Rational Design of Microfluidic Glaucoma Stent

Abstract

Glaucoma is a common, irreparable eye disease associated with high intraocular pressure. One treatment option is implantation of a stent to lower the intraocular pressure. A systematic approach to develop a microchannel stent meshwork that drains aqueous humor from the anterior chamber of the eye into the subconjunctiva space is presented. The stent has a large number of outlets within its mesh structure that open into the subconjunctiva. The development approach includes a flow resistance model of the stent. Local adaption of the stent’s tubular dimensions allows for adjustment of the flow resistance. In this way, an evenly distributed outflow into the subconjunctiva is achieved. We anticipate that microblebs will form at the stent outlets. Their size is crucial for drainage and control of intraocular pressure. An analytical model for bleb drainage is developed based on the porous properties of the subconjunctival tissue. Both models—the stent flow resistance model and the bleb drainage model—are verified by numerical simulation. The models and numerical simulation are used to predict intraocular pressure after surgery. They allow for a systematic and personalized design of microchannel stents. Stents designed in this way can stabilize the intraocular pressure between an upper and lower limit.

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

“…4c, Eberle's group presents a microchannel stent meshwork composed of three parts to facilitate the drainage. 144 Particularly, part A collects the AH from the anterior chamber and drains it via part B into part C (a microfluidic meshwork). The meshwork consists of honeycomb structures to preserve the miniature channel dimensions and uniform aqueous outflow to reduce fibrosis, while keeping the conformity of the meshwork to the tissue in the out-of-plane direction at low mechanical stress.…”

“…However, in the late stage typically 4 to 6 weeks after implantation, the formation of a fibrous capsule can provide an additional flow resistance to stabilize the IOP. 249 The resistance of a capsule in vivo is typically in the range from 3 to 4 mmHg (μL min −1 ) −1 , 144,250 thus the corresponding pressure head can be 7.5 to 10 mmHg, assuming an averaged aqueous rate of 2.5 μL min −1 . Notably, unlike the conventional GDDs, the valveless MIGS devices (e.g., XEN, PRESERFLO, EX-PRESS) are designed with a noticeable flow resistance in the range from 1.73 to 5.36 mmHg (μL min −1 ) −1 with a resultant pressure drop from 4.3 to 13.4 mmHg.…”