces. Also, FTIR showed the successful deposition of PAT on these surfaces. The PAT release was investigated for up to two weeks using high performance liquid chromatography. Al(2)O(3) grit blasted bare microrough surfaces showed sustained release profiles, while the glass bead grit blasted surfaces showed burst release profiles. All SAM coated surfaces showed biphasic drug release profiles, which is an initial burst release followed by a slow and sustained release. SAM coated Al(2)O(3) grit blasted surfaces prolonged the sustained release of PAT in a significant amount during the second week of drug elution studies, while this behavior was not observed for any other surfaces used in this study. Thus, this study demonstrates the use of different microrough Co-Cr alloy surfaces for delivering PAT for potential applications in DES and other medical devices.

Drug-eluting stent restenosis: effect of drug type, release kinetics, hemodynamics and coating strategy

Restenosis following stent implantation diminishes the procedure's efficacy influencing long-term clinical outcomes. Stent-based drug delivery emerged a decade ago as an effective means of reducing neointimal hyperplasia by providing localized pharmacotherapy during the acute phase of the stent-induced injury and the ensuing pathobiological mechanisms. However, drug-eluting stent (DES) restenosis may still occur especially when stents are used in complex anatomical and clinical scenarios. A DES consists of an intravascular metallic frame and carriers which allow controlled release of active pharmaceutical agents; all these components are critical in determining drug distribution locally and thus anti-restenotic efficacy. Furthermore, dynamic flow phenomena characterizing the vascular environment, and shear stress distribution, are greatly influenced by stent implantation and play a significant role in drug deposition and bioavailability within local vascular tissue. In this review, we discuss the performance of DES and the interaction of the different DES components with the hemodynamic milieu emphasizing on the inhibition of clinical restenosis.

One-year clinical outcome of a randomized trial of polymer-free paclitaxel-eluting stents versus biodegradable polymer-based rapamycin-eluting stents in patients with coronary heart disease

BACKGROUND

 More widespread use of drug-eluting stents (DES) to treat coronary heart disease (CHD) has recently generated more attention to thrombosis, which was relative to the polymer. Polymer-free and biodegradable polymer-based stents are more frequently studied, but their efficacy on preventing detrimental clinical events is unclear.

METHODS AND RESULTS

To assess whether polymer-free paclitaxel-eluting stent (YINYI stent) was noninferior or equivalent to biodegradable polymer-based rapamycin-eluting stents (EXCEL stent) in preventing detrimental clinical cardiovascular events, a total of 167 consecutive CHD patients requiring DES implantation were randomly divided into the YINYI group (n = 82) and the EXCEL group (n = 85). The primary end-point was major adverse cardiac events (MACE). The secondary end-points included stent thrombosis events, all-cause mortality, and rehospitalization. The study was designed to test the noninferiority or equivalence of the YINYI stent compared with the EXCEL stent with respect to one-year MACE according to a noninferiority or equivalence margin of 0.1. One-year MACE was 6.10% in the YINYI group versus 5.88% in the EXCEL group. The lower limit of the one-sided 95% confidence interval was -0.0582 (P = 0.002 from the test for noninferiority). The 95% confidence interval for the equivalence test was [-0.0698, 0.0742] (P1 =0.004 and P2 =0.007 from 2 times the 1-sided test for equivalence). There was no statistically significant difference in thrombosis events, all-cause death, and rehospitalization (all P > 0.05).

CONCLUSIONS

In this small randomized trial, polymer-free paclitaxel-eluting stents appear to be noninferior or equivalent to biodegradable polymer-based rapamycin-eluting stents.