Fortus 250mc

Markers were casted out of silicone. A mold was 3D printed using a Fortus 250MC (Stratasys, Ltd.) printer with a rubber-like print material, Tango (Stratasys, Ltd.). This resulted in a flexible mold that allowed releasing the markers from the mold after curing. The resulting marker is a disk of 2 mm thick and 5 mm in diameter. Initially, a marker of 10 mm in diameter was produced and was only used on the first two patients. The marker’s material is Ecoflex™ GEL (Smooth-on Inc.) which is commercially available and tested skin safe that conform with the OECD TG 439 test guidelines which are closely related to the ISO 10993 standards for medical devices [15 (link)]. For this pilot study, we rely on these test results and patients were asked to report any adverse events. The two components of uncured silicone were mixed, stirred, and carefully poured into the mold. Any excess material was scraped off. The markers were left to cure for 4 h of which the first hour in a vacuum chamber at 100 mbar to extrude any trapped air. After curing, the markers were removed from the mold and stored on a plastic sheet for later application. The permanently sticky silicone allowed for long-term storage of the marker without changes to geometrical or acoustic properties.

The methodology for prototype development is presented in Figure 2. Regarding the sensor and actuator fabrication, first, the triboelectric sensor was patterned using 1 wt.% MWCNTs plus 1 wt.% of magnetite in PU. Then, the triboelectric sensor was placed inside the mould of the actuator and, finally, it was filled with PU rubber. The actuator’s mould consisted of a polymeric part produced by 3D printing. The structure also comprises two channels on the sides, where the string moves. The motion is comparable to the movement of a tendon, bending the structure after pulling the sting. The mould presents several folds on the front and back, facilitating the movement of the actuator and decreasing the force needed for the micro servo to pull the strings.
The mould and the prototype were designed with SolidWorks and fabricated using a 3D printing machine (Stratasys Fortus 250mc, Edina, MN, EUA). The hardware to control the prototype consisted of an Arduino Uno, electrical resistances, LEDs and two micro servo motors (DFRobot SER0006, Hubai, China). All the components were assembled inside the 3D printing prototype structure to test the prototype.