3D printing by two-photon polymerization in biomimetics

High-precision manufacturing tools allow scientists to mimic highly complex surfaces from nature
02 September 2022
3D printing by two-photon polymerization
3D printing by two-photon polymerization enables the fabrication of complex structures to mimic the unique properties of organisms, such as the angle-insensitive structural color of blue-winged Morpho butterflies Credit: Zyla et al., doi 10.1117/1.JOM.2.3.031203.

Through time, many animals and plants have developed essential abilities to ensure their survival in different environments. Mostly, these abilities rely on remarkable properties of their surfaces, e.g., enhanced adhesion, wear resistance, superhydrophobicity, or coloration. Usually, such properties are only known by superheroes from the cinema. Still, in this case, they do not originate from supernatural phenomena but, in most cases, from sophisticated systems of surface structures at the micro- and nanoscale.

Hence, nature provides a vast hidden potential to gain new ideas on how to develop novel products or solve technological problems. As a result, the interdisciplinary research area of learning from nature and developing biologically inspired designs defined as “biomimetics” has become significantly attractive, especially nowadays, when scientists can rely on high-precision manufacturing tools that allow them to mimic even highly complex surfaces from nature. In this context, the use of two-photon polymerization (2PP) is particularly suitable. This approach enables the maskless processing of photosensitive resins in all three dimensions. More precisely, highly intense laser radiation makes it possible to fabricate computer-aided designs with incredibly small feature sizes down to sub-100 nm. Thus, high-resolution 3D printing of polymer structures can be realized without the need for a vacuum atmosphere, harsh chemicals, or cleanroom facilities.

The great potential for the use of 2PP in biomimetics has been vigorously promoted by scientists from the Ruhr University Bochum and Kiel University in their latest publication in the Journal of Optical Microsystems. The authors had previously used 2PP in this field. At that time, they realized the 3D printing of hierarchically composed micro-/nanostructures, including certain degrees of imperfections typically found in nature. In this way, they found a way to mimic the complex surface structures of the blue Morpho butterflies, which generate their famous structural coloration. Consequentially, an intense blue color also arose from the 2PP-printed specimens, and as in the case of these organisms, the color exhibited the same unique angle-insensitive optical properties.

As shown in their new work, the authors have now achieved how to redesign structures inspired by the Morpho butterflies to observe the resulting angle-insensitive blue color uniformly or only from specific directions. For this purpose, they first closely analyzed the optical properties and morphology of the upper wing surface of a Morpho didius butterfly. Afterward, the authors derived from these results that they could control the direction in which the angle-insensitive color appears by modifying the geometry of their previously developed structures only at the microscale. The production of modified structures could then be realized in a simple workflow using 2PP due to the unique 3D capabilities of the printing approach. The novel designs proposed by the authors are suitable for generating highly complex anti-counterfeiting features. In addition, the authors discussed the use of novel photosensitive materials and recent optimizations on the 2PP process, which could enable studying a broad diversity of functional structures found in nature, as they assumed.

Structural color generated by hierarchically composed at the micro- and nanoscale

Structural color generated by hierarchically composed designs at the micro- and nanoscale. The results for a blue-winged Morpho butterfly are illustrated on the left and those for novel designs printed by two-photon polymerization are shown on the right. The presented 2PP structures enable to observe the resulting angle-insensitive blue color uniformly. Credit: Zyla et al., doi 10.1117/1.JOM.2.3.031203

Read the Gold Open Access article by Zyla et al., “Two-photon polymerization as a potential manufacturing tool for biomimetic engineering of complex structures found in nature,“ J. Opt. Microsystems 2(3) 031203 (2022), doi 10.1117/1.JOM.2.3.031203

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