Socket Air Pump System V2

Acknowledgements

Video

Elevator Pitch

The main goal of this project was to design an insert for a prosthetic that would swell and contract to adjust to the change in volume of a residual limb. Normally, a user would first put a silicone liner on, then add socks on top of it. Then, they would insert the limb into a carbon fiber socket and activate the negative pressure system to hold their limb in place. At this point, they may need to add or subtract socks to be comfortable. Once they have the right number of socks, they must stomp down on the socket to fully activate the negative pressure, then put on the outer liner. Throughout the day, the limb will change size, and the discomfort will require changing the amount of socks worn and restarting the process. The process may take 10-15 minutes.

The air bladder process would be much simpler. It would still require putting on the silicone liner, putting the bladder over the liner, inserting this into the carbon fiber socket, activating the negative pressure, and putting on the silicone liner. However, it would eliminate the need for using socks to adjust the comfort level, making the whole process much easier.

Design Approach

Material Testing

To ensure proper integrity of the vinyl plastic used in our design, we designed a testing device and procedure to directly measure material tensile stresses. Our first iteration (insert reference) used a linear loading system where weight would be stacked on top gradually till significant yield behavior was observed. This initial design iteration had issues as it had a tedious mounting system with six screws that caused tear out points on the samples. It was also dependent on careful gradual application of weight through known masses, which inherently left the design vulnerable to poor measurement accuracy and overshoot of the failure point. Our second design (reference pic 2) accounts for this issue by simplifying the mounting system to be four hand tightened screws with no holes drilled into the samples, eliminating points for tear out failure. Through the ratcheting system and in-line fish scale, more direct and gradual force application is possible on the sample to get a more precise yield failure. The sample was also cut so that the failure point consistently failed in a predictable manner to better observe and compare testing results.

Seam Manufacturing Testing

To determine the best type of seal we had three different criteria that we were looking at. The first was determining the type of material that would best work. We decided to go with a thin gauge plastic because it was easy to mold and melt to itself,  skin friendly, and cost effective. The second thing that we looked at was the best way to seam the plastic with the use of different heating elements. We started off using a chisel tipped iron and heat roller at first, but later determined that an iron worked best for what we were trying to do because it had an easier temperature regulation, got hot enough to melt the plastic, and had a solid edge that made an even equal seam. The third criteria that we looked at was seam strengthening and different things we could do such as sewing the seam prior to heating, flex sealing edge, and super gluing the more complex areas to add support. What we determined was that flex seal and super glue did not work effectively and were waiting to test the sewing on the seam, but ultimately ran out of time.

Pressure Hotspot Identification

Bladder Integrity/Max Pressure Testing

Initial plans for bladder testing involved high pressure air (see procedure), but through consultation and reassessment it became obvious it would be prohibitively expensive to get an appropriate air compressor to reach the pressures we were interested in, as well as require additional safety precautions associated with sudden pressure failure. Instead, we recommend direct application of weight to the complete bladder (see other drawing) in an actual socket to more realistically model the pressures affecting the bladder. This same setup with a proper 

Design Solution

Our design fulfilled all of our client needs, as well as some of the client wants. These objectives are displayed in a table below, along with a description of the design choice that addresses the client want/need.

An additional goal of the bladder design was to not modify any pre-existing device (silicone liner, socket, etc.) that was sponsored by the VA. By creating our bladder to fit between the silicone liner and the socket without modification to either, we have achieved this goal. The pre-existing carbon fiber socket also has a built in negative pressure system to assist with keeping the socket in place. This vacuum is created by a one-way air valve on the back of the socket that can be activated by stepping or stomping in the socket, and released with a button. Since our device does not modify the pre-existing equipment, the negative pressure system remains intact, and there is an additional positive pressure system added by the bladder. The concept is that the negative pressure system will hold the residual limb within the socket, and the positive pressure system will fill in any additional space and further assist with holding the residual limb in the socket.

Next Steps

The next steps to be taken for the project are to finalize bladder design with a final prototype, testing, and iteration. The first step that should be taken is using the testing rig that we made to test the tensile strength of the different seams and finalize the design for a final prototype. We were able to design a bladder that could hold air well enough for concept, but was not air tight so looking forward there should be another one produced for a final test. Once a final bladder is produced then testing can be done with the model limb that we produced and the force sensors. This testing then should be analyzed to locate hot spots or other failures in the bladder itself and its design. Once failure locations are determined the bladder should be altered to best overcome these and then tested again till a finalized design can be made. This design could be sent off to a professional manufacturing company for the final design as well. Looking forward we would recommend that this project is not pursued by another team in the future because our limiting factor before we ended was manufacturing capabilities. Our recommendation is to send the bladder designs off to a manufacturer who can rapid prototype bladder designs. All they need is either a blueprint or sketch of the bladder design and some instruction including the location of valves, type of seam, and material to be used. 

Meet the Team

Acknowledgements

We would like to recognize Court Allen for assisting us through the beginning of the project as our client, and we would like to thank Scott Huyvaert for assisting us through the end of the project as our client. Thank you to QL+ for being our client company, and for providing the opportunities and resources to make this project possible. An additional thank you to Jon Monett, the founder of QL+. Thank you for creating this organization, and for the honor of allowing us to be a part of it.

Thank you to Chris Rosenberry for being our Challenger, and challenging us to engineer a new solution to adjust prosthetic sockets.

We would like to thank Dr. Zach Harvey for assisting us through our initial research, and providing a tangible scope to our challenge.

Last, but certainly not least, thank you Donna Bodeau for helping us throughout the entire project as our Project Advisor.