Hypothesis / aims of study
A human bladder phantom model is often used for cystoscopy training, and recently, developments of bladder simulator have been reported in the literature [1,2]. In a previous work, the surface color and texture of the internal wall of the bladder were mimicked on a silicone-based soft bladder phantom for cystoscopy training [1]. The soft bladder was distensible to a volume of 480mL with an initial volume of 180mL; however, the system is limited to provide urodynamic scenarios.
The development of a urodynamic simulation test bench offers various controls and functionalities to resemble human urodynamics [2]. Despite its expandability due to modular design, the overall system is rather large limiting transportability and adoption.
In our work, we developed a soft human bladder phantom system that simulates the pressure-volume curve by mimicking the bladder anatomy and the filling and voiding phases. The phantom is made of liquid silicone rubber, situated in an air-tight closed chamber. The system, as we call it – Silicone-based Interactive Model of the Bladder Anatomy, SIMBA – employs a simple setup of liquid and air pumps and a pressure sensor with a visual interface on a laptop for a user to control the filling rate and the voiding event and to generate urodynamic pressure-volume curve.
The aim of our work is to provide a functional urinary bladder system that offers an ex-vivo tool for medical education and the development and validation of novel medical devices in the areas of lower urinary tract symptoms.
Study design, materials and methods
We approached to understand a human urinary bladder as a distensible balloon, which is filled with urine peristaltically traveling from the kidneys in two separate channels, via ureters, and empties in a single channel, via urethra, at a certain pressure or volume. Therefore, we devised our system with the following subsystems:
Soft distensible bladder:
In order to mimic the bladder, was a soft distensible bladder molded using a commercially available liquid silicone rubber (EcoflexTM 00-10, Smooth-On). The shape of the bladder was estimated and modelled in a CAD design software based on medical textbooks Based on the 3D model of the bladder, molds for two mirrored halves were 3D-printed using an FDM printer. A molding process recommended by the manufacturer of the liquid silicone rubber was followed, which involves thorough 50:50 mixing by volume, removing air bubbles using a vacuum chamber, slow pouring and room-temperature over 4 hours. Two mirrored halves of the cured silicone rubbers were bonded to each other using silicone-based adhesive.
Functional system
A system of hydraulic and pneumatic components was devised to mimic the filling and the voiding of the bladder. The system was comprised of 1) a sealed chamber made of Plexiglass cylinder and plates withstanding a positive pressure, which also houses the soft distensible bladder, 2) an air pump that supplies air into the chamber for generating a positive pressure, 3) a peristaltic pump for filling liquid into the soft distensible bladder and mimicking ureteric jetting, 4) a pressure sensor for measuring the internal pressure of the soft bladder, which represents intravesical pressure, 5) a solenoid valve representing the urinary sphincter, and 6) PVC tubings representing ureters and urethra.
Control & User Interface system
Control & UI system powers and controls the functional system using a generic power supply unit and offers graphical user interface on a computer for a user to set volumetric flow rate of liquid and displays pressure readings of a filling-voiding cycle. Two motor driver units were controlled by a microcontroller (Arduino Uno), and a MATLAB was written for visual user interface.
Interpretation of results
As an anatomy simulator, SIMBA is a demonstrative anatomical and physiological system that visualizes the filling and voiding states with a physical distensible phantom and provides reproducible urodynamic pressure-volume plots.