Development of a biodegradable flow resisting polymer membrane for a novel glaucoma microstent

Within this paper we analyzed the technical feasibility of a novel microstent for glaucoma therapy. For lowering of intraocular pressure, the flexible polyurethane (PUR) implant is designed to drain aqueous humour from the anterior chamber of the eye into subconjunctival, or alternatively suprachoroidal, space. The microstent includes a biodegradable, flow resisting polymer membrane serving as temporary flow resistance for the prevention of early postoperative hypotony. A biodegradable local drug delivery (LDD)-device was designed to prevent fibrous encapsulation. Biodegradable components were made of flexible, nonwoven membranes of Poly(4-hydroxybutyrate) (P(4HB)). Polymer samples and microstent prototypes were manufactured by means of dip coating, electrospinning and femtosecond-laser micromachining and characterized in vitro with regard to structural and fluid mechanical properties, degradation behavior and drug release. Bending stiffness of PUR-tubing (62.53 ± 7.57 mN mm²) is comparable to conventional glaucoma drainage devices in a tube-plate design. Microstent prototypes yield a flow resistance of 2.4 ± 0.6 mmHg/μl min^-1 which is close to the aspired value corresponding to physiological pressure (15 mmHg) and aqueous humour flow (2 μl min^-1) conditions inside the eye. Degradation of electrospun P(4HB) specimens was found to be almost completely finished after six months in vitro. Within this time frame, flow capacity of the microstent increases, which is beneficial to compensate potentially increasing flow resistance of fibrous tissue in vivo. Fast drug release of the LDD-device was found. One microstent prototype was implanted into a porcine eye ex vivo. Future preclinical studies will allow further information about Microstent performance.