Functional advancements in intravascular catheters: materials, sensors, actuators, and robot integration

3.1 Biocompatible materials

Biocompatibility (Figure 3) is a core requirement for catheter materials given their sustained exposure to blood and vessel walls. Ideal materials should minimize immune activation, resist thrombosis, and maintain long-term mechanical and chemical stability in physiological environments. Commonly used polymers such as polyurethane (PU), silicone, and polyethylene terephthalate are favored for their flexibility and baseline hemocompatibility^[35]. Fluorinated polymers like polytetrafluoroethylene (PTFE) are also widely studied for their low surface energy and reduced protein adsorption, which limit the thrombus formation. Recent research efforts have focused on enhancing antifouling properties and biological inertness through advanced surface modifications and functional coatings^[36].

To address challenges related to thrombosis and infection, functional surface coatings have gained increasing attention. Liu et al. (Figure 3A)^[17] developed a heparin network coating that significantly suppressed thrombus adhesion in vitro while achieving high antibacterial efficiency against both Staphylococcus aureus and Escherichia coli. Zhang et al. (Figure 3B)^[31] also introduced hydrophobic domains into heparin films via ethyl lauroyl arginate (ELA), enhancing coating stability and antibacterial performance. The resulting ELA heparin complex sustained heparin release for 21 days and reduced bacterial colonization by more than 99%, thereby overcoming the burst-release limitation associated with unmodified hydrophilic coatings. More recently, bioinspired dynamic materials have emerged. Wang et al. (Figure 3C)^[32,37] fabricated magnetically responsive hydrogel fibers from autologous blood and magnetic nanoparticles for intracranial use; the fibers matched brain tissue stiffness (~100 kPa) and enabled on-demand drug release under a magnetic field while maintaining integrity in confined channels. Park et al. (Figure 3D)^[33] developed a porous carboxymethyl chitosan (p-CMC)-coated catheter that reduced E. coli and platelet adhesion by over 90% while enhancing trackability and durability. Zhang et al. (Figure 3E)^[34] reported a PTFE coating modified with imipenem/cilastatin sodium via dendritic mesoporous silica nanoparticles (IC@dMSNs), achieving >99.9% antibacterial efficiency.

Overall, balancing mechanical robustness, controlled degradability, and long-term biocompatibility of the catheter remains challenging. Specifically, we note that intravascular catheter systems must comply with international sterilization and regulatory standards to ensure clinical translation. Common sterilization methods include ethylene oxide (ISO 11135:2014^[38]) and steam sterilization (ISO 17665-1:2024^[39]). Adherence to these standards ensures material safety, sterilization stability, and provides a clear pathway toward clinical application.

3.2 Lubricious materials

Lubricity (Figure 4) is a key requirement for intravascular catheters, enabling smooth navigation through complex vascular anatomy while minimizing endothelial damage. To address this, various surface modification strategies have been explored to reduce interfacial friction and improve clinical maneuverability. Among these, hydrophilic coatings have attracted particular interest due to their ability to form stable hydration layers that significantly lower the coefficient of friction (COF)^[8].

For example, Lai et al. (Figure 4A)^[40] developed a polyvinylpyrrolidone–polyethylene glycol (PVP–PEG) copolymer coating on thermoplastic polyurethane (TPU) substrates, which achieved long-lasting lubricity under physiological flow, maintaining low COF and excellent mechanical integrity after 60 cycles of wet friction testing. Similarly, Zhang et al. (Figure 4B)^[8] designed a waterborne polyurethane (WPU) stabilized hydrogel coating with a low COF of 0.0357 under 1 Hz reciprocating motion, along with an interfacial bonding strength up to 536 N/m, indicating both robust adhesion and durable lubrication. The coating also demonstrated antimicrobial efficacy with inhibition zones of 4.2 mm (Bacillus subtilis) and 1.9 mm (E. coli). Beyond traditional hydrogel approaches, liquid-infused and bioinspired coatings have demonstrated unique capabilities. Wang et al. (Figure 4C)^[41] developed a liquid-fibrous catheter with spatially controlled drug release and adaptive lubrication. The COF varied depending on drug properties and pore size, highlighting the crucial role of matrix liquid interactions. Park et al.^[33] introduced a p-CMC coating via selective PEG leaching. The p-CMC exhibited superhydrophilicity and a significant reduction in COF while maintaining performance over 60 minutes of continuous friction. The coating also reduced bacterial and platelet adhesion, thereby enhancing biocompatibility.

Although hydrophobic coatings generally lack hydration lubrication, certain designs achieve reduced adhesion via low surface energy or physical surface structuring. Armugam et al. (Figure 4D)^[42] synthesized a PDMS catheter coating exhibiting intrinsic hydrophobicity and notable broad-spectrum antimicrobial activity, suitable for long-term implantation. In another approach, Zhang et al. (Figure 4E)^[34] utilized a PTFE coating loaded with IC@dMSNs. This construction demonstrated a 6.4% increase in antibacterial efficacy against E. coli (from 50.8% to 56.9%) and a 5.8% increase against S. aureus (from 83.5% to 89.3%), along with sustained anticoagulant function and hydrophobicity (water contact angle >150 °). Integrating multifunctional coatings has emerged as a frontier. Lim et al.^[43] constructed a polydopamine peptide surface with combined antimicrobial, antithrombotic, and lubricating functions using a 1-step immobilization strategy.

Although significant progress has been made, challenges such as coating delamination, limited durability under dynamic blood flow, and difficulties integrating embedded functionalities still persist. To overcome these issues, continued efforts in developing bioinspired, multifunctional, and stable lubricating coatings will be instrumental in advancing intravascular catheter systems.

3.3 Variable stiffness materials

Variable stiffness (Figure 5) is a critical functional requirement for intravascular catheters, balancing rigidity for navigation with flexibility for safe traversal of tortuous vasculature. Traditional designs often incorporate passive stiffness gradients, but these lack intraoperative adaptability. Recent advancements focus on active stiffness modulation through phase change materials, smart polymers, and engineered architectures that respond to thermal, electrical, or magnetic stimuli.

Thermally responsive shape memory polymers (SMPs), particularly PU or thermoset variants, offer large modulus changes when transitioning across their glass transition temperature. For instance, Mattmann et al. (Figure 5A)^[44] developed a thermoset SMP catheter with heating times of ~7 s and cooling below 15 s. The device maintained biocompatibility and stiffness reversibility without the need for encapsulation, illustrating the feasibility of rapid intraoperative stiffness tuning. Piskarev et al. (Figure 5B)^[45] introduced a conductive SMP variable stiffness thread that combines stiffness modulation with integrated heating and sensing functions. Their device achieved a stiffness change factor of 21 and enabled selective segmental bending under a 20 mT magnetic field in a 2.0 mm diameter catheter. To improve response time and scalability, Piskarev et al.^[49] also developed a fast-response SMP catheter with integrated water cooling, achieving a 26-fold faster stiffening response (from 115 s to 4.4 s) and a 66-fold change in modulus within a 2.3 mm-diameter profile. This work highlights the importance of integrating efficient thermal management strategies for clinical applicability. Choi et al.^[50] extended this paradigm with thermally drawn SMP fibers (SMPFs), enabling continuous fabrication of long-length catheters with embedded wires and lumens for actuation, sensing, and fluid transport. Their SMPF catheter exhibited a 31-fold change in stiffness within 8.4 s and operated safely within the 20–37 °C temperature window. Phantom studies confirmed stable navigation and shape locking in tortuous vasculature.

Low-melting-point alloys (LMPAs) offer an extreme stiffness ratio (>400 times) and have been used in magnetic-steering catheters. Mao et al. (Figure 5C)^[46] demonstrated a 3–4 mm diameter catheter incorporating alternating “Guider” and “Follower” segments, each composed of LMPAs, achieving apical elongation and following the leader (FTL) behavior under magnetic actuation. Their system responded within 5–10 s for softening and ~15 s for restiffening in water environments, maintaining safe surface temperatures under 50 °C. Other variable stiffness mechanisms include jamming systems (granular, layer, or fiber), which exhibit <1 s response times but are difficult to miniaturize below 3 mm diameter due to the need for air channels or particles. While suitable for larger endoscopic instruments, their bulk limits cardiac applications. In contrast, fiber-jamming catheters, such as those by Sun et al. (Figure 5D)^[48], achieve rapid stiffness modulation within sub-2.5 mm diameters suitable for cardiovascular use. Fabrication approaches also influence design feasibility. Thermal drawing, as demonstrated by Abdelaziz et al. (Figure 5E)^[48], allows rapid prototyping of multilumen, tendon-driven, or actively tracked catheters with programmable mechanical and imaging properties, showing comparable performance to commercial systems in preclinical trials. These approaches support broader integration with MR guidance or robotic control.

Overall, the key challenges in current variable-stiffness catheter technologies include substantial energy requirements for thermal actuation, limited stiffness-tuning ranges in some polymeric materials, difficulty integrating sensing and actuation components, and unresolved concerns about long-term biocompatibility. In particular, the long-term stability of SMPs and LMPAs under repeated actuation in blood remains uncertain, as hydrolytic degradation or particle release may induce inflammation or thrombosis. Further in vitro and in vivo evaluations, including fatigue and hemocompatibility testing, are required to verify their safety for chronic intravascular applications.

4.1 Intravascular ultrasound

IVUS has emerged as 1 of the most mature and effective intraluminal imaging modalities for real-time assessment of vascular structures, particularly in the context of atherosclerosis diagnosis and interventional guidance. At its core, IVUS employs high-frequency ultrasound transducers to generate cross-sectional images of vessel walls, providing detailed visualization with axial resolution^[51]. Several commercial IVUS systems exemplify the advancement of this technology. For instance, the Philips Eagle Eye Platinum catheter utilizes a digital transducer with advanced features like ChromaFlo^[52] for flow visualization; Boston Scientific’s OptiCross^[53] series offers high-resolution rotational imaging for coronary assessment; and Insight Lifetech TrueVision^[54] system integrates a catheter with a high frame rate console, representing a new generation of high-frequency IVUS platforms.

To overcome the challenges of miniaturization and mechanical complexity in high-frequency ultrasound systems, various research strategies have been proposed. For instance, Xu et al.^[55] developed a mechanical scanning IVUS system. Their design included a motion-compensation algorithm that corrected for nonlinear scanning distortion, achieving a spatial resolution of 51 µm and an imaging depth of 8 mm. Hou et al. (Figure 6A)^[56] introduced a distal micromotor-driven side-looking IVUS catheter. This eliminated the friction-induced nonuniform rotational distortion (NURD) typically seen in traditional designs, thereby improving maneuverability in curved vessels. Similarly, Peng et al. (Figure 6B)^[57] proposed a synchronous electromagnetic micromotor for IVUS applications, achieving high rotational stability with angular errors below 7 ° and a rotation speed of up to 275 revolutions per second.

NURD has also been addressed through sensing and correction. Han et al. (Figure 6C)^[58] developed a miniature 50 MHz rotary ultrasonic encoder that directly measures angular position during catheter rotation. Liu et al. (Figure 6D)^[59] presented a dual-element IVUS catheter featuring 2 back-to-back transducers operating at 40 MHz. This configuration enabled complementary imaging: when distortion or signal loss occurred on 1 side due to vessel curvature or tissue obstruction, the opposing transducer could provide undistorted data.

More recently, robotic and magnetically actuated IVUS systems have opened new possibilities for imaging in highly tortuous vessels. Yang et al. (Figure 6E)^[9] developed a dual-mode magnetic IVUS robot that combines static magnetic steering and dynamic magnetic beam scanning, allowing precise tip navigation and high-speed imaging. Their catheter design integrates a permanent magnet with a single-element transducer, enabling real-time ultrasound acquisition and controllable positioning using external magnetic fields. This innovation eliminates mechanical shafts entirely, significantly reducing the risk of NURD.

Collectively, these approaches improve IVUS resolution, mechanical stability, and imaging flexibility through complementary strategies. Whether through mechanical optimization, dual-transducer redundancy, solid-state transducer integration, or robotic actuation, each study offers a unique solution to the technical challenges that continue to shape the future of IVUS systems.

4.2 Optical coherence tomography

OCT is an intravascular imaging technique that utilizes near-infrared light to provide real-time, high-resolution visualization of vascular structures. OCT catheters consist of a rotating optical fiber within a transparent sheath, delivering wavelength light to achieve penetration depths of 0.1–2 mm^[66]. With axial resolutions typically ranging from 1 to 10 μm and lateral resolutions as fine as 5 μm, OCT catheters outperform IVUS catheters in resolving microstructures such as thin fibrous caps, lipid pools, cholesterol crystals, and stent struts, which are critical for identifying vulnerable plaques and evaluating stent deployment outcomes^[67]. Commercial OCT catheters include Abbott’s Ilumien Optis^[68] integrated with Ultreon software for AI-assisted image interpretation, and Conavi Medical’s Novasight Hybrid^[69], combining OCT and IVUS in a single catheter.

Modern intravascular OCT catheter designs aim for compactness and flexibility. Some OCT catheters^[70] have diameters of ≤1 mm, though some novel designs report probes as thin as 0.457 mm using 3D-printed freeform optics or even 0.52 mm using monolithic ball-lens microprobes^[69]. These ultrathin designs enable imaging in extremely narrow vessels or lumens (eg, small airways, deep brain)^[61] without inducing trauma.

Functional advances are also evident in catheter scanning mechanisms. Probe innovations include meta-lenses that eliminate spherical and astigmatic aberrations, achieving diffraction-limited performance over an extended depth of focus^[71]. Traditional torque coil systems suffer from NURD, especially in tortuous vessels. Wang et al. (Figure 6F)^[60] developed a miniature piezoelectric-driven fiber optic slip ring (FOSR) probe, achieving 360 ° scanning at 10,000 rpm within a 0.85 mm form factor. Similarly, Zhang et al.^[72] presented a pneumatic OCT probe with a turbine scanner reaching 446 revolutions per second, offering distortion-free imaging even in tortuous bronchial lumens. They also developed a Magnetic-OCT system^[73] for motor-free telerobotic endomicroscopy, enabling steerable and programmable imaging in complex, curved, and localized areas. Beyond diagnosis, OCT is expanding toward theranostic applications. Yuan et al. (Figure 6G)^[61] reported an OCT microneedle integrating 800 nm imaging and 1448 nm laser ablation in a 580 μm probe for real-time deep brain tumor imaging and treatment.

Challenges persist, particularly in improving blood tolerance and imaging depth. Efforts include polarization-sensitive and adaptive-optics OCT, as well as improved swept-source systems for enhanced signal robustness. Integration with AI and robotic platforms is actively pursued to enable intelligent, image-guided navigation and intervention.

4.3 Fiber Bragg grating

FBG sensors have emerged as a promising technology for enabling high-resolution within minimally invasive intravascular catheters^[74]. By reflecting a specific Bragg wavelength in response to strain and temperature changes, FBGs provide real-time feedback on mechanical interactions without relying on electronic components, making them inherently compatible with magnetic resonance imaging (MRI) and other electromagnetically noisy environments^[75].

Li et al.^[76] demonstrated a triaxial force sensor utilizing an FBG triaxial force sensor with integrated flexure structure, achieving force resolutions of 2.13–2.52 mN for transverse and 23.12 mN for axial directions. Simulation and in vitro vessel phantom tests confirmed the effective decoupling of force and temperature effects. Subsequently, Li et al. (Figure 6H)^[62] also developed a 3D-printed FBG sensor optimized for robustness and high resolution (0.52–0.64 mN), achieving <3% RMS error in dynamic force measurements and improved temperature compensation across 25–50 °C. More recently, Wang et al. (Figure 6I)^[63] introduced a miniaturized FBG sensor with a compliant mechanism and an integrated laser-ablation channel, reporting force resolutions of 4.7–11.6 mN across 3 axes. Their use of a reduced-order global transfer matrix method enabled rapid modeling and optimization. The sensor supported ex vivo cardiac ablation, confirming its applicability in functional surgical tasks.

In robotic settings, FBGs have been employed for shape sensing and closed-loop feedback. Dong et al. (Figure 6J)^[64] integrated a multicore FBG array into a steerable MRI catheter, achieving real-time shape reconstruction with 1.53 mm tip accuracy and enabling autonomous navigation in simulated ablation procedures. Similarly, Zhou et al.^[13] reported a fiber robot that combines macro-scale tendon-driven motion and microscale precision via integrated optical fiber waveguides, enabling decoupled multiscale manipulation in endoluminal contexts. Abdelaziz et al.^[48] developed a thermal actuated fiberbot with <50 μm positioning accuracy for laparoscopic navigation and molecular tissue ablation, showcasing scalable fabrication via fiber drawing. Zhang et al. (Figure 6K)^[65] further demonstrated a 0.95 mm continuum robot with magnetic steering and embedded optical fiber array for imaging, ablation, and drug delivery, offering <30 μm motion precision in constrained anatomical pathways.

Despite these advances, integrating FBGs into submillimeter or highly flexible catheter systems poses challenges, such as maintaining stable fiber alignment under deformation and preserving signal fidelity during physiological motion.

4.4 MEMS

MEMS (Figure 7) have emerged as a transformative approach to functionalize intravascular catheters by integrating microscale sensors and actuators onto compact, low-power platforms^[20]. Their capacity for high-resolution, real-time monitoring makes them ideal for applications requiring precise measurement of pressure, flow, temperature, and mechanical interaction forces^[80].

Recent developments illustrate the breadth of MEMS integration into catheter systems. For instance, Kwon et al. (Figure 7A)^[77] reported a battery-less wireless implant incorporating silicon nanomembrane sensors for continuous tri-modal monitoring of vascular pressure, flow, and temperature, achieving high sensitivity under in vivo conditions. Han et al. (Figure 7B)^[14] demonstrated soft multilayer catheter integrated arrays capable of simultaneous electrical mapping, pressure sensing, and electroporation, offering conformal tissue contact and dynamic adaptability. The mechanical interface between MEMS sensors and soft tissue remains critical. Shen et al. (Figure 7C)^[78] introduced a flounder-shaped stretchable electrode system for pulsed-field ablation, achieving uniform electric fields and mechanical stability under 87% compression. This configuration enhanced ablation depth and reduced electrode failure rates to below 0.1%. Meanwhile, Xue et al. (Figure 7D)^[79] adapted balloon-assisted 3D MEMS electrode arrays for colon electrophysiology, capturing pacemaker-like signals with signal-to-noise ratios exceeding 25 dB in vivo.

In addition to sensing, MEMS systems are increasingly used for actuation and localized therapy. Singh et al.^[81] developed an electroceutical catheter using retractable nitinol electrodes to deploy a voltage-activated adhesive patch, sealing 2 mm vascular defects under 350 mm Hg burst pressure and tolerating over 20,000 deformation cycles. The patch demonstrated minimal electrical leakage and stable adhesion under blood flow. Huang et al. (Figure 7E)^[20] emphasized modular integration of sensing, imaging, and therapy through catheter platforms embedded with MEMS arrays, suggesting synergistic designs for neural, vascular, and gastrointestinal applications.

The development of fully integrated smart catheters depends not only on advanced materials and sensing modules but also on reliable power transmission and data telemetry within the confined intravascular environment. Inductive coupling remains the leading approach for wireless power transfer, enabling safe milliwatt-level delivery through tissue, although alignment and depth constraints persist. Optical energy transmission and communication via fiber optics provide simultaneous power and high-speed data transfer but require careful management of bending losses. Battery-free energy harvesting from intravascular flow, vibration, or ambient radio frequencies, such as triboelectric nanogenerators^[82], offers a promising route to eliminate bulky batteries. Integrating these technologies may enable multifunctional, miniaturized, and biocompatible catheters for next-generation clinical applications.

5.1 Ablation catheter

Ablation catheters are designed to deliver energy precisely to targeted tissues, allowing clinicians to eliminate abnormal or diseased structures with minimal invasiveness^[88]. In cardiology, they are central to treating arrhythmias by selectively destroying ectopic foci or reentrant pathways, enabling high-precision intervention inside the heart. Representative systems include the Farapulse pulsed field ablation system by Boston Scientific^[89], offering nonthermal lesion formation with high tissue selectivity; Medtronic’s Arctic Front Advance cryoballoon^[90], which enables circumferential pulmonary vein isolation with a single application; and the Thermocool Smart Touch SF catheter from Biosense Webster^[91], integrating contact force sensing with open irrigation for precise thermal ablation.

Radiofrequency (RF) ablation remains the most widely used modality. Nguyen et al. (Figure 8A)^[83] integrated transparent silicon carbide electrodes into an endoscopic platform, combining excellent optical visibility with stable electrical performance. At 450 kHz, their system raised tissue temperature to 80 °C while supporting real-time feedback and multimodal sensing. Pulsed field ablation, which relies on nonthermal irreversible electroporation, is emerging as a promising alternative. Xu et al. (Figure 8B)^[84] developed a catheter with microelectrodes that produced precise lesions in large-animal hearts using 300 V pulses and achieved lesion widths as narrow as 3.8 mm, thereby improving safety in complex anatomies. Accurate energy delivery depends on robust intraoperational sensing. Koh et al.^[92] introduced ultrathin injectable sensors that measure temperature, thermal conductivity, and heat capacity in situ during RF and cryoablation. Their multilayer polymer needle provided depth-resolved thermal maps, showing a strong correlation between thermal profiles and lesion transmurality.

Progress in materials, sensing, and lesion assessment is steadily moving ablation technology toward multifunctional, intelligent catheters that offer real-time feedback, tighter energy control, and greater procedural safety—key steps toward more effective and tailored intravascular therapies.

5.2 Thrombectomy catheter

Thrombectomy mechanisms in intravascular catheters aim to mechanically remove resistant obstructions, such as calcified plaques or organized thrombi, especially when standard angioplasty is ineffective. Common applications include atherectomy procedures for restoring vessel patency in chronic total occlusions or severely calcified lesions. Commercialization technologies include rotational (eg, Rotablator^[93]), orbital (eg, Diamondback 360^[94]), and directional atherectomy, each using different high-speed or orbiting cutters.

Heunis et al. (Figure 8C)^[85] developed a magnetically actuated rotablation catheter featuring a spring-loaded mechanism that achieves a maximum axial force of 2.63 N and torque of 5.69 mN·m. Their device demonstrated effective plaque removal, reducing the stenosis cross-sectional area by up to 35%, using interchangeable drill bits activated by internal electromagnetic coils (EMNS). Yang et al. (Figure 8D)^[86] proposed a driller-tipped guidewire integrated with magnetic navigation and ultrasound imaging, enabling real-time control for penetrating chronic total occlusions. Their system combined directional and rotational magnetic fields to switch between steering and drilling modes, achieving successful unclogging within tissue-mimicking vascular phantoms. Huang et al. (Figure 8E)^[87] developed a Petromyzontidae-inspired microneedle-integrated bioelectronic catheter featuring multifunctional microneedle tips capable of biochemical sensing, electroporation, and drug delivery. Khalil et al.^[95] introduced a helical microrobot for mechanical clot removal via magnetic rubbing. The in vitro experiments quantified a clot-removal rate of −0.885 mm³/min at 35 Hz, approximately 5 times more effective than conventional streptokinase thrombolysis (−0.17 mm³/min).

On the other hand, Mao et al.^[46] presented a millimeter-scale magnetic continuum robot capable of “follow-the-leader” deployment via tip-steered elongation. Their design enabled safe navigation through tortuous lumina and morphing into functional configurations at the target site. The robot employed dual-phase transition materials for stability and mobility and demonstrated in vivo capabilities such as knotting, pressure sensing, and instrument delivery. Rivkin et al. (Figure 8F)^[12] reported a self-assembled microcatheter with integrated actuated digits and a magnetic sensor. The device, with a diameter of only 120 μm, supports fluid delivery, micromanipulation, and real-time magnetic tracking. It demonstrated clot manipulation and precise liquid administration within ex vivo and artificial vascular models.

The thrombectomy catheter systems require atraumatic, precise control in complex vascular anatomy. While imaging guidance and robotic assistance improve surgical safety, limitations remain, including incomplete capture, vessel trauma, and poor visibility. Future designs are expected to emphasize miniaturization, force feedback, and multifunctionality to enable intelligent and adaptive intervention in complex vascular environments.

5.3 Steerable catheter

Steerable catheters (Figure 9) are intravascular tools equipped with tip actuation mechanisms that provide enhanced directional control, enabling precise navigation in tortuous vascular anatomies^[99]. Unlike conventional passive systems that rely on guidewires and torque transfer, steerable platforms improve access to challenging targets, such as the cerebral vasculature and coronary bifurcations^[100]. Commercially, systems such as the SwiftNINJA^[101] microcatheter offer dual-directional 180 ° tip deflection for rapid vessel selection, while NAVISTAR^[97] catheters integrate electroanatomical mapping with steerable control for precise ablation during electrophysiological procedures.

Pull wire systems remain a foundational design approach, but achieving high control accuracy and reliability is critical for their clinical effectiveness. Zhou et al. (Figure 9A)^[13] developed a macro-micro decoupled continuum robot with a 1 mm outer diameter, integrating tendon-driven macro steering with light-driven micro actuation via liquid crystal elastomer fibers. Their system demonstrated sub-300 μm resolution and a mean trajectory error of just 4.8% in in vivo tympanic membrane procedures, highlighting its potential for precise endoluminal manipulation. Abdelaziz et al.^[48] reported a fiber-drawn electrothermal actuator with sub-50 μm positioning accuracy and up to 10 mm/s tip speed. By embedding resistive wires within polymer fibers, this platform achieved planar tip steering suitable for precision surgical navigation. Compared to pull wire systems, concentric tube robots offer superior controllability. Girerd et al. (Figure 9B)^[96] proposed a hand-held concentric tube robot capable of 6 degrees of freedom (DOF) tip manipulation with submillimeter accuracy, and demonstrated its effectiveness in simulated percutaneous abscess drainage procedures.

Hydraulically actuated steerable tips offer smooth, continuous motion with high flexibility. Gopesh et al.^[101] designed a soft robotic microcatheter with 4 saline-filled microchannels (50 μm) to achieve 3D tip steering without a guidewire, enabling successful embolization in vivo in a porcine model. Rogatinsky et al. (Figure 9C)^[97] further expanded this concept by integrating a soft manipulator and deployable stabilization mechanism for intracardiac navigation. Their robotic system could apply up to 1.2 N of radial force and maintain stable contact with dynamic cardiac tissue. Nguyen et al. (Figure 9D)^[98] introduced an electricity-free, hydraulically coupled actuator system termed the soft fibrous syringe architecture, capable of tip steering and built-in sensing. Their flexible catheter achieved 4 cm of displacement via fiber-reinforced muscle actuation and demonstrated self-sensing control in a fully soft design. Alternative actuation schemes have advanced the miniaturization and precision control of steerable catheters. Kim et al.^[102] Fabricated a magnetorheological elastomer microactuator (0.7 mm diameter) capable of 124 ° bending with only 12 µm positional error, leveraging a novel dip coating process that achieves tunable eccentricity and high repeatability.

The performance of steerable systems hinges on DOF and control strategies^[103]. Despite advances, challenges persist in miniaturizing actuation mechanisms without compromising output force, ensuring mechanical durability under cyclic loading, and maintaining biocompatibility^[104].

6.1 Magnetically actuated robot

Magnetically actuated robots (Figure 10) represent a transformative approach for achieving precise, remote, and minimally invasive control of catheters within complex vascular environments. Magnetically steerable robotic systems generally comprise a catheter integrated with permanent magnets, soft magnetic materials, or magnetized composites^[112]. These devices are actuated through external magnetic fields generated by permanent magnets, EMNS, or MRI scanners. The applied torque and force induce tip deflection or whole-body bending, depending on the device’s stiffness and magnetic profile^[113]. One notable clinical implementation is the Niobe system by Stereotaxis^[114], which utilizes a pair of computer-controlled permanent magnets to generate a dynamic magnetic field around the patient, enabling precise navigation of magnetically tipped catheters with submillimeter accuracy. This technique is particularly promising for intracranial and cardiovascular interventions, where traditional mechanical actuation methods often face limitations due to friction, buckling, or poor steerability.

Kim et al. (Figure 10A)^[16] developed ferromagnetic soft continuum robots that achieve omnidirectional bending via programmed magnetic domains, successfully navigating through tortuous cerebrovascular phantoms with diameters below 1 mm. Dreyfus et al. (Figure 10B)^[107] introduced a helical magnetic robot with a screw like outer geometry, where tip rotation generated forward propulsion along the vessel wall; the device achieved stable navigation in millimeter-scale cerebral arteries and successfully operated in a live porcine model. Phelan et al. (Figure 10C)^[108] demonstrated Lorentz force steering using a quad configuration micro coil catheter compatible with MRI fields up to 7 T, achieving a tip deflection of 110 ° with only 0.44 W of power and without the need for active cooling. Tiryaki et al. (Figure 10D)^[109] further investigated magnetic actuation under ultrahigh magnetic fields, showing that guidewires embedded with permanent magnets could achieve torque steering even inside 7T MRI environments via in situ magnetization switching, thus enabling dynamic reconfiguration during navigation. Magnetic navigation systems provide actuation infrastructure for such devices. Hwang et al. (Figure 10E)^[110] developed a clinically translatable electromagnetic actuation system combined with a micro robotic guidewire for real-time cardiovascular intervention, demonstrating teleoperated navigation in vivo in swine coronary and renal arteries. Pittiglio et al. (Figure 10F)^[111] proposed a cart-mounted permanent magnet system that actuates a ball-chain magnetic catheter, demonstrating a comparable treatment effect to clinical ablation catheters while significantly reducing size.

Some groups have integrated magnetic steering with therapeutic delivery^[115]. Torlakcik et al.^[116] engineered a magnetically guided microcatheter with a 15 mm reservoir for iron oxide nanoparticles, demonstrating targeted release within a spinal cord phantom under pulsatile cerebrospinal flow. 86.5% of particle aggregates were successfully delivered at an ejection rate of 200 μL/s. Yan et al.^[117] developed a soft tool incorporating a magnetized deformation segment, which achieved 0.06 mm average error in occlusion morphology mapping and selectively crossed microchannels down to 0.2 mm via magneto fluidic interaction in pulsatile flow. Wang et al.^[118] expanded this concept to multirobot systems, enabling independent control of over 5 soft magnetic robots in a 3D lumen network by exploiting resistance decoupling between robots.

The main advantage of magnetic steering catheters lies in their use of miniaturized magnetic materials. However, MRI-compatible designs must avoid image artifacts and heating, while permanent magnet systems face spatial constraints and safety concerns. Moreover, achieving precise control in real-time, patient-specific anatomy requires continued advancement in actuation modeling, sensing, and robotic integration.

6.2 Teleoperation robot

Teleoperated control architectures (Figure 11) are central to modern endovascular robotic systems, enabling physicians to perform delicate catheter and guidewire manipulations from remote, radiation shielded consoles. By decoupling the operator from the procedural field, these systems not only mitigate radiation exposure and physical strain but also lay the foundation for long-distance robotic interventions and crossinstitutional telemedicine. Notable commercial platforms include the CorPath GRX^[128,129] by Siemens, which is widely used in coronary and peripheral vascular procedures. The R-One^[130] system from Robocath delivers CE-certified precision and offers intuitive control for PCI. In addition, the RoboAngio^[131] system developed by Abrobo has supported numerous remote vascular interventions and incorporates force feedback to enhance surgical dexterity and tactile awareness.

Conventional teleoperation systems rely on user inputs to drive linear and rotational motions at the catheter tip, often through mechanical or electromagnetic transmission. Jin et al. (Figure 11A)^{[119–120–121]} developed a robotic catheter system with integrated force sensing and tactile feedback, allowing the operator to detect vessel collision forces in real-time. Their design distinguished between contact and inertial forces using a custom sensor array, improving procedural safety. Addressing the limitations of standard joystick interfaces, Bao et al. (Figure 11B)^[122,123] introduced a dual-hand haptic system that preserves the surgeon’s habitual handling of catheters and guidewires. Their interface achieved closed-loop force and torque feedback via MR fluid actuators and pantograph transmission, delivering resolution of 0.06 N and 0.07 mN·m, respectively, with 5 Hz control bandwidth during animal studies.

Hooshiar et al. (Figure 11C)^[124,125] proposed an inertial free orientation measurement framework for teleoperated catheterization. By integrating stereo accelerometry and neural network fusion, their system captured rotational motion with a mean absolute error of 1.7 ° and enabled high-frequency sampling at 117 Hz. Kim et al. (Figure 11D)^[126] demonstrated a magnetically guided robotic platform for neurovascular interventions, combining a 7 DOF robotic arm with steerable magnetic guidewires and motorized catheter advancement. Their system enabled real-time manipulation under fluoroscopy and achieved successful embolization and thrombectomy in porcine models, navigating tortuous vasculature otherwise inaccessible to manual methods. Dagnino et al. (Figure 11E)^[127] reported an in vivo evaluation of a pneumatic robotic platform that performed robotic angioplasty in porcine arteries. The system combined ergonomic teleoperation with dynamic haptic feedback and virtual fixtures, achieving a 100% procedural success rate and reducing vessel trauma compared with manual navigation.

As robotic teleoperation converges with intelligent assistance, multimodal sensing, and networked connectivity, it is poised to transform interventions into standardized, remotely operable procedures, thereby broadening access to specialized care across geographic and institutional settings.

6.3 Robotic navigation

Accurate and responsive navigation (Figure 12) is fundamental to the safe and effective deployment of intravascular robotic systems. As catheter interventions increasingly target deep and tortuous anatomical regions such as cerebral arteries or the aortic arch, robust navigation technologies have become indispensable^[137]. These systems provide real-time localization and trajectory control, minimizing procedural risks while supporting autonomous or semiautonomous operation. Representative commercial solutions include Philips’ VesselNavigator^[138], which overlays preoperative computed tomography angiography/magnetic resonance angiography data onto live fluoroscopy to guide complex vascular access. Therenva’s EndoNaut system^[139] enables 3D fusion of intraoperative images, allowing for precise catheter tracking. Additionally, Centerline Biomedical’s IOPS platform^[140] offers radiation-free 3D navigation using electromagnetic localization.

Fluoroscopic imaging remains the clinical gold standard, offering widespread accessibility and continuous visualization. However, Vandini et al.^[141] point out that the inherent 2D projection and poor soft-tissue contrast limit fluoroscopy’s utility, especially during dynamic or complex interventions. To address these challenges, they developed a guidewire-tracking algorithm using segment-like features that achieved an F1 score of 92% under large deformation conditions, outperforming prior methods. Electromagnetic tracking offers an alternative, enabling real-time 3D localization of embedded sensors without requiring a direct line of sight. Suligoj et al. (Figure 12A)^[132] demonstrated ultrasound-integrated robotic EM tracking of microagents with 99.8% tracking accuracy, leveraging visual servoing for catheter navigation under breathing motion and flow simulations. MRI navigation presents another promising modality^[142,143]. Azizi et al.^[144] utilized the fringe field of a clinical MRI scanner to generate directional magnetic gradients of up to 2 T/m for robotic guidewire navigation. This approach enabled selective pulling of microguidewires through multibifurcated and tortuous vessels that were otherwise inaccessible by manual pushing, demonstrating in vivo feasibility in swine models. Felfoul et al.^[145] achieved closed-loop commutation control of an MRI-powered rotor actuator using interleaved imaging and propulsion sequences. Their system delivered a peak force of 9.4 N, representing a key step toward MRI-driven robotic actuation within clinical environments.

At the microscale, Yang et al. (Figure 12B)^[133] implemented autonomous navigation of magnetic microrobots in large workspaces using a mobile coil system. Their approach combined real-time visual feedback with modified A* planning and model predictive control, enabling microrobots to traverse maze-like environments of up to 230 mm in diameter. Expanding upon this, Yang et al. (Figure 12C)^[134,135] leveraged deep learning to endow microrobot swarms with environment-adaptive distribution planning. Their framework enabled microrobots to autonomously reconfigure in response to obstacles, enabling fully autonomous navigation to dynamically assigned targets. Magnetically guided microcatheters have also shown potential for targeted delivery. Torlakcik et al. (Figure 12D)^[116] developed a 1-mm-diameter microcatheter capable of magnetically steered intrathecal delivery of nanoparticle swarms. Numerical simulations and in vitro spinal cord phantom experiments confirmed controlled deployment against physiological counterflows. Complementary to this, Wang et al. (Figure 12E)^[136] demonstrated that rotating magnetic microrobot swarms in blood can be localized using ultrasound Doppler imaging. The Doppler signals induced by collective microrobot motion enabled indirect localization even when imaging planes were misaligned, facilitating upstream navigation against blood flow at velocities up to 5.97 mm/s. Autonomous control strategies are also emerging. Fagogenis et al.^[146] introduced a robotic catheter using haptic vision for autonomous wall following navigation within a beating heart. Their system achieved 99% success rate in navigating from the apex to the aortic valve, performing comparably to expert clinicians while reducing reliance on fluoroscopy.

In summary, advances in fluoroscopy enhanced feature tracking, EM and MRI localization, ultrasound guided microscale tracking, and learning-based swarm control are collectively transforming intravascular navigation from passive guidance to intelligent, autonomous execution. Each modality offers distinct advantages, and their fusion facilitates the development of robust, adaptive navigation systems in future endovascular robotics.