In vitro flow properties of Preserflo Michroshunt with an intraluminal stent

Objectives: This study aimed to evaluate the impact of varying stent sizes and materials on the outflow of the Preserflo Microshunt (PMS). Methods: In vitro experiments were conducted using five new PMS samples. Intraluminal stents of two materials (nylon and polypropylene) and two sizes (9-0 and 10-0) were tested. Flow was measured using a balanced saline solution (BSS) under a constant hydrostatic pressure, and the resistance was calculated. Theoretical calculations based on the Hagen-Poiseuille law were compared with in vitro results, and the results were corrected to calculate resistance to flow using aqueous humour properties. Five measurements were obtained for each material and size. Results: Without any stent, the median resistance internal to PMS corrected for aqueous humour viscosity was 1.59 mmHg/µL/min. Median resistances were 6.35 mmHg/µL/min (range: 3.88-7.42) for the 10-0 nylon and, 11.79 mmHg/µL/min (range: 7.08-13.71) for the 10-0 polypropylene. The 9-0 stents showed higher resistance: 10.99 mmHg/µL/min (range: 7.34-22.75) for 9-0 nylon, finally, the 9-0 polypropylene resulted in a resistance of 37.55 mmHg/µL/min (range: 36.52-38.41). Conclusions: This study indicates that the tested suture materials and sizes have a significant impact on the outflow resistance of the PMS device. Larger sutures and/or polypropylene materials seem to offer more resistance to aqueous outflow.