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Diffusion of substances in tissue is an extremely complex process. Various phantoms have been proposed as a model to simulate biological organs and to study physicochemical effects on the human body. Low concentration aqueous agar phantoms systems are specially suited for this purpose (Madsen et al., 2005), because they resemble the desired tissue, and are inexpensive to prepare (Bauman et al., 2004). Recently, they have been suggested for the study of the treatment of neurodegenerative diseases of the central nervous system (CNS) by implantation of nanoreservoirs, for controlled drug release into the brain (Staples et al., 2006). A variety of experimental methods have been developed for the study of drug diffusion phenomena in such a complex system. Methylene blue can be used to monitor the diffusion processes inside a gel-like material to simulate the actual process that takes place in the living tissue, since the size of this molecule is similar to that of some chemotherapeutic drugs (Buchholz et al., 2008). Methylene blue is a heterocyclic aromatic chemical compound with the molecular formula C16H18N3SCl, a scheme of the molecule is shown in Figure 1. Additionally, methylene blue is a molecule that has played important roles in microbiology and pharmacology. It has been widely used to stain living organisms, to treat methemoglobinemia, and recently it has been considered as a drug for photodynamic therapy (Tardivo et al., 2005). This compound shows in-vivo activity against several types of tumors, when locally injected and illuminated with read laser light (Tardivo et al., 2005). Orth and coauthors have demonstrated that intratumoral injection of 1% methylene blue followed by illumination by an argon-pumped dye laser, was able to kill xenotransplanted tumors in animals and recurrent esophageal tumors in patients (Orth et al., 1998). |
