Polymeric check valve with an elevated pedestal for precise cracking pressure in a glaucoma drainage device

Abstract

This paper presents the design, fabrication, and characterization of a polymeric micro check valve for a glaucoma drainage device (GDD) featuring the precise regulation of intraocular pressure (IOP) and effective aqueous humor turnover (AHT). The pedestal, slightly elevated by selective coating of a parylene C film, induces pre-stress in the thin valve membrane, which enhances the predictability of the cracking pressure of the GDD. The proposed GDD comprises a cannula and a normally closed polymeric micro check valve, which are made of PDMS, a biocompatible polymer, with three layers: top (cover), intermediate (thin valve membrane), and bottom (base plate). A feedback channel, located between the top and intermediate layers, prevents reverse flow by feeding the pressure of the outlet channel back to the thin valve membrane. To achieve a precise cracking pressure and sufficient drainage of humor for humans, the thicknesses of the valve membrane and parylene C film are designed to be 58 μm and 1 μm, respectively, which are confirmed using a COMSOL simulation. The experimental results show that the cracking pressure of the fabricated GDD lies within the range of normal IOP (1.33-2.67 kPa). The forward flow rate (drainage rate), 4.3 ± 0.9 μL/min at 2.5 kPa, is adequate to accommodate the rate of AHT in a normal human eye (2.4 ± 0.6 μL/min). The reverse flow was not observed when a hydrostatic pressure of up to 4 kPa was applied to the outlet and the feedback channel.

Development of a Novel Valve-Controlled Drug-Elutable Microstent for Microinvasive Glaucoma Surgery: In Vitro and Preclinical In Vivo Studies

“…If the microstent tube were fully open, according to Hagen Poiseuille's law the expected volumetric flow rate extends the physiological aqueous humor production of approximately 2.5 µL min −1 by more than two orders of magnitude and, therefore, an ocular hypotony would be highly probable. 29 , 30 Considering ocular boundary conditions, the flow resistance of a constantly draining GDD should be approximately 6 mm Hg/µL min −1 (flow resistance = pressure difference/volume flow). For a need-based discontinuous drainage, a pressure adapted flow resistance of a GDD would be highly desirable.…”

“…In this regard, different experimental valve mechanisms for GDD are described in literature. 30 – 34 Nevertheless, the surgically implanted Ahmed glaucoma valve currently represents the only commercially available valved GDD with a pressure dependent flow resistance ranging from 2.86 mm Hg/µL min −1 (valve closed) to 0.05 mm Hg/µL min −1 (valve opened). 35 Within the current work, we developed a pressure-controlled valve mechanism with a comparable flow resistance.…”

Microfluidics in the eye: a review of glaucoma implants from an engineering perspective

“…5g. 152 A pedestal that is slightly elevated by selective parylene C coating induces preloaded stress in the thin valve membrane, which enhances the predictability of the threshold valving pressure. When the IOP elevates above a threshold, the valve membrane is lifted to facilitate the outflow of the AH.…”

“…g) Operating principle of a polymeric micro check valve. 152 The micro check valve is normally closed, consisting of three layers. When IOP is greater than the threshold, the intermediate membrane is lifted upwards, thus allowing AH outflow.…”

Biocompatible magnetic nanocomposite microcapsules as microfluidic one-way diffusion blocking valves with ultra-low opening pressure

“…Capillary-based passive valves also face similar issues, as the microchannels are normally open, failing to block vapor from one side to another, resulting in contamination of fluids [10]. Conventional passive mechanical valves based on cantilever-type flaps [17], membranes [18], or spherical balls [19], rely on the backpressure to seal the valve into the seat. These generally provide robust rectification to high backpressure, but suffer from poor performance at low backpressure where the valve is not completely closed [20].…”