The other product idea that I wanted to prototype for the product design sprint was another idea that I had from the very beginning of thesis. One of the hardest things for people with spinal cord injuries to adjust to is the incontinence that they develop as a result of the injury. The area of neural control of the bladder is in the S2-S4 region of the spine, way down in the sacral vertebrae [hence the S]. This is the part of the spinal cord that is attached to the hip bones, forming the pelvis. After a spinal cord injury, if the level of injury is above this point, bladder sensation is very limited. Users have to cath regularly to empty their bladders, but not even regular cathing can prevent an accident if the injured person suffers from a spastic bladder. The state of technology being what it is, with implants and smart objects, I was extremely surprised that a device like this didn’t exist already.
And in fact it does, kind of. I was tipped off to this fact fairly early on in my thesis interviews, but for some reason my Googlefu didn’t kick in until way later in the thesis process - until this design sprint. Sacral Nerve Stimulators are a class of device that are implanted in the hip of patients who suffer from incontinence. From what I understand - the websites are very vague, but I’m trying to get in touch with someone from Medtronic in order to understand the product better - the implant feeds a stimulating current to the nerves that control the external urethral sphincter. This current stabilizes the muscle and makes sure that it stays closed, until the user decides to void - so this device was/is intended for use by people who still have control over their bladders.
I have heard tell of magnetic switches that can be used to exercise bladder release remotely as well - but this is fairly useless for people with spinal cord injuries as they need to get MRIs frequently in order to understand how their physical condition is progressing. The device that I’m proposing uses Bluetooth Low Energy to communicate with the user’s cellphone. I prototyped this product twice, just as with the rollable ramp.
For the first iteration, I used a stretch sensor in a circuit controlled by an Arduino that also output 5V via another wire in the circuit. When the stretch sensor was stretched past a certain threshold, the Arduino sent a message to my phone asking it if I wanted to void my “bladder”. In this case, what voiding meant was turning off the 5V power supply to that extra wire until the stretch sensor returned to normal. This was meant to simulate the implant wherein a sensor would be embedded in the exterior wall of the bladder taking the place of the stretch sensor, and probes would be attached to the external urethral bladder taking the place of the 5V wire. This design was problematic because irritating the bladder [i.e. implanting something into its wall] can lead to the onset of cancer.
I realized that a more elegant way to fashion this implant was to simply place an electrode array on the pelvic nerve, which signals to the spinal cord that the bladder is full, and the pudendal nerve, which innervates the external urethral sphincter. The latter sends a constant voltage to the muscle to keep it closed. Upon observing increased neural activity along this nerve, the implant messages to the user’s phone, which is when he/she can decide to void it. When the user decides to void, the voltage being supplied by the second electrode array is ceased while the bladder empties.
For this more elegant idea, I crafted a much more complicated model that sought to represent how the bladder and urine excretory system function altogether. I've sent this video to one of my contacts at Medtronic; I haven't heard back yet, but hopefully I can start talking to people in the industry about this idea.