Origami is the ancient art of paper folding, which consists of a 2D pattern with regions of rigid panels and flexible hinges. The folding pattern for origami can be generated from a flat 2D sheet and converted into a complex 3D shape by local mountain and valley folds. Such structures have great potential as medical implants as they provide a route to fold large implant into a compact area to be loaded into a catheter. The main challenge lies in fabricating these microscale devices with varying stiffness for the rigid planes and the flexible hinges without compromising the quality and performance.

On the other hand, microsystem technology offers a method to fabricate freestanding NiTi shape memory thin films using UV lithography, magnetron sputtering, and wet chemical etching. This method allows for high design freedom, e.g., the ability to fabricate films with multiple thicknesses, reflecting on the structure's stiffness. Moreover, thin films realized using this fabrication method have low impurities which reflect on excellent fatigue life and have the ability to monolithically integrate functional layers. Realizing such origami-based designs from shape memory thin films can offer self-expanding smart implants.

In the current study, a group theory approach provides a flexible method for the design of implants. Its main advantage is that, once a few matching conditions are satisfied at the boundary of a unit cell, the group automatically determines the complete design of a foldable extended structure. The identified designs were fabricated with different porosities using thin-film technology and could be successfully folded to a fraction of their initial size. We like to discuss our approach, fabrication details, and the challenges faced when compared to the theory.