I. Core Research Summary

• Rotating the workpiece enables full‑area vertical deposition, resulting in highly uniform line thickness.

When printing the cylindrical sidewall with conventional AJ, the incident angle is oblique, resulting in a film‑thickness variation exceeding 50%. In contrast, LAJ employs synchronous rotation of the workpiece, ensuring that the nozzle maintains a 90° perpendicular incidence at any circumferential position; the thickness deviation along the entire line is less than 5%, and 20‑μm ultra‑fine lines are rendered completely without breakage.

• The tooth‑diameter ratio precisely controls printing speed and film thickness.

Comes with four gear options—7.5 mm, 15 mm, 25 mm, and 50 mm—enabling the establishment of quantitative models that relate the gear ratio (substrate diameter / gear diameter) to film thickness and sheet resistance. A low gear ratio yields slower rotation, thicker deposition, and superior conductivity, while a high gear ratio is suited for high-speed, large‑batch prototyping; patterns can be precisely replicated with proportional compensation.

• Ultra-high‑precision multi‑layer register alignment, with fully carbon‑based active devices integrally molded.

The minimum printing pitch in both the circumferential and axial directions can reach 20 μm. With multi-layer graphene electrodes, nanotube channels, and a cellulose dielectric, registration errors are extremely small, enabling the complete fabrication of top-gate carbon nanotube thin-film transistors on a paper-based cylindrical substrate. These devices exhibit an on/off ratio of 10² to 10³ and stable switching behavior with a low threshold voltage of less than 1 V.

• In-situ graphene sensing layer for medical expansion catheters

Directly conformally print serpentine graphene strain‑temperature sensors onto the surface of an inflatable TPU endoscopic balloon, with PDMS biocompatible encapsulation; linear temperature sensing over the 25–80°C range, enabling stable detection of deformation‑induced resistance changes during inflation and deflation, without the need for secondary transfer‑printing.

• Multi-surface compatible universal process

Compatible with cylindrical, concave‑cylindrical, 15° conical, and micro‑pipette‑shaped curved surfaces; simply replace the rotary spindle to switch substrates. It supports a wide range of conductive inks, including graphene, carbon nanotubes, and silver nanowires, without requiring replacement of the print head assembly.

II. Complete Aerosol Preparation Process and Core Technological Advantages of the Lathe-Type LAJ System

(1) Complete LAJ Surface Printing Process

• The rotating mandrel, flexible membrane, and medical catheter are secured in the lathe fixture; the bubble level is adjusted to ensure rotational coaxiality.
• Match the corresponding drive gear and input the CAD‑printed path after tooth‑diameter ratio compensation.
• Ultrasonic‑atomized graphene/CNT/cellulose ink, with the nozzle maintained at a safe standoff distance of 3–5 mm;
• The X-axis linear motion of the printing platform synchronously drives the workpiece to rotate about the θ axis, enabling vertical deposition on curved surfaces throughout the process.
• Room-temperature/low-temperature drying; multi-layer devices are aligned and registered layer by layer.
• The medical balloon sample has undergone PDMS-based biological encapsulation, and temperature‑dependent as well as inflation/deflation sensing tests have been conducted.

(II) Five Core Process Advantages (Comparison of Flat AJ, Five-Axis, and Transfer Printing)

• Low-cost retrofitting, no need for expensive five-axis equipment.

Only a 3D‑printed mechanical fixture needs to be added to standard three‑axis aerosol equipment; no multi‑axis motion platform is required. The equipment investment is just one‑tenth of that for a five‑axis system, and both laboratories and production lines can be rapidly retrofitted.

• Full‑area vertical deposition, completely eliminating the defect of uneven thickness caused by tilting.

The workpiece rotates instead of the nozzle oscillating, ensuring a constant 90° incidence angle at any point along the circumference, resulting in line morphology and thickness uniformity that far surpasses conventional planar printing on curved surfaces.

• Suitable for both rigid and flexible tubular substrates, compatible with expandable medical balloons.

Hard cylindrical components, flexible PI/paper, and inflatable TPU catheters can all be clamped in a rotating configuration; during printing, continuous inflation maintains the substrate’s shape, while soft interventional devices are directly fabricated with integrated sensing circuits.

• Multi-layer precision overprinting enables the fabrication of complex devices such as active transistors.

20 μm‑level axial and circumferential positioning accuracy; multi‑layer conductive/dielectric alternating printing with no misalignment; a single process can fabricate both passive circuits and active transistors.

• Wide‑ink compatibility, lightweight all‑carbon electronic green manufacturing.

Graphene, carbon nanotubes, and cellulose‑ion‑mediated water‑based inks can all be atomized, are free of heavy‑metal contamination, and exhibit superior flexibility and biocompatibility for medical applications.

III. Five Key Technological Innovations

Innovation 1: Lathe–Gear Rack–Linkage LAJ Cylindrical Coordinate Printing Architecture

Innovative Digital Path Algorithm for Gear Tooth Diameter Ratio Dimensional Compensation

Innovative 3D In-Situ Direct-Writing Process for Integrated Sensing in Inflatable Catheters

Innovation 4: Additive Manufacturing of Curved Surfaces for All-Carbon Flexible Active Devices

Innovation: A Universal Printing System Compatible with Multiple Curvatures

IV. Existing Process Challenges and Corresponding Solutions for Overcoming Them

Challenge 1: In conventional three-axis aerosol jet printing, oblique incidence on the cylindrical sidewall leads to significant variations in line thickness and unstable signal quality.

Challenge 2: The procurement and maintenance costs of five-axis curved-surface printing equipment are extremely high, making it difficult for small and medium-sized organizations to adopt.

Challenge 3: Medical-grade soft inflatable catheters cannot be securely printed, and the transfer film is prone to peeling off and leaking air.

Challenge 4: Misregistration in multi-layer printing on curved surfaces, which prevents the fabrication of multilayer devices such as transistors.

Challenge 5: Cylinders of different diameters require redesigning the print geometry, resulting in low iteration efficiency.

V. Future Diversified Industrial Application Scenarios

• Medical Interventional Intelligent Balloon Catheter

• Flexible Sensing Array for Industrial Cylindrical Pipelines

• Biomimetic Electronic Skin for Robotic Rotational Joints

• Miniature RF Tube Components

• Flexible Electronics Rapid Prototyping Platform for Universities

Figure 1. Schematic of the laser-assisted jet (LAJ) printer and the effect of the incidence angle on conformal thin films. a CAD schematic of the LAJ printer attachment, along with a close-up image of the rack-and-pinion mechanism equipped with a shaft clamp; b Schematic showing the LAJ printer attachment mounted on the printing system, with the deposition nozzle positioned above a cylindrical rotating mandrel; c Schematic illustrating the incidence angles during AJ printing in the planar direction (linear motion of the stage in the x‑direction) and the milling direction (rotational motion of the substrate about the θ‑axis); d Images of graphene traces produced by planar AJ printing at positions 1, 2, and 3 (with inter‑point spacing of approximately 5.9 mm; dashed lines indicate cross‑sectional locations; scale bar = 250 µm); e Thickness distribution profiles of the planar AJ‑printed graphene traces at positions 1, 2, and 3—note the pronounced reduction in thickness at position 3, where the incidence angle is approximately 75°; f Thickness distribution profiles of the LAJ‑printed graphene traces at positions 1, 2, and 3, demonstrating consistent thickness across all points.

Figure 2. Characterization of the translational motion characteristics of the lathe system. a shows schematic diagrams of four design variants for tuning the diameter ratio in lathe‑assisted aerosol jet (LAJ) printing of graphene tracks; b presents micrographs of LAJ‑printed graphene tracks at different diameter ratios, with a scale bar of 1 mm; c depicts the relationship between the thickness of graphene tracks and the rotational printing speed for various diameter ratios, with error bars indicating the standard deviation across n = 3 samples at each ratio; d illustrates the sheet resistance distribution of printed graphene tracks at different diameter ratios, with error bars representing the standard deviation across n = 3 samples at each ratio.

Figure 3. Determination of the resolution of the lathe system’s motion. The figure shows a comparison between the target lead and the measured lead in the a‑direction (circumferential) and the b‑direction (axial); error bars represent the standard deviation. Each data point is calculated from n = 4 samples. The dashed line indicates a 1:1 correspondence between the target and measured leads (the inset provides an enlarged view of the minimum lead).

Figure 4. Graphene and carbon nanotube thin-film transistors (CNT‑TFTs) fabricated by lathe‑assisted aerosol jet printing. a Resistance comparison of graphene traces with varying arc lengths and filling directions; error bars represent the standard deviation for each data point, based on n = 3 samples. b Resistance comparison of graphene traces printed on substrate‑wrapped mandrels with different diameters and arc lengths. c Normalized capacitance values of graphene/carbon nanocrystal capacitors as a function of frequency. d Charge–discharge curves of graphene/carbon nanocrystal capacitors. e Fabrication process of CNT‑TFTs printed on paper substrates using the LAJ technique on a 25‑mm mandrel. f Subthreshold characteristics of CNT‑TFT devices (inset: schematic diagrams of devices with channel lengths of 225 µm and widths of 200 µm); both curves show the average of seven devices (solid line) ± the standard deviation (shaded area).

Figure 5. Application of lathe‑based aerosol jet printing on complex substrates. a: Schematic of an AJ printing nozzle positioned at the focal point above a concave mandrel; b and c show, respectively, the printed graphene in serpentine patterns on the concave mandrel and the parallel line patterns on a curved, concave paper substrate; d: Schematic of a conical mandrel bearing printed silver nanowire (AgNW) traces; e: LAJ‑printed image progressing along the entire length of the conical mandrel, illustrating the movement along the cone’s axis after 5 seconds of printing; f and g depict, respectively, the printing of a graphene helical structure using a 1000 µL pipette tip and an enlarged view of this structure.

Figure 6. Lathe‑based aerosol jet printing technology for functionalizing smart catheters. a CAD drawing and schematic of the lathe mechanism, illustrating the flow path by which pressurized air inflates the catheter balloon axially; b a comparative diagram showing the diameter of commercial catheter balloons versus the applicable range of the lathe system (with a maximum supported diameter of 40 mm); c a physical image of a 14‑mm‑diameter inflatable catheter balloon, designed for demonstration and suitable for endoscopic procedures; d the fabrication process for graphene sensors on the catheter balloon; e a schematic of the LAJ printing technique used to pattern serpentine graphene‑based sensors around the circumference of an inflated catheter balloon; the figure also presents the normalized curve of the resistance change rate f of the printed graphene sensor as a function of temperature, demonstrating its sensitive response, and analyzes, via a polynomial model with a high R² fit, how the sensor’s g‑value varies over time during balloon inflation and deflation, thereby fully validating the sensor’s capability to monitor the balloon’s inflation state.