Three-Dimensional Optical Imaging of Internal Deformations in Polymeric Microscale Mechanical Metamaterials

Abstract

Recent advances in two-photon polymerization fabrication processes are paving the way to creating macroscopic metamaterials with microscale architectures, which exhibit mechanical properties superior to their bulk material counterparts. These metamaterials typically feature lightweight, complex patterns such as lattice or minimal surface structures. Conventional tools for investigating these microscale structures, such as scanning electron microscopy, cannot easily probe the internal features of these structures, which are critical for a comprehensive assessment of their mechanical behavior. In turn, we demonstrate an optical confocal microscopybased approach that allows for high-resolution optical imaging of internal deformations and fracture processes in microscale metamaterials under mechanical load. We validate this technique by investigating an exemplary metamaterial lattice structure of 80 × 80 × 80 μm 3 in size. This technique can be extended to other metamaterial systems and holds significant promise to enhance our understanding of their real-world performance under loading conditions.

Nondestructive Imaging of Manufacturing Defects in Microarchitected Materials

“…In this experimental setup, the formation of the image relies on spatially detecting fluorescence emitted from the microarchitected material at successive depths. This requires that the base material is both transparent and either autofluorescent or suitably functionalized with fluorescent particles or dyes . These requirements immediately suggest that many metallic or ceramic materials may not be conducive to this imaging process due to their opacity.…”

“…Continuous-wave excitation at 488 nm can produce images with high signal-to-background contrast at low <100 μW power . In these investigations, we use a 60X 1.25 NA oil immersion lens to image the structures.…”

“…This requires that the base material is both transparent and either autofluorescent or suitably functionalized with fluorescent particles or dyes. 22 These requirements immediately suggest that many metallic or ceramic materials may not be conducive to this imaging process due to their opacity. Nevertheless, a broad spectrum of photopolymerizable materials is known to fulfill these requirements, making them suitable candidates for this technique.…”

“…Confocal microscopy, a widely used tool in biological imaging, effectively addresses each of these challenges by providing nondestructive imaging of the entire structure at submicrometer resolutions. Our previous study has shown both the ability to render microarchitected materials with reasonably accurate dimensions and observe their external and internal deformation during in situ mechanical loading . In this work, we enhance the versatility of this technique by demonstrating its capacity to precisely identify both the location and the nature of incorporated manufacturing defects within the lattice.…”

“…Our previous study has shown both the ability to render microarchitected materials with reasonably accurate dimensions and observe their external and internal deformation during in situ mechanical loading. 22 In this work, we enhance the versatility of this technique by demonstrating its capacity to precisely identify both the location and the nature of incorporated manufacturing defects within the lattice.…”