Shape memory polymers have been ‘4D-printed’ at sub-micron dimensions, opening up potential applications including optical anti-counterfeiting.
Researchers from the Singapore University of Technology and Design (SUTD) and collaborators developed the new technique, which is capable of high resolutions comparable to the wavelength of visible light. Applications could also include tuneable photonic devices.
4D printing is the 3D printing of objects that can change shape and transform in response to external stimuli. It is used in fields including soft robotics, flexible electronics and medical devices.
Printing methods such as stereolithography have previously been limited to resolutions of about 10 microns.
To improve on that figure, the research team developed a shape memory polymer (SMP) photoresist suitable for two-photon polymerisation lithography (TPL). Integrating the two, they investigated sub-micron 4D printing of SMPs. At that scale, the printed structures can interact strongly with visible light. By programming with pressure and heat, the researchers were able to ‘switch’ the sub-micron structures between colourless and colourful states.
“It's remarkable that these 3D-printed nanostructures are able to recover their shapes and structural colour after they've been mechanically flattened into a colourless, transparent state. This new resist that we've concocted allows for really fine structures to be printed, while still retaining their properties as a shape memory polymer,” said associate professor Joel K W Yang, principal investigator of the team from SUTD.
“The resolution is an order of magnitude higher than traditional high-resolution printing methods such as digital light processing and stereolithography,” said first author Wang Zhang. “The dimensions of the structures can be conveniently controlled by varying the printing parameters such as laser power, write speed and nominal height.”
The research was published in Nature Communications.
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