The effect of variable dose and release kinetics on neointimal hyperplasia using a novel paclitaxel-eluting stent platform: the Paclitaxel In-Stent Controlled Elution Study (PISCES)

Unravelling the progress and potential of drug-eluting stents and drug-coated balloons in cardiological insurgencies

AIM

Coronary artery disease (CAD) is the leading cause of mortality. Though percutaneous transluminal angioplasty followed by stenting is still the default treatment of choice for revascularization of obstructive CAD, the high rate of restenosis compromises the outcomes of endovascular procedures. To overcome restenosis, drug-eluting stents (DES) and drug-coated balloons (DCB) are designed that release antiproliferative drugs like sirolimus, paclitaxel, everolimus, etc., over time to inhibit cell growth and proliferation. Our review aims to summarize the challenges and progress of DES/DCBs in clinical settings.

MATERIAL AND METHODS

The comprehensive review, search and selection encompasses in relevant articles through Google Scholar, Springer online, Cochrane library and PubMed that includes research articles, reviews, letters and communications, various viewpoints, meta-analyses, randomized trials and quasi-randomized trials. Several preclinical and clinical data have been included from National Institutes of Health and clinicaltrials.gov websites.

KEY FINDINGS

Challenges like delayed endothelialization, stent thrombosis (ST), and inflammation was prominent in first-generation DES. Second-generation DES with improved designs and drug coatings enhanced biocompatibility with fewer complications. Gradual absorption of bioresorbable DES over time mitigated long-term issues associated with permanent implants. Polymer-free DES addressed the inflammation concerns but still, they leave behind metallic stents in the vasculature. As an alternative therapeutic strategy, DCB were developed to minimize inflammation in the vessel. Although both DES and DCBs have shown considerable progress, challenges persist.

SIGNIFICANCE

This review illustrates the advancements in the designs, preparation technologies, biodegradable materials, and drugs used as well as challenges associated with DES and DCBs in clinical settings.

Drug Coated Balloon in the Treatment of De Novo Coronary Artery Disease: A Narrative Review

Drug coated balloons (DCBs) are currently indicated in guidelines as a first choice option in the management of instant restenosis, whereas their use in de novo lesions is still debated. The concerns raised after the contrasting results of the initial trials with DCBs in de novo lesions have been more recently overcome by a larger amount of data confirming their safety and effectiveness as compared to drug-eluting stents (DES), with potentially greater benefits being achieved, especially in particular anatomical settings, as in very small or large vessels and bifurcations, but also in selected subsets of higher-risk patients, where a 'leave nothing behind' strategy could offer a reduction of the inflammatory stimulus and thrombotic risk. The present review aims at providing an overview of current available DCB devices and their indications of use based on the results of data achieved so far.

Evolution of drug-eluting coronary stents: a back-and-forth journey from the bench-to-bedside

Coronary stents have revolutionized the treatment of coronary artery disease. Compared with balloon angioplasty, bare-metal stents effectively prevented abrupt vessel closure but were limited by in-stent restenosis due to smooth muscle cell proliferation and neointimal hyperplasia. The first-generation drug-eluting stent (DES), with its antiproliferative drug coating, offered substantial advantages over bare-metal stents as it mitigated the risk of in-stent restenosis. Nonetheless, they had several design limitations that increased the risk of late stent thrombosis. Significant advances in stent design, including thinner struts, enhanced polymers' formulation, and more potent antiproliferative agents, have led to the introduction of new-generation DES with a superior safety profile. Cardiologists have over 20 different DES types to choose from, each with its unique features and characteristics. This review highlights the evolution of stent design and summarizes the clinical data on the different stent types. We conclude by discussing the clinical implications of stent design in high-risk subsets of patients.

Neointimal hyperplasia of ultra-thin stents with microcrystalline sirolimus or durable polymer everolimus-eluting stents: 6- and 24-month results of the DESSOLVE III OCT study

AIMS

The DESSOLVE III OCT substudy aimed to compare serially neointimal hyperplasia volume obstruction (%VO) between the thin-strut MiStent with early polymer elimination and nine-month sustained drug release from microcrystalline sirolimus and the durable polymer-coated everolimus-eluting XIENCE stent at six and 24 months after implantation.

METHODS AND RESULTS

The efficacy endpoint was %VO, calculated as abluminal neointimal volume/stent volume. Thirty-six patients (MiStent 16 patients, 16 lesions; XIENCE 20 patients, 22 lesions) underwent serial OCT evaluation at both six and 24 months. At six months, mean abluminal %VO was significantly lower in the MiStent group than in the XIENCE group (14.54±3.70% vs 19.11±6.70%; p=0.011), whereas the difference in %VO between the two groups decreased at 24 months (20.88±5.72% vs 23.50±7.33%; p=0.24). There was no significant difference in percentage malapposed struts and percentage uncovered struts between the two groups at both time points.

CONCLUSIONS

In the serial comparative OCT analysis of the MiStent versus the XIENCE, the MiStent showed a more favourable efficacy for preventing neointimal formation with comparable strut tissue coverage, as compared with the XIENCE at six months, but this difference in %VO decreased at 24 months so that the difference in neointima at 24 months was no longer significant.

Targeting and deep-penetrating delivery strategy for stented coronary artery by magnetic guidance and ultrasound stimulation

Stent placement is an effective treatment for atherosclerosis, but is suffered from in-stent restenosis (ISR) caused by stent mechanical damage. Conventional ISR treatment such as drug-eluting stents (DES) is challenged by the low therapeutic efficacy and severe complications, unchangeable drug dosage for individuals, and limited drug penetration in the vascular tissue. We hypothesize that magnetic targeting and deep-penetrating delivery strategy by magnetic guidance and ultrasound stimulation might be an effective approach for ISR treatment. In the present study, antiproliferative drug (paclitaxel, PTX) loaded poly (lactide-co-glycolide) (PLGA) nanoparticles (PLGA-PTX) were embedded within the shells of the magnetic nanoparticle coated microbubbles (MMB-PLGA-PTX). Once being targeted to the stent under a magnetic field, a low intensity focused ultrasound (LIFU) is applied to activate stable microbubble oscillations, thereby triggering the release of PLGA-PTX. The generated mechanical force and microstreaming facilitate the penetration of released PLGA-PTX into the thickened vascular tissue and enhance their internalization by smooth muscle cells (SMCs), thereby reducing the clearance by blood flow. In an ex vivo experiment, magnetic targeting improved the accumulation amount of MMB-PLGA-PTX by 10 folds, while the LIFU facilitated the penetration of released PLGA-PTX into the tunica media region of the porcine coronary artery, resulting in prolonged retention time at the stented vascular tissue. With the combination effects, this strategy holds great promise in the precision delivery of antiproliferative drugs to the stented vascular tissue for ISR treatment.

Health Care Monitoring and Treatment for Coronary Artery Diseases: Challenges and Issues

In-stent restenosis concerning the coronary artery refers to the blood clotting-caused re-narrowing of the blocked section of the artery, which is opened using a stent. The failure rate for stents is in the range of 10% to 15%, where they do not remain open, thereby leading to about 40% of the patients with stent implantations requiring repeat procedure within one year, despite increased risk factors and the administration of expensive medicines. Hence, today stent restenosis is a significant cause of deaths globally. Monitoring and treatment matter a lot when it comes to early diagnosis and treatment. A review of the present stent monitoring technology as well as the practical treatment for addressing stent restenosis was conducted. The problems and challenges associated with current stent monitoring technology were illustrated, along with its typical applications. Brief suggestions were given and the progress of stent implants was discussed. It was revealed that prime requisites are needed to achieve good quality implanted stent devices in terms of their size, reliability, etc. This review would positively prompt researchers to augment their efforts towards the expansion of healthcare systems. Lastly, the challenges and concerns associated with nurturing a healthcare system were deliberated with meaningful evaluations.

Comparison of 3-year clinical outcomes between Endeavor Resolute® and Resolute Integrity® zotarolimus-eluting stents in an Asian population

Objective:

There is a scarcity of comparative studies between Endeavor Resolute^®-zotarolimus-eluting stent (R-ZES) and Resolute Integrity^®-ZES (I-ZES) during long-term follow-up periods. Although the stent alloy and the polymer of these two ZESs are similar, the platform and the design of these two stents are different. This study was conducted to compare the efficacy and safety of these two different ZESs in the all-comer Korean patients who underwent percutaneous coronary intervention (PCI) during a 3-year follow-up period.

Methods:

This study was performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki. In this single-center, retrospective, and all-comer patients’ cohort study, a total of 889 patients who underwent PCI with R-ZES (n=394) or I-ZES (n=495) were enrolled. The primary endpoint was the occurrence of major adverse cardiac events (MACEs) defined as all-cause death, nonfatal myocardial infarction (MI), any repeat revascularization including target lesion revascularization (TLR), target vessel revascularization (TVR), and non-TVR, and the secondary endpoint was stent thrombosis (ST) at 3 years.

Results:

To adjust for any potential confounders, the propensity score-adjusted multivariable analysis was performed using the logistic regression model (C-statistics=0.689). The cumulative incidence rates of MACEs [adjusted hazard ratio (aHR), 1.341; 95% confidence interval (CI), 0.615–2.922; p=0.461], all-cause death, nonfatal MI, any repeat revascularization, and ST (aHR, 2.090; 95% CI, 0.163–26.77; p=0.571) were similar between the two groups during the 3-year follow-up period.

Conclusion:

R-ZES and I-ZES demonstrated comparable efficacy and safety after PCI during a 3-year follow-up period. However, these results can perhaps be more precisely defined by other large and long-term follow-up studies in the future.

Comparison of the Major Clinical Outcomes for the Use of Endeavor® and Resolute Integrity® Zotarolimus-Eluting Stents During a Three-Year Follow-up

Background

Endeavor®-zotarolimus-eluting stent (E-ZES) was the first ZES to be developed, and Resolute integrity®-ZES (I-ZES) has been developed more recently. Comparative studies on long-term usage of these two ZESs have been rare.

Objectives

The aim of this study was to compare the efficacy and safety of E-ZES and I-ZES during a long-term follow-up of patients who underwent percutaneous coronary intervention (PCI).

Methods

A total of 767 patients who underwent PCI with E-ZES or I-ZES were eligible for this study. The primary endpoint was the occurrence of major adverse cardiac events (MACEs), defined as the composite of all-cause death, non-fatal myocardial infarction (MI), and any repeat revascularization. The secondary endpoint was stent thrombosis (ST).

Results

After propensity score-matched (PSM) analysis, two PSM groups (193 pairs, n = 386, C-statistic = 0.824) were generated. During the 3-year follow-up period, the cumulative incidence of MACEs (hazard ratio [HR], 0.837; 95% confidence interval [CI], 0.464-1.508; p = 0.553) and ST (HR, 0.398; 95% CI, 0.077-2.052; p = 0.271) was similar for the E-ZES and I-ZES groups. Additionally, the cumulative incidences of all-cause death, cardiac death, non-fatal MI, and any repeat revascularization were not significantly different between the two groups.

Conclusions

Although I-ZES utilizes a more advanced stent platform, stent design, and polymer system than E-ZES, both the ZESs showed comparable efficacy and safety during the 3-year follow-up period in this single-center, all-comers registry. However, further large-scaled, randomized, well-controlled trials with long-term follow-up are needed to verify these results.

Do outcomes following intervention for drug-eluting stent restenosis depend on whether the restenosed stent was polymer-free or polymer-coated?

INTRODUCTION AND OBJECTIVES

Outcomes of patients undergoing percutaneous intervention for drug-eluting stent (DES) restenosis are poorer than those in patients with bare-metal stent restenosis. It is unknown if this is related to the presence of polymer coating. We sought to compare outcomes after interventions for in-stent restenosis (ISR) of polymer-free DES vs durable polymer DES.

METHODS

Patients enrolled in the ISAR-TEST 5 randomized trial who underwent repeat percutaneous intervention for ISR during follow-up were included. Angiographic outcomes at 6 to 8 months and clinical outcomes at 2 years were analyzed and compared between 2 groups according to whether the restenosed stent was a polymer-free or a durable polymer DES. Multivariate analysis was used to adjust for differences between groups.

RESULTS

A total of 326 patients with ISR were included: 220 with ISR in polymer-free DES and 106 with ISR in durable polymer DES. Angiographic follow-up was available for 83.4% of patients. No difference was observed in recurrent binary restenosis between the 2 groups (31.7% vs 27.0%; P=.38; P_adjusted=.29). At 2 years, the composite of death, myocardial infarction, or repeat target lesion revascularization were similar between the 2 groups (35.7% vs 34.0%; HR=1.04, 95%CI, 0.70-1.55; P=.83; P_adjusted=.79). The rate of repeat target lesion revascularization was also similar in the 2 groups (29.8% vs 31.5%; HR=0.91, 95%CI, 0.60-1.39; P=.68; P_adjusted=.62).

CONCLUSIONS

In patients undergoing reintervention for DES-ISR, we found no evidence of differences in outcomes according to whether the restenosed stent was a polymer-free or durable polymer DES.

Micelle-Embedded Layer-by-Layer Coating with Catechol and Phenylboronic Acid for Tunable Drug Loading, Sustained Release, Mild Tissue Response, and Selective Cell Fate for Re-endothelialization

Tunable/sustained drug loading/releasing are of significance in addressing low cytotoxicity, long-term performance, and localized mild healing response in biomedical applications. With an ingenious design, a self-healing sandwiched layer-by-layer (LBL) coating was constructed by using chitosan/heparin as adopted polyelectrolytes with embedding of micelles, in which the chitosan backbone was grafted with catechol and the micelle was modified with exposed phenylboronic acid, endowing the coating with enhanced stability by abundant interactions among coating components (e.g., boric acid ester bond formation, weak intermolecular cross-linking, π-π interactions, and H-bonding). Moreover, rapamycin and atorvastatin calcium were selected as drug candidates and loaded into micelles, followed by drug-releasing behavior study. It was found that the LBL coating maintained a linear growth mode up to 30 cycles, giving a favorable tunability of coating construction and drug loading. The coating could also support sustained release of payloads and provide wild tissue response. With the systematic in vitro and in vivo study, such catechol-phenylboronic acid-enhanced LBL coating with drug loading would also address enhanced antiplatelet adhesion/activation and direct cell fate of endothelial cells and smooth muscle cells via tuning of coating cycles and loaded drugs. With modular assembly, such coating indicated potential for achieving enhanced re-endothelialization for vascular implants.

Biodegradable-Polymer Versus Polymer-Free Drug-Eluting Stents for the Treatment of Coronary Artery Disease

BACKGROUND/PURPOSE

Biodegradable-polymer (BP) and polymer-free (PF) drug eluting stents (DES) were developed to reduce the risk of delayed arterial healing observed with durable-polymer (DP) platforms. Although trials demonstrate BP-DES and PF-DES are non-inferior to DP-DES, there is limited data directly comparing these technologies. We performed a meta-analysis to assess the efficacy and safety of BP-DES versus PF-DES for the treatment of coronary artery disease.

METHODS/MATERIALS

Electronic searches were performed identifying randomized trials comparing BP-DES with PF-DES. Co-primary efficacy endpoints were target vessel revascularization (TVR), target lesion revascularization (TLR) and angiographic in-stent late lumen loss (LLL). Co-secondary safety endpoints were all-cause death, myocardial infarction (MI) and stent thrombosis (ST).

RESULTS

Of 208 studies, 5 met inclusion criteria including 1975 patients. At mean follow-up (14 ± 5 months), BP-DES were associated with significantly reduced rates of TVR (OR 0.58, 95%CI 0.37-0.92, p = 0.02), TLR (4.7% vs 9.5%) (OR 0.48, 95%CI 0.31-0.75, p = 0.001) and in-stent LLL (pooled mean difference -0.20 mm, 95%CI -0.24 to -0.16, p < 0.001). There was no difference in safety, including all-cause death (OR 1.24, 95%CI 0.68-2.28, p = 0.48), MI (OR 0.92, 95%CI 0.54-1.56, p = 0.75) or ST (OR 1.58, 95%CI 0.67-3.73, p = 0.30).

CONCLUSIONS

These data suggests that BP-DES are more efficacious when compared with PF-DES for the treatment of CAD.

Sustained drug release using cobalt oxide nanowires for the preparation of polymer-free drug-eluting stents

Polymer-based drug-eluting stents (DESs) represented attractive application for the treatment of cardiovascular diseases; however, polymer coating has caused serious adverse responses to tissues such as chronic inflammation due to acidic by-products. Therefore, polymer-free DESs have recently emerged as promising candidates for the treatment; however, burst release of drug(s) from the surface limited its applications. In this study, we focused on delivery of therapeutic drug from polymer-free (or -less) DESs through surface modification using cobalt oxide nanowires (Co₃O₄ NWs) to improve and control the drug release. The results demonstrated that Co₃O₄ NWs could be simply fabricated on cobalt-chromium substrate by ammonia-evaporation-induced method. The Co₃O₄ NWs were uniformly arrayed with diameters of 50-100 nm and lengths of 10 µm. It was found that Co₃O₄ NWs were comparatively stable without any delamination or change of the morphology under in vitro long-term stability using circulating system. Sirolimus was used as a model drug for studying in vitro release behavior under physiological conditions. The sirolimus release behavior from flat cobalt-chromium showed an initial burst (over 90%) after one day. On the other hand, Co₃O₄ NWs presented a sustained sirolimus release rate for up to seven days. Similarly, the polymer-less specimens on Co₃O₄ NWs substrates sustained sirolimus release for a longer-period of time when compared to flat Co-Cr substrates. In summary, the current approach of using Co₃O₄ NWs-based substrates might have a great potential to sustain drug release for drug-eluting implants and medical devices including stents.

Palliating Premature Infants With Obstructed Total Anomalous Pulmonary Venous Connection via Catheterization

Obstructed total anomalous pulmonary venous connection (TAPVC) involves anomalous drainage of all pulmonary veins to a location other than the left atrium and typically causes significant respiratory symptoms requiring urgent surgical repair. Premature infants born with obstructed TAPVC are often not considered to be suitable surgical candidates due to their size and therefore pose a significant treatment dilemma. Catheter-based interventions provide a temporizing option for infants with obstructed TAPVC, allowing for hemodynamic stabilization and growth until surgical intervention is feasible. We describe the course of two premature infants with obstructed TAPVC who were palliated with stenting of their anomalous pulmonary veins. Both infants required repeat catheter-based intervention for recurrent stenosis and ultimately underwent successful surgical repair at an acceptable weight and corrected gestational age. We propose that a novel catheter-based approach to initial management may be a beneficial option in the premature and low-weight patient population.

Novel bifurcation stents coated with bioabsorbable nanofibers with extended and controlled release of rosuvastatin and paclitaxel

A novel bifurcation stent coated with bioabsorbable nanofibers that deliver the extended and controlled release of rosuvastatin and paclitaxel was developed. Bioabsorbable bifurcation stents, consisting of a double-slit tubular main body and two spiral branches, were manufactured. Bi-layered poly (lactic-co-glycolic acid) nanofibers that contained rosuvastatin and paclitaxel were used for treating the stents. Various properties of the fabricated stents, including compression strengths, collapse pressure, water contact angle and flow properties within a circulation model, were quantified. In vitro nanofibrous elution chromatography assays from the drug-loading bifurcation stents were carried out for the release patterns of pharmaceuticals. The effectiveness of eluted rosuvastatin and paclitaxel in inhibiting the adhesion of platelets as well as the proliferation of smooth muscle cells (SMCs) were studied, respectively. The experimental results suggest that bioabsorbable nanofibrous bifurcation stents released high concentrations of rosuvastatin and paclitaxel for 27 and 70 days, respectively. The eluted drugs of rosuvastatin and paclitaxel effectively reduced adherent platelets and the proliferation of SMCs. The developed bioabsorbable nanofibrous bifurcation stents herein may provide a promising means of treating cardiovascular bifurcation lesions.

Rhombic-Shaped Channel Stent with Enhanced Drug Capacity and Fatigue Life

A drug-eluting stent with rhombic-shaped drug reservoirs is proposed, aimed at providing long-term drug delivery and enhanced fatigue life. Unique rhombic-shaped reservoirs or channels on the stent struts can increase the total drug capacity and improve the stress distribution for longer fatigue life, without compromising other important clinical attributes. Our rhombic-shaped channel stent increases the total drug capacity by multiple times. Its fatigue safety factor, even with the large rhombic cutouts on the stent struts, could be 50% higher than that of the conventional drug-eluting stent. A pulsed fiber-optic laser and a series of expansions and heat treatments were used to make the first prototype of our rhombic-shaped channel stent. This new concept may open up a wide variety of new treatment options and opportunities for the medical industry in the future.

Stent Polymers: Do They Make a Difference?

The necessity of polymers on drug-eluting stent (DES) platforms is dictated by the need of an adequate amount and optimal release kinetic of the antiproliferative drugs for achieving ideal DES performance. However, the chronic vessel wall inflammation related to permanent polymer persistence after the drug has been eluted might trigger late restenosis and stent thrombosis. Biodegradable polymers have the potential to avoid these adverse events. A variety of biodegradable polymer DES platforms have been clinically tested, showing equal outcomes with the standard-bearer permanent polymer DES within the first year of implantation. At longer-term follow-up, promising lower rates of stent thrombosis have been observed with the early generation biodegradable polymer DES platforms compared to first-generation DES. Whether this safety benefit still persists with newer biodegradable polymer DES generations against second-generation permanent polymer DES needs to be explored.

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

BACKGROUND

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

OBJECTIVES

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

SEARCH METHODS

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

SELECTION CRITERIA

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

DATA COLLECTION AND ANALYSIS

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

MAIN RESULTS

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

AUTHORS' CONCLUSIONS

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

Development of a New Hybrid Biodegradable Drug-Eluting Stent for the Treatment of Peripheral Artery Disease

This study aimed to develop a new biodegradable stent for peripheral artery disease (PAD) that could provide sufficient radial force to maintain long-term patency and flexibility. All self-expandable hybrid biodegradable stents were designed by using a knitting structure composed of poly-L-lactic acid (PLLA) and nitinol. Four different types of stents were implanted in 20 iliac arteries in 10 mini pigs as follows: a bare-metal stent (BMS) (group 1, n = 5), a drug-free hybrid stent (group 2, n = 5), a 50% (50 : 100, w/w) paclitaxel (PTX)/poly-lactide-co-glycolic acid (PLGA; fast PTX-releasing form) hybrid stent (group 3, n = 5), and a 30% (30 : 100, w/w) PTX/PLGA (slow PTX-releasing form) hybrid stent (group 4, n = 5). We performed follow-up angiography and intravascular ultrasonography (IVUS) at 4 and 8 weeks. In a comparison of groups 1, 2, 3, and 4, less diameter stenosis was observed in the angiographic analysis for group 4 at the 4-week follow-up (19.0%  ±  12.7% versus 39.3%  ±  18.1% versus 46.8%  ±  38.0% versus 4.8%  ±  4.2%, resp.; p = 0.032). IVUS findings further suggested that the neointima of the patients in group 4 tended to be lesser than those of the others. Our new biodegradable 30% PTX/PLGA (slow-releasing form) stent showed more favorable results for patency than the other stent types.

Numerical simulation on the effects of drug-eluting stents with different bending angles on hemodynamics and drug distribution

Implantation of drug-eluting stents in curved blood vessels may cause changes in hemodynamics and drug distribution, and even provoke in-stent restenosis. Due to the complexity of building three-dimensional (3-D) curved stent model, few studies have gone through such numerical simulations. In this study, three virtual stent models with different bending angles (0°, 30° and 90°) were developed to numerically investigate the distribution of wall shear stress (WSS) and drug concentration. The results showed that (1) the low-WSS regions in the inner bend of the stent models increased with the bending angles; (2) the drug concentration differed between the inner and outer bends of the stents but irrespective to the changes of bending angle; (3) the pattern of drug concentration for the curved stents found similar to that of the straight stents, and the phenomenon, 'proximal part low and distal part high' in the drug concentration showed in both the straight and curved stents. The increase in bending angles from 30° to 90° had little effect on the WSS and drug concentration; however, the largest effect of the curved stents was the remarkable difference of drug concentration between the inner and outer bends of the stents-about 20 %. Hence, it is feasible that quick analysis focused on the straight stents instead of the curved stents.

Novel Sirolimus–Coated Balloon Catheter

Background—

Limus-eluting stents are dominating coronary interventions, although paclitaxel is the only drug on balloon catheters with proven inhibition of restenosis. Neointimal inhibition by limus-coated balloons has been shown in few animal studies, but data from randomized clinical trials are not available. The aim of the present preclinical studies was to achieve high and persistent sirolimus levels in the vessel wall after administration by a coated balloon.

Methods and Results—

Different coating formulations and doses were studied in the porcine coronary model to investigate sirolimus tissue levels at different time points as well as efficacy at 1 month using quantitative coronary angiography and histomorphometry. Loss of the selected coating in the valve, guiding catheter, and blood was low (2±14% of dose). Acute drug transfer to the vessel wall was 14.4±4.6% with the crystalline coating, whereas the amorphous coatings were less effective in this respect. Persistence of sirolimus in the vessel wall until 1 month was 40% to 50% of the transferred drug. At 1-month follow-up, a modest but significant reduction of neointimal growth was demonstrated in a dose range from 4 μg/mm 2 to 2×7 μg/mm 2 , for example, maximum neointimal thickness of 0.38±0.13 versus 0.65±0.21 mm in the uncoated control group.

Conclusions—

Various sirolimus-coated balloons effectively reduce neointimal proliferation in the porcine coronary model but differ considerably in retention time in the vessel wall. It has to be determined if such a formulation with persistent high vessel concentration will result in a relevant clinical effect.

Relative dose and vascular response after drug-eluting stent implantation: A dosimetric 3D-intravascular ultrasound study

BACKGROUND

In drug-eluting stents (DESs), the theoretical drug dose exposed to the vessel wall per stent surface area may vary due to the fixed loading dose and differences in the stent surface area once expanded in varying vessel sizes. The aim of this study was to evaluate the potential effects of different dose intensities, as estimated by 3D-IVUS dosimetry, on vascular response after DES implantation.

METHODS

Follow-up (6-9 months) 3D-IVUS was performed in 840 coronary lesions treated with a single DES of the following types: sirolimus (SES, n=148), paclitaxel (PES, n=162), Endeavor zotarolimus (E-ZES, n=233), Resolute zotarolimus (R-ZES, n=147), and everolimus (EES, n=150). Volume index (volume/length, mm(3)/mm) was obtained for vessel, lumen, plaque, stent, and neointima. In each lesion, exposed dose intensity was calculated as known loading dose divided by measured luminal surface area of the stented segment. Lesions were divided into tertiles based on the exposed dose intensity: high, medium, and low dose groups.

RESULTS

The exposed dose intensity ranged 0.74-1.76 μg/mm(2) for SES, 0.41-1.18 μg/mm(2) for PES, 0.71-1.57 μg/mm(2) for E-ZES, 0.72-1.63 μg/mm(2) for R-ZES, and 0.40-0.99 μg/mm(2) for EES. All types of DES showed no significant difference in neointimal hyperplasia among the 3 groups, except that E-ZES showed significantly less neointimal hyperplasia in the high dose group.

CONCLUSIONS

Detailed 3D-IVUS revealed significant lesion-to-lesion variability in dose intensity exposed to the vessel wall following DES implantation. However, the major types of DES appear to yield equally effective neointimal suppression, despite the varying dose intensity, except for E-ZES.

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.

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.

NUMERICAL ANALYSIS OF THE IMPACT OF ATHEROSCLEROTIC PLAQUE AND DIFFERENT STENT SPACING ON DRUG DEPOSITION

Objectives: To investigate the influence of atherosclerotic plaque and different drug-eluting stent (DES) spacing on drug deposition in the curved artery wall. Methods: Based on the computational fluid dynamics (CFD) method, the numerical investigation on distributions of drug concentration in the artery wall was carried out considering three different interstrut distances and five values of the plaque diffusion coefficients. The results were compared with those of the model without plaque. Results: Under the same stent spacing, drug deposition weakly increased with the increasing plaque diffusion coefficient. When the same diffusion coefficient value was taken, drug deposition presented steady growth with the expansion of stent spacing. When the stent spacing was of 1-strut length or the diffusion coefficient of plaque was much smaller than the diffusion coefficient of tissue (an order of magnitude or more), the drug deposition would be evidently reduced. Conclusions: In a curved artery, the stent spacing is still an important factor in drug deposition. The diffusion coefficients of plaque have little influence on the average drug concentration, but they show a relatively obvious effect on drug distributions.

Mechanisms of tissue uptake and retention of paclitaxel-coated balloons: impact on neointimal proliferation and healing

Background

The efficacy of paclitaxel-coated balloons (PCB) for restenosis prevention has been demonstrated in humans. However, the mechanism of action for sustained drug retention and biological efficacy following single-time drug delivery is still unknown.

Methods and results

The pharmacokinetic profile and differences in drug concentration (vessel surface vs arterial wall) of two different paclitaxel coating formulations (3 µg/mm²) displaying opposite solubility characteristics (CC=crystalline vs AC=amorphous) were tested in vivo and compared with paclitaxel-eluting stents (PES). Also, the biological effect of both PCB formulations on vascular healing was tested in the porcine coronary injury model. One hour following balloon inflation, both formulations achieved similar arterial paclitaxel levels (CC=310 vs AC=245 ng/mg; p=NS). At 24 h, the CC maintained similar tissue concentrations, whereas the AC tissue levels declined by 99% (p<0.01). At this time point, arterial levels were 20-fold (CC) and 5-fold (AC) times higher compared to the PES group (p<0.05). At 28 days, arterial levels retained were 9.2% (CC) and 0.04% (AC, p<0.01) of the baseline levels. Paclitaxel concentration on the vessel surface was higher in the CC at 1 (CC=36.7% vs AC=13.1%, p<0.05) and 7 days (CC=38.4% vs AC=11%, p<0.05). In addition, the CC induced higher levels of neointimal inhibition, fibrin deposition and delayed healing compared with the AC group.

Conclusions

The presence of paclitaxel deposits on the vessel surface driving diffusion into the arterial tissue in a time-dependent fashion supports the mechanism of action of PCB. This specific pharmacokinetic behaviour influences the patterns of neointimal formation and healing.

Reinforcement of interfacial adhesion of a coated polymer layer on a cobalt-chromium surface for drug-eluting stents

During the balloon expansion of several commercially available drug-eluting stents, various types of defects in the polymer layer have been observed. The aim of this study is to prevent these defects by increasing the interfacial adhesion between the metal substrate and the drug-in-polymer matrix using poly(caprolactone) (PCL) brushes onto a cobalt-chromium (Co-Cr or CC) alloy surface. The chemical modification of the Co-Cr surface was accomplished by grafting ricinoleic acid (RA) onto the metal substrate followed by surface-initiated ring opening polymerization of ε-caprolactone. The unmodified, RA-grafted (CC-RA), and PCL-grafted Co-Cr substrates (CC-RA-PCL3D and CC-RA-PCL6D) were characterized by various surface analyses. Poly(d,l-lactide) containing sirolimus was spray coated onto the unmodified and modified substrates. The adhesion property of the polymer coating on the PCL-grafted surfaces was improved compared to those of other samples. Among all of the drug-in-polymer coated samples, both CC-RA-PCL3D and CC-RA-PCL6D exhibited a stabilized drug release profile over 49 days. It was also revealed that CC-RA-PCL6D showed the slowest drug release of all the samples. On the basis of these results, the proposed nanocoupling method has shown not only improved adhesion of the drug-in-polymer matrix to the Co-Cr substrate but also controlled drug release.

Intracoronary optical coherence tomography and histology of overlapping everolimus-eluting bioresorbable vascular scaffolds in a porcine coronary artery model: the potential implications for clinical practice

OBJECTIVES

This study sought to assess the vascular response of overlapping Absorb stents compared with overlapping newer-generation everolimus-eluting metallic platform stents (Xience V [XV]) in a porcine coronary artery model.

BACKGROUND

The everolimus-eluting bioresorbable vascular scaffold (Absorb) is a novel approach to treating coronary lesions. A persistent inflammatory response, fibrin deposition, and delayed endothelialization have been reported with overlapping first-generation drug-eluting stents.

METHODS

Forty-one overlapping Absorb and overlapping Xience V (XV) devices (3.0 × 12 mm) were implanted in the main coronary arteries of 17 nonatherosclerotic pigs with 10% overstretch. Implanted coronary arteries were evaluated by optical coherence tomography (OCT) at 28 days (Absorb n = 11, XV n = 7) and 90 days (Absorb n = 11, XV n = 8), with immediate histological evaluation following euthanasia at the same time points. One animal from each time point was evaluated with scanning electron microscopy alone. A total of 1,407 cross sections were analyzed by OCT and 148 cross sections analyzed histologically.

RESULTS

At 28 days in the overlap, OCT analyses indicated 80.1% of Absorb struts and 99.4% of XV struts to be covered (p < 0.0001), corresponding to histological observations of struts with cellular coverage of 75.4% and 99.6%, respectively (p < 0.001). Uncovered struts were almost exclusively related to the presence of "stacked" Absorb struts, that is, with a direct overlay configuration. At 90 days, overlapping Absorb and overlapping XV struts demonstrated >99% strut coverage by OCT and histology, with no evidence of a significant inflammatory process, and comparable % volume obstructions.

CONCLUSIONS

In porcine coronary arteries implanted with overlapping Absorb or overlapping XV struts, strut coverage is delayed at 28 days in overlapping Absorb, dependent on the overlay configuration of the thicker Absorb struts. At 90 days, both overlapping Absorb and overlapping XV have comparable strut coverage. The implications of increased strut thickness may have important clinical and design considerations for bioresorbable platforms.

Emerging technologies: polymer-free phospholipid encapsulated sirolimus nanocarriers for the controlled release of drug from a stent-plus-balloon or a stand-alone balloon catheter

Drug-eluting stents have proven to be effective in reducing the risk of late restenosis. In order to achieve a controlled and prolonged release of the antiproliferative agent, current drug-eluting stents utilise various biodegradable as well as non-erodible polymeric blends to coat the stent surface and to serve as drug carriers. The utilisation of polymeric compounds in current drug-eluting stents may eventually limit their performance as well as their clinical applicability due to the potential induction of undesirable local reactions. The development of alternative, polymer-free drug carriers has the potential to overcome some of the limitations of current drug-eluting stent formulations. Moreover, improvements in drug carriers may also result in an expansion of the technological possibilities for other intravascular drug delivery systems, such as metal-free or even implant-free solutions. This article describes the structure and the preclinical validation profile of a novel phospholipid encapsulated sirolimus nanocarrier, used as a coating in two formulations: a coronary stent-plus-balloon system and a stand-alone balloon catheter. The nanoparticles provided a stable, even and homogenous coating to the devices in both formulations. Dose-finding studies allowed the most appropriate identification of the best nanoparticle structure associated with an extremely efficient transfer of drug to all layers of the vessel wall, achieving high tissue concentrations that persisted days after the application, with low systemic drug leaks.

Safety and efficacy of low-dose paclitaxel utilizing the cobra-P drug-eluting stent system with a novel biodegradable coating in de novo coronary lesions: the PLUS-ONE first-in-man study

BACKGROUND

The Cobra-P drug-eluting stent (DES) system consists of cobalt chromium alloy with bio-absorbable siloxane sol-gel matrix coating that elutes low dose paclitaxel within 6 months. The aim of this first-in-man trial was to evaluate the safety and performance of 2 doses of the Cobra-P DES.

METHODS

A total of 60 lesions (54 patients) were sequentially assigned to 2 different paclitaxel doses: group A (3.7 μg/18mm, n=30) or group B (8 μg/18mm, n=30). The primary endpoint was MACE at 4 months defined as cardiac death, myocardial infarction, and target lesion revascularization.

RESULTS

Patient and lesion characteristics were matched between the 2 groups except for male sex. MACE at 4 months was 3.3% and 0% respectively (P=1.000) and at 1-year follow-up remained unchanged. In-stent late loss at 4 months was similar in both groups (0.36 ± 0.30mm and 0.34 ± 0.20mm P=.773).

CONCLUSIONS

In this FIM study, implantation of the Cobra-P low dose paclitaxel-eluting stent with a bioabsorbable sol-gel coating was proven to be feasible and safe. Moderate neointimal proliferation was observed as well as an acceptable MACE rate up to 1 year.

NUMERICAL SIMULATION ON THE EFFECTS OF DRUG-ELUTING STENTS WITH DIFFERENT LINKS ON HEMODYNAMICS AND DRUG CONCENTRATION DISTRIBUTION

The changes of hemodynamics and drug distribution caused by the implantation of drug-eluting stents (DES) have a significant influence on the in-stent restenosis. The present study numerically carried out a comparative study of hemodynamics and drug distribution using four different links of DES: Cordis BX velocity (Model A), Jostent flex (Model B), Sorin Carbostent (Model C), and DT-2 (Model D). The results showed that (1) low wall shear stress (WSS) distribution region spread widely in Model C (16.16%), with the least in Model B (10.35%); (2) Model C has relatively uniform drug concentration and causes of fewer low drug concentration region; and (3) Model A has the largest drug concentration, but also the most uneven distribution of drug. It was concluded that DES with circumferential links helps to improve in-stent restenosis as compared with that with longitudinal designs, and flexible links led to more uniformly and smoothly distributed blood flow than rigid links. However, the links with longitudinal designs had a better performance as drug release carrier than that with circumferential design. And if the links are too close together, the drug cannot be released effectively in the blood vessels. The current study helps to enhance our understanding of the performance of DES and provides assistance for optimal design and selection of DES.

Critical challenges to the design of drug-eluting medical devices

Drug-eluting devices cover a wide variety of possible product concepts. The design constraints for modified or sustained local delivery technologies that are compatible with medical devices are quite different from those constraints with any conventional dosage forms. To develop a successful development strategy from proof-of-concept to commercialization, it is of paramount importance to assess how drug delivery affects the desired mechanism of action of such combination products. Starting at the feasibility stage, the project team must have a clear understanding of the performance targets expected by patients and physicians/surgeons. In addition, R&D staff must anticipate and proactively address the differences in technical, quality and regulatory requirements from drug delivery and medical device perspectives. Through the eyes of drug delivery, this article will describe common challenges encountered in the development of drug-eluting devices and offer relevant mitigation strategies.

Comparative efficacy of 2 zotarolimus-eluting stent generations: resolute versus endeavor stents in patients with coronary artery disease

BACKGROUND

The Resolute zotarolimus-eluting stent (R-ZES) utilizes the same metallic platform and anti-restenotic drug as the Endeavor zotarolimus-eluting stent (E-ZES) but is coated with a more biocompatible polymer with enhanced drug-release kinetics. The aim of this study was to compare the long-term clinical outcomes of 2 zotarolimus-eluting stent generations.

METHODS

In two randomized trials with broad inclusion criteria (ISAR-TEST 2 and ISAR-TEST 5), 1,000 patients were treated with R-ZES and 339 patients treated with E-ZES. In both trials follow-up angiography was scheduled at 6 to 8 months. The efficacy endpoint of interest was target lesion revascularization and the safety endpoints were the combined incidence of cardiac death or myocardial infarction related to target vessel as well as the incidence of definite stent thrombosis at 2-year follow-up.

RESULTS

The incidence of target lesion revascularization at 2 years was 12.0% in the R-ZES group and 16.0% in the E-ZES (HR 0.72 [95% CI: 0.52-1.00], P = .052). The incidence of cardiac death or myocardial infarction was 5.5% vs. 4.8% (HR 1.15, [95% CI: 0.66-2.02], P = .62) and of definite stent thrombosis was 0.4% vs. 0.6% (HR 0.68, [95% CI: 0.12-3.72], P = .66), respectively. All measures of angiographic restenosis were in favor of the R-ZES; in-stent late lumen loss was 0.29 ± 0.56 with the R-ZES versus 0.58 ± 0.55 with the E-ZES (P < .0001).

CONCLUSIONS

Comparison of the 2 Food and Drug Administration-approved zotarolimus-eluting stents suggested that the R-ZES as compared to the E-ZES displayed overall superior antirestenotic efficacy. Both devices were associated with a similar low risk of adverse safety events through 2 years.

Biodegradable versus durable polymer drug eluting stents in coronary artery disease: insights from a meta-analysis of 5,834 patients

BACKGROUND

Biodegradable polymer drug eluting stents (BP-DES) have been developed to overcome the limitations of first generation durable polymer DES (DP-DES) but the clinical results of different BP-DES are not consistent. We performed a meta-analysis to compare the outcomes of BP-DES and DP-DES in the treatment of coronary artery disease (CAD).

METHODS AND RESULTS

Online databases including MEDLINE were searched for studies comparing BP-DES and DP-DES for obstructive CAD that reported rates for overall mortality, myocardial infarction (MI), late stent thrombosis (LST), target lesion revascularization (TLR) and late lumen loss (LLL) with a follow-up of ≥ 6 months. Ten studies (5834 patients) with a 1-year median follow-up were included in the meta-analysis. When comparing patients treated with DP-DES and BP-DES those treated with BP-DES had lower LLL (in-stent: weighted mean difference (WMD) -0.10 mm, 95% CI = -0.17 to -0.03 mm, p = 0.004; in-segment: WMD -0.06 mm, 95% CI = -0.10 to -0.01 mm, p = 0.01) with lower TLR rates (OR 0.67, 95% CI = 0.47 to 0.98, p = 0.04). However, BP-DES did not improve mortality (OR 0.97, 95% CI = 0.73 to 1.29, p = 0.83), MI (OR 1.13, 95% CI = 0.87 to 1.46, p = 0.36) or LST rates (OR 0.64, 95% CI = 0.36 to 1.16, p = 0.14). A pre-specified subgroup analysis of Biolimus BP-DES confirmed significant LLL reduction without differences in other clinical endpoints. Meta-regression analysis demonstrated a strong significant inverse correlation between LLL and reference coronary diameter (p < 0.001).

CONCLUSIONS

Our present meta-analysis showed that BP-DES when compared with DP-DES significantly reduced LLL and TVR but without clear benefits on mortality, MI and LST rates. (Clinicaltrials.gov identifier: NCT01466634).

Effects of through-hole drug reservoirs on key clinical attributes for drug-eluting depot stent

Atherosclerosis, a condition related to cholesterol build-up and thickening of the inner wall of the artery, narrows or occludes the artery lumen. The drug-eluting stent is a major breakthrough for the treatment of such coronary artery diseases. In recent years, another innovative variation of the drug-eluting stent with drug reservoirs has been introduced. It allows programmable drug delivery with spatial and temporal control and has several potential advantages over traditional drug-eluting stents. However, creating such reservoirs on the stent struts may weaken the stent scaffolding and compromise its mechanical integrity. In this paper, the effects of these micro-sized through-hole drug reservoirs on several key clinically relevant functional attributes of the depot stent were investigated. Finite element models were developed to predict the mechanical integrity of a balloon-expandable stent at various stages such as manufacturing and deployment, as well as the stent radial strength and fatigue life. Results show that (1) creating drug reservoirs on a stent could impact the stent fatigue resistance to some degree; (2) drug reservoirs on the stent crowns led to much greater loss in all key clinical attributes than reservoirs on other locations; (3) reservoir shape change resulted in little differences in all key clinical attributes; (4) for the same drug loading capacity, larger and fewer reservoirs yielded lower equivalent plastic strain and radial strength but higher fatigue safety factor; and (5) the proposed depot stent was proven to be a feasible design. Its total drug capacity could be tripled with acceptable marginal trade-off in key clinical attributes. These results can serve as the guidelines to help future stent designs to achieve the best combination of stent mechanical integrity and smart drug delivery in the future, thereby opening up a wide variety of new treatment potentials and opportunities.

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.