Introduction to the problem

Background Research Summary

Defining the problem:

The Amputee Coalition of America estimates that there are 185,000 new lower extremity amputations each year just within the United States and that there is an estimated population of 2 million American amputees. The recent wars in Iraq and Afghanistan have caused an increase in the number of service members who undergo an amputation. These are typically young individuals who were otherwise healthy at the time of their injury.  Many removed limbs are replaced by prosthetics. Lower artificial limbs range from very complex and expensive microprocessor-controlled devices with hydraulic knees to more inexpensive prostheses that are mechanical in nature.

Though the type of prosthesis varies greatly in size, shape, technology, and cost ($5000 -$60,000), our interviews with local businesses found some commonalties regardless of whether the limb was mechanical or electric in nature: a) After the surgeon amputates a limb, a team of specialists take over including a Certified Prosthetist and Orthotist to begin working with the patient. The relationships they form with the patient are sometimes for a lifetime; b) When people lose a limb, they go through a grieving process just like losing a loved one; c) Working with/through the patient’s insurance company to get the best artificial limb for the patient’s lifestyle is the most challenging part of the process; d) To create a socket to support (suspend) the residual limb above prosthesis below it, a mold and cast must be created. A sleeve (or sock) then fits over the residual limb and the limb slides into the newly molded socket. Newer sockets are made of polyurethane and can have silicon sleeves (see illustration #1). e) Limb shrinkage is the most common reason a well-fitting prosthesis can become uncomfortable and painful during a regular day. 

Illustration #1

Traditional prosthetic sockets do not have the ability to change shape with the limb. This mismatch between a changing limb and a fixed socket has the potential to create interface pressures and shear stresses that create pressure sores, dermatological problems, and circulation issues. The key point here is that the prosthesis should never feel loose after short periods of in activity. A comparison for us would be how our foot changes in size during the day based on whether we are running, walking, or sitting.  Residual limb friction in the socket can create pain and discomfort for the user which can even lead to the person choosing not to wear the artificial limb.

With external mechanical vacuums there is no way to tell how much or how well the vacuum is being maintained. Conventional suspension technology requires the amputees to progressively tighten the socket either by adding socks or further compressing the residual limb as essential limb fluid & volume is lost throughout the day. The user must walk several steps before vacuum is achieved in the socket. The prosthesis will feel loose as the user begins walking, until the vacuum level rises. Mechanical pumps can add to the "pistoning" effect which allows the residual limb to move up and down until vacuum is achieved. There may also be hoses and ports that are a source of vacuum leaks. 

An example of an electric vacuum pump solution is the “Smart Puck” from 5280 Prosthetics. Unlike conventional prosthetic suspension methods such as pin systems, lanyards, suction liners and adjustable sockets, the 5280 hypobaric socket technology improves on external vacuums because the puck is inside the negative pressure environment so there is no place to leak vacuum (see illustration #2). This internal vacuum device can be controlled by an App and a Bluetooth connection on a smartphone to let the user increase or decrease pressure on his/her residual limb depending on activity level. 5280 Prosthetics has offered to donate a Smart Puck to our team to experiment with and test.

Illustration #2

According to 5280 Prosthetics, the battery life in the Smart Puck device will last between 24-48 hours, depending on use. At night when the patient goes to bed, he/she takes off the artificial limb and then plugs it into a wall charger to recharge the 1000 mA battery for the next day.

Why is a solution needed for this problem?

The problem with having to charge the system nightly is that it restricts the user’s freedom. Mobility and functionality is limited to the charge.  What if the user wanted to go hiking or backpacking for five days where no power was available? What if the user forgot to charge it, there was a charging system failure, or the battery ran out during a high-use day? What if a catastrophic event like a hurricane, a flood or a tornado knocked out power for days (or even weeks), and the user did not have a way to charge the system? What about amputees in other countries where electricity is not readily available?

Mr. Robert Loper (Certified Prosthetist-Orthotist and Branch Manager at Hanger Clinic in La Crosse) feels that developing a new type of charging system that could reduce the size of or replace the battery in vacuum pumps would help reduce the weight of the artificial limb and provide more independence, reliability, and confidence for the user. 

Mr. Jared Smith (Prosthetic & Orthotic Fitter at the Limb Lab in La Crosse) agreed that a new type of charging system would greatly increase patient independence. He also felt that harvesting the energy from movement to supply electricity for the vacuum pump would be a very innovative way to do it. To his knowledge, no other manufacturer has that type of system in place.

According to Mr. Clint Accinni, who is one of the inventors (patent holder) of the 5280 Smart Puck management system, inventing a system that could charge or even replace a battery would be a “huge” development for two reasons: 1) It is critical to keep a constant vacuum in the socket for limb health. If, for example, the user is walking around at Disneyland and a hole in the air sleeve occurs, the battery will run down quickly because the vacuum pump would have to work constantly; 2) The Bluetooth 4.0 management

system application that the user activates on his/her phone to monitor and control the Smart Puck is a continual drain on the battery. Unlike the vacuum pump, this system is on all the time when in use. If the user loses this interface because the battery dies, he/she loses the ability to control the vacuum in his/her socket.

We also questioned why using a bigger battery or an additional external battery weren’t possible solutions. According to Mr. Accinni, the build height for vacuum pumps (2” for their device) is very important. Increasing the size of the battery would increase the build height of their device. It would negatively impact the floor-to-socket distance, which is “valuable space.” This affects the overall length of the artificial limb and what a prosthetist/orthotist can do to properly fit it to a user. External batteries are used with some other vacuum pump makers, but the batteries can be exposed to the environment (water), and they protrude on the outside of the artificial limb frame. The 5280 design keeps the battery and pump inside the socket to prevent this from happening.

We want to build an invention that will create a solution to this problem. Our solution would allow a person who has a lower leg prosthesis to wake up in the morning and not have to worry if his/her electric vacuum device was charged, allowing him/her the freedom to go where he/she wanted for as long as he/she wanted. 

Performance Specifications of the Invention:
The performance specifications of our invention are to have weight, volume, and form factor compatible with the existing prosthesis available space. Possible locations would be foot/heel, ankle, or lower leg. It would have minimal effect on prosthetic dynamics (feel) to user, and  provide significant energy harvesting to support battery recharging within prosthetic use timeframe. The battery capacity would be1000mAh, 3.7 VDC. Minimum use period is 24 hours.

The invention (energy harvesting and management system) will be used in the context of the typical daily use cycle of the prosthetic leg(s) by the user. It must support and be compatible with the electronic vacuum pump or regulator providing vacuum to the prosthesis socket. It is expected to provide effective energy harvesting by conversion of the available mechanical energy from leg use in the act of walking or running. It is also expected to provide effective customer use and control by communicating critical operating variables and status to remote electronic devices.

This device is technically feasible because energy recovery and conversion is currently being accomplished in products using piezoelectric assemblies and high-energy magnets with induction coils. Two different forms of energy conversion and storage exist in portable products such as hand cranked flashlights and walking motion powered consumer electronics. A form suitable for prosthetic application has been demonstrated in research using the electric machine mounted in the heel of a shoe powering a low-power electronic circuit/transmitter. This application requires a change or increase in scale of the electromechanical technology to provide the energy storage necessary for this project. A rough estimate of the energy requirement shows that there is adequate energy available in the foot and leg structure, and the conversion and storage efficiency required is less than 50%. We have found research which shows basic piezoelectric modules used to harvest the energy of the footfall during walking and creating an output voltage between 150 mW and 675 mW. By mounting multiple piezoelectric modules (or other electromechanical devices) in different locations on the lower artificial limb we feel we can harvest the required voltage, send it to a storage unit, and manage it, to be utilized by the electric vacuum pump. The fabrication of this device will be done in the Technology & Engineering Department at Logan High School which has existing electronics and fabrication spaces available.

In order to test our invention, we will design and fabricate a testing device to simulate the heel strike and motion of the artificial limb.  The testing device will allow us to replicate the movements of lower limb motion and test the amount of energy we can harvest from different locations on the limb with our invention. No human subject will be used.

Testing Device

Review of Intellectual Property:
In a review of intellectual property and patents, we found a number of patents for electric vacuum pumps and its components. We also found patents using piezoelectric technology to harvest energy. However, we did not find any patents using piezoelectric or electromechanical elements to harvest energy for electric vacuum pumps in a lower limb prosthesis. We also did not find any patents on software that specifically shows the amputee how much energy he/she has left in his/her electric vacuum pump to do certain activities. Patents in this area focused on a percentage of battery life left without taking the activity into consideration.

List of patents we researched in this area: Prosthetic Device Utilizing Electric Vacuum Pump, United States Patent 9333098 B2 · Filed: 09/13/2011; Limb volume accommodation in people with limb amputation United States Patent 8784340 B2 · Filed: 02/07/2012; Intelligent Prosthetic Socket Systems with Active User Feedback and Real Time Prosthesis Diagnostics, United States Patent Application 20120022667 A1 · Filed: 07/20/201; Piezoelectric Energy Harvester, United States Patent Application 20080174273 A1 · Filed: 03/27/2008; Device for generating power from a locomotion energy associated with leg muscles acting across a joint, United States Patent 8235869 B2 · Filed: 01/10/2010; Electromechanical energy harvesting system, United States Patent 8030807 B2 · Filed: 12/09/2005

Works Cited
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