Can topography make a water-loving resin repel water? Two-photon polymerisation produced re-entrant and hierarchical OrmoComp arrays. At 20 µm spacing, multi-crown surfaces measured a 151° water contact angle and 9° sliding angle without repellent coatings. Mainly 2D simulations explain contact-line pinning and air retention, with a Cassie–Baxter state sustained to 40 µm for this design. Tests used 2 × 2 mm arrays; large-area throughput and mechanical/environmental durability remain open.

Two-photon lithography · surface science

A material that likes water can become a surface that sheds it. The secret is a forest of microscopic mushrooms—and the air they hold.

Multi-crown surface · 20 μm spacing · 0.5 μL water

Change the shape, keep the material. Ying and colleagues used two-photon polymerisation to print three mushroom-like textures in hydrophilic OrmoComp resin. Adding tiny pillars to an overhanging cap produced the strongest water repellency.

01 / A virtual wetting experiment

Build the surface. Watch the water.

Choose a shape, then spread its pillars apart. Can your surface keep a cushion of air beneath the drop?

Choose a geometry

Change the spacing

Try 40 μm: which geometry still holds its air cushion?

Seven tiny pillars sit on each cap: one at the centre and six around it. They add pinning sites for the advancing water.

The drop rests on solid and air: a Cassie–Baxter state. The measured contact angle is 151°.

Contact angle measures the angle where the drop meets the surface: a larger angle means more beading. This teaching model follows the wetting trends in Figure 9 and Figures S6–S8. Microstructures are enlarged to reveal the mechanism; droplet and feature scales differ. Contact-angle readouts at 20 μm are experimental measurements.

What is doing the work?

A drop can sit on air.

Water does not have to touch every part of a textured surface. An overhanging cap can hold the liquid’s contact line in place while air remains in the spaces below.

Catch the contact line

The cap’s re-entrant edge resists the water front moving down the pillar. The inverted crown increases this barrier.

Keep the air cushion

Trapped air reduces direct contact with the resin. Wide gaps make this cushion easier to displace.

Add a second scale

Tiny pillars reduce initial water–solid contact and add pinning forces that resist the advancing contact line, even after they submerge.

The printed structures

From geometry to a real microtexture

Scanning electron microscopy reveals the three designs fabricated by two-photon polymerisation.

Original microscopy images: Ying & Yu (2026), Zenodo supporting dataset, CC BY 4.0. Resized and converted to WebP; full frames and scale bars retained.

02 / The tilt test

Round is good. Rolling is better.

A high contact angle describes a drop’s shape. A sliding angle tells you how easily it leaves. Tilt these three surfaces and watch which one lets go first.

Tilt the platform

Increase the tilt. Multi-crown reaches its measured sliding angle first, at 9°.

Motion is illustrative; release thresholds are measured values from Figure 11. The flat hydrophilic resin held its drop even when inverted.

03 / Watch the trapped air leave

The invisible cushion makes itself visible.

As a drop evaporates, its changing curvature raises the pressure on the air below. Bubbles appearing inside the drop reveal that trapped air is being released.

An evaporation experiment

Bubbles first appeared at 295 s and disappeared at 366 s in this evaporation sequence.

Recorded 0.5 μL evaporation sequence on 20 μm-spaced arrays.

Experimental images: Xiaojing Ying & Wenhui Yu (2026), supporting dataset on Zenodo, CC BY 4.0. Images resized and converted to WebP. Capture times: Supplementary Figures S11–S13. The scrubber displays the most recent observed frame, with its actual capture time.

How the surfaces were made

Write a texture with light.

Two-photon polymerisation builds a three-dimensional structure inside a light-sensitive resin. A tightly focused ultrafast laser writes the chosen geometry; unpolymerised resin is then washed away.

Here, it created 2 × 2 mm arrays on glass coverslips using hydrophilic OrmoComp. The experiment changes the topography rather than adding a water-repellent coating.

63×, NA 1.4 focusing objective · ethanol development for 2 hours

What this opens up

Water repellency by design.

The central result is a route to superhydrophobicity on a hydrophilic material, using geometry alone. Re-entrant caps and a second level of texture work together to resist wetting.

Functional surfaces

The paper points toward self-cleaning and anti-icing surfaces as potential applications of this design strategy.

Larger patterns

Replication and multifocal printing are proposed routes to carry carefully designed microtextures beyond small printed areas.

Longer service

Mechanical robustness and durability under UV, humidity and thermal cycling are next steps.

Explore the research

The paper behind the surface.

Two-photon polymerisation of synergistic re-entrant and hierarchical structures enables superhydrophobicity on hydrophilic substrates

Xiaojing Ying, Weilong Cao, Zheyu Yao, Wenhui Yu, Zhen Xiao, Dongfeng Qi, Lihua Zhu, Wuhong Xin & Hongyu Zheng.

Virtual and Physical Prototyping 21(1), e2684216 (2026).

Contact angles: Figure 8; sliding angles: Figure 11. Wetting states and spacing trends: Figure 9 and Supplementary Figures S6–S8. Evaporation images and bubble timing: Figure 10 and Supplementary Figures S11–S13. Geometry and fabrication: Sections 2.1–2.2. Contact-line pinning and dual-scale air retention: Section 4 (Discussion), Section 3.3.1, and Figure 12.

The paper combines measured water contact and sliding angles with numerical wetting simulations. This companion’s animated models illustrate those mechanisms; they do not solve the fluid equations. The 0.5 μL drops were tested on small printed arrays. The paper is licensed CC BY-NC 4.0; the supporting dataset used here is CC BY 4.0.