Page 129 - Flexible Robotics in Medicine

Modular origami joint operator to create bendable motions with multiple radii 115

propensity for breakage and lower mechanical strength than a 3D printed hinge. Given a
more advanced 3D printer, it might be possible to 3D print a superior hinge with better
durability and flexibility than the PVC hinge.

A key factor to be considered during the design of this prototype was the possibility of hinge
breaking, which could be dangerous due to the possibility of piercing the inner walls of the
trachea. The first material that was used was polyethylene terephthalate (PET), which was
unsuitable as it broke after a few bends due to its rigidity. Polypropylene (PP), from plastic
files, was then used but was found to break easily due to ductile fracture due to the small
thickness of the plastic film and the characteristics of the material, making it unsuitable for
long-term bending. The third material that was utilized was paper coated with silicone. From
Table 5.1, better results were obtained in the cyclic loading tests in comparison with PET and
PP. However, the paper eventually showed signs of tearing. Even though the silicone coating on
the outside still managed to hold the torn piece of paper together, the hinge would not be able
to bend at the predetermined angle. Another drawback associated with the coating of silicone
was the unevenness in coating thickness due to the paper being manually coated. Consequently,
the thicker silicone layer at the joints prevented the hinges from bending at the predetermined
angle. The next material that was tried was PVC, which showed greater flexibility and lasted
longer. PVC also has the potential of breaking, but only when it has been utilized for a certain
number of times. In the test conducted, PVC was shown to be a promising material, being able
to withstand cyclic loading for more than 500 times (Table 5.1).
When the device was fully stabilized or when bending angles were fully achieved, the
whole device would move together such that individual modules would not move
individually when a force was inflicted. The device was able to achieve the desired bending
angles, as mentioned during MOJO experiments. The material of the hinge was PVC
plastic, which exhibits a certain amount of rigidity and flexibility. Cyclic loading tests
showed that the hinges would tear or break off entirely after a certain amount of use, with
differing results for each angle. The hinges were able to withstand more than 500 bending
cycles carried out using human hands. Moreover, the hinge had more potential for tears
when it moved in the left and right directions. Hence we designed the device for one-time
use to avoid wear and tear, which may cause injuries to the subject.

5.2.4 Description of prototype

5.2.4.1 Summary of the device

The device is composed of a flexible tubular manipulator and a distal tip capable of
curvilinear manipulation with a bistable property. The device is intended for use as a
surgical aid in transoral tracheostomy to achieve vertical deflection of the distal tip to
perform curvilinear needling. The device makes use of a modified origami universal joint