Photomechanical transdermal delivery: The effect of laser confinement

Background and Objectives: Photomechanical waves can transiently permeabilize the stratum corneum and facilitate the delivery of drugs into the epidermis and dermis. The present study was undertaken to assess the effect of pulse characteristics to the penetration depth of macromolecules delivered into the skin. Study Design/Materials and Methods: Photomechanical waves were generated by confined ablation with a Q-switched ruby laser. Fluorescence microscopy of frozen biopsies was used to assay the delivery of macromolecules through the stratum corneum and determine the depth of penetration. Results: Photomechanical waves generated by confined ablation of the target have a longer rise time and duration than those generated by direct ablation. Confined ablation required a lower radiant exposure (from ∼7 J/cm² to ∼5 J/cm²) for an increase in the depth of delivery (from ∼50 μm to ∼400 μm). Conclusions: Control of the characteristics of the photomechanical waves is important for transdermal delivery as they can affect the depth of drug penetration into the dermis.