Near-infrared light triggered and separable microneedles for transdermal delivery of metformin in diabetic rats

Near-infrared light triggered and separable microneedles (MNs) were fabricated by a unique molding method. The photothermal conversion agent (Prussian blue nanoparticles, PB NPs) and hypoglycemic drug (metformin) were embedded into the separable polycaprolactone (PCL) MNs arrowheads. These MNs arrowheads were capped on dissolving polyvinyl alcohol/polyvinyl pyrrolidone (PVA/PVP) solid supporting substrate. The as-fabricated MNs exhibited excellent photothermal conversion properties under near-infrared light (NIR) irradiation, causing the MNs arrowheads to melt due to the photothermal conversion of PB NPs. After applying on skin, the separable MNs arrowheads could be embedded in the skin due to the dissolution of supporting substrates after absorbing the interstitial fluid. When the embedded MNs arrowheads were exposed to NIR irradiation, the MNs arrowheads underwent a rapid thermal ablation from a solid to a liquid state, thus enabling the release of encapsulated metformin to be NIR modulated. They allowed on-demand control of timing and dose of the drug released. This suggests that the developed NIR-triggered and separable MNs are a promising transdermal drug delivery system that enables the patient or physician to adjust therapy precisely in an active manner, thus improving treatment efficiency and reducing side-effects.