ENGS 89/90 Reports

Project Advisor

Ryan J. Halter

Document Type

Report

Publication Date

Winter 3-1-2019

Abstract

Following a radical prostatectomy, the main surgical treatment for prostate cancer, a majority of men will experience some level of urinary incontinence. When severe, this incontinence creates social isolation, leads to risk of infection from dried urine, and prevents men from participating in activities they love. The most common treatment in the US is a surgically placed AMS 800, produced by Boston Scientific. The AMS 800 surgery is highly invasive with a lengthy recovery time. Also, the device requires manual activation using a pump in the scrotum and erodes the urethra over time by constant compression.

Our group’s design is a combination of pressure relief valve and shock absorber design. The dynamics of the valve’s opening and closing are controlled by a spring in parallel with a damper. The valve, made of silicone, will be triggered to allow urine flow by the natural increase in bladder pressure that accompanies urination. The trigger point is set to the pressure of a completely full bladder. Short pulses of higher pressure, such as from coughing and laughing, will not cause leakage because the damper will slow the descent of the plunger and the spike in pressure will subside before the valve opens. The valve is held in the bladder neck by a silicone balloon filled with saline. The entire device is inserted nonsurgically by a urologist with a cystoscope during an outpatient procedure using local anesthesia. The device should be replaced every 6 months, with a chance to lengthen that time based on device performance.

Owing to financial and time constraints, the current prototype is made of aluminium and at two-times-scale. This prototype was CNC machined and epoxied together. Large scale manufacturing of this device should be done using injection molding for its cost-efficiency and accurate tolerancing.

As an implanted medical device, the device’s safety and functionality were key concerns and the focus of testing. Stone formation is one of the largest risks with a device that sits in the bladder. As there are currently no devices that sit inside the lower bladder for a period of longer than a month, we ran independent stone formation tests using static urine to accelerate stone formation. These tests indicated that silicone and nitinol coated in pTFE resist stone formation, and the addition of antimicrobial silver oxide nanoparticles to the coating does not promote stone formation. Mechanical testing demonstrated functionality, with the spring triggering as predicted and the damper working, but with a higher damping coefficient than expected.

The device would be a viable substitute for most men in the AUS market, baring those with weak detrusor muscles from seperate medical issues. While other patents have added valves to the bladder neck, none have used a pressure relief valve or included a damper. The device is financially comparable with the AMS 800.

Moving forward, the device needs to be made to-scale with silicone injection molding to check the mechanical properties of the final material. Following proof of functionality in animal cadavers, the device should be tested inside animals (likely pigs), then inserted into human cadavers. Finally, the device could seek FDA approval for use in humans.

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