Final Design

To successfully simplify the current procedure, the Auto-Injector must be a portable device that eliminates the need for a second person, maintains a similar procedure workflow, and provides some form of haptic feedback to the user that indicates injection pressure. A WOW solution would be a device that meets all the objectives just listed, but also replicates the injection force with 1:1 tactile force feedback and completely maintains the workflow of the current procedure.

The WOW solution was ambitiously pursued and nearly achieved with a hydraulic haptic feedback system mounted to a linear lead screw syringe actuator. The four main components listed in the diagram below form a loop that attempts to replace the second person with an incremental injection approach. A small injection controller houses a shortened 20cc syringe (at just 40mm in length). The shortened syringe is filled with water and connected with tubing up to a 50cc syringe mounted to the linear actuator, thus forming a hydraulic system. The displacement of the controller syringe plunger is translated proportionally to a separate syringe fixed to the front of the linear actuator. The medication line runs from the medication syringe through a pinch valve until it reaches a nerve block needle mounted to the front of the controller syringe, which completes the loop of the system. The concept is that the hydraulics translate the force required for each injection or aspiration stroke to the user in real time. After each injection stroke of the controller plunger, a combination of sensor inputs trigger the engagement of a pinch valve. The simultaneous forward displacement of the drive plate resets the hydraulics to the original position.

The final design iteration was a successful proof-of-concept prototype that reduces the procedure to a one-person operation, maintains a similar workflow, and provides tactile haptic feedback. However, this prototype must be improved in future iterations to inject at least 5 cc of medication per injection stroke. Furthermore, the hydraulics of future iterations must be tuned to provide truly 1:1 tactile haptic feedback during the initial stages of injection. Finally, sterility issues must also be addressed. Our written report provides detailed recommendations for solving these issues and paves the way for future improvements that will hopefully lead to a successful end product.