PDMS embedded microneedles as a controlled release system for the eye

Purpose: 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. Methods: Hollow glass microneedles (5 mm 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 mm 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. Results: 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 mu g of Rose Bengal was released into buffered saline over a 20-min infusion at a delivery rate of 50 mu L/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. Conclusions: 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.