Initial findings of impact of strut width on stent coverage and apposition of sirolimus-eluting stents assessed by optical coherence tomography

Effects of fused deposition modeling (FDM) printing parameters on quality aspects of polycaprolactone (PCL) for coronary stent applications: A review

Fused deposition modeling (FDM) is emerging as a promising technique for manufacturing bioresorbable stents (BRS), particularly for coronary artery disease treatment. Polycaprolactone (PCL) has emerged as a favored material due to its biocompatibility, controlled degradation rate and mechanical properties. This review provides a comprehensive analysis of the effects of key FDM printing parameters on the quality aspects of PCL-based BRS, focusing on morphological, mechanical and biological characteristics. This review also highlights inconsistencies in previous studies, particularly in the impact of these parameters on stent dimensions and mechanical properties, emphasizing the need for standardization in experimental methodologies. Additionally, the current gaps in research related to the mechanical and biological performances of PCL-based BRS are discussed, with a call for further studies on long-term effects. This review aims to guide future research by offering insights into optimizing FDM parameters for improving the overall performance and clinical outcomes of PCL-based BRS.

Stent Thrombosis and Restenosis with Contemporary Drug-Eluting Stents: Predictors and Current Evidence

Iterations in stent technologies, advances in pharmacotherapy, and awareness of the implications of implantation techniques have markedly reduced the risk of stent failure, both in the form of stent thrombosis (ST) and in-stent restenosis (ISR). However, given the number of percutaneous coronary interventions (PCI) performed worldwide every year, ST and ISR, albeit occurring at a fairly low rate, represent a public health problem even with contemporary DES platforms. The understanding of mechanisms and risk factors for these two PCI complications has been of fundamental importance for the parallel evolution of stent technologies. Risk factors associated with ST and ISR are usually divided into patient-, lesion-, device- and procedure-related. A number of studies have shown how certain risk factors are related to early (1 month) versus late/very late ST (between 1 month and 1 year and >1 year, respectively). However, more research is required to conclusively show the role of time-dependence of risk factors also in the incidence of ISR (early [1 year] or late [>1 year]). A thorough risk assessment is required due to the complex etiology of ST and ISR. The most effective strategy to treat ST and ISR is still to prevent them; hence, it is crucial to identify patient-, lesion-, device- and procedure-related predictors.

Long-term safety and absorption assessment of a novel bioresorbable nitrided iron scaffold in porcine coronary artery

This study aimed to investigate the long-term biocompatibility, safety, and degradation of the ultrathin nitrided iron bioresorbable scaffold (BRS) in vivo, encompassing the whole process of bioresorption in porcine coronary arteries. Fifty-two nitrided iron scaffolds (strut thickness of 70 μm) and 28 Vision Co–Cr stents were randomly implanted into coronary arteries of healthy mini-swine. The efficacy and safety of the nitrided iron scaffold were comparable with those of the Vision stentwithin 52 weeks after implantation. In addition, the long-term biocompatibility, safety, and bioresorption of the nitrided iron scaffold were evaluated by coronary angiography, optical coherence tomography, micro-computed tomography, scanning electron microscopy, energy dispersive spectrometry and histopathological evaluations at 4, 12, 26, 52 weeks and even at 7 years after implantation. In particular, a large number of struts were almost completely absorbed in situ at 7 years follow-up, which were first illustrated in this study. The lymphatic drainage pathway might serve as the potential clearance way of iron and its corrosion products.

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This study investigated the long-term safety and the total degradative process of nitrided iron scaffold in porcine coronary artery.

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The safety and biocompatibility of the nitrided iron scaffold were comparable to those of the Vision stent within 12 months after implantation.

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This ultrathin nitrided iron scaffold can be degraded and bioresorbed completely with long-term biocompatibility in porcine coronary artery.

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Interestingly, the lymphatic metabolic pathway might serve as the potential absorption route for iron and its corrosion products.

Polymer–Metal Composite Healthcare Materials: From Nano to Device Scale

Metals have been investigated as biomaterials for a wide range of medical applications. At nanoscale, some metals, such as gold nanoparticles, exhibit plasmonics, which have motivated researchers’ focus on biosensor development. At the device level, some metals, such as titanium, exhibit good physical properties, which could allow them to act as biomedical implants for physical support. Despite these attractive features, the non-specific delivery of metallic nanoparticles and poor tissue–device compatibility have greatly limited their performance. This review aims to illustrate the interplay between polymers and metals, and to highlight the pivotal role of polymer–metal composite/nanocomposite healthcare materials in different biomedical applications. Here, we revisit the recent plasmonic engineered platforms for biomolecules detection in cell-free samples and highlight updated nanocomposite design for (1) intracellular RNA detection, (2) photothermal therapy, and (3) nanomedicine for neurodegenerative diseases, as selected significant live cell–interactive biomedical applications. At the device scale, the rational design of polymer–metallic medical devices is of importance for dental and cardiovascular implantation to overcome the poor physical load transfer between tissues and devices, as well as implant compatibility under a dynamic fluidic environment, respectively. Finally, we conclude the treatment of these innovative polymer–metal biomedical composite designs and provide a future perspective on the aforementioned research areas.

A biodegradable magnesium alloy vascular stent structure: Design, optimisation and evaluation

The existing biodegradable magnesium alloy stent (BMgS) structure is prone to problems, such as insufficient support capacity and early fracture at areas of concentrated stress. Herein, a stent structural design, which reduced the cross section of the traditional sin-wave stent by nearly 30% and introduces a regular arc structure in the middle of the support ring. The influence of the dual-parameter design of bending radius (r) and ring length (L) on plastic deformation, expansion and compression resistance performances are discussed. The non-dominated sorting genetic algorithm II (NSGA-II) was used to search for the optimal solution. It was found that the introduction of parameter r effectively improved the plastic deformation and expansion performance, and the reduction of L improved stent compression resistance. Finally, an optimized stent configuration was obtained. In vitro mechanical tests, including balloon inflation, radial strength and flexibility, verified the simulation results. The radial strength for the optimised stent increases by approximately 40% compared with that for the sinusoidal stent. Microarea X-ray diffraction result shows that the circumferential residual stress for the optimised stent decreases by half compared with that for the sinusoidal stent, thus effectively reducing the stress concentration phenomenon. STATEMENT OF SIGNIFICANCE: Despite current progress in BMgS research, the optimal design of the structure is limited. We present a new type of structurally designed stent. The performance of this stent was analysed by a finite element method and experimentally verified. The structural design positively influenced stent performance.

Comparable neointimal healing in patients with stable coronary lesions and acute coronary syndrome: 3-month optical coherence tomography analysis

We aimed to assess a possible difference of the neointimal coverage status and its quality after implantation of the current-generation metallic stents in patients with acute coronary syndrome (ACS) vs. stable coronary lesions (non-ACS). We comprehensively analyzed three prospective single-center observational studies RESTORE (UMIN000033009), HEAL-BioFreedom (UMIN000029692), and HEAL-BioFreedom ACS (UMIN000034769). All patients who received successful optical coherence tomography (OCT) examination at planned 3-month follow-up after stent implantation were analyzed. Study population was divided into two groups, ACS vs. non-ACS groups. We evaluated standard OCT variables, coverage percent, and the quantitative light property values including light intensity, attenuation, and backscatter of neointima. A total of 177 lesions from 154 patients (ACS 44 lesions vs. non-ACS 133 lesions) were analyzed. At 3-month follow-up, coverage percent (ACS 91.5  ±  9.5% vs. non-ACS 91.8  ±  9.0%, P = 0.722) and neointimal thickness (ACS 59.5  ±  32.3 µm vs. non-ACS 58.2  ±  32.3 µm, P = 0.760) did not significantly differ. Light property values were similar between both groups (light intensity 159.29  ±  72.20 vs. 159.45   ± 63.78, P = 0.654; light attenuation 0.88  ±  0.26 vs. 0.87   ±  0.24 m^-1, P = 0.988; backscatter 4.86   ±  0.58 vs. 4.83   ±  0.57, P = 0.812). The similarity of the neointimal quality in ACS and non-ACS patients was consistent across the 6 different types of current-generation metallic stents (P for interaction  > 0.05). Our findings suggested the comparable neointimal characteristics 3 months after implantation of the current-generation metallic stents in patients with ACS and stable coronary lesions by quantitative OCT methodology.

Multi-Objective Optimizations of Biodegradable Polymer Stent Structure and Stent Microinjection Molding Process

Biodegradable stents made of poly-l-lactic acid (PLLA) have a promising prospect thanks to high biocompatibility and a favorable biodegradation period. However, due to the low stiffness of PLLA, polymeric stents have a lower radial stiffness and larger foreshortening. Furthermore, a stent is a tiny meshed tube, hence, it is difficult to make a polymeric stent. In the present study, a finite element analysis-based optimization method combined with Kriging surrogate modeling is firstly proposed to optimize the stent structure and stent microinjection molding process, so as to improve the stent mechanical properties and microinjection molding quality, respectively. The Kriging surrogate models are constructed to formulate the approximate mathematical relationships between the design variables and design objectives. Expected improvement is employed to balance local and global search to find the global optimal design. As an example, the polymeric ART18Z stent was investigated. The mechanical properties of stent expansion in a stenotic artery and the molding quality were improved after optimization. Numerical results demonstrate the proposed optimization method can be used for the computationally measurable optimality of stent structure design and stent microinjection molding process.

Design optimization of stent and its dilatation balloon using kriging surrogate model

BACKGROUND

Although stents have great success of treating cardiovascular disease, it actually undermined by the in-stent restenosis and their long-term fatigue failure. The geometry of stent affects its service performance and ultimately affects its fatigue life. Besides, improper length of balloon leads to transient mechanical injury to the vessel wall and in-stent restenosis. Conventional optimization method of stent and its dilatation balloon by comparing several designs and choosing the best one as the optimal design cannot find the global optimal design in the design space. In this study, an adaptive optimization method based on Kriging surrogate model was proposed to optimize the structure of stent and the length of stent dilatation balloon so as to prolong stent service life and improve the performance of stent.

METHODS

A finite element simulation based optimization method combing with Kriging surrogate model is proposed to optimize geometries of stent and length of stent dilatation balloon step by step. Kriging surrogate model coupled with design of experiment method is employed to construct the approximate functional relationship between optimization objectives and design variables. Modified rectangular grid is used to select initial training samples in the design space. Expected improvement function is used to balance the local and global searches to find the global optimal result. Finite element method is adopted to simulate the free expansion of balloon-expandable stent and the expansion of stent in stenotic artery. The well-known Goodman diagram was used for the fatigue life prediction of stent, while dogboning effect was used for stent expansion performance measurement. As the real design cases, diamond-shaped stent and sv-shaped stent were studied to demonstrate how the proposed method can be harnessed to design and refine stent fatigue life and expansion performance computationally.

RESULTS

The fatigue life and expansion performance of both the diamond-shaped stent and sv-shaped stent are designed and refined, respectively. (a) diamond-shaped stent: The shortest distance from the data points to the failure line in the Goodman diagram was increased by 22.39%, which indicated a safer service performance of the optimal stent. The dogboning effect was almost completely eliminated, which implies more uniform expansion of stent along its length. Simultaneously, radial elastic recoil (RR) at the proximal and distal ends was reduced by 40.98 and 35% respectively and foreshortening (FS) was also decreased by 1.75%. (b) sv-shaped stent: The shortest distance from the data point to the failure line in the Goodman diagram was increased by 15.91%. The dogboning effect was also completely eliminated, RR at the proximal and distal ends was reduced by 82.70 and 97.13%, respectively, and the FS was decreased by 16.81%. Numerical results showed that the fatigue life of both stents was refined and the comprehensive expansion performance of them was improved.

CONCLUSIONS

This article presents an adaptive optimization method based on the Kriging surrogate model to optimize the structure of stents and the length of their dilatation balloon to prolong stents fatigue life and decreases the dogboning effect of stents during expansion process. Numerical results show that the adaptive optimization method based on Kriging surrogate model can effectively optimize the design of stents and the dilatation balloon. Further investigations containing more design goals and more effective multidisciplinary design optimization method are warranted.

First-generation versus second-generation drug-eluting stents in current clinical practice: updated evidence from a comprehensive meta-analysis of randomised clinical trials comprising 31 379 patients

Background

First-generation drug-eluting stents (DES) have become the most widely used devices worldwide for management of coronary artery disease. As remote follow-up data were becoming available, concerns emerged in regard to their long-term safety. Second-generation DES were designed to overcome safety issues, but the results of randomised clinical trials remain conflicting.

Methods

We compared the safety and efficacy of first-generation versus second-generation Food and Drug Administration approved DES; the following devices were included: first-generation sirolimus-eluting stent (SES) and paclitaxel-eluting stents (PES); second-generation everolimus-eluting stent (EES), zotarolimus-eluting stent Endeavor and ZES-Resolute (ZES-R). Prespecified safety end points comprised ≤1 and >1 year: overall and cardiac mortality, myocardial infarction (MI), definite/definite or probable ST; efficacy end points were target lesion revascularisation and target vessel revascularisation. Composite end points were analysed as well.

Results

33 randomised controlled trials involving 31 379 patients with stable coronary artery disease or acute coronary syndrome undergoing DES implantation were retrieved. No differences in mortality among devices were found. In the overall class comparison, second-generation DES were associated with a 22% reduction of odds of MI at short-term OR 0.77 (95% CI 0.68 to 0.89) p=0.0002; EES reduced the odds of definite-probable ST compared with PES: OR 0.33 (95% CI 0.15 to 0.73) p=0.006; First-generation SES along with second-generation EES and ZES-R showed similar efficacy in decreasing the odds of repeat revascularisation.

Conclusions

Second-generation EES and ZES-R offer similar levels of efficacy compared with first-generation SES, but are more effective than PES; however, only second-generation EES significantly reduced the incidence of MI and ST, and therefore should be perceived as the safest DES to date.

Safety and efficacy outcomes of first and second generation durable polymer drug eluting stents and biodegradable polymer biolimus eluting stents in clinical practice: comprehensive network meta-analysis

OBJECTIVES

To investigate the safety and efficacy of durable polymer drug eluting stents (DES) and biodegradable polymer biolimus eluting stents (biolimus-ES).

DESIGN

Network meta-analysis of randomised controlled trials.

DATA SOURCES AND STUDY SELECTION

Medline, Google Scholar, Embase, and Cochrane Central Register of Controlled Trials (CENTRAL) database search for randomised controlled trials comparing at least two of durable polymer sirolimus eluting stents (sirolimus-ES) and paclitaxel eluting stents (paclitaxel-ES), newer durable polymer everolimus eluting stents (everolimus-ES), Endeavor and Resolute zotarolimus eluting stents (zotarolimus-ES), and biodegradable polymer biolimus-ES.

PRIMARY OUTCOMES

Safety (death, myocardial infarction, definite or probable stent thrombosis) and efficacy (target lesion and target vessel revascularisation) assessed at up to one year and beyond.

RESULTS

60 randomised controlled trials were compared involving 63,242 patients with stable coronary artery disease or acute coronary syndrome treated with a DES. At one year, there were no differences in mortality among devices. Resolute and Endeavor zotarolimus-ES, everolimus-ES, and sirolimus-ES, but not biodegradable polymer biolimus-ES, were associated with significantly reduced odds of myocardial infarction (by 29-34%) compared with paclitaxel-ES. Compared with everolimus-ES, biodegradable polymer biolimus-ES were associated with significantly increased odds of myocardial infarction (by 29%), while Endeavor zotarolimus-ES and paclitaxel-ES were associated with significantly increased odds of stent thrombosis. All investigated DES were similar with regards to efficacy endpoints, except for Endeavor zotarolimus-ES and paclitaxel-ES, which were associated with significantly increased the odds of target lesion and target vessel revascularisations compared with other devices. Direction of results beyond one year did not diverge from the findings for up to one year follow-up. Bayesian probability curves showed a gradient in the magnitude of effect, with everolimus-ES and Resolute zotarolimus-ES offering the highest safety profiles.

CONCLUSIONS

The newer durable polymer everolimus-ES and Resolute zotarolimus-ES and the biodegradable polymer biolimus-ES maintain the efficacy of sirolimus-ES; however, for safety endpoints, differences become apparent, with everolimus-ES and Resolute zotarolimus-ES emerging as the safest stents to date.