Multi-Layered Microneedles Loaded with Microspheres.

Delivery of therapies into skin is attractive for medical indications including vaccination and treatment of dermatoses but is highly constrained by the stratum corneum barrier. Microneedle (MN) patches have emerged as a promising technology to enable non-invasive, intuitive, and low-cost skin delivery. When combined with biodegradable polymer formulations, MN patches can further enable controlled-release drug delivery without injection. Herein, we sought to expand on the capability of MN patches to deliver therapies into skin by providing improved spatiotemporal control. Polylactic-co-glycolic acid (PLGA) microspheres were used to encapsulate model dye and then loaded into MN patches through a layer-by-layer fabrication method that created multiple layers of different composition within each MN. MN patches were loaded with up to 5 μg/MN of PLGA microspheres. Mechanical testing demonstrated that mechanical strength of MNs decreased with increasing number of microsphere layers. Microsphere-loaded MN patches inserted into porcine skin ex vivo and murine skin in vivo fully dissolved within 15 min, administering drug-loaded microspheres for controlled release lasting over 45 days. These data support the feasibility of multi-layered, microsphere-loaded MN patches designed for spatially targeted and sustained delivery of therapies into skin.