Page 374 - Control Theory in Biomedical Engineering

340 Control theory in biomedical engineering

stiffness was consistently observed in the chiral design. We inferred that this
lack of evidence of jamming was because the test was very sensitive to the
loading geometry and fabrication precision, which was less controlled in the
preliminary study. While care was taken to ensure that the test piece was as
central as possible, it is possible that changes in the position might have
occurred while applying the elongation. Furthermore, we observed that
the PVA material showed a wide variance for test cases with 6mm elonga-
tion. This might due to the PVA had passed its elastic phase and entered the
plastic phase at 6mm, resulting in cracks.
NPR materials display interesting and unique characteristics that are
inherent to their metamaterial structure. These characteristics can be utilized
by precisely designing the structure and carefully altering it to suit the stiff-
ness tuning needs.

7 Kirigami and origami methods
7.1 Kirigami methods
Recently, a new form of fabrication process for 2D materials called kirigami,
the art of paper cutting, has gained interest. This method of fabrication is
quick and economical and in this study was done through the help of Sil-
houette Curio, a DIY cutting machine. Auxetics structures such as rotating
polygons are best suited for fabrication through this process, and their behav-
ior is obtained from the rotation of rigid polygons about their hinges. Fig. 20
shows the mechanism of the opening of the slots when a longitudinal strain is

Extension

q
l
Force

Fig. 20 2D rotating squares.