The influence of positive or negative charges in the passive and iontophoretic skin penetration of porphyrins used in photodynamic therapy - Gelfuso, Guilherme Martins; Gratieri, Tais; Souza, Joel Gonçalves de; Thomazine, José A.; Lopez, Renata Fonseca Vianna (European Journal of Pharmaceutics and Biopharmaceutics, 2011)