Engineering a partially degradable glaucoma microshunt for controlled intraocular pressure reduction

Abstract

Purpose : Electrospinning is a versatile platform for glaucoma microshunts as it allows incorporation of almost any polymer into nano-structured devices of varying dimensions and degradation profiles. We hypothesize that incorporation of a biodegradable inner core into a microshunt will allow gradual inner diameter (ID) expansion after implantation, regulate aqueous humor outflow, and control post-surgical IOP reduction.

Methods : Pressure control shunts (PCS) were electrospun with a patent, 25 µm thick inner core of degradable polyglycolic acid (PGA) nanofibers surrounded by an outer core of non-absorbable polyethylene terephthalate (PET) nanofibers (length:6mm, ID:75 µm and outer diameter (OD):421±8 µm). Control shunts were electrospun from PET (length:6mm, ID:100 µm and OD:426±5 µm). PCS size, morphology, and ID change after inner core degradation in vitro were characterized via scanning electron microscopy (SEM). Pressure difference across the shunt was evaluated by in vitro flow (27 days) of phosphate-buffered saline (PBS) at 150 µl/hour. PCS (n=3) and control (n=3) microshunts were implanted into New Zealand White rabbits with the proximal end in the anterior chamber and the distal end in the subconjunctival space. IOP, shunt patency, bleb morphology, ID, and biocompatibility were evaluated for 27 days after implantation.

Results : A statistically significant (p=0.036), 44% reduction in IOP as compared to non-operated contralateral eyes was observed in eyes with PCS 27 days after in-vivo placement. Post-surgical hypotony was not observed in eyes with PCS (n = 3) whereas hypotony was observed in all (n=3) eyes following control shunt implantation. Microshunts were patent in all (n=3) PCS surgeries and in 1 out of 3 eyes with control shunts. ID increased from 75 to 102 ± 3.3 μm following PCS in vivo placement. Histological examination of eyes with PCS showed a fibrotic response and luminal patency.

Conclusions : PCS shunts are biocompatible and regulate aqueous humor outflow via a degradable inner core that prevents post-operative hypotony and ultimately expands to provide additional IOP reduction and resistance to biofouling and lumen blockage.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

SEM micrographs show ID expansion due to PGA degradation. (A) PCS lumen prior and (B) after 28 days of in-vitro flow of PBS.(C) ID increase correlates with pressure drop across shunt in-vitro.