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Design Iterations

Future Design Recommendations

syringe_controller_v4.mov

In our final prototype, the injection needle makes contact with the 3D printed injection controller. Due to sterility concerns, this renders the controller disposable. However, the controller contains important electromechanical components.

To solve this, we propose the addition of a detachable clamp for the needle. This CAD simulation by Walter shows the disposable front clamp that we would propose for future iterations of the Auto-injector device.

Final Device

Final Prototype Demonstration

Final.mp4

Our second CAD prototype is pictured to the right. The 3D printed hook at the top will allow the doctor to pull back with their thumb to aspirate. A resistive pressure sensor will be mounted on the circular portion of the hook, as shown in the schematic below, where the clinician will push down with the thumb to inject.

Physical Prototype 5.15.21.mov

In the video above, Tyler demonstrates the performance of our physical prototype of the Auto-Injector from May 15, 2021. This prototype successfully implements Device Design #2.

Physical Prototype - May 11, 2021.mp4

In the video above, Tyler tests the Auto-Injector prototype on May 11, 2021. The prototype is nearly complete, but still releases medication at unwanted times to relieve pressure.

First Device

Our first CAD prototype is pictured above. The rubber lining will provide grip to the ultrasound wand. An elastic Velcro strap will be looped through the handles to fully secure the device. The silver material will be 3D printed for maximum customization and cost effectiveness.

To the left is an assembly showing how the handle would be clamped to the ultrasound wand used for the nerve block procedure. However, based on clinician feedback, this design was abandoned in favor of device use in the left hand (traditionally holding the syringe instead of the ultrasound wand).

Our first handle mock-up allowed a physical demonstration of the injector utility for the clinicians. The MAE 156 team and our sponsor gained a better understanding of how the design will be ergonomically implemented in real life with an early proof of concept test. From this test we learned that non-dominant hand injection with the index finger would feel unnatural for the physician and would most likely not be adopted.

Overall System Iteration #3

The final design of the Auto-Injector consists of four key components: (1) Injection Controller, (2) Haptic Feedback System, (3) Linear Actuator, and (4) Pinch Valve. They form a loop that provides haptic feedback with a hydraulic system. The hydraulics translate the force required for each injection or aspiration stroke to the user in real time.

A small injection controller houses a shortened 20cc syringe. 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. 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.

Overall System Iteration #2

In the second iteration of our overall system, we switched to an ergonomic handle that mimicked the form of an ultrasound transducer instead of a trigger mechanism. This design change was in response to sponsor feedback that doctors would be much more comfortable adapting the new technology that has familiar form and function. We also addressed design needs with more specific solutions, such as the T-fitting, Luer locks, pressure sensor, and microcontroller. In this design a pressure sensor reading would dictate the response intensity of an electromechanical haptic feedback device that was yet to be decided. Possible haptic feedback components considered at this stage were piezo-electric actuators, solenoids, and air pumps.

Overall System Iteration #1

For the first iteration of our overall system design, we planned to retrofit a drill handle to house the haptic feedback mechanism. As shown above, a pressure sensor sends signals to the haptic feedback device in the trigger-based handle.

Parts & Hardware

3D Printed Handle Sensor Test.mov

In the video above, Tyler demonstrates a working prototype of the 3D Printed Autoinjector design. A resistive pressure sensor controls the injection, while a Hall Effect sensor tracks the displacement of his thumb.

Syringe Actuator.mp4

Above, Tyler shows the purchased syringe actuator in action. Having an automated actuator allowed our team to focus on refining the most challenging aspect of the project: the haptic feedback mechanism.

DC Motor Controlled with Pressure Sensor.mp4

In the video above, Wiley demonstrates the control of a DC motor using our purchased sensor. From this test, we learned that the motor reaction time is actually quite fast. However, further signal conditioning will be needed for smooth haptic response.

Research

Procedure Background

The video above shows an ultrasound-guided nerve block. From this video, we learned that needle placement and precision are of utmost importance for patient safety. We aim to increase the ease and efficiency of this procedure by helping the doctors operate as comfortably as possible.

SAFIRA® is an existing medical device for regional anesthesia procedures that reduces the need for multiple clinicians. However, the device is foot pedal based, which means that doctors will not have a seamless transition to implementation. The SAFIRA® product website is linked in the image above.

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