The effect of pulse duration, power and energy of fractional Er:YAG laser for transdermal delivery of differently sized FITC dextrans.

We studied fractional Er:YAG laser to enhance transdermal drug delivery of compounds possessing different molecular weights: FITC-dextrans (or FD) with average molecular weights of 4, 10 and 20kDa. Vertical glass Franz diffusion cells were used to study molecular transport through dermatomed porcine skin and histological analysis of laser-treated skin was performed after treatment with different laser pulse protocols. We were comparing different pulse durations at constant or varying pulse energies. We found that the energy of the delivered pulses mostly dictates the size/depth of laser-created microchannels, while the duration of the pulses dictates the extent of thermally altered tissue. That is, tissue ablation threshold is lowered at shorter pulse durations with higher power, which is preferred as it lowers thermal effects on viable skin layers. Especially for smaller molecules, transdermal delivery is increased by increasing laser-created microchannel size, but also by making partitioning into tissue easier when less thermal damage is caused on tissue. For large molecules, molecular transport through the remainder of skin tissue becomes increasingly difficult regardless of laser pulse parameters.