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Composite material flower shunt for fetal LUTO optimizing force of dislodgement and patency
Swarali Panse, Bachelors of Science, Anika Kamisetty, Bachelors of Science, Jacquelin Stanberry, Bachelors of Science, Maria A. Erquiaga, Bachelors of Mechanical Engineering, Jason Schutt, Bachelors of Science, Haley B. Clark, Bachelors of Science, Sanjna Sandeep, Bachelors of Science.
Texas A&M University, Houston, TX, USA.
BACKGROUND: Fetal lower urinary tract obstructions (LUTO) are a group of congenital conditions resulting in an inability to void urine from the bladder during development. This can cause a buildup of fluid in the urinary tract inducing megacystitis, hydronephrosis, and eventually oligo- or anhydramnios leading to lung hypoplasia. Current treatment for this condition involves in utero placement of a vesicoamniotic shunt (VAS) to redirect fluid from the bladder to the amniotic space. VAS devices on market are prone to dislodgement and often require multiple insertions, increasing risk to both the fetus and the mother. Therefore, our group sought to design a VAS that is compatible with minimally invasive insertion and can resist dislodgement while still effectively draining fluid from the bladder.
METHODS: The shunt was fabricated using a shape-memory composite and a flexible polymer. The specific materials were chosen due to their biocompatibility and mechanical properties. Specific material formulations, structural geometries, and processing methods are proprietary and not disclosed pending provisional patent filing. To manufacture the composite shunt, shape-memory wire was cured to the desired shape. through a process of heating and cooling. The shaped wire was coated with a flexible polymer. Qualitative testing was conducted by inserting each shunt model into a 2.5 mm ID tube to evaluate the shunt's size and ease of fit in the desired tube. A second qualitative test consisting of compressing and releasing the shunt petals was performed to evaluate behavior of shunt on deployment. Lastly, patency was evaluated through insertion in a water-filled plastic bag and observing fluid flow dynamics. Quantitative testing was performed first by obtaining the dimensions of the shunt and then utilizing a tensile testing machine to pull shunts through a silicone modeled bladder wall to measure the force needed for dislodgement.
RESULTS: All composite shunt prototypes maintained patency and continuous flow under pressure. The polymer-coated proprietary shape compressed easily into the 2.5 mm inner diameter cannula and expanded readily on deployment. Moreover, the force of dislodgement for the composite shunt exceeded existing solutions at an average of 0.619 lbF (industry standard 0.08 lbF). This value increased with increased number of coats and minimal change in outer diameter: an iterative five layer polymer coat shunt had an average force of dislodgement of 0.815 lbF with an outer diameter of 2.5 mm.
CONCLUSIONS: The composite shunt developed demonstrated qualitative properties consistent with current and future clinical use. Additionally, the quantitative results of this study demonstrate improved force of dislodgement. Taken together, this composite shunt improves upon the current clinical standard of care and presents a viable opportunity for advancing the treatment of fetal LUTO. Future work will focus on optimizing the manufacturing process and moving towards more advanced testing procedures such as utilizing a porcine bladder and investigating biocompatibility with cell culture and animal studies.
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