Figure. (A) 3D porous microstructures in living organisms; (B)Assembly of an octopus-like mesosurface based on the microlatticedesigns. (see Science,379: 1225-1232, 2023)

With the support from the National Natural Science Foundation of China (Grant Nos. 12050004 and 12225206), a research team led by Prof. Yihui Zhang from Tsinghua University, reported their findings in programming 3D curved mesosurfaces with rational microlattice designs. The research results were published in Science on March 24, 2023, with the title “Programming 3D curved mesosurfaces usingmicrolattice designs”. (Science, 379: 1225-1232, 2023, full article link at https://www.science.org/doi/10.1126/science.adf3824).

Cellular microstructures form naturally in many living organisms (e.g., flowers and leaves) to provide diverse and vital functions in their 3D shape formation, synthesis/transport of nutrients, and regulation of growth/reproduction (Fig. A). Owing to the light weight and high strength, high specific surface area, and excellent thermal properties of cellular structures, bio-inspired cellular designs have been exploited in the development of materials and functional systems. Examples include lattice materials and foams with high specific stiffness/strength, artificial tissues/organs with hierarchical vascularized networks and electromagnetic metamaterials. However, the shape programming for 3D curved mesosurfaces through biomimetic cellular microstructures remains unexplored. The design and fabrication of 3D curved mesosurfaces and devices with programmable curvatures based on the application scenarios, play important roles in fields of bioelectronics, micro-robotics, nanooptics and so on.

Inspired by cellular biological surfaces, Prof. Yihui Zhang led his group at Tsinghua University to develop a microlattice design strategy as a powerful route to achieve desired stiffness distribution of 2D micro-films, thereby allowing their transformation into programmable 3D curved mesosurfaces through the mechanically-guided assembly. Both an analytical model and a machine-learning-based computational approach are established for the inverse design of target 3D curved mesosurfaces from 2D microlattice patterns with optimized distributions of porosity and cell sizes(Fig. B). Compared with the reported design strategies through thickness engineering, the microlattice design strategy bypasses the great technical challenges in finely tuning the thickness distribution of micro-films.With the developed microlattice designs, this work presents more than 30 examples of rational assembly of regular curved mesosurfaces (e.g., hemispherical, hemi-ellipsoidal, and hemi-toroidal surfaces) and complex biological mesosurfaces (e.g., flower-/fruit-like plant surfaces, and ant-/octopus-/stingray-like animal surfaces), in diverse materials (e.g., silicon, metal, chitosan, polyimide and laser-induced graphene), with feature sizes spanning from ~ 2.7 μm to 30 μm in film thickness, and ~ 250 μm to 30 mm in lateral dimension.

The bioinspired microlattice designs allow construction of 3D electronic systems with desired curvature distributions. Demonstrations of conformable cardiac electronic device, stingray-like dual-mode actuator and 3D electronic cell scaffold suggest rich opportunities in fields of bioelectronics, microelectromechnicalsystems, micro-robotics and so on.