Multimedia

CADs and Designs of Final Prototype

Video 1: Animation of final design. This is a simulation of what the device is designed to do when it is fully implanted and performing the nerve lengthening procedure.

Figure 1: Full render of the final design in an implanted environment.

Figure 2: Cross section of final design with each component annotated. From here, it is possible to see how a majority of the mechanism function.

Indexing Mechanism

Video 2: Animation of indexing mechanism. This animation simulates how the indexing mechanism functions by utilizing the mechanical stops and one-way bearings. 

Figure 3: Render of mechanical stops and driveshaft. Due to the placements of the mechanical stops, the driveshaft is always stopped at those specific points. Thus, this ensures that each iteration of actuation always actuates the distance between the mechanical stops, which roughly translates to 2 mm in linear distance.

Figure 4: Illustration and summary of the dual one-way bearing mechanism that is primarily used to index the distance actuated by the device.

The indexing mechanism it the primary method of measuring and indexing the number of actuations the device performs. It utilizes dual one-way bearings to index the distance actuated and mechanical stops in the enclosure are used to ensure that the distance actuated at each iteration is constant and controlled. The figures above illustrate how each components was designed to ensure that the device could properly index the amount of nerve actuated. The video above demonstrates how the entirety of this mechanism functions.

Initial Designs/Solutions

Ratchet-Release Mechanism

Figures 5 and 6: CAD renders of the initial ratchet-release mechanism (right) and 7:1 scaled prototype of ratchet-release mechanism (left).

One of the two preliminary designs that were approached in the beginning of this project was the idea of a ratchet release mechanism. This concept was based on the importance of the device being able to index each step after every actuation. This design was useful because it offered a purely mechanical solution that could easily index it's position after every use and pull with a high amount of force. However, after creating a prototype that was 7:1 scale to the real model, it was found that a ratchet mechanism that is within the size of the bounding box would offer too many complications and difficulties.

Motor-Spool Design

Figure 7: CAD render of initial spool-motor design. The initial design boasts a very cylindrical design, making it particularly hard to mount during implantation.

Figure 8: CAD render of initial spool-motor design in an implanted environment to demonstrate how the design would have functioned it was implanted.

Figure 9: Fabricated prototype of initial spool-motor design. The prototype is placed next to a quarter in order to demonstrate how small the device actually is.

The motor-spool design was the other early concept for the nerve lengthening device because it offered many desirable features such as being compact and simple to design. Many aspects of the original motor-spool design were able to be passed on to the final design such as the indexing mechanism utilizing the dual one-way bearings and the mechanical stops designed into the enclosure. However, aspects of early designs were also improved upon to in order to be more optimal to implant. For example, the the enclosure of the original design was changed from a purely cylindrical design, as shown above in figure 7, to a more flat design with mounting holes that makes it much easier to implant, as shown in pictures of the final prototype in figure 1.

Figure 10: The early spool-motor design also utilized the dual one-way bearing mechanism as the method of indexing distance. This mechanism was passed on final iterations of the device.