I. Core Research Summary

• Conformal Double-Layer All-Printed LC Resonant Tracking Tag

The catheter’s outer wall features direct aerosol‑based fabrication of a 10‑turn, 22.5°‑inclined double‑helix inductor, paired with parallel strip‑shaped distributed capacitors. The conductive traces are 250 μm wide, with a single‑layer thickness of 4 μm; after multilayer stacking, the overall outer diameter of the catheter is only 2.264 mm—significantly smaller than the 3.2 mm of conventional hand‑wound coils—making it well suited for navigating the narrow lumens of the carotid artery.

• 3T MRI with omnidirectional signal enhancement delivers excellent imaging contrast.

The coil is inductively coupled to the MRI radiofrequency (RF) field, locally amplifying the B₁ RF field. In two orientations—parallel and perpendicular to the magnetic field—the signal‑amplification factors are 1.67 and 1.63, respectively. In in vivo testing of the carotid artery, signal amplification reaches 1.81, and under low flip‑angle sequences, the catheter’s contour is clearly discernible.

• MRI radiofrequency-induced localized heating is zero, ensuring clinical safety and reliability.

During prolonged FSE MRI sequence scanning, neither the temperature probe nor the MRI-based thermometry imaging exhibits any significant temperature rise, resulting in an extremely low radiofrequency absorption (SAR) risk. This approach effectively avoids the potential for vascular thermal injury associated with conventional metallic coils and complies with interventional device safety standards.

• Flexible integrated molding significantly enhances vascular passability.

The aerosol‑thin catheter features a curved outer wall with no protruding rigid structures, maintaining its flexibility to safely reach distal intracranial vessels, making it suitable for stroke thrombectomy and minimally invasive neurointerventional procedures.

• Digital maskless batch fabrication

CAD‑based customization of helical turns and capacitor length; the entire coil can be printed and cured in just 6–7 hours, with highly repeatable processes that address the pain points of poor consistency in manual winding and difficulties in mass production.

II. Complete Preparation Process Flow and Core Technological Advantages of Aerosol Spraying

(1) Complete Printing Process for Catheter Resonant Coils

• PTF liner + PEEK braid + Pebax outer layer—pre‑treatment for medical catheter cleaning;
• Pneumatic atomization silver nanoparticle conductive ink is used to perform conformal printing of the first-layer single-turn inductor along the curved surface of the catheter, followed by curing at 120°C for 1 hour.
• Switch to polyimide dielectric ink, perform full‑area printing of the insulating isolation layer, and cure for 2 hours.
• A secondary aerosol is printed to form a reverse double-helix conductive layer, thereby establishing a complete inductive structure.
• The outer layer is fully encapsulated with a PI insulating protective coating, completing the wireless LC tracking tag.

(II) Five Core Process Advantages (Hand-Winding / Vacuum Thin-Film / Photolithography Compared)

• 3D Curved-Surface Conformal Precision Deposition

Aerosol-based non-contact jetting can uniformly deposit conductive traces around the outer surface of circular conduits, whereas planar lithography and thin-film deposition are ill-suited for tubular, irregularly shaped substrates; a fully encapsulated helical coil can be formed in a single step.

• Ultra-thin, low-profile wiring reduces the outer diameter of the conduit.

The single-layer silver coating is only 4 μm thick, and the total bulge height of the multilayer structure is extremely low, without further increasing the catheter’s outer diameter. This allows smooth passage through small intracranial vessels, while the manually coiled wire exhibits a noticeable increase in thickness.

• Rapid switching between high- and low-viscosity inks, with multi-layer integration.

Silver conductive ink and PI dielectric ink can be alternately atomized and printed, enabling in-situ layered fabrication of conductive and insulating layers without the need for multiple transfer or lamination steps, thereby simplifying circuit fabrication.

• Low-temperature curing compatible with medical thermoplastic catheters

The curing temperature is maintained below 140°C, which is lower than the melting range of the Pebax substrate (134–174°C), thereby preserving the catheter’s elasticity and mechanical properties.

• Digitalization enables rapid iteration, with high device consistency.

Helix pitch, number of turns, and capacitor length can be directly adjusted on the drawing without the need for molds; batch‑printed coils exhibit minimal deviations in electromagnetic parameters, whereas manually wound coils show substantial variations from one conductor to another.

III. Five Key Technological Innovations

Innovation 1: Integrated Process for Aerosol‑Curved Surface Conformal Dual‑Helix LC Coil

Innovative 2‑way omnidirectional dual‑helix topology with a 22.5° tilt angle

Innovation 3: Distributed Parallel Strip Capacitor Structure

Innovative 4 Low-Dielectric-Constant Lead-Free Medical Insulation System

Innovative 5 Low-SAR, Heat-Free Interventional Marking Solution

IV. Existing Process Challenges and Corresponding Solutions for Overcoming Them

Challenge 1: Tubular curved conduits cannot be processed by planar lithography or thin-film deposition.

Challenge 2: The outer diameter of the manual coil is too large, making it impossible to reach the distal vessel.

Challenge 3: In conventional metal-coil MRI, localized heating under RF excitation can damage blood vessels.

Challenge 4: Discrete chip capacitors are bulky, prone to detachment, and exhibit poor consistency.

Challenge 5: Custom coils are time-consuming to produce by hand and difficult to mass‑produce.

V. Future Diversified Industrial Application Scenarios

• Acute Stroke MRI‑Guided Endovascular Thrombectomy Catheter

• Cardiac Electrophysiology MRI–Guided Interventional Devices

• Neurosurgical minimally invasive interventional microcatheter

• Animal-Experiment MRI-Interventional Research Catheter

• Multi-Department General-Purpose MRI Minimally Invasive Instruments

Figure 1. Schematic diagram of the resonant marker design: an inductively coupled RF coil–based marker can be used for tracking during MRI examinations. The figure shows a side cross-section of a single helical arm (as this structure represents the first printed unit). A top‑down view illustrates the inductor’s 10‑turn double‑helix geometry and the two‑lead transmission‑line capacitor, rendered using dielectric ink (red) and conductive ink (blue). Solid lines indicate the trajectory anterior to the catheter, while dashed lines indicate the trajectory posterior to the catheter (in green).

Figure 2. Manufacturing method and implementation example of aerosol jet‑deposited circuits. a) A simplified schematic of aerosol jet deposition is shown: pneumatic atomization and propulsion are driven by nitrogen, with excess gas vented through a virtual impactor; an outer sheath gas collimates the jet and prevents aerosols from contacting the nozzle. b) An example of a test printing process is presented. c) An implementation example of a ten‑turn double‑helix structure is shown. d) This marked printed part is compared with a hand‑wound marking pen, highlighting its extremely low profile.

Figure 3. Under a 3 T magnetic field, in vitro phantom experiments demonstrate excellent signal intensity. The figure presents a schematic of the double-helix resonant marker, aerosol jet‑deposition images, and bSSFP sequence images: (a) with coronal imaging planes, showing the marker aligned parallel and perpendicular to the B0 field; (b) bSSFP sequence images acquired with a slice thickness of 10 mm. Sequences employing low flip angles of 5° and 15° clearly reveal signal enhancement around the circuitry, contrasting with the background signal and excessive signal oversaturation observed at a 90° flip angle; (c) bSSFP sequence images of the full-length marker along with the B1+ distribution map; (d) electromagnetic field simulation results further validate the magnetic field distribution pattern.

Figure 4. In a phantom at a 3 T field strength, both temperature measurements and MR thermometry results indicate an extremely minor heating effect. (a) shows the arrangement of the temperature probes within the gel; (b) reveals no significant heating compared with the reference probe; (c) further corroborates this finding after three FSE sequence scans.

Figure 5. In a preclinical in vivo setting at a 3 T field strength, the wireless resonant marker exhibits strong signal intensity. The figure shows the marker positioned within the right (dashed arrow) and left (solid arrow) carotid arteries of the same pig, as visualized on a) MRI and b) coronal X‑ray images; c) an enlarged view reveals clearer details (the left artery was imaged with contrast agent, while the right artery was not). d) On sagittal slices, B1+–weighted MR images allow quantification of the degree of signal enhancement. e) A GRE sequence employing a smaller flip angle (5°) yields reduced background signal and pronounced marker‑specific signal enhancement. f) Increasing the flip angle to 20° results in a marked increase in signal intensity from surrounding tissues. g) Further increasing the flip angle to 45° leads to excessive flip‑angle effects near the marker, causing a reduction in marker signal while concurrently enhancing background signal.

Table I lists the dimensions of the polymer delivery catheter and the ink material properties for aerosol jet deposition MARKERS.

Table II MRI Acquisition Parameters for Each Dataset in This Study