Enhanced drug delivery capabilities from stents coated with absorbable polymer and crystalline drug

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.

Regulatory perspectives of combination products

Combination products with a wide range of clinical applications represent a unique class of medical products that are composed of more than a singular medical device or drug/biological product. The product research and development, clinical translation as well as regulatory evaluation of combination products are complex and challenging. This review firstly introduced the origin, definition and designation of combination products. Key areas of systematic regulatory review on the safety and efficacy of device-led/supervised combination products were then presented. Preclinical and clinical evaluation of combination products was discussed. Lastly, the research prospect of regulatory science for combination products was described. New tools of computational modeling and simulation, novel technologies such as artificial intelligence, needs of developing new standards, evidence-based research methods, new approaches including the designation of innovative or breakthrough medical products have been developed and could be used to assess the safety, efficacy, quality and performance of combination products. Taken together, the fast development of combination products with great potentials in healthcare provides new opportunities for the advancement of regulatory review as well as regulatory science.

Viscoelastic Behavior of Drug-Loaded Polyurethane

Drug-eluting stents are desirable platforms for local medicine delivery. However, the incorporation of drugs into polymers can influence the mechanical and physicochemical properties of said matrix, which is a topic that is still poorly understood. In fact, this is more noticeable since the apposition is most often accompanied by mechanical stresses on the polymer coating, which can induce therapeutic failure that can result in death. It is therefore necessary to better understand their behavior by examining their properties in conditions such as those in living beings. We studied polyurethane drug carriers made in-house. Diclofenac epolamine was chosen as a model hydrophilic medicine. We used thermal measurements (DMTA) and tensile tests. The aim was to establish the influence of the loading and release of the drug on the physicochemical properties of this polymer in the presence of a stagnant or circulating fluid medium, phosphate-buffered saline (PBS). For the two PU/drug loadings studied, the effect of the initial drug load was more marked. The free volume fraction and the number of pores in the samples increased with the increasing percent of the drug and with release time. The kinetic profiles were accelerated with the loading ratio and with the presence of flow. Young's modulus and ultimate stress were not significantly influenced by the release time. A relevant relationship between the tensile properties and the viscoelastic behavior of the samples was developed. Our results have implications for optimizing the performance of drug coatings for stents.

Degradation Behavior of Polymers Used as Coating Materials for Drug Delivery-A Basic Review

The purpose of the work was to emphasize the main differences and similarities in the degradation mechanisms in the case of polymeric coatings compared with the bulk ones. Combined with the current background, this work reviews the properties of commonly utilized degradable polymers in drug delivery, the factors affecting degradation mechanism, testing methods while offering a retrospective on the evolution of the controlled release of biodegradable polymeric coatings. A literature survey on stability and degradation of different polymeric coatings, which were thoroughly evaluated by different techniques, e.g., polymer mass loss measurements, surface, structural and chemical analysis, was completed. Moreover, we analyzed some shortcomings of the degradation behavior of biopolymers in form of coatings and briefly proposed some solving directions to the main existing problems (e.g., improving measuring techniques resolution, elucidation of complete mathematical analysis of the different degradation mechanisms). Deep studies are still necessary on the dynamic changes which occur to biodegradable polymeric coatings which can help to envisage the future performance of synthesized films designed to be used as medical devices with application in drug delivery.

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.

The state-of-the-art coronary stent with crystallized sirolimus: the MiStent technology and its clinical program

Drug-eluting stents (DES) have been developed over recent decades and the implantation of DES is the standard of care in contemporary percutaneous coronary intervention for patients with coronary artery disease. The MiStent sirolimus-eluting stent has several unique features; ultra-thin (64 μm) struts, a bioresorbable polymer and a controlled drug release from microcrystalline sirolimus as a reservoir embedded in the vessel wall. Results of recent clinical trials demonstrated the potential performance of this state-of-the-art DES. In the present review, we provide an overview of the development of DES, in particular the design and performance of the novel MiStent sirolimus-eluting stent from technological and clinical points of view and discuss the potentials of this new type of DES.

Comparison of One-Year Outcomes Between the ihtDEStiny BD Stent and the Durable-Polymer Everolimus- and Zotarolimus-Eluting Stents: A Propensity-Score-Matched Analysis

OBJECTIVES

We sought to evaluate clinical outcomes in patients treated with the drug-eluting stent ihtDEStiny BD.

BACKGROUND

The ihtDEStiny BD stent is a metallic sirolimus eluting stent with a biodegradable polymer with both drug and polymer coating the abluminal surface of the stent and balloon.

METHODS

In this study, the clinical outcomes of a multicenter prospective registry of patients treated with this stent (DEStiny group) were analyzed and compared with those of a control group of patients treated with durable polymer everolimus or zotarolimus eluting stents (CONTROL group) paired by propensity score matching. Primary outcome was the target vessel failure (TVF) at 12 months defined as a composite of cardiac death, target vessel myocardial infarction (TV-MI) and target vessel revascularization (TVR).

RESULTS

A total of 350 patients were included in the DESTtiny group. The control group consisted initially of 1368 patients, but after matching (1:1) 350 patients were selected as CONTROL group. The baseline clinical, angiographic and procedural characteristics were quite comparable in both groups. At 12 months follow up the TVF was 6.6% in DEStiny group and 6.3% in CONTROL group (p = 0.8). No differences were observed for any of the individual components of the primary endpoint: cardiac death 1.1% vs. 1.4%, TV-MI 3.4% vs. 3.7% and TVR 2.6% vs. 2.3% respectively.

CONCLUSIONS

The use of ihtDEStiny stent in real practice is associated with a clinical performance at 12 months follow up that appears to be non-inferior to the most widely used and largely evidence supported durable polymer drug eluting stents. A longer follow up is warranted.

Final 3-Year Outcomes of MiStent Biodegradable Polymer Crystalline Sirolimus-Eluting Stent Versus Xience Permanent Polymer Everolimus-Eluting Stent: Insights From the DESSOLVE III All-Comers Randomized Trial

BACKGROUND

Numerous randomized clinical trials have demonstrated the superiority of thin-strut biodegradable polymer second-generation drug-eluting stent to the first-generation drug-eluting stent and the noninferiority to the thin-strut second-generation permanent polymer drug-eluting stent. Data on long-term clinical outcomes with a novel ultrathin drug-eluting stent, to date, are limited.

METHODS

The DESSOLVE III trial (Multicenter Randomized Study of the MiStent Sirolimus Eluting Absorbable Polymer Stent System for Revascularization of Coronary Arteries; n=1398) is a prospective, multicenter, single-blinded, all-comers, randomized controlled trial (NCT02385279), allocating in a 1:1 ratio to either ultrathin-strut biodegradable polymer MiStent sirolimus-eluting stent or to thin-strut permanent polymer Xience everolimus-eluting stent. The primary end point was device-oriented composite end point, defined as the composite of cardiac death, target vessel myocardial infarction, or clinically indicated target lesion revascularization. The secondary end point was patient-oriented composite end point, defined as the composite of all-cause mortality, any myocardial infarction, or any revascularization.

RESULTS

At 3 years, follow-up data were available in 1381 patients (98.8%). The primary end point of device-oriented composite end point occurred in 10.5% for MiStent sirolimus-eluting stent and in 11.5% for Xience everolimus-eluting stent (P=0.55). Rates of cardiac death (3.9% versus 3.8%; P=0.88), target vessel myocardial infarction (3.2% versus 2.5%; P=0.43), and clinically indicated target lesion revascularization (5.2% versus 6.5%; P=0.30) did not differ significantly between the 2 devices. The rate of definite or probable stent thrombosis was infrequent and similar between the 2 arms (1.2% versus 1.5%; P=0.64). The 90-day landmark analysis showed no significant difference in device-oriented composite end point between the 2 groups after polymer degradation of MiStent. The risk of patient-oriented composite end point was comparable between the 2 groups (22.7% versus 22.9%; P=0.34).

CONCLUSIONS

In the DESSOLVE III trial, early safety and efficacy with MiStent sirolimus-eluting bioabsorbable polymer-coated stent are confirmed at a longer term follow-up when compared with Xience everolimus-eluting permanent polymer-coated stent in a large all-comers population. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02385279.

Clinical Prognosis Associated With the Use of Overlapping Stents With Homogenous Versus Heterogeneous Pharmacological Characteristics for the Treatment of Diffuse Coronary Artery Disease

BACKGROUND

The clinical impact of percutaneous coronary intervention (PCI) and implantation of overlapping stents (OS) using platforms with the same versus different pharmacological characteristics is unknown. Our objective was to compare the outcomes of PCI with OS according to their pharmacological characteristics.

METHODS

In this observational single-center registry, we included all PCI performed from April 2014 to December 2018 in which overlapping drug-eluting stents were implanted. Two groups were created according to whether the stents release the same drug [homogeneous: (HO)] or different [heterogeneous: (HE)]. The primary endpoint was the need for target lesion revascularization (TLR). Clinical assessment was performed after the procedure, bianually and at the end of follow-up (June 2019).

RESULTS

381 lesions with OS (HO: 209; HE: 172) were included (75.1% male, 66.7 ± 11.6 years). Clinical presentation was stable coronary artery disease in 49.9%. Syntax score was 23.7 ± 13.3. The number of OS implanted was 2.2 ± 0.5 and the total stent length was 59.5 ± 20.1 mm (HE: 61.5 ± 21.6 vs. HO: 57.8 ± 18.8 mm; p < 0.01). After a median follow-up of 21 months, the HE group showed a lower TLR rate than the HO group (HE:2.3% vs HO:7.2%; p = 0.03). The rates of cardiac death (p = 0.44), myocardial infarction (p = 0.36) and stent thrombosis (p = 0.85) were similar between groups. In the multivariate analysis, the OS with homogeneous-drug devices was an independent predictor of a higher rate of TLR.

CONCLUSIONS

PCI using OS with homogeneous pharmacological characteristics was associated with a higher rate of TLR in comparison with the implantation of OS with heterogeneous pharmacological characteristics.

Taking paclitaxel coated balloons to a higher level: Predicting coating dissolution kinetics, tissue retention and dosing dynamics

Paclitaxel coated balloons (PCBs) are a promising non-implantable alternative to drug-eluting stents, whereby drug is delivered to the arterial wall in solid form as a semi-continuous solid coating or as micro drug depots. To date, it has been impossible to predict or even infer local tissue dosing levels and persistence, making it difficult to compare in vivo performance of different devices in healthy animals or to extrapolate such data to diseased human arteries. Here we derive and analyze a coupled reaction diffusion model that accounts for coating dissolution and tissue distribution, and predicts the concentration of dissolved drug in the tissue during and post dissolution. Time scale analysis and numerical simulations based on estimated diffusion coefficients in healthy animal and diseased human arteries both imply that dissolution of crystalline paclitaxel coating is mass transfer coefficient-limited, and can therefore be solved for independently of the tissue transport equations. Specifically, coating retention is predicted to follow piecewise linear kinetics, reflecting the differential and faster dissolution of lumenal versus tissue-embedded coating owing to a disparity in convective forces. This prediction is consistent with published data on a range of PCBs and allowed for the estimation of the associated dissolution rate-constants and the maximal soluble drug concentration in the tissue during coating dissolution. Maximal soluble drug concentration in the tissue scales as the product of the solubility and ratio of the dissolution and diffusion rate-constants. Thus, coatings characterized by micromolar solubilities give rise to nanomolar soluble concentrations in healthy animal arteries and ~0.1 micromolar in calcified atherosclerotic arteries owing to slower tissue diffusion. During dissolution, retention in porcine iliofemoral arteries is predicted to be dominated by solid coating, whereas post dissolution it is dominated by receptor-bound drug (3.7 ng receptors/g tissue). Paclitaxel coating dissolution and dosing kinetics can now be modeled based upon accepted principles of surface dissolution and tissue transport to provide insights into the dependence of clinical efficacy on device properties and the interplay of lesion complexity and procedural parameters.

Multiscale Experimental and Computational Modeling Approaches to Characterize Therapy Delivery to the Heart from an Implantable Epicardial Biomaterial Reservoir

Delivery of therapeutic-laden biomaterials to the epicardial surface of the heart presents a promising method of treating a variety of diseased conditions by offering targeted, localized release with limited systemic recirculation and enhanced myocardial tissue uptake. A vast range of biomaterials and therapeutic agents using this approach been investigated. However, the fundamental factors that govern transport of the drug molecules from the biomaterials to the tissue are not well understood. Here, the transport of a drug analog from a biomaterial reservoir to the epicardial surface is characterized using experimental techniques and microscale modeling. Using the experimentally determined parameters, a multiscale model of transport is developed. The model is then used to study the effect of important design parameters such as loading conditions, biomaterial geometry, and orientation relative to the cardiac fibers on drug delivery to the myocardium. The simulations highlight the significance of the cardiac fiber anisotropy as a crucial factor in governing drug distribution on the epicardial surface and limiting factor for penetration into the myocardium. The multiscale model can be useful for rapid iteration of different device concepts and for determination of designs for epicardial drug delivery that may be optimal and most promising for the ultimate therapeutic goal.

An Overview on the Considerations for the Planning of Nonclinical Necropsies for Medical Device Studies

The terminal collection and histological processing of medical devices is an expensive, labor-, and material-intensive endeavor, which requires adequate experience, innovation, and preparation for success. It is also an exciting endeavor that continually challenges, intellectually engages, and improves the skills and knowledge of the pathologist. Awareness of the importance of the medical device pathologist's involvement, communication, and oversight throughout the development, implementation, and execution of a nonclinical assessment of a medical device is in the best interest of the test facility, the histopathology laboratory, the pathologist, the sponsor, and, ultimately, the patients. This article serves to present as a primer of key considerations for the approach and conduct of "nontoxicological" studies, defined as studies involving animal models of deployment or implantation of medical devices as well as surgical animal models.

NIR-Triggered Crystal Phase Transformation of NiTi-Layered Double Hydroxides Films for Localized Chemothermal Tumor Therapy

Construction of localized drug-eluting systems with synergistic chemothermal tumor-killing abilities is promising for biomedical implants directly contacting with tumor tissues. In this study, an intelligent and biocompatible drug-loading platform, based on a gold nanorods-modified butyrate-inserted NiTi-layered double hydroxides film (Au@LDH/B), is prepared on the surface of nitinol alloy. The prepared films function as drug-loading "sponges," which pump butyrate out under near-infrared (NIR) irradiation and resorb drugs in water when the NIR laser is shut off. The stimuli-responsive release of butyrate is verified to be related with the NIR-triggered crystal phase transformation of Au@LDH/B. In vitro and in vivo studies reveal that the prepared films possess excellent biosafety and high efficiency in synergistic thermochemo tumor therapy, showing a promising application in the construction of localized stimuli-responsive drug-delivery systems.

Protective Layer Development for Enhancing Stability and Drug-Delivery Capabilities of DES Surface-Crystallized Coatings

Carrier-free drug-eluting stents (DES)-based crystalline coatings are gaining prominence because of their function, skipping many limitations and clinical complications of the currently marketed DES. However, their usage has been humbled by inflexibility of the crystalline coating and limited mechanical and physical properties. This study reports for the first time the development of a protective top coating for enhancing the merits and delivery capabilities of the crystalline coating. Flexible and water-soluble polysaccharide top coating was developed and applied onto rapamycin (RM) crystalline carpet. The top coating prevented crystalline coating delamination during stent crimping and expansion without affecting its release profile. Crystalline coating strata and its interfaces with the metallic substrate and top coating were fully studied and characterized. The crystalline top-coated stents showed significant physical, mechanical, and chemical stability enhancement with ∼2% RM degradation after 1 year under different storage conditions. Biocompatibility study of the top-coated stents implanted subcutaneously for 1 month into SD rats did not provoke any safety concerns. Incorporating RM into the top coating to develop a bioactive protective coating for multilayer release purposes was also investigated. The developed protective coating had wide applicability and may be further implemented for various drugs and implantable medical devices.

Crystalline paclitaxel coated DES with bioactive protective layer development

Drug eluting stents (DES) based on polymeric-carriers currently lead the market, however, reports on clinical complications encourage the development of safer and more effective DES. We recently reported on carrier-free DES based on rapamycin crystalline coating as a potential therapeutic solution. Here, we report for the first time surface crystallization of paclitaxel (PT) onto metallic stents. The physicochemical principles of crystallization and key process parameters were extensively studied for fabrication of controllable and homogeneous crystalline coatings on stent scaffolds. Stents loaded with nearly 100μg PT were chosen as a potential therapeutic device with a multilayer coating of 4-7μm thickness. In vitro PT release from these coated stents shows constant release for at least 28days with 10% cumulatively released. The effect of fast dissolving top coating on the physical stability of the coated stent was determined. The top coating enhances the mechanical stability of the crystalline coating during deployment and expansion simulations. Also, incorporating PT in the protective top coating for developing bioactive top coating for multilayer controlled release purpose was intensively studied. This process has wide applications that can be further implemented for other drugs for effective local drug delivery from implantable medical devices.

Defining drug and target protein distributions after stent-based drug release: Durable versus deployable coatings

BACKGROUND

Innovations in drug eluting stent designs make it increasingly important to develop models for differentiating performance through spatial definition of drug, receptor binding and cell state.

METHODS

Two designs of sirolimus analog eluting stents were implanted into porcine coronary arteries for 28, 60 or 90 days (n = 9/time point), durable coating (Xience) and deployable absorbable coating (MiStent). Explanted arteries were evaluated for drug content (n = 3/time point) by LC-MS/MS and for drug and target protein (mTOR) distributions by immunofluorescence (IF, n = 6/time point). A computational model was developed to predict drug release and arterial distribution maps.

RESULTS

Both stents released the majority of drug load by 28 days, with different tissue retention efficiencies (91.4 ± 4.9% MiStent versus 21.5 ± 1.9% Xience, P < 0.001). Computational modeling of MiStent coating deployment and microcrystal dissolution recapitulated in vivo drug release and net tissue content and predicted that >98.5% of deployed drug remains crystalline through 90 days. Immunofluorescence and computational modeling showed peristrut drug localization for both stents, with similar peaks, but high interstrut levels only at sites of coating deployment from the absorbable coating. Co-localization of mTOR-IF with drug-IF for both devices showed persistent drug effects, though with differential drug-receptor pharmacokinetics.

CONCLUSIONS

Immunofluorescence and computational modeling provide insights into drug distribution and binding status that can help differentiate drug delivery technologies. Herein we found that tissue deployment of slow dissolving crystalline drug particles results in temporally and spatially more uniform drug delivery to interstrut zones that might otherwise be under-dosed without excess peristrut drug.

A sirolimus-eluting bioabsorbable polymer-coated stent (MiStent) versus an everolimus-eluting durable polymer stent (Xience) after percutaneous coronary intervention (DESSOLVE III): a randomised, single-blind, multicentre, non-inferiority, phase 3 trial

BACKGROUND

MiStent is a drug-eluting stent with a fully absorbable polymer coating containing and embedding a microcrystalline form of sirolimus into the vessel wall. It was developed to overcome the limitation of current durable polymer drug-eluting stents eluting amorphous sirolimus. The clinical effect of MiStent sirolimus-eluting stent compared with a durable polymer drug-eluting stents has not been investigated in a large randomised trial in an all-comer population.

METHODS

We did a randomised, single-blind, multicentre, phase 3 study (DESSOLVE III) at 20 hospitals in Germany, France, Netherlands, and Poland. Eligible participants were any patients aged at least 18 years who underwent percutaneous coronary intervention in a lesion and had a reference vessel diameter of 2·50-3·75 mm. We randomly assigned patients (1:1) to implantation of either a sirolimus-eluting bioresorbable polymer stent (MiStent) or an everolimus-eluting durable polymer stent (Xience). Randomisation was done by local investigators via web-based software with random blocks according to centre. The primary endpoint was a non-inferiority comparison of a device-oriented composite endpoint (DOCE)-cardiac death, target-vessel myocardial infarction, or clinically indicated target lesion revascularisation-between the groups at 12 months after the procedure assessed by intention-to-treat. A margin of 4·0% was defined for non-inferiority of the MiStent group compared with the Xience group. All participants were included in the safety analyses. This trial is registered with ClinicalTrials.gov, number NCT02385279.

FINDINGS

Between March 20, and Dec 3, 2015, we randomly assigned 1398 patients with 2030 lesions; 703 patients with 1037 lesions were assigned to MiStent, of whom 697 received the index procedure, and 695 patients with 993 lesions were asssigned to Xience, of whom 690 received the index procedure. At 12 months, the primary endpoint had occurred in 40 patients (5·8%) in the sirolimus-eluting stent group and in 45 patients (6·5%) in the everolimus-eluting stent group (absolute difference -0·8% [95% CI -3·3 to 1·8], p_{non-inferiority}=0·0001). Procedural complications occurred in 12 patients (1·7%) in the sirolimus-eluting stent group and ten patients (1·4%) in the everolimus-eluting stent group; no clinical adverse events could be attributed to these dislodgements through a minimum of 12 months of follow-up. The rate of stent thrombosis, a safety indicator, did not differ between groups and was low in both treatment groups.

INTERPRETATION

The sirolimus-eluting bioabsorbable polymer stent was non-inferior to the everolimus-eluting durable polymer stent for a device-oriented composite clinical endpoint at 12 months in an all-comer population. MiStent seems a reasonable alternative to other stents in clinical practice.

FUNDING

The European Cardiovascular Research Institute, Micell Technologies (Durham, NC, USA), and Stentys (Paris, France).

3D-Printed Multidrug-Eluting Stent from Graphene-Nanoplatelet-Doped Biodegradable Polymer Composite

Patients with percutaneous coronary intervention generally receive either bare metal stents or drug-eluting stents to restore the normal blood flow. However, due to the lack of stent production with an individual patient in mind, the same level of effectiveness may not be possible in treating two different clinical scenarios. This study introduces for the first time the feasibility of a patient-specific stenting process constructed from direct 3D segmentation of medical images using direct 3D printing of biodegradable polymer-graphene composite with dual drug incorporation. A biodegradable polymer-carbon composite is prepared doped with graphene nanoplatelets to achieve controlled release of combinatorics as anticoagulation and antirestenosis agents. This study develops a technology prototyped for personalized stenting. An in silico analysis is performed to optimize the stent design for printing and its prediction of sustainability under force exerted by coronary artery or blood flow. A holistic approach covering in silico to in situ-in vivo establishes the structural integrity of the polymer composite, its mechanical properties, drug loading and release control, prototyping, functional activity, safety, and feasibility of placement in coronary artery of swine.

Ultra-hydrophilic stent platforms promote early vascular healing and minimise late tissue response: a potential alternative to second-generation drug-eluting stents

AIMS

Simple surface modifications can enhance coronary stent performance. Ultra-hydrophilic surface (UHS) treatment of contemporary bare metal stents (BMS) was assessed in vivo to verify whether such stents can provide long-term efficacy comparable to second-generation drug-eluting stents (DES) while promoting healing comparably to BMS.

METHODS AND RESULTS

UHS-treated BMS, untreated BMS and corresponding DES were tested for three commercial platforms. A thirty-day and a 90-day porcine coronary model were used to characterise late tissue response. Three-day porcine coronary and seven-day rabbit iliac models were used for early healing assessment. In porcine coronary arteries, hydrophilic treatment reduced intimal hyperplasia relative to the BMS and corresponding DES platforms (1.5-fold to threefold reduction in 30-day angiographic and histological stenosis; p<0.04). Endothelialisation was similar on UHS-treated BMS and untreated BMS, both in swine and rabbit models, and lower on DES. Elevation in thrombotic indices was infrequent (never observed with UHS, rare with BMS, most often with DES), but, when present, correlated with reduced endothelialisation (p<0.01).

CONCLUSIONS

Ultra-hydrophilic surface treatment of contemporary stents conferred good healing while moderating neointimal and thrombotic responses. Such surfaces may offer safe alternatives to DES, particularly when rapid healing and short dual antiplatelet therapy (DAPT) are crucial.

A review of drug delivery systems based on nanotechnology and green chemistry: green nanomedicine

This review discusses the impact of green and environmentally safe chemistry on the field of nanotechnology-driven drug delivery in a new field termed "green nanomedicine". Studies have shown that among many examples of green nanotechnology-driven drug delivery systems, those receiving the greatest amount of attention include nanometal particles, polymers, and biological materials. Furthermore, green nanodrug delivery systems based on environmentally safe chemical reactions or using natural biomaterials (such as plant extracts and microorganisms) are now producing innovative materials revolutionizing the field. In this review, the use of green chemistry design, synthesis, and application principles and eco-friendly synthesis techniques with low side effects are discussed. The review ends with a description of key future efforts that must ensue for this field to continue to grow.

Interleukin-1β is associated with coronary endothelial dysfunction in patients with mTOR-inhibitor-eluting stent implantation

Implantation of mammalian target of rapamycin (mTOR)-inhibitor drug-eluting stents (DESs) impairs coronary endothelial function. There are no known non-invasive biomarkers of coronary endothelial dysfunction. We aimed to assess the association between serum interleukin-1beta (IL-1β) and coronary endothelial dysfunction in patients with mTOR-inhibitor DES implantation and to investigate the association between the mTOR pathway and IL-1β. We enrolled 35 patients who had implanted DESs for coronary artery disease. At a 10-month follow-up, peripheral venous blood samples were collected to measure IL-1β levels. Coronary endothelial dysfunction was evaluated by intracoronary infusion of incremental doses of acetylcholine. Serum IL-1β levels were significantly associated with the magnitude of vasoconstriction to acetylcholine at the segment distal (P < 0.05) but not proximal to the stent. Serum IL-1β levels were positively correlated with stent length (P < 0.05). To examine the direct effects of mTOR inhibition on IL-1β release, sirolimus was incubated in cultured human umbilical vein endothelial cells (HUVECs) or coronary artery smooth muscle cells (CASMCs). Sirolimus directly increased IL-1β mRNA expression (P < 0.01) and enhanced IL-1β release into the culture media (P < 0.01) in CASMCs, but not in HUVECs. Inhibition of mTOR triggers IL-1β release through transcriptional activation in CASMCs. Serum IL-1β levels are a potential biomarker for mTOR-inhibitor DES-associated coronary endothelial dysfunction.

Poly(styrenesulfonate)-Modified Ni-Ti Layered Double Hydroxide Film: A Smart Drug-Eluting Platform

Drug-eluting stents (DESs) are widely used in the palliative treatment of many kinds of cancers. However, the covered polymers used in DESs are usually associated with stent migration and acute cholecystitis. Therefore, developing noncovered drug-loading layers on metal stents is of great importance. In this work, Ni-Ti layered double hydroxide (Ni-Ti LDH) films were prepared on the surface of nitinol via hydrothermal treatment, and the LDH films were further modified by poly(styrenesulfonate) (PSS). The anticancer drug doxorubicin could be effectively loaded onto the modified films, and drug release could be smartly controlled by the pH. Besides, the drug absorption amounts of cancer cells cultured on the films could be effectively improved. These results indicate that the PSS-modified LDH film may become a promising drug-loading platform that can be used in the design of DESs.

Drug deposition in coronary arteries with overlapping drug-eluting stents

Drug-eluting stents are accepted as mainstream endovascular therapy, yet concerns for their safety may be under-appreciated. While failure from restenosis has dropped to below 5%, the risk of stent thrombosis and associated mortality remain relatively high. Further optimization of drug release is required to minimize thrombosis risk while maintaining therapeutic dose. The complex three-dimensional geometry of deployed stents together with the combination of diffusive and advective drug transport render an intuitive understanding of the situation exceedingly difficult. In situations such as this, computational modeling has proven essential, helping define the limits of efficacy, determine the mode and mechanism of drug release, and identify alternatives to avoid toxicity. A particularly challenging conformation is encountered in coronary arteries with overlapping stents. To study hemodynamics and drug deposition in such vessels we combined high-resolution, multi-scale ex vivo computed tomography with a flow and mass transfer computational model. This approach ensures high geometric fidelity and precise, simultaneous calculation of blood flow velocity, shear stress and drug distribution. Our calculations show that drug uptake by the arterial tissue is dependent both on the patterns of flow disruption near the wall, as well as on the relative positioning of drug-eluting struts. Overlapping stent struts lead to localized peaks of drug concentration that may increase the risk of thrombosis. Such peaks could be avoided by anisotropic stent structure or asymmetric drug release designed to yield homogeneous drug distribution along the coronary artery and, at the least, suggest that these issues need to remain in the forefront of consideration in clinical practice.

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.

Comparison of the Absorbable Polymer Sirolimus-Eluting Stent (MiStent) to the Durable Polymer Everolimus-Eluting Stent (Xience) (from the DESSOLVE I/II and ISAR-TEST-4 Studies)

We compared the outcomes of a novel, thin-strut, cobalt-chromium, absorbable, polymer sirolimus-eluting stent (APSES; MiStent) to the durable polymer cobalt-chromium everolimus-eluting stent (EES; Xience). A propensity-matched analysis was performed comparing data from the DES With Sirolimus and a Bioabsorbable Polymer for the Treatment of Patients With De Novo Lesions in the Native Coronary Arteries (DESSOLVE) I and II studies, evaluating the APSES to the EES arm of the Intracoronary Stenting and Angiographic Results: Test Efficacy of 3 Limus-Eluting Stents-4 study. Target lesion failure (TLF) and its components were evaluated at 12 months and annually to 3 years; 805 patients (APSES = 153; EES = 652) were included with propensity matching in 204 patients (APSES = 102; EES = 102). APSES compared with EES had lower TLF at 1 year (3.0% vs 8.0%, p = 0.12) driven by a difference in target lesion revascularization (TLR; 1% vs 6%, p = 0.05), with no difference in target vessel myocardial infarction (p = 0.56) or stent thrombosis (p = 0.31). At 3 years, TLF (5.0% vs 12.5%, p = 0.07) and TLR (2.0% vs 8.4%, p = 0.04) remained lower with APSES. By landmark analysis, there was no significant difference in TLF between 1 and 3 years (p = 0.36). In conclusion, in a propensity-matched analysis, the APSES demonstrated reduced clinically indicated TLR rates at 1 and 3 years compared with the durable polymer EES, with minimal accrual of events between 1 and 3 years.

Modelling the Impact of Atherosclerosis on Drug Release and Distribution from Coronary Stents

Although drug-eluting stents (DES) are now widely used for the treatment of coronary heart disease, there remains considerable scope for the development of enhanced designs which address some of the limitations of existing devices. The drug release profile is a key element governing the overall performance of DES. The use of in vitro, in vivo, ex vivo, in silico and mathematical models has enhanced understanding of the factors which govern drug uptake and distribution from DES. Such work has identified the physical phenomena determining the transport of drug from the stent and through tissue, and has highlighted the importance of stent coatings and drug physical properties to this process. However, there is limited information regarding the precise role that the atherosclerotic lesion has in determining the uptake and distribution of drug. In this review, we start by discussing the various models that have been used in this research area, highlighting the different types of information they can provide. We then go on to describe more recent methods that incorporate the impact of atherosclerotic lesions.

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.

Effects of fluid shear stress on polyelectrolyte multilayers by neutron scattering studies

The structure of layer-by-layer (LbL) deposited nanofilm coatings consists of alternating polyethylenimine (PEI) and polystyrenesulfonate (PSS) films deposited on a single crystal quartz substrate. LbL-deposited nanofilms were investigated by neutron reflectomery (NR) in contact with water in the static and fluid shear stress conditions. The fluid shear stress was applied through a laminar flow of the liquid parallel to the quartz/polymer interface in a custom-built solid-liquid interface cell. The scattering length density profiles obtained from NR results of these polyelectrolyte multilayers (PEM), measured under different shear conditions, showed proportional decrease of volume fraction of water hydrating the polymers. For the highest shear rate applied (ca. 6800 s(-1)) the water volume fraction decreased by approximately 7%. The decrease of the volume fraction of water was homogeneous through the thickness of the film. Since there were not any significant changes in the total polymer thickness, it resulted in negative osmotic pressures in the film. The PEM films were compared with the behavior of thin films of thermoresponsive poly(N-isopropylacrylamide) (pNIPAM) deposited via spin-coating. The PEM and pNIPAM differ in their interactions with water molecules, and they showed opposite behaviors under the fluid shear stress. In both cases the polymer hydration was reversible upon the restoration of static conditions. A theoretical explanation is given to explain this difference in the effect of shear on hydration of polymeric thin films.

Similarities and differences in coatings for magnesium-based stents and orthopaedic implants

Magnesium (Mg)-based biodegradable materials are promising candidates for the new generation of implantable medical devices, particularly cardiovascular stents and orthopaedic implants. Mg-based cardiovascular stents represent the most innovative stent technology to date. However, these products still do not fully meet clinical requirements with regards to fast degradation rates, late restenosis, and thrombosis. Thus various surface coatings have been introduced to protect Mg-based stents from rapid corrosion and to improve biocompatibility. Similarly, different coatings have been used for orthopaedic implants, e.g., plates and pins for bone fracture fixation or as an interference screw for tendon-bone or ligament-bone insertion, to improve biocompatibility and corrosion resistance. Metal coatings, nanoporous inorganic coatings and permanent polymers have been proved to enhance corrosion resistance; however, inflammation and foreign body reactions have also been reported. By contrast, biodegradable polymers are more biocompatible in general and are favoured over permanent materials. Drugs are also loaded with biodegradable polymers to improve their performance. The key similarities and differences in coatings for Mg-based stents and orthopaedic implants are summarized.

Metallic implant drug/device combinations for controlled drug release in orthopaedic applications

The study of metallic drug/device combinations for controlled drug release in orthopaedic applications has gained significant momentum in the past decade, particularly for the prevention and reduction of implant associated infection. Such combinations are commonly based upon a permanent metallic implant (such as stainless steel or titanium) and are then coated with a drug-eluting polymer or ceramic system. Drug elution is also possible from the implant itself by utilising metallic foams, porous architectures and bioresorbable metals. This review will explore the current research into metallic implant drug/device combinations via a critical review of the relevant literature.