ReviewImpact of stent strut design in metallic stents and biodegradable scaffolds☆
Introduction
Since the emergence of the first coronary stents nearly 30 years ago, stent designs have constantly evolved through the use of new material and adaptation in stent architecture.
The impact of strut thickness on stent design has been recognized early on: in pre-clinical studies, bare stents with thicker stent struts were shown to develop more inflammation and restenosis than thin strut designs [1], [2]. Furthermore, randomized studies in patients showed that a reduction of strut thickness of coronary stents is associated with improved follow-up angiographic and clinical results [3], [4].
The first generation DESs were shown to be superior to BMS but were limited by recurrent problems of late target lesion revascularization (late catch-up) and Stent Thrombosis (ST). The second generation DESs with more conformable designs, more hemo- and biocompatible polymers and improved kinetics of drug release have proven superior to previous DES technology in terms of both safety and efficacy.
Evolution towards new platforms and thinner struts has been driven by clinicians' desire for more consistently deliverable stents that cause less injury and restenosis. PCI practice has considerably evolved as a result of the emergence of new devices, allowing for more complex lesions and procedures to be performed, with improved clinical results. Nowadays, emerging fully biodegradable stent technologies available in clinical practice are constantly challenging existing beliefs derived from studies with permanent metallic platforms.
The aim of this article is to review recent advancements, both in metal and biodegradable stent materials and understand their influence on stent design. To understand how strut design may impact stent performance and clinical outcomes, the article reviews the evidence from the evolution and development of stent design from bare stents to the latest DESs and fully biodegradable technologies.
Section snippets
Strut design in the bare metal stent (BMS) era
Several preclinical studies have reported early on the effect of stent strut geometry on the degree of vessel injury and restenosis [1], [2], [5], [6]. In particular, strut thickness and stent flexibility have been recognized to impact degree of injury, risk of rupture of the elastic laminae and overall inflammation, with a larger strut design generally leading to higher inflammation and restenosis than the thinner strut and open cell design [1], [2], [5], [6], [7].
Thicker stent struts have
Strut design in the DES era
The impact of strut design in DES is less evident compared with BMS since the addition of a drug coating acts as a barrier against neointimal proliferation which retards the natural healing process [11].
Biodegradable coating
Pathology and IVUS studies suggested that the polymer in the first generation DES might trigger a delayed hypersensitivity reaction resulting in very-late stent thrombosis [24], [34], [35]. These evidences encouraged the idea that a strategy of “leaving no polymer” could be better than leaving a durable polymer “behind”.
In biodegradable coated stents, such as the Biolimus-eluting BioMatrix stent (Biosensors International, Morges, Switzerland), the polymer coating is progressively absorbed,
Impact of strut thickness with DES
The impact of strut thickness is less evident in DES as each DES differs not only in terms of platform design but also in polymer formulation, drug type and concentration, release kinetics, polymer degradation, etc.., all of which contribute to the in vivo response.
Comparison of the first generation thick DES with thinner bare stents showed that the effect of drug coating prevails over strut thickness [11], [32], [39], [40]. Therefore, the impact of strut thickness can be hard to delineate in
Fully biodegradable scaffolds
Although conformable platforms with thinner strut and more biocompatible coating have resulted in improved outcomes, permanent metal implants still have some inherent drawbacks, including the risk of late-catch-up, hypersensitivity reaction to the polymer, allergic reaction to the metal, stent fracture or late stent thrombosis. Furthermore, the presence of a metallic stent implanted in a diseased vessel can preclude further interventions or by-pass surgery. For these reasons, numerous companies
Biodegradable polymers
Polymers are macromolecules built from large volumes of repeating small monomer units. The polymer's mechanical characteristics such as strength, stiffness and degradation rate are linked to the number of monomer units (molecular weight) and their arrangement. Polymers with longer chains (higher molecular weight) are usually stronger and have longer absorption times. Similarly, dense linear arrangement of the monomers (high linearity/crystallinity) results in higher strength and slower
Biodegradable polymer based scaffolds
A number of scaffolds based on PLLA, PDLLA or PLGA biodegradable polymers have been developed in recent years. The Igaki-Tamai stent (Kyoto Medical Planning Co., Kyoto, Japan) was the first of this type of PLA based biodegradable scaffolds [46], [61]. It has a PLLA based architecture with a strut thickness of 170 μm and an absorption time of approximately 24–36 months. Encouraging initial results with this scaffold [62] has raised the interest of the clinical community and industry for such
Magnesium based biodegradable alloys
In addition to scaffolds based on biodegradable polymer materials, biodegradable metal stents based on Iron or Magnesium biodegradable alloys, have also been recently investigated. Data about the clinical performance of bioabsorbable metallic stents is emerging [71], [72], [73].
In contrast to conventional metal stents, which are made resistant to corrosion, biodegradable metals use a controlled corrosion by body fluids as a mechanism of biodegradation. Pure magnesium degrades rapidly in body
Impact of strut thickness with bioresorbable technologies?
The impact of strut thickness has been evidenced in the number of studies for metallic stents. Can these results be extended to biodegradable scaffolds?
The neointimal thickness has been shown to be large in biodegradable scaffolds, in a similar way that large metallic stent strut does produce larger neointimal area than the thinner strut design [68], [74], [75], [76]. However, the healing response with biodegradables is markedly different to that of the metal stents; remodeling continues as the
Conclusion
Thinner struts produce less arterial injury, faster re-endothelialization and reduce the risk of restenosis and thrombosis. Because of its fundamental impact on vessel response, reducing strut dimension while maintaining radial support remains the focus for manufacturers looking for ways to improve stent deliverability and performances.
Conflict of interest
None of the authors has a direct conflict of interest in this connection with this article. Dr. Joner and Virmani are employees of CV Path.
References (82)
- et al.
Effect of endovascular stent strut geometry on vascular injury, myointimal hyperplasia, and restenosis
J Vasc Surg
(2002) - et al.
Role of stent design and coatings on restenosis and thrombosis
Adv Drug Deliv Rev
(2006) Restenosis following implantation of bare metal coronary stents: pathophysiology and pathways involved in the vascular response to injury
Adv Drug Deliv Rev
(2006)- et al.
In-stent restenosis in small coronary arteries: impact of strut thickness
J Am Coll Cardiol
(2002) - et al.
Increased artery wall stress post-stenting leads to greater intimal thickening
Lab Invest
(2011) - et al.
Five-year follow-up after sirolimus-eluting stent implantation results of the SIRIUS (Sirolimus-Eluting Stent in De-Novo Native Coronary Lesions) Trial
J Am Coll Cardiol
(2009) - et al.
Long-term safety and efficacy with paclitaxel-eluting stents: 5-year final results of the TAXUS IV clinical trial (TAXUS IV-SR: treatment of de novo coronary disease using a single paclitaxel-eluting stent)
J Am Coll Cardiol Intv
(2009) - et al.
Coronary stents: current status
J Am Coll Cardiol
(2010) - et al.
Outcomes associated with drug-eluting and bare-metal stents: a collaborative network meta-analysis
Lancet
(2007) - et al.
Comprehensive meta-analysis on drug-eluting stents versus bare-metal stents during extended follow-up
Am J Med
(2009)
Pathology of drug-eluting stents in humans: delayed healing and late thrombotic risk
J Am Coll Cardiol
Stent thrombosis with drug-eluting and bare-metal stents: evidence from a comprehensive network meta-analysis
The Lancet
Efficacy and safety of zotarolimus-eluting stents compared with sirolimus-eluting stents in patients undergoing percutaneous coronary interventions — A meta-analysis of randomized controlled trials
International Journal of Cardiology
Endothelial cell recovery between comparator polymer-based drug-eluting stents
J Am Coll Cardiol
Biolimus-eluting stent with biodegradable polymer versus sirolimus-eluting stent with durable polymer for coronary revascularisation (LEADERS): a randomised non-inferiority trial
Lancet
Abluminal biodegradable polymer biolimus-eluting stent versus durable polymer everolimus-eluting stent (COMPARE II): a randomised, controlled, non-inferiority trial
Lancet
Optical coherence tomography assessment of in vivo vascular response after implantation of overlapping bare-metal and drug-eluting stents
J Am Coll Cardiol Intv
Coronary stents: looking forward
J Am Coll Cardiol
Stent longitudinal integrity bench insights into a clinical problem
J Am Coll Cardiol Intv
Stent flexibility versus concertina effect: mechanism of an unpleasant trade-off in stent design and its implications for stent selection in the cath-lab
Int J Cardiol
Evaluation of the second generation of a bioresorbable everolimus-eluting vascular scaffold for the treatment of de novo coronary artery stenosis: 12-month clinical and imaging outcomes
J Am Coll Cardiol
Mechanisms of polymer degradation and erosion
Biomaterials
A bioabsorbable everolimus-eluting coronary stent system for patients with single de-novo coronary artery lesions (ABSORB): a prospective open-label trial
Lancet
A bioabsorbable everolimus-eluting coronary stent system (ABSORB): 2-year outcomes and results from multiple imaging methods
Lancet
ABSORB II randomized controlled trial: a clinical evaluation to compare the safety, efficacy, and performance of the Absorb everolimus-eluting bioresorbable vascular scaffold system against the XIENCE everolimus-eluting coronary stent system in the treatment of subjects with ischemic heart disease caused by de novo native coronary artery lesions: rationale and study design
Am Heart J
Temporary scaffolding of coronary arteries with bioabsorbable magnesium stents: a prospective, non-randomised multicentre trial
Lancet
Early- and long-term intravascular ultrasound and angiographic findings after bioabsorbable magnesium stent implantation in human coronary arteries
J Am Coll Cardiol Intv
Bioresorbable scaffolds: current knowledge, potentialities and limitations experienced during their first clinical applications
Int J Cardiol
Effect of the endothelial shear stress patterns on neointimal proliferation following drug-eluting bioresorbable vascular scaffold implantation: an optical coherence tomography study
J Am Coll Cardiol Intv
A platinum–chromium steel for cardiovascular stents
Biomaterials
Intracoronary stenting and angiographic results: strut thickness effect on restenosis outcome (ISAR-STEREO) trial
Circulation
Intracoronary stenting and angiographic results: strut thickness effect on restenosis outcome (ISAR-STEREO-2) trial
J Am Coll Cardiol
Endovascular stent design dictates experimental restenosis and thrombosis
Circulation
Stent and artery geometry determine intimal thickening independent of arterial injury
Circulation
Morphological predictors of restenosis after coronary stenting in humans
Circulation
Drug-eluting stents compared with thin-strut bare stents for the reduction of restenosis: a prospective, randomized trial
Eur Heart J
A randomized comparison of a sirolimus-eluting stent with a standard stent for coronary revascularization
N Engl J Med
Outcomes associated with drug-eluting and bare-metal stents: a collaborative network meta-analysis
The Lancet;
Clinical efficacy of polymer-based paclitaxel-eluting stents in the treatment of complex, long coronary artery lesions from a multicenter, randomized trial: support for the use of drug-eluting stents in contemporary clinical practice
Circulation
Stent thrombosis late after implantation of first-generation drug-eluting stents: a cause for concern
Circulation
Mortality in randomized controlled trials comparing drug-eluting vs. bare metal stents in coronary artery disease: a meta-analysis
Eur Heart J
Cited by (140)
Mg alloy cardio-/cerebrovascular scaffolds: Developments and prospects
2023, Journal of Magnesium and AlloysDevelopment of a soft robotic catheter for vascular intervention surgery
2023, Sensors and Actuators A: PhysicalThe impact of structure and temperature on the mechanical properties and radiopacity of Ta-W coatings for tiny endovascular medical implants
2023, Materials Chemistry and Physics
- ☆
Dr. Joner and Virmani are employees of CV Path. Dr Wong is a founder and Chief Scientific Officer of Innoheart Plc.