Page 247 - Flexible Robotics in Medicine

236 Chapter 10

Figure 10.3
Schematic showing the steps involved in thermomechanical programming of the SMA wire in the
tentacle.

10.2.2 Design of the tentacle

The tentacle is designed to carry an endoscope camera and bend in all directions to a
specific angle based on the actuation of the SMA wires. Different angles can be achieved in
a specific range by actuating at different input currents. The tentacle is a long cylinder
(50 mm long with a diameter of 5 mm) designed to have one channel for the endoscope
camera and six channels for the SMA wires to actuate and bend in all directions. The
endoscope channel is located in the center with a diameter of 3 mm, and the channel for
SMA wires is 1 mm in diameter. The dimensions of the tentacle are sufficient to navigate
the nasal canal and reach the nasopharyngeal cavity for manipulation in adults [25],
although this device needs to be further scaled down to produce a prototype size that is
fitting for a transnasal endoscopy surgery in infants. The tentacle is fabricated using the
silicone elastomer as the passive element and SMA wires as an active element, and the
tentacle is fabricated by the soft casting method. The mold for the soft casting of silicone
elastomer is 3D printed with polylactic acid (PLA) materials using LulzBot from Aleph
Objects, Inc. (Colorado, United States). The mold is printed in three parts and then sealed
together using a silicone sealant to prevent leakage of silicone during the 4 8 hours curing
session. The design and assembly of the mold are shown in Fig. 10.3.

10.2.3 Silicone elastomer

Ecoflex 00 30 silicone elastomer obtained from Smooth-On, Inc. (Pennsylvania, United
States) is used as an encapsulation material of the SMA wires in the tentacle. Ecoflex
consists of platinum-catalyzed silicones that come in two parts, A and B, and these two
parts need to be mixed in a 1:1 ratio by volume or weight. Rigorous mixing can be done
manually or using a centrifugal mixer and then degassed to remove the air bubbles (air is
entrapped during mixing due to its viscosity) present in the mixture. The mixture can then