Shape Controllable Building Blocks for 3D Collective Assembly via Residual Stress Engineering

초록

In nature, the collective assembly is often observed which enrich the structural and functional diversities. For example, DNA for various creatures consist with double helix architecture via collective assembly of only 4 distinct types of building blocks (Adenine, Guanine, Cytosine, Tymine). The hierarchical structures via collective assembly can highly release the limitations on geometries and functionalities through a spatial arrangement of diversely designed 3D building blocks. In this presentation, geometrically tailorable 3D building blocks are introduced by controlling residual stress with rapid and reproducible fabrication without complicate and/or expensive equipment. Frontal photopolymerization (FPP) with variously designed photomask and different curing time are employed for spatiotemporal regulation of photopolymerization. The employed photocurable resin is composed of bio-compatible poly(ethylene glycol)diacrylate (PEGDA) matrix, photo-initiator and photo-absorber. The photo-absorber generates drastic gradient of light intensity during the photopolymerization, resulting in a residual stress via crosslinking density mismatch through the thickness. When the photopolymerization is terminated, a curvilinear 3D shape morphing occurs within 1 min as a result of shrinkage mismatch induced by immediate relaxation of the residual stress. The geometries of 3D building blocks are programmed by systematic change of spatiotemporal conditions of pre- and post-curing. The 3D morphed structures are hierarchically assembled to achieve self-similar scaled-up structures inspired by designs of famous landmark (e.g. the great pyramid in Giza). The regularly stacked geometry allows 3D assembled structure to withstand 150 times of its own weight by homogeneous distribution of normal stress. Furthermore, the electrically conductive property is rendered to 3D assembled structural by applying conductive silver pastes on the 3D layered structures. Hence, our design strategy of tai