Is There Light at the End of the Thin-Strut Tunnel?: In Vitro Insights on Strut Thickness Impact on Thrombogenicity in Bioresorbable Stents or Scaffolds

Coronary bioresorbable metallic stents: Advancements and future perspectives

Percutaneous coronary intervention is a critical treatment for coronary artery disease, particularly myocardial infarction, and is highly recommended in clinical guidelines. Traditional metallic stents, although initially effective, remain permanently in the artery and can lead to complications such as in-stent restenosis, late thrombosis, and chronic inflammation. Given the temporary need for stenting and the potential for late complications, bioresorbable stents have emerged as a promising alternative. However, bioresorbable polymeric stents have encountered significant clinical challenges due to their low mechanical strength and ductility, which increase the risks of thrombosis and local inflammation. Consequently, bioresorbable metals are being considered as a superior option for coronary stents. This review examines the progress of bioresorbable metallic stents from both preclinical and clinical perspectives, aiming to provide a theoretical foundation for future research. Iron, zinc, and magnesium are the primary materials used for these stents. Zinc-based bioresorbable stents have shown promise in preclinical studies due to their biocompatibility and vascular protective properties, although human clinical studies are still limited. Magnesium-based stents have demonstrated positive clinical outcomes, being fully absorbed within 12 months and showing low rates of late lumen loss and target lesion failure at 6- and 12-months post-implantation. Initial trials of iron-based stents have indicated favorable mid-term safety and efficacy, with complete absorption by the body within three years and consistent luminal expansion beyond six months post-implantation. Despite these advancements, further trials are needed for comprehensive validation. In conclusion, while current materials do not fully meet the ideal requirements, ongoing research should focus on developing bioresorbable stents with enhanced performance characteristics to better meet clinical needs.

Restoring endothelial function: shedding light on cardiovascular stent development

Complete endothelialization is highly important for maintaining long-term patency and avoiding subsequent complications in implanting cardiovascular stents. It not only refers to endothelial cells (ECs) fully covering the inserted stents, but also includes the newly formed endothelium, which could exert physiological functions, such as anti-thrombosis and anti-stenosis. Clinical outcomes have indicated that endothelial dysfunction, especially the insufficiency of antithrombotic and barrier functions, is responsible for stent failure. Learning from vascular pathophysiology, endothelial dysfunction on stents is closely linked to the microenvironment of ECs. Evidence points to inflammatory responses, oxidative stress, altered hemodynamic shear stress, and impaired endothelial barrier affecting the normal growth of ECs, which are the four major causes of endothelial dysfunction. The related molecular mechanisms and efforts dedicated to improving the endothelial function are emphasized in this review. From the perspective of endothelial function, the design principles, advantages, and disadvantages behind current stents are introduced to enlighten the development of new-generation stents, aiming to offer new alternatives for restoring endothelial function.

Polymer Coating Integrity, Thrombogenicity and Computational Fluid Dynamics Analysis of Provisional Stenting Technique in the Left Main Bifurcation Setting: Insights from an In-Vitro Model

Currently, the provisional stenting technique is the gold standard in revascularization of lesions located in the left main (LM) bifurcation. The benefit of the routine kissing balloon technique (KBI) in bifurcation lesions is still debated, particularly following the single stent treatment. We compared the latest-generation drug-eluting stent (DES) with no side branch (SB) dilatation “keep it open” technique (KIO) vs. KBI technique vs. bifurcation dedicated drug-eluting stent (BD-DES) implantation. In vitro testing was performed under a static condition in bifurcation silicone vessel models. All the devices were implanted in accordance with the manufacturers’ recommendations. As a result, computational fluid dynamics (CFD) analysis demonstrated a statistically higher area of high shear rate in the KIO group when compared to KBI. Likewise, the maximal shear rate was higher in number in the KIO group. Floating strut count based on the OCT imaging was significantly higher in KIO than in KBI and BD-DES. Furthermore, according to OTC analysis, the thrombus area was numerically higher in both KIO and KBI than in the BD-DES. Scanning electron microscopy (SEM) analysis shows the highest degree of strut coating damage in the KBI group. This model demonstrated significant differences in CFD analysis at SB ostia with and without KBI optimization in the LM setting. The adoption of KBI was related to a meaningful reduction of flow disturbances in conventional DES and achieved results similar to BD-DES.

Effects of Simulated COVID-19 Cytokine Storm on Stent Thrombogenicity

BACKGROUND

Cytokine storm-related hypercoagulation may be important in the pathogenesis of stent thrombosis in patients with SARS-CoV-2. Whether stent polymers behave differently under such conditions has never been explored.

METHODS

Fluorinated polymer-nanocoated and uncoated COBRA stents (CeloNova), BioLinx-polymer-coated Resolute Onyx stents (Medtronic), and Synergy stents (Boston Scientific), which are abluminally coated with a bioabsorbable polymer, were exposed to human blood from healthy donors which was supplemented with 400 pg/mL IL-6 and 100 pg/mL TNF-α, similar to what is seen in cytokine storm caused by SARS-CoV-2. Platelet adhesion and neutrophil activation, assessed by immunofluorescence, were compared under cytokine storm and control conditions (untreated blood) (n = 4 experimental runs).

RESULTS

Platelet adhesion values, defined as %platelet-covered area x staining intensity, were significantly lower in coated and uncoated COBRA and in Resolute Onyx than in Synergy under control conditions (1.28 × 107 ± 0.43 × 107 vs. 2.92 × 107 ± 0.49 × 107 vs. 3.57 × 107 ± 0.73 × 107 vs. 9.94 × 107 ± 0.99 × 107; p ≤0.0001). In cytokine storm, platelet adhesion values remained low in coated COBRA-PzF (1.78 × 107 ± 0.38 × 107) compared to all other devices (uncoated COBRA: 5.92 × 107 ± 0.96 × 107; Resolute Onyx: 7.27 × 107 ± 1.82 × 107; Synergy: 11.28 × 107 ± 1.08 × 107; p ≤ 0.0001). Although cytokine storm conditions significantly increased neutrophil activation in all stents, it was significantly less in coated and uncoated COBRA, and in Resolute Onyx than in Synergy.

CONCLUSIONS

Blood-biomaterials interactions may determine the thrombogenic potential of stents. Under simulated cytokine storm conditions, fluoropolymer-coated stents showed the most favorable anti-thrombogenic and anti-inflammatory properties.

Progress in drug-delivery systems in cardiovascular applications: stents, balloons and nanoencapsulation

Drug-delivery systems in cardiovascular applications regularly include the use of drug-eluting stents and drug-coated balloons to ensure sufficient drug transfer and efficacy in the treatment of cardiovascular diseases. In addition to the delivery of antiproliferative drugs, the use of growth factors, genetic materials, hormones and signaling molecules has led to the development of different nanoencapsulation techniques for targeted drug delivery. The review will cover drug delivery and coating mechanisms in current drug-eluting stents and drug-coated balloons, novel innovations in drug-eluting stent technologies and drug encapsulation in nanocarriers for delivery in vascular diseases. Newer technologies and advances in nanoencapsulation techniques, such as the use of liposomes, nanogels and layer-by-layer coating to deliver therapeutics in the cardiovascular space, will be highlighted.

Nanoparticles-reinforced poly-l-lactic acid composite materials as bioresorbable scaffold candidates for coronary stents: Insights from mechanical and finite element analysis

Current generation of bioresorbable coronary scaffolds (BRS) posed thrombogenicity and deployment issues owing to its thick struts and overall profile. To this end, we hypothesize that the use of nanocomposite materials is able to provide improved material properties and sufficient radial strength for the intended application even at reduced strut thickness. The nanocomposite formulations of tantalum dioxide (Ta₂O₅), L-lactide functionalized (LA)-Ta₂O₅, hydroxyapatite (HA) and LA-HA with poly-l-lactic acid (PLLA) were evaluated in this study. Results showed that tensile modulus and strength were enhanced with non-functionalized nanofillers up until 15 wt% loading, whereas ductility was compromised. On the other hand, functionalized nanofillers/PLLA exhibited improved nanofiller dispersion which resulted higher tensile modulus, strength, and ductility. Selected nanocomposite formulations were evaluated using finite element analysis (FEA) of a stent with varying strut thickness (80, 100 and 150 μm). FEA data has shown that nanocomposite BRS with thinner struts (80-100 μm) made with 15 wt% LA-Ta₂O₅/PLLA and 10 wt% LA-HA/PLLA have increased radial strength, stiffness and reduced recoil compared to PLLA BRS at 150 μm. The reduced strut thickness can potentially mitigate issues such as scaffold thrombosis and promote re-endothelialisation of the vessel.

COBRA PzF™ coronary stent in clinical and preclinical studies: setting the stage for new antithrombotic strategies?

Major advances have been made in coronary artery stent technology over the last decades. Drug-eluting stents reduced in-stent restenosis and have shown better outcomes compared with bare metal stents, yet some limitations still exist to their use. Because they delay healing of the vessel wall, longer dual antiplatelet therapy is mandatory to mitigate against stent thrombosis and this limitation is most concerning in subjects at high risk for bleeding. The COBRA PzF nanocoated coronary stent has been associated with accelerated endothelialization relative to drug-eluting stents, reduced inflammation and thromboresistance in preclinical studies, suggesting more flexible dual antiplatelet therapy requirement with potential benefits especially in those at high bleeding risk. Here, we discuss the significance of COBRA PzF in light of recent experimental and clinical studies.

Serial evaluation of vascular responses after implantation of everolimus-eluting coronary stent by optical coherence tomography

AIM

To evaluate healing response at strut-level and cross-section level after implanting an ultra-thin strut, everolimus-eluting stent with biodegradable polymer (Tetrilimus) using optical coherence tomography (OCT) at 3 and 6 months.

METHODS

This was prospective, multi-centre, single-arm, and investigator-initiated study performed at seven Indian sites between January, 2017 and September, 2018. OCT evaluations were performed in 57 patients who underwent Tetrilimus stent implantation. Follow-up OCT was scheduled at 3 months for first 16 patients and at 6 months for 41 patients. Primary outcomes included degree of strut coverage, malapposition and thickness of neointimal hyperplasia (NIH) over covered struts.

RESULTS

Sixty one Tetrilimus stents were implanted to treat 59 lesions in 57 patients. Paired (baseline and follow-up) OCT data was available for 12 patients and 30 patients at 3 and 6 months, respectively. At 3 months, rapid early healing was indicated by 95.48% covered struts per lesion with very low (0.11 ± 0.06 mm) NIH. At 6 months, NIH accumulation was greater (0.21 ± 0.07 mm) as compared to 3 months. 99.77% of struts per lesion were covered at 6 months. There was a very symmetrical healing as shown by very low eccentricity index. There was no difference in vascular healing between stents with small to moderate size vessels (≤3.00 mm) and large size vessels (>3.00 mm).

CONCLUSION

Present study demonstrated nearly complete endothelization and low NIH accumulation at 3 and 6 months following implantation of ultra-thin strut everolimus-eluting biodegradable polymer-coated Tetrilimus stent. Moreover, though being an ultra-thin strut stent, there was no difference in vascular healing and eccentricity after implantation of the Tetrilimus stents with smaller and larger diameters.

Comparison of overexpansion capabilities and thrombogenicity at the side branch ostia after implantation of four different drug eluting stents

Interventions in bifurcation lesions often requires aggressive overexpansion of stent diameter in the setting of long tapering vessel segment. Overhanging struts in front of the side branch (SB) ostium are thought to act as a focal point for thrombi formation and consequently possible stent thrombosis. This study aimed to evaluate the overexpansion capabilities and thrombogenicity at the SB ostia after implantation of four latest generation drug-eluting stents (DES) in an in-vitro bifurcation model. Four clinically available modern DES were utilized: one bifurcation dedicated DES (Bioss LIM C) and three conventional DES (Ultimaster, Xience Sierra, Biomime). All devices were implanted in bifurcation models with proximal optimization ensuring expansion before perfusing with porcine blood. Optical coherence tomography (OCT), immunofluorescence (IF) and scanning electron microscope analysis were done to determine thrombogenicity and polymer coating integrity at the over-expanded part of the stents. Computational fluid dynamics (CFD) was performed to study the flow disruption. OCT (p = 0.113) and IF analysis (p = 0.007) demonstrated lowest thrombus area at SB ostia in bifurcation dedicated DES with favorable biomechanical properties compared to conventional DES. The bifurcated DES also resulted in reduced area of high shear rate and maximum shear rate in the CFD analysis. This study demonstrated numerical differences in terms of mechanical properties and acute thrombogenicity at SB ostia between tested devices.

Preclinical evaluation of a thin-strut bioresorbable scaffold (ArterioSorb): acute-phase invasive imaging assessment and hemodynamic implication

AIMS

The aim of this study was to assess the acute performance of the 95 µm ArterioSorb oriented poly L-lactic acid (PLLA) scaffold in comparison with the XIENCE metallic drug-eluting stent (DES) in porcine coronary arteries.

METHODS AND RESULTS

In 15 non-atherosclerotic Yucatan mini pigs, the ArterioSorb (3.0/14 mm) and XIENCE (3.0/15 mm) were implanted in 25 and 15 vessels, respectively. Acute performance was evaluated by using quantitative coronary angiography (QCA) and optical coherence tomography (OCT). Following three-dimensional reconstruction of the coronary arteries, endothelial shear stress (ESS) was quantified using non-Newtonian steady-flow simulation. Acute recoil measured by QCA was comparable in the two arms. Post-procedural flow and scaffold/stent area by OCT did not differ between the two devices. ESS post procedure was comparable between ArterioSorb and XIENCE (2.21±1.97 vs 2.25±1.71 Pa, p=0.314).

CONCLUSIONS

Acute recoil, luminal dimensions and ESS in the ArterioSorb oriented PLLA scaffold with thin struts of 95 µm were comparable to those in the XIENCE metallic DES.

Comparison of neointimal coverage between ultrathin biodegradable polymer-coated sirolimus-eluting stents and durable polymer-coated everolimus-eluting stents: 6 months optical coherence tomography follow-up from the TAXCO study

Aim

The TAXCO study was designed to compare the degree of neointimal coverage and the prevalence of malapposition at 6 months subsequent to implantation of ultrathin biodegradable polymer‐coated sirolimus‐eluting stents (SES) and durable polymer‐coated everolimus‐eluting stents (EES) of thin strut thickness using optical coherence tomography (OCT).

Methods

The TAXCO study included a total of 42 patients who gave consent and underwent OCT examination between August 2017 and September 2017. Of 42, five patients' OCT examinations were of insufficient quality for quantitative analysis. Thus, the OCT analysis group consisted of 37 patients. Among them, 16 patients were treated with Xience (Abbott Vascular) and 21 with Tetriflex (Sahajanand Medical Technologies Pvt. Ltd., Surat, India), 6 (±1) months earlier at our institution. The OCT was performed using a C7 Dragonfly™ imaging catheter (St. Jude Medical Inc.). All OCT images were analyzed at an independent core laboratory (Cardiovascular Research Center, São Paulo, Brazil) by analysts who were blinded to patient and procedural information.

Results

A total of 763 crosssections (6,882 struts) were analyzed in Xience group, and 1,127 crosssections (9,968 struts) in Tetriflex group. At 6 months, on per‐lesion basis, no significant differences were observed between Xience group and Tetriflex group in mean percentage of uncovered struts (1.87 ± 3.86 vs. 2.42 ± 3.46, p = .137) and malapposed struts (0.05 ± 0.2 vs. 0.21 ± 0.69, p = .302). Strut‐level neointimal thickness also did not differ between Xience group and Tetriflex group (0.18 ± 0.12 vs. 0.14 ± 0.08 mm, p = .286).

Conclusion

This OCT study found no significant difference in strut coverage and neointimal thickness at 6 months after implantation of biodegradable polymer‐coated Tetriflex, when compared with durable polymer‐coated Xience.

Outcomes of Optimised Implantation Technique with Bioresorbable scaffolds: A Pooled Analysis of ABSORB-IV and COMPARE-ABSORB Trials

Randomised trials have demonstrated higher midterm rates of adverse events and device thrombosis with Absorb-BVS compared to contemporary drug-eluting-stents (DES). BVS failure was ascribed to the implantation technique and consequently two large randomised trials evaluated the clinical impact of an optimised scaffold-implant-procedure. However, pooling together data from ABSORB-IV and those of the COMPARE-ABSORB, the scaffold was still associated with a statistically significant increased risk of target-vessel myocardial-infarction (OR 1.5; 95% CI 1.04-2.17; P = 0.03) and thrombotic events (OR 2.85; 95% CI 1.33-6.11; P = 0.007) at 1-year. Such kind of results could be in part attributed to a lower radial force and the higher acute recoil of the BVS as observed in previous studies. Besides a painstaking implantation technique, future generations of bioresorbable stents should incorporate an excellent mechanical propriety in order to compete with the current-generation DES.

Radiopaque Fully Degradable Nanocomposites for Coronary Stents

Bioresorbable scaffolds (BRS) were introduced to overcome limitations of current metallic drug-eluting stents and poly-L-lactide (PLLA) has been used in the fabrication of BRS due to its biodegradability and biocompatibility. However, such polymers have weaker mechanical properties as compared to metals, limiting their use in BRS. We hypothesized that nanofillers can be used to enhance the mechanical properties considerably in PLLA. To this end, polymer-matrix composites consisting of PLLA reinforced with 5-20 wt% barium sulfate (BaSO4) nanofillers as a potential BRS material was evaluated. Stearic-acid (SA) modified BaSO4 nanofillers were used to examine the effect of functionalization. Rigid nanofillers improved the tensile modulus and strength of PLLA (60% and 110% respectively), while the use of SA-BaSO4 caused a significant increase (~110%) in the elongation at break. Enhancement in mechanical properties is attributed to functionalization which decreased the agglomeration of the nanofillers and improved dispersion. The nanocomposites were also radiopaque. Finite element analysis (FEA) showed that scaffold fabricated from the novel nanocomposite material has improved scaffolding ability, specifically that the strut thickness could be decreased compared to the conventional PLLA scaffold. In conclusion, BaSO4/PLLA-based nanocomposites could potentially be used as materials for BRS with improved mechanical and radiopaque properties.