Photomechanical drug delivery

ABSTRACTPhotomechanical waves (PW) are generated by Q-switched or mode-locked lasers. Ablation is a reliable method for generating PWs with consistent characteristics. Depending on the laser wavelength and target material, PWs with differentparameters can be generated which allows the investigation of the interactions ofPWs with cells and tissue. PWs have beenshown to permeabilize the stratum comeum (SC) in vivo and facilitate the transport of drugs into the skin. Once a drug hasdiffused into the dermis it can enter the vasculature, thus producing a systemic effect. Fluorescence microscopy of biopsiesshow that 40-kDa molecules can be delivered to a depth of>300 m into the viable skin of rats. Many important drugs suchas insulin (6 kDa), and erythropoetin (48 kDa) are smaller or comparable in size, making the PWs attractive for transdermaldrug delivery. There are three possible pathways through the SC : Transappendageal via hair follicles or other appendages,transcellular through the corneocytes, and intercellular via the extracellular matrix. The intercellular route appears to be themost likely pathway ofdrug delivery through the SC.Keywords: Ablation, drug delivery, membrane permeability, photoacoustics, photomechanical effects, pressure waves, shockwaves, stress waves, trandennal delivery