Fabrication and characterization of hyaluronic acid microneedles to enhance delivery of magnesium ascorbyl phosphate into skin.

This study investigated the in vitro transdermal delivery of magnesium ascorbyl phosphate (MAP) through porcine ear skin treated with hyaluronic acid (HA) microneedles (MNs). In this study, the micro-molding method was used to fabricate HA MNs. HA solution (10% w/v) containing 3% of MAP was placed onto a poly(dimethyl siloxane) mold to fill the microchannels under vacuum followed by drying in a desiccator. Scanning electron microscopy was performed to record the dimensions of the MNs. Skin microporation was demonstrated by dye binding. Histological skin sections revealed the shape of microchannels under hematoxylin-eosin staining. The actual depth of the microchannels and drug distribution pathways were studied by confocal microscopy. In vitro permeation on Franz diffusion cells were performed to determine the rate and extent of drug delivery into and across the skin. SEM captured individual MNs from the array, and the length of each MN was found to be ~400 μm. The 10 × 10 MN array prepared, resulted in the formation of 95 to 100 microchannels after 2 mins of treatment. In addition, the histological evaluations showed the formation of microchannels in the skin, complementary in shape to the MNs. The depths of the formed microchannels amounted to ~125 μm as determined by confocal microscopy. The application of the current MN technology enhanced the delivery of MAP into skin (96.8 ± 3.9 μg/cm) compared to the passive delivery strategy of MAP (44.9 ± 16.3 μg/cm). HA MNs markedly enhanced the in vitro transdermal delivery of MAP into and across skin.