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Stent

A stent is a small, expandable tube, typically made of metal or other biocompatible materials, inserted into a narrowed or weakened passage in the body—such as a , , or airway—to keep it open and restore normal flow. These devices are most commonly used in cardiovascular procedures to treat blockages in arteries, particularly affected by , where they prop open the vessel walls after to prevent re-narrowing. First developed in the mid-1980s as an improvement over plain , stents have evolved to significantly reduce the risk of artery closure and complications like heart attacks. Stents consist of a basic design featuring a tubular scaffold that expands radially upon deployment, providing mechanical support to the wall. Common components include the framework, sometimes with coatings for release or bioabsorption, though detailed classifications by and function are covered elsewhere. As of 2025, drug-eluting stents remain the most prevalent type in coronary applications. Beyond cardiovascular uses, stents are deployed in peripheral arteries, the , , and trachea to alleviate obstructions. Placement generally involves minimally invasive catheterization techniques, with the stent delivered in a compressed state on a , expanded at the site, and the delivery system withdrawn. This approach, particularly () for coronary arteries, is a key treatment for conditions like and , with over two million procedures performed annually worldwide as of 2023. While effective, potential risks such as necessitate antiplatelet ; further details on complications and recent innovations like thinner struts and bioactive coatings are addressed in subsequent sections.

Overview

Definition and Purpose

A stent is a small, expandable tube-like device, typically constructed from a material, that is inserted into a , duct, or hollow organ to maintain its openness and prevent collapse or narrowing due to or . This medical implant acts as an internal scaffold, expanding to fit the of the structure and providing ongoing support against compressive forces or . The primary purposes of stents include restoring blood flow in obstructed arteries, such as by preventing restenosis after balloon angioplasty in coronary vessels; supporting weakened or narrowed structures in the ureters to facilitate urine drainage or in bile ducts to alleviate blockages; and treating obstructions in the , like esophageal strictures or malignant compressions. Stents find broad application across medical specialties, including for treating arterial blockages, for managing ureteral obstructions, for biliary and esophageal interventions, and for glaucoma control via micro-stents that enhance aqueous humor outflow. As of 2023, over 2 million coronary stents are implanted annually worldwide, underscoring their critical role in cardiovascular care. In distinction from related devices, stents differ from catheters, which serve as temporary conduits for fluid drainage, medication delivery, or procedural guidance without providing long-term structural reinforcement. They also contrast with vascular grafts, which function as prosthetic replacements for entire segments of damaged vessels rather than merely propping open existing lumens. This supportive, non-replicative design emphasizes stents' role in minimally invasive preservation of native .

Basic Design and Components

A typical stent consists of a mesh-like cylindrical designed to provide within a . This is composed of interconnected struts, which form the primary load-bearing elements; nodes, serving as junction points where struts meet; and bridges or links, which connect adjacent segments to allow for controlled deformation during deployment. These components collectively enable the stent to expand radially and maintain patency against vessel . Stent designs vary primarily in their expansion mechanisms, with self-expanding variants relying on inherent elasticity to deploy upon release from a constraining , and balloon-expandable types requiring of an integrated to achieve their final shape. Key parameters include , typically ranging from 2 to 50 mm to match sizes; length, often between 8 and 100 mm to cover lesions adequately; and cell , where open-cell configurations enhance flexibility for tortuous , while closed-cell designs prioritize uniform expansion and radial strength. Mechanically, stents exhibit elasticity to accommodate vessel pulsation, hoop strength to resist compressive forces from the surrounding , and minimal foreshortening—the axial reduction upon , ideally less than 5% in optimized designs. The radial force, which counters vessel , can be modeled simply as F = k \cdot \Delta r, where F is the force, k is the radial constant, and \Delta r is the radial ; this relationship underscores the balance between support and overexpansion risks. Delivery systems integrate the compressed stent onto low-profile catheters or within protective sheaths, facilitating minimally invasive endovascular navigation and precise placement via access.

Classification of Stents

By Anatomical Application

Stents are classified by their anatomical application, reflecting adaptations to the specific anatomical and physiological demands of different regions, such as vessel size, flexibility requirements, and obstruction types. Cardiovascular stents constitute the majority of all stent usage, accounting for approximately 87% of the global market as of recent data. Cardiovascular stents are primarily designed for arterial blockages due to . Coronary stents target the heart's arteries, where vessels are narrow, typically requiring diameters of 2 to 4 mm to restore blood flow and prevent . Peripheral vascular stents address obstructions in the legs or arms, often necessitating longer lengths up to 200 mm to cover extended segments of the femoropopliteal artery while accommodating movement and flexibility. Urological stents facilitate urinary tract drainage in cases of obstruction. Ureteric stents, commonly featuring a double-J shape with curled ends to anchor in the and , are used for blockages from kidney stones or strictures, maintaining patency of the . Prostatic stents provide temporary support to the in patients with , alleviating outflow obstruction without permanent implantation. Gastrointestinal stents address luminal narrowing in the digestive tract. Colonic stents are deployed to relieve tumor-induced obstructions in the large bowel, enabling bowel and avoiding emergency surgery. Esophageal stents treat strictures or cancer-related blockages, with options for covered designs to prevent tumor ingrowth into the stent mesh or uncovered variants for better tissue integration, depending on the clinical scenario. Biliary and pancreatic stents ensure drainage of or pancreatic fluids in ductal obstructions. These are indicated for blockages from gallstones or tumors, often incorporating side holes along the length to promote effective drainage and reduce sludge accumulation. Other specialized stents include those for ocular conditions, such as drainage devices that reduce by shunting aqueous humor. The iStent, approved by the FDA in 2012, exemplifies a trabecular micro-bypass stent implanted during . Recent advancements as of 2023 incorporate microfluidic designs in microstents to enhance drug elution and flow control for improved long-term efficacy. Some cardiovascular stents may include drug-eluting variants to reduce restenosis, though detailed functionality is covered elsewhere.

By Material and Functionality

Stents are classified by material and functionality based on their post-implantation biological interactions, such as resistance to restenosis, mechanisms, profiles, or specialized coverings that influence tissue response and vessel patency. This classification emphasizes performance enhancements that mitigate complications like neointimal or while tailoring to specific clinical needs. Bare-metal stents (BMS) consist of metallic frameworks, typically or cobalt-chromium alloys, providing immediate mechanical support to maintain vessel without additional coatings. These stents interact biologically by allowing rapid endothelialization but carry a higher of in-stent restenosis due to unchecked smooth muscle cell proliferation, with rates reported between 10% and 40%. BMS are particularly indicated in scenarios where prolonged anticoagulation is contraindicated, such as high patients, as they require shorter dual antiplatelet therapy durations compared to coated variants. Drug-eluting stents () enhance functionality through polymer coatings that release antiproliferative agents, such as or , directly into the vessel wall to inhibit neointimal and reduce restenosis. This controlled promotes a more favorable biological response by delaying excessive tissue growth, achieving restenosis rates below 10% in most cases. By 2023, accounted for over 90% of () procedures, reflecting their widespread adoption for improved long-term patency. Bioresorbable stents represent an advanced functional category designed to degrade over time, typically 6 to 36 months, using materials like poly-L-lactic acid (PLLA) or , thereby restoring natural vessel pulsatility and eliminating chronic foreign body reactions. These stents support initial radial force while gradually resorbing, allowing vasomotion recovery and potentially reducing late risks associated with permanent implants. Notable examples include the Absorb PLLA-based scaffold, discontinued in 2017 following trials showing elevated rates, and the Magmaris stent, which is approved and in clinical use in , with ongoing clinical evaluations for broader applications and refined safety profiles. A next-generation variant, Freesolve, received approval in 2024, featuring improved design for enhanced deliverability and resorption. Other functional stent types include covered stents, which incorporate fabric linings such as (PTFE) to seal aneurysms by excluding blood flow from the aneurysmal sac while preserving parent vessel patency. These interact biologically by promoting formation within the covered space and endothelialization over the graft material. Radioactive stents, employing beta-emitting isotopes like , were explored for targeted radiation to inhibit but remain rare in use, primarily in palliative settings for malignancy-related obstructions due to challenges and limited efficacy data.

Materials and Manufacturing

Common Materials

Stents are primarily constructed from metallic biomaterials that provide the necessary mechanical strength, flexibility, and durability for vascular support. , particularly the 316L variant (ASTM F138), is a widely used due to its excellent corrosion resistance in physiological environments, high durability, and ease of processing into intricate stent geometries. However, 316L stents can exhibit magnetic susceptibility artifacts during (MRI), potentially compromising image quality in some cases, though they are generally considered MRI-conditional rather than fully incompatible. Nitinol, a nickel-titanium , enables self-expanding stents through its superelastic properties, which arise from the reversible austenite-to-martensite at body temperature, allowing radial force application without permanent deformation. Cobalt-chromium alloys offer a superior strength-to-weight ratio compared to , along with inherent radiopacity that facilitates fluoroscopic visualization during implantation, making them suitable for thinner struts in modern bare-metal and drug-eluting designs. Bioresorbable metallic stents, made from alloys such as magnesium, , or iron, are an emerging class designed to provide temporary support while degrading over 6-12 months, often eluting drugs to prevent restenosis and potentially reducing long-term complications associated with permanent implants. As of , several such stents have entered clinical trials. Polymeric materials are increasingly employed in bioresorbable vascular scaffolds (BVS), where poly(L-lactic acid) (PLLA) serves as a key that gradually degrades via , ultimately breaking down into biocompatible monomers that are metabolized by the body. The degradation process involves hydrolytic chain scission, following pseudo-first-order influenced by factors such as , temperature, and polymer crystallinity, leading to bulk over 6–24 months . This temporary scaffolding supports vessel patency until endothelialization occurs, after which the scaffold resorbs completely, potentially reducing long-term complications associated with permanent implants. To enhance performance, stents often incorporate coatings and surface modifications. Biocompatible polymers such as polyethylene-co-vinyl acetate (PEVA) are applied as matrices for drug-eluting stents, providing controlled release of antiproliferative agents like while maintaining adhesion to the metallic substrate. Bioactive surfaces, including immobilization, promote anticoagulation by binding III and inhibiting activity, thereby reducing thrombogenicity at the blood-material . All stent materials must adhere to biocompatibility standards outlined in ISO 10993, which includes testing for cytotoxicity (via cell viability assays), sensitization, and thrombogenicity (through hemocompatibility evaluations like platelet adhesion studies). A notable challenge with nitinol is the potential release of nickel ions, which can occur through corrosion in vivo and may elicit allergic responses in susceptible patients, necessitating surface passivation or electropolishing to minimize ion leaching below safe thresholds (e.g., <0.5 μg/cm²/week per EN 1811 standards). These standards ensure that materials interact minimally with biological tissues, supporting safe implantation across diverse patient populations.

Production Techniques

Stents are primarily fabricated through processes that transform raw materials into functional devices capable of withstanding physiological stresses. One of the most common techniques for producing balloon-expandable stents involves from hypotubes, which are thin-walled metal tubes typically made of or cobalt-chromium alloys. In this method, lasers with output are used to etch intricate strut patterns with tolerances as fine as 10 micrometers or less, ensuring minimal heat-affected zones and high structural integrity. This process allows for the creation of complex geometries while maintaining the tube's cylindrical form until removes burrs and refines the surface. For self-expanding stents, braiding and techniques are employed using superelastic wires, such as nitinol filaments with diameters around 50-150 micrometers. These wires are interwoven on a to form a , where the weave directly influences radial and expansion behavior; denser braids provide greater hoop strength for vessel support. After braiding, the structure undergoes shape-setting through in a fixture to impart the desired expanded , typically followed by to enhance and fatigue resistance. modeling studies have validated this approach, predicting performance under radial to optimize wire count and for clinical . Coating application is a critical step, particularly for drug-eluting stents, where thin polymer layers deliver antiproliferative agents like or to prevent restenosis. Techniques such as dip-coating immerse the stent in a polymer-drug , followed by to achieve uniform thicknesses of 5-10 micrometers, while plasma spraying deposits bioactive coatings via ionized particles for enhanced . Spin-coating rotates the stent to spread the solution evenly, minimizing defects and enabling controlled drug loading; efficiency is quantified as the release, calculated by (initial dose - residual dose)/initial dose × 100, often exceeding 80% over 30 days . These methods ensure conformal coverage without compromising mechanical properties, as verified in release kinetic studies. Post-fabrication, stents undergo sterilization using (EtO) gas or gamma irradiation to achieve a of 10^{-6}, with EtO preferred for heat-sensitive polymers to avoid degradation. involves rigorous testing, including burst assessments exceeding 1.5 times the deployment (typically >2 for coronary stents) to confirm radial strength, and accelerated fatigue simulations simulating 10^8 cycles to mimic 10 years of cardiac pulsation without fracture. These evaluations, guided by FDA recommendations, ensure compliance with ISO 25539 standards for dimensional accuracy and durability. Recent advancements include for custom stents using additive manufacturing with resorbable polymers like poly-L-lactic acid, enabling patient-specific designs via techniques such as fused deposition modeling or vat photopolymerization, with notable progress in the early . This approach allows for complex, porous structures tailored to vascular anatomy, potentially reducing mismatch issues while incorporating bioresorbable material processing for temporary support.

Implantation Procedures

General Methods

Stent implantation is typically performed using minimally invasive approaches, where a is inserted through a peripheral , most commonly the femoral or , to deliver the stent to the target site. This method avoids open surgery and reduces recovery time, with providing real-time X-ray imaging for guidance, often supplemented by (IVUS) or (OCT) for detailed visualization of vessel walls and stent placement. Stents are deployed via two primary expansion mechanisms: balloon-expandable or self-expanding. Balloon-expandable stents, commonly used in rigid vessels like , are mounted on a and expanded through plastic deformation by inflating the to pressures of 6-20 atmospheres, permanently reshaping the stent to match the vessel . In contrast, self-expanding stents, often made from nickel-titanium alloys with shape memory properties, are constrained within a delivery sheath and expand automatically upon release, driven by the body's temperature to regain their pre-set shape, making them suitable for dynamic or tortuous anatomies. The general workflow begins with diagnostic to identify the site using contrast dye and , followed by optional predilation with a to prepare the vessel if the is severe. The stent is then advanced over a guidewire, deployed via the chosen expansion method, and often post-dilated with a higher-pressure to ensure optimal to the vessel wall. Final or imaging confirms patency and rules out complications like . Patients are prepared with at the access site and mild , while general is reserved for complex cases; pre-procedure antiplatelet , such as a dual regimen of aspirin and clopidogrel, is administered to prevent during and after implantation. Procedural success is high, with immediate vessel patency achieved in over 95% of cases, and typical procedure times range from 30 to 90 minutes, depending on complexity and access route.

Specific Techniques by Type

In cardiovascular applications, (PCI) involves advancing a balloon-mounted stent over a guidewire to the site, followed by balloon inflation to deploy the stent and restore luminal patency. This technique is particularly suited for balloon-expandable stents, which are crimped onto the and expand radially upon inflation to conform to the wall. For lesions, where a main branches into two, the provisional stenting strategy deploys a single stent in the main branch and only stents the side branch if significant compromise occurs post-dilation, minimizing procedural complexity and reducing risks compared to upfront two-stent approaches like the double-kissing crush technique. The two-stent strategy, reserved for complex cases with large side branches or extensive disease, involves sequential stenting of both branches but is associated with higher rates of failure in some analyses. Urological stent implantation for ureteric obstruction typically employs cystoscopic retrograde insertion, where a flexible cystoscope is passed through the and to guide the stent into the under direct visualization, allowing precise placement from the to the . This approach is preferred for its minimally invasive nature and high success rate in non-obstructed ureters, though antegrade placement via is used when access fails, such as in cases of severe distal obstruction or altered . Ureteric stents generally have a of 3-6 months, after which they require exchange or removal to prevent encrustation and , with polymeric stents necessitating regular replacement in malignant or obstructions. Gastrointestinal stents, particularly for esophageal strictures, are deployed endoscopically using a gastroscope to traverse the , followed by advancement of the compressed stent over a guidewire and release for radial expansion. Self-expanding metal stents are favored for malignant strictures due to their ability to maintain patency without balloon assistance, providing rapid symptom relief in and accommodating irregular stricture shapes through gradual expansion over 24-48 hours. Biliary stents are placed under (ERCP) guidance, involving duodenoscopy to access the papilla, cannulation of the , and deployment of the stent across the obstruction to ensure drainage. biliary stents, commonly used for benign or short-term malignant obstructions, require every 3 months to mitigate from sludge accumulation, contrasting with self-expanding metal alternatives for longer-term palliation. Ophthalmic stents in micro-invasive surgery (MIGS) utilize trabecular microbypass devices like the iStent inject, implanted via an ab interno approach through a clear corneal incision under gonioscopic guidance to bypass the and enhance aqueous outflow. This outpatient procedure, often combined with , involves injecting the pre-loaded stent into using a specialized handpiece, achieving reduction with minimal conjunctival disruption and rapid recovery. Functional adjustments in stent implantation account for device-specific properties; drug-eluting stents (DES) necessitate prolonged dual antiplatelet therapy for 6-12 months post-implantation to mitigate thrombosis risk from the polymer and antiproliferative drug release. Bioresorbable stents demand precise vessel sizing via intravascular imaging to prevent malapposition, as their thicker struts and degradation profile increase vulnerability to incomplete wall contact and late scaffold dismantling.

Complications and Management

Potential Risks

Stent thrombosis represents a critical following implantation, categorized by timing: acute (within 24 hours, incidence 0.4%), subacute (24 hours to 30 days, 1.1%), late (30 days to 1 year, 0.5%), and very late (beyond 1 year, 0.6%), with an overall incidence of 2.4% over approximately 22 months of follow-up in earlier studies. With contemporary drug-eluting stents as of 2025, rates have declined to approximately 0.7% in the first year and 0.2-0.6% annually thereafter. This complication carries a high of 5% to 45%. Restenosis, the re-narrowing of the stented , primarily arises from neointimal , a biological response involving and extracellular matrix deposition triggered by vascular injury from the stent. In bare-metal stents (BMS), restenosis rates reach approximately 15% at 1 year for target lesion revascularization, driven by homogeneous neointimal peaking at 6 to 8 months; drug-eluting stents () reduce this to 1% to 2% annual target lesion revascularization rates through antiproliferative agents, though they may delay healing and elevate late risk. Mechanical failures unique to stents include , , and malapposition. Stent , resulting from repetitive vessel motion such as or torsion, occurs in 0.8% to 19% of coronary cases, with a mean incidence of 4.9%, and is associated with increased restenosis and . Malapposition, defined as incomplete contact between the stent and wall (late persistent or acquired), promotes turbulent and formation, contributing to late and very late without a precisely quantified universal incidence but noted as a key . , the unintended displacement of the device, affects 1% to 5% of gastrointestinal stents and up to 2% of peripheral stents, often due to anatomical forces or undersizing. Infection and inflammation pose additional biological risks. Coronary stent infections are exceedingly rare, with only 17 documented cases since 1987, typically involving and carrying a 50% survival rate in early-onset forms (<10 days post-implantation), though late-onset cases often necessitate surgical intervention. associated with stents occurs in <1% of cases, generally as a secondary complication from bacteremia. Hypersensitivity reactions to components like or polymers trigger type IV immune responses, fostering via T-lymphocyte activation and elevated expression, which heightens restenosis (10% to 30% incidence) and (0.5% to 2%) risks, particularly in metal-allergic patients. Organ-specific risks highlight procedural and device-related vulnerabilities. In coronary (PCI), contrast media used for visualization can precipitate renal failure, especially in patients with pre-existing impairment. For glaucoma drainage devices like the XEN gel stent, erosion of the exposes the implant in 1.1% to 2.3% of cases, while hypotony (excessively low ) develops in 1.9% to 4.6%, potentially leading to maculopathy. Long-term outcomes underscore persistent challenges in . exhibit lower ISR rates than BMS (2.5% vs. 14.7% revascularization at 1 year), with recurrent ISR escalating to 8.3% after first reintervention and 22.8% after third. Bioresorbable stents, intended for temporary support, show higher early risks (up to 1.8% very late vessel thrombosis) and revascularization (14.1% at 3 years) compared to contemporary (5.2%), based on 2024 analyses of first-generation devices; newer generations as of 2025 demonstrate improved outcomes with reduced complications.

Treatment and Prevention

Pharmacological strategies play a central role in preventing stent-related complications, particularly and restenosis. Dual antiplatelet (DAPT) with aspirin and a inhibitor, such as clopidogrel, , or , is recommended post-implantation to reduce the risk of stent . For bare-metal stents (BMS), a minimum duration of 1 month of DAPT is advised, while for drug-eluting stents (), should continue for at least 6 to 12 months in patients without high risk, depending on clinical presentation and ischemic risk. Statins are also utilized for endothelial protection, as pretreatment or ongoing use reduces post-percutaneous coronary (PCI) inflammatory responses and lowers the incidence of stent by stabilizing plaques and improving vascular function. Procedural techniques during implantation further mitigate risks by ensuring proper stent deployment. Optimal stent sizing, guided by the distal reference lumen diameter, helps avoid undersizing, which can lead to malapposition and increased thrombosis risk; intravascular ultrasound (IVUS) or optical coherence tomography (OCT) imaging is employed to confirm adequate apposition and expansion, targeting a minimum stent area greater than 5.5 mm² in non-left main vessels. Patient-specific factors influence prevention strategies, with risk stratification essential for those with diabetes, which is associated with higher rates of in-stent restenosis due to accelerated neointimal hyperplasia. Lifestyle interventions, including smoking cessation, are strongly recommended, as continued smoking post-PCI elevates the risk of stent thrombosis and overall cardiovascular events, while quitting reduces mortality by approximately 36% in coronary artery disease patients. Treatment of complications requires prompt intervention tailored to the issue. For acute stent , aspiration combined with balloon or additional stenting is the primary mechanical approach, often alongside intensified therapy. In-stent restenosis () is managed with drug-coated balloons (DCB), which deliver antiproliferative agents like to inhibit neointimal growth and have demonstrated superiority over plain balloon in randomized trials for both BMS-ISR and DES-ISR; alternatively, intravascular may be used for recurrent or refractory cases, delivering localized to suppress cellular . Stent , though rare, typically necessitates surgical removal if endoscopic retrieval fails, particularly when causing obstruction or . Monitoring protocols post-implantation focus on detecting early complications without routine invasive procedures. Follow-up is reserved for symptomatic patients or high-risk cases, typically performed at 6 to 12 months if clinically indicated, to assess patency and restenosis. Noninvasive biomarkers, such as elevated levels, serve as indicators of risk, with prospective studies showing a between higher and increased incidence of stent after . Regular clinical follow-up, including assessment every 3 to 6 months, integrates these elements to optimize long-term outcomes.

History

Origins and Etymology

The term "stent" in traces its roots to the 17th-century Scots , where it derived from "stent" or "stynt," meaning to stretch, extend, or , often referring to a or brace used to hold structures in place, such as in fishing nets or taxation props. This conceptual foundation of support and expansion later influenced its medical adoption. The word gained prominence through English dentist Charles Thomas Stent (1807–1885), who in the mid-19th century developed a specialized gutta-percha-based compound for taking dental impressions of edentulous mouths, which he improved by incorporating stearine and other fillers to enhance its moldability and supportive properties. Stent's material, known as "Stent's compound," became widely used in for creating stable, form-fitting molds that supported tissue during procedures. By the early , the term "stent" had evolved into an engineering and medical descriptor for props or braces beyond pure , particularly in plastic and . Dutch surgeon F. Esser popularized its use in 1916–1917 when he applied Stent's compound as a supportive in reconstructions, such as after tumor excisions, to maintain shape and prevent collapse during healing. This non-vascular application extended the word's meaning to any device or material that provided internal support or stretching, akin to its Scots origins, though it remained distinct from modern implantable devices. While ancient civilizations employed rudimentary tubular supports—like Egyptian reed catheters documented in the around 1550 BCE for urinary drainage—these were temporary conduits rather than indwelling, expandable structures, and thus not true stents in the contemporary sense. Although Dotter and Judkins proposed the concept of an intraluminal splint in their 1964 paper on transluminal angioplasty, referring to rigid, tapered catheters or sheaths used to dilate and support atherosclerotic arteries in the legs, the term "stent" first appeared in cardiovascular literature in 1966 by Weldon et al., describing a stented prosthetic . This marked a pivotal shift toward endovascular support devices. By the 1980s, as balloon-expandable and self-expanding stents emerged for coronary use—exemplified by the 1986 implantations of the first human coronary stents by Jacques Puel and Ulrich Sigwart—the terminology evolved from broader "vascular prostheses" to the concise "stent," reflecting their specialized role in maintaining vessel patency and gaining ubiquity in interventional literature.

Key Developments

The development of stent technology began in the mid-20th century with pioneering work by Charles Dotter, who performed the first percutaneous transluminal angioplasty on January 16, 1964, using a to dilate a clogged leg artery in an elderly patient, marking the inception of minimally invasive vascular interventions and laying the foundation for modern stenting. In 1969, Dotter advanced this by implanting the first wire prototype—uncoated coil springs—into the of dogs, demonstrating modest success in maintaining vessel patency and establishing the concept of an endovascular scaffold, retrospectively recognized as the inaugural stent design. A significant occurred in 1986, when the first human coronary stents were implanted: by Jacques Puel on March 28 in , , and by Ulrich Sigwart in June in , , using the self-expanding Gianturco-Grüntzig Wallstent during to treat restenosis following balloon angioplasty, which provided immediate vessel support and reduced acute closure risks. This represented the transition from experimental prototypes to clinical application in , paving the way for broader adoption of stenting in . In 1994, the U.S. (FDA) approved the Palmaz-Schatz (BMS) for coronary use, the first such device based on rigorous clinical trials like BENESTENT, which demonstrated improved outcomes, including lower rates of abrupt vessel closure leading to emergency CABG (1.2% vs. 1.9% in ), compared to alone. Overall, stents reduced such rates from around 5% in early PTCA to under 2%. This approval solidified BMS as a standard therapy, transforming outcomes for patients with by minimizing periprocedural complications and improving long-term vessel patency. The early 2000s introduced drug-eluting stents (), with the FDA approving the sirolimus-eluting stent in 2003 and the paclitaxel-eluting stent in 2004, which coated metal scaffolds with antiproliferative drugs to inhibit neointimal . These innovations dramatically lowered restenosis rates from 25-30% with BMS to about 8%, as evidenced in trials like RAVEL and SIRIUS, reducing the need for repeat interventions and establishing as the dominant type. During the , bioresorbable vascular scaffolds (BVS) emerged as a promising , with Abbott's Absorb BVS receiving FDA approval in 2016 for treating , designed to provide temporary support before fully degrading within 3 years to restore natural vessel motion. However, post-approval studies revealed higher rates of scaffold and , leading to its voluntary withdrawal from the market in 2017 due to safety concerns and suboptimal performance compared to metallic . Concurrently, advancements in peripheral artery stents addressed critical limb ischemia (CLI), with trials in the mid-2010s validating drug-eluting options like everolimus-eluting stents for infrapopliteal disease, improving amputation-free survival rates in CLI patients by enhancing below-the-knee vessel patency over bare-metal alternatives. Regulatory progress extended stent applications beyond vasculature, as the granted CE marks for glaucoma stents in 2004, including devices like the iStent trabecular micro-bypass, enabling minimally invasive implantation to reduce by improving aqueous humor outflow in open-angle glaucoma patients. By 2023, these cumulative innovations drove global market growth for coronary stents to approximately $8 billion, reflecting widespread adoption and iterative improvements in design and materials.

Advancements and Future Directions

Recent Innovations

In recent years, advancements in have focused on bioengineered coatings that enhance endothelial cell promotion while minimizing restenosis risks. For instance, the BioMime™ sirolimus-eluting incorporates a biomimetic coating designed to accelerate re-endothelialization and reduce neointimal hyperplasia, building on sirolimus's antiproliferative effects. Clinical trials in 2024-2025 have also demonstrated the feasibility of shortening dual antiplatelet therapy (DAPT) to as little as 30 days in high-bleeding-risk patients undergoing with biodegradable-polymer sirolimus-eluting ultra-thin stents, showing comparable safety and efficacy to longer regimens without increased ischemic events. Surface functionalization techniques have introduced nano-coatings with anti-thrombotic properties to improve stent and reduce complications like . Zwitterionic coatings, which form a layer to repel proteins and platelets, have shown significant reductions in formation—up to 98% in preclinical models—when applied to blood-contacting devices including stents. A 2024 study on bioinspired zwitterionic block -armored surfaces further confirmed inhibition of and , highlighting their potential for coronary applications with approximately 50% lower rates compared to uncoated controls in short-term evaluations. Titanium-nitride-oxide (TiNO)-coated stents continue to evolve for enhanced , particularly in complex scenarios. A 2023 meta-analysis of TiNO-coated stents versus drug-eluting stents reported lower rates of in-stent restenosis () and recurrent at one year, with sustained benefits in patients over five years. These coatings promote endothelialization while reducing neointimal proliferation, making them suitable for high-risk lesions where traditional may increase risks. Complementary treatments have advanced lesion preparation prior to stenting, notably with the FDA clearance of the Shockwave Medical intravascular (IVL) system on March 22, 2024, for lithotripsy-enhanced balloon dilatation of calcified peripheral artery lesions. This sonic pressure wave technology fractures calcium without vessel trauma, facilitating safer stent deployment in heavily calcified cases. In peripheral applications, the Eluvia™ system, featuring a fluoropolymer-based sustained release over 12 months, has demonstrated superior patency rates in femoropopliteal lesions, as evidenced by 2024 multicenter registry data showing reduced restenosis compared to bare-metal alternatives. In , innovations in stents include the MINIject® supraciliary micro-stent, a suprachoroidal delivery device approved under regulations since 2021, with 2024 clinical updates confirming its efficacy in reducing by 20-30% in open-angle patients through bleb-free aqueous humor diversion. Two-year outcomes from prospective studies indicate sustained safety and IOP lowering without significant adverse events, positioning it as a next-generation minimally invasive surgery (MIGS) option.

Emerging Research

Recent advancements in stent technology are focusing on integrating smart sensors to enable of vascular conditions. Prototypes of sensor-integrated stents, such as those using sensors in self-rollable structures, have demonstrated the ability to detect cardiovascular changes noninvasively from distances up to 50 cm, facilitating early of stent edge restenosis through membrane-based sensing mechanisms. Similarly, ultrasonic sensor-equipped smart stents have shown promise in computational simulations for restenosis in the descending by measuring flow disruptions caused by tissue proliferation. These developments, often prototyped in 2024-2025 studies, aim to transition from passive implants to active diagnostic tools, though integration with materials like nitinol for enhanced flexibility remains in early exploration. Gene-eluting and stem cell-based coatings represent another frontier, with 2025 research emphasizing (VEGF)-releasing mechanisms to promote vessel regeneration post-implantation. Studies on (EPC) infusion and capturing technologies have highlighted their role in enhancing endothelial repair, where stents coated to attract EPCs reduce and support neointimal formation without excessive . Complementary efforts involve CRISPR-modified approaches for endothelial capture, including nanoparticle delivery systems that enable precise in vascular walls to improve and regeneration, as demonstrated in preclinical models targeting ischemic tissues. These innovations build on VEGF therapy's proven benefits in ischemic models, projecting stents that actively regenerate vessels rather than merely supporting them. Next-generation fully bioresorbable stents are advancing with zinc-based alloys, which offer degradation rates more controlled than magnesium counterparts, typically spanning 1-3 years but tunable toward faster profiles in optimized compositions. Preclinical evaluations of zinc-copper-manganese alloys implanted in porcine models have confirmed over extended periods, with reduced inflammatory responses compared to magnesium due to slower and lower gas production. 2025 reviews underscore zinc's advantages, including minimal toxicity from degradation products, positioning it as a viable alternative for temporary scaffolding that fully dissolves without long-term artifacts. Efforts to accelerate zinc degradation to 3-6 months via alloying are ongoing, aiming to match acute healing timelines while preserving mechanical integrity. Personalized 3D-printed stents are gaining traction through additive manufacturing, leveraging patient-specific scans to fabricate devices tailored for complex anatomies like . Ongoing 2024-2025 demonstrates how these techniques produce stents with intricate geometries that conform to individual vessel curvatures, reducing malapposition risks in lesions via or fused deposition modeling. Simulations and bench tests confirm improved deployment in 3D-printed coronary models derived from data, enabling customized radial force and for enhanced patency in challenging sites. This approach not only addresses one-size-fits-all limitations but also integrates bioresorbable polymers for transient support. Artificial intelligence is optimizing stent designs by employing machine learning algorithms to refine strut patterns that minimize hemodynamic disturbances, particularly wall shear stress (WSS), defined briefly as \tau = \mu \frac{du}{dy} where \mu is viscosity and \frac{du}{dy} the velocity gradient near the wall. In 2025 computational studies, deep learning integrated with differential evolution has optimized flow-diverting stent configurations, achieving reductions in maximum WSS by up to 40% through simulated iterations on aneurysm models. These AI-driven simulations prioritize low-shear geometries, enhancing endothelial function and reducing thrombosis risk without exhaustive physical prototyping. Despite these promises, emerging stent technologies face significant challenges, including the management of long-term products from bioresorbable materials, which can induce localized or altered vascular remodeling if not fully biocompatible. Ethical considerations in clinical trials are paramount, particularly for high-risk patients with comorbidities, where balancing innovation benefits against potential adverse events requires rigorous and phased escalation protocols to mitigate unforeseen complications.

References

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