  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.
