3D Printing of Stiff Photonic Microparticles into Load-Bearing Structures

Structural colors are bright and possess a remarkable resistance to light exposure, humidity, and temperature such that they constitute an environmentally friendly alternative to chemical pigments. Unfortunately, upscaling the production of photonic structures obtained via conventional colloidal self-assembly is challenging because defects often occur during the assembly of larger structures. Moreover, the processing of materials exhibiting structural colors into intricate 3D structures remains challenging. To address these limitations, rigid photonic microparticles are formulated into an ink that can be 3D printed through direct ink writing (DIW) at room temperature to form intricate macroscopic structures possessing locally varying mechanical and optical properties. This is achieved by adding small amounts of soft microgels to the rigid photonic particles. To rigidify the granular structure, a percolating hydrogel network is formed that covalently connects the microgels. The mechanical properties of the resulting photonic granular materials can be adjusted with the composition and volume fraction of the microgels. The potential of this approach is demonstrated by 3D printing a centimeter-sized photonic butterfly and a temperature-responsive photonic material.