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Figure 1. CAD rendering of final design of cranial distraction device (left). The drive mechanism is a lead screw (top right) that is driven by a bevel gear design (bottom right), with a magnet attached to the exterior gear. The magnet is actuated by external rotating magnets. Rendering taken in SolidWorks.

The final design contains two 12-hole plates, one attached at the end of the device and the other attached to the lead screw drive mechanism. The primary design for magnetic actuation includes a bevel gear design that could be actuated using an 3/8 inch height by 3/16 inch diameter neodymium permanent magnet. The gears are oriented 90 degrees to each other, with the teeth facing inward. The plates that attach the device to the skull each use twelve M1 screws to maintain compact size and to account for the variance of skull thinness of infants from age 3 to 6 month. The cranial distraction device final design is rendered above in Fig. 1, and the delivered device is rendered and photographed below in Fig. 2. Due to time and manufacturing limitations, the bevel gears in the final design have been replaced with standard spur gears. The performance between these two designs is nearly identical, but the spur gears are much more accessible at its small scale. Both a bevel gear drive and spur gear drive have been modeled, but all testing has been made with a spur gear driven prototype.

Figure 2. CAD rendering of delivered cranial distraction device (left). Machined cranial distraction device proof of concept with 3D printed stainless steel plates (right). 

External Remote Control

Figure 3. Remote magnetic control device. A high-torque motor is attached to the magnet (right), which will be monitored and controlled by an Arduino Uno (left). Renderings taken in SolidWorks.

The external remote control uses a magnetic system to communicate with the distraction device. A single rotating neodymium permanent magnet is rotated with a gear ratio of by a DC motor with a torque rating 140kg.cm and speed 50rpm. The rotating magnet actuates the magnet that will be integrated into the distraction device. The distraction distance is translated by the number of magnet rotations, which is measured by a hall sensor. Demonstrations of the device are shown in the videos below. 

CAD animations and annotated drawings 

Shared Components

Bevel Gear Exclusive (Final Design)

Spur Gear Exclusive (Final Delivered Device)

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