Characterization of solid maltose microneedles and their use for transdermal delivery

Purpose. To characterize solid maltose microneedles and assess their ability to increase transdermal drug delivery. Materials and Methods. Microneedles and microchannels were characterized using methylene blue staining and scanning electron microscopy. Diffusion pattern of calcein was observed using confocal scanning laser microscopy. Transepidermal water loss (TEWL) measurements were made to study the skin barrier recovery after treatment. Uniformity in calcein uptake by the pores was characterized and percutaneous penetration of nicardipine hydrochloride (NH) was studied in vitro and in vivo across hairless rat skin. Results. Microneedles were measured to be 508.46 +/- 9.32 mu m long with a radius of curvature of 3 mu m at the tip. They penetrated the skin while creating microchannels measuring about 55.42 +/- 8.66 mu m in diameter. Microchannels were visualized by methylene blue staining. Pretreatment with microneedles resulted in the migration of calcein into the microchannels. TEWL increased after pretreatment and uptake of calcein by the pores was uniform as measured by the pore permeability index values. NH in vitro transport across skin increased significantly after pretreatment (flux 7.05 mu g/cm(2)/h) as compared to the untreated skin (flux 1.72 mu g/cm(2)/h) and the enhanced delivery was also demonstrated in vivo in hairless rats. Conclusion. Maltose microneedles were characterized and shown to create microchannels in the skin, which were also characterized and shown to improve the transdermal delivery of NH.