A Chinese research team has developed a single-step femtosecond laser 4D printing technology that enables rapid and precise micro-scale deformation of smart hydrogels. This innovation, inspired by the hierarchical structure of butterfly wings, holds significant promise for applications in flexible electronics and minimally invasive medicine.

The findings were published online in ACS Materials Letters on February 17.

Led by Prof. LIU Lianqing from the Shenyang Institute of Automation of the Chinese Academy of Sciences and Prof. LI Wenjung from the City University of Hong Kong, the researchers drew inspiration from the wing structure of Papilio maackii, a butterfly species known for its remarkable balance of lightness and toughness.

They discovered that the honeycomb-like pores and reinforced textures of butterfly wings work synergistically to dissipate mechanical stress during flight. Mimicking this natural design, the researchers employed femtosecond laser technology to sculpt pH-responsive hydrogel structures with a pre-programmed mechanical gradient.

By adjusting laser scanning modes, they encoded alternating soft and rigid regions into the material, effectively embedding a “deformation code.” Experimental results and finite element analysis demonstrated that when exposed to an acidic environment, the hydrogel automatically folds within one second, shrinking to just 25% of its original volume.

The key breakthrough lies in its single-step fabrication. Unlike traditional methods that require layering multiple materials to achieve deformability, this approach directly encodes mechanical heterogeneity during printing. As a result, the hydrogel exhibits dual functionality—sensing environmental changes and actuating structural responses.

In medical demonstrations, smart hydrogel dressings were shown to autonomously enwrap biomembranes with micron-level precision in response to pH shifts. For sensing applications, the material’s fluorescence intensity fluctuated by up to 110% during acid-base transitions, highlighting its potential as an adaptive sensor.

This streamlined 4D printing approach marks a significant advance in micro/nanoscale manufacturing, unlocking novel applications for responsive hydrogel systems—from adaptive medical devices to eco-friendly flexible electronics.

Two potential applications based on 4D printed customized hydrogels design of microstructures (Image by the research group)