To demonstrate intraocular drug delivery using a novel device fabricated by embedding hollow glass microneedles within a soft and flexible poly (dimethylsiloxane) (PDMS) substrate for ease of device insertion into the eye.
Hollow glass microneedles (5 µm ID tips), fabricated using standard glass drawing techniques, were assembled into a photolithographically micropatterned PDMS substrate. The microneedles were fluidically coupled to a drug reservoir through a 300 µm microchannel to test for in vitro release of 6-aminoquinolone (144 Da) and Rose Bengal (1044 Da). Intravitreal delivery in ex vivo bovine eyes was also studied.
The microneedles penetrated UV-crosslinked collagen and excised bovine sclera without breaking or delaminating from the PDMS matrix. A total of 45 ng of 6-aminoquinolone and 16 µg of Rose Bengal was released into buffered saline over a 20-min infusion at a delivery rate of 50 µL/min. Microinjection of Rose Bengal for 8 h into ex vivo bovine vitreous resulted in a total mass accumulation of 0.0202 mg into both phases of the vitreous humor and to the uveal face of the sclera without clogging of the internal needle microchannel.
PDMS-embedded microneedles offer an integrated method of drug targeting to the intraocular tissues using a less invasive and less painful approach when compared with macroscale hypodermic needles. The release rates from the microneedles were controllable on demand using a syringe pump and were independent of the properties of the drugs tested. The device demonstrated a new hybrid approach of coupling rigid microneedles strong enough to penetrate the tough, fibrous sclera with a soft and pliable PDMS substrate that could conform to the contours of the eye.