4D Printing of Shape Memory Polymers

Singapore University of Technology and Design, Singapore

(a) Different colors as printed, compressed, and recovered, respectively, observed by the objective lens. (b) Tilted (30° tilt angle) and top view of SEM images before and after programming and after recovery. (Image: SUTD)

Researchers have successfully demonstrated the four-dimensional (4D) printing of shape memory polymers in submicron dimensions that are comparable to the wavelength of visible light. 4D printing enables 3D-printed structures to change their configurations over time and is used in a variety of fields such as soft robotics, flexible electronics, and medical devices.

Different materials such as hydrogels, liquid crystal elastomers, and magnetic nanoparticle-embedded resists — along with corresponding printing methods like Direct Ink Writing (DIW), Polyjet, Digital Light Processing (DLP) lithography, and Stereolithography (SLA) — have been developed for 4D printing; however, the material and patterning challenges inherent in these methods limit the resolution of 4D printing to ~10 μm at best.

To improve the resolution of 4D printing, the team developed a shape memory polymer (SMP) photoresist suitable for two-photon polymerization lithography (TPL). Integrating this resist with TPL, they investigated submicron 4D printing of SMPs at a scale where the printed structures can interact strongly with visible light. By programming with pressure and heat, the submicron structures can switch between colorless and colorful states.

The nanostructures are able to recover their shapes and structural color after they’ve been mechanically flattened into a colorless, transparent state. The resist allows for very fine structures to be printed while still retaining their properties as a shape memory polymer.

By characterizing the photoresist, the SMPs were printed with ~300-nm half pitch. The resolution is an order of magnitude higher than traditional high-resolution printing methods such as DLP and SLA. The dimensions of the structures can be controlled by varying the printing parameters such as laser power, write speed, and nominal height.

For more information, contact Joel Yang, Associate Professor, at This email address is being protected from spambots. You need JavaScript enabled to view it.; +656-499-4767.