Automated folding of origami lattices: from nanopatterned sheets to stiff meta-biomaterial

Abstract

Folding nanopatterned flat sheets into complex 3D structures enables the fabrication of meta-biomaterials that combine a rationally designed 3D architecture (e.g., to tune mechanical and mass transport properties) with nanoscale surface features (e.g., to guide the differentiation of stem cells). Self-folding is an attractive approach for realizing such materials. However, self-folded lattices are generally too compliant as there is an inherent competition between the ease-of-folding requirements and the final load-bearing characteristics. Inspired by sheet metal forming, we propose an alternative route for the fabrication of origami lattices. This automated folding approach allows for the introduction of sharp folds into thick metal sheets, thereby enhancing their stiffness. We then demonstrate the first time ever realization of automatically folded origami lattices with bone-mimicking mechanical properties (elastic modulus = 0.5 GPa). The proposed approach is highly scalable given that the unit cells making up the meta-biomaterial can be arbitrarily large in number and small in dimensions. To demonstrate the scalability and versatility of the proposed approach, we fabricated origami lattices with > 100 unit cells, lattices with unit cells as small as 1.25 mm, and auxetic lattices. We then used inductively coupled plasma reactive ion etching to nanopattern the surface of the sheets prior to folding. Protected by a thin layer of coating, these nanoscale features remained intact during the folding process. A cell culture assay was then used to assess the bone tissue regeneration performance of the folded origami. We found that the nanopatterned folded specimens exhibit significantly increased mineralization as compared to their non-patterned counterparts.