The study asks how to metallize and selectively insulate complex 3D-printed neural probes without lithographic masks. Two-photon polymerization creates a four-electrode, 2-mm shank whose re-entrant trenches guide line-of-sight Ti/Pt evaporation and whose convex electrode edges stop capillary-driven SU-8 encapsulation. Measured resistance, electrochemical characterization, microscopy and insertion into 0.6% agarose support electrical and mechanical integrity; finite-element simulations separately predict buckling thresholds. The demonstrated device is a proof of concept, with long-term stabilit

TWO-PHOTON PRINTING · NEURAL INTERFACES

Can a shape do the masking?

This neural probe is printed with tiny trenches and mushroom-shaped electrodes. Its geometry then guides metal and liquid resin into place—turning a polymer scaffold into an insulated electrical device.

Sedighi, Hasan, Feng & Xu Additive Manufacturing Letters · 2026

penetrating shank

mushroom electrodes

electrode diameter

lithographic masks for metal & encapsulation

The instructions are in the shape.

The challenge: coat a complex 3D surface while keeping four electrical paths separate, then insulate the paths while leaving the electrode sites open. Here, the printed geometry handles both tasks.

Choose a step. Watch the geometry respond.

A scaffold waiting to become a circuit.

Select Print to create the structure. Or jump to any step to inspect what the previous steps make possible.

Shadow defines the circuit

The narrowed trench opening hides its re-entrant sidewalls from straight-line evaporation. Metal on the trench floor stays electrically separate from the film on the upper surface. A 45° ramp connects each trace to its cap.

An edge stops the liquid

SU-8 wicks through the trenches. A sharp convex rim pins the liquid boundary around the mushroom electrode, leaving its surface exposed. The surrounding traces become insulated after UV curing.

Print. IP-S photoresist, a 25× objective and adaptive slicing at 0.4–1.5 µm. A shell-and-scaffold writing strategy takes about 2.5 hours per probe. The complete device is 7.26 mm long.

Barrier & metal. A 1 µm Parylene C coating covers the polymer. Oxygen plasma removes about 100 nm to activate the surface for adhesion; it does not pattern the coating. Thermal evaporation deposits 15 nm Ti and 150 nm Pt.

Encapsulate. SU-8 2000.5 is dispensed near the contact pads. Cyclopentanone vapor suppresses solvent loss so the liquid can travel along the trenches, followed by a 5-minute UV cure.

The bench is an animated teaching schematic, not a transport or deposition simulation. Feature sizes, coating thicknesses and process times are exaggerated for visibility. The paper’s four electrodes are spaced 200 µm apart.

A little support. A big difference.

As the tip is held more firmly, the probe resists buckling at a higher load.

The authors modeled a homogeneous polymer probe and fixed different lengths of its distal tip. Change that constraint to see the six reported simulation results.

This is a simulation boundary condition, not an insertion depth.

Measured separately: ≈0.7 mN Maximum insertion force in 0.6% agarose gel, at 2 mm/min to a depth of about 2 mm.

Methods §2.10; Results §§3.6–3.7; Figs. 10–11.

The least-supported case still exceeds the measured gel-insertion force.

Boundary-condition sketch Deformation exaggerated

See the geometry become functional.

The paper’s electron micrographs show the printed architecture, separated metal films and the final resin boundary. Explore these details alongside the authors’ gel-insertion footage.

The printed architecture

The shank’s taper, recessed traces and mushroom electrodes are built directly into the 3D scaffold.

Separated by a shadow

The cross-section makes the separation visible: metal on top and at the trench bottom, with no continuous sidewall bridge.

Open caps. Insulated paths.

SU-8 stays in the trenches, while the raised electrode surfaces remain available for contact with the surrounding electrolyte.

Electrical checks. All four tested ramp geometries gave 4.1–8.0 Ω across three devices; adjacent pads remained open circuit. Table 1 · Results §3.4

Into the gel.

The probe enters 0.6% agarose, a brain-mimicking test medium. The sequence progresses from initial contact and surface dimpling to about 2 mm insertion.

After insertion, microscopy showed no observable structural damage, and electrochemical measurements retained similar behavior.

Cyclopentanone vapor slows SU-8 solvent evaporation, helping the resin continue traveling down the trenches.

Design the form. Guide the function.

Two-photon printing does more than make a small object. It puts the features that control later processing inside the object’s shape.

That offers a route to customized neural probes, microscale sensors and other 3D bioelectronic devices. This paper demonstrates fabrication, electrical characterization and gel insertion; neural recording and long-term in vivo performance are directions for future work.

3D-printed penetrating neural probes with maskless metallization and encapsulation

Armin Sedighi, Mehedi Hasan, Xiaoce Feng, Yong Xu. Additive Manufacturing Letters 18 (2026), 100408.

Paper © 2026 The Authors. CC BY-NC 4.0. Source figures and supplementary material retain this license. Interactive models are conceptual explanations; exact reported buckling values are identified separately.

Paper figure

Sedighi et al., 2026. Cropped from the paper; CC BY-NC 4.0.