Core-shell microneedle patch for six-month controlled-release contraceptive delivery

There is a tremendous need for simple-to-administer, long-acting contraception, which can increase access to improved family planning. Microneedle (MN) patches enable simple self-administration and have previously been formulated for 1-2 months' controlled release of contraceptive hormone using monolithic polymer/drug MN designs having first-order release kinetics. To achieve zero-order release, we developed a novel core-shell MN patch where the shell acts as a rate-controlling membrane to delay release of a contraceptive hormone, levonorgestrel (LNG), for 6 months. In this approach, LNG was encapsulated in a poly(lactide-co-glycolide) (PLGA) core surrounded by a poly(l-lactide) (PLLA) shell and a poly(D,L-lactide) (PLA) cap that were fabricated by sequential casting into a MN mold. Upon application to skin, the core-shell MNs utilized an effervescent interface to separate from the patch backing within 1 min. The core-shell design limited the initial 24 h burst release of LNG to 5.8 ± 0.5% and achieved roughly zero-order LNG release for 6.2 ± 0.1 months in vitro. A monolithic MN patch formulated with the same LNG and PLGA core, but without the rate-controlling PLLA shell and PLA cap had a larger LNG burst release of 22.6 ± 2.0% and achieved LNG release for just 2.1 ± 0.2 months. This study provides the first core-shell MN patch for controlled months-long drug release and supports the development of long-acting contraception using a simple-to-administer, twice-per-year MN patch.