In support of future research of valve-bypass features for valved Glaucoma Drainage Devices (GDD's), we conducted some preliminary benchtop measurements as part of an undergraduate Mechanical Engineering Laboratory course at California Baptist University's College of Engineering. This work includes the research of methods to retrofit (at the time of surgery) current valved GDD's with bioabsorbable products such as sutures. By employing a time-delayed bypass, it is expected that the performance of valved GDD's can significantly increase approximately 6 weeks post-operation, at which time the valve is expected to no longer be needed and likely provides unwanted ocular flow resistance. It was found quite feasible - even without surgical training - that an 8-0 to 10-0 suture can be through the miniature implant tubing and tied in a loop. If a bioabsorbable suture is used, this can serve to provide a potential (wanted) leak later in time as the suture dissolves - creating a delayed bypass upstream of the valve. Characterization of the real-time pressure-flow behavior of the prototypes was performed using an in vitro bench top perfusion setup (e.g., syringe pump, pressure sensor), with measurements repeated for various cases: valve only (no suture), suture passed through and residing in tubing, and suture passed through and removed (leaving holes in tubing wall). It was found that a 10-0 suture was not sufficient in size to seal the holes created by the track of the suture needle. However, it was successfully demonstrated that a larger, 8-0 suture passed through and residing in the implant tubing wall can maintain pressure in the tube. This finding verifies feasibility of the proposed method of utilizing an absorbable suture to provide a delayed valve bypass for valved GDD's. Several surface tensions effects were observed in the study, which enlightened our team to the intricacies associated with microfluidic experimentation and the ultrasensitivities to liquid-gas interfaces.
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