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Methylene Diffusion in Agar Phantoms


Researchers have long considered diffusion of substances as an extremely complex process and proposed various phantoms as models to study the effects of physicochemical on the human body and to stimulate biological organs. Studies show that aqueous agar phantom systems of low concentrations best suit this purpose as they are inexpensive to prepare, in addition to resembling the desired tissue . Various experimental methods have been suggested to treat the drug diffusion phenomena in complex systems. Moreover, researchers have proposed methylene blue in monitoring the diffusion process in gel-like materials to stimulate processes taking place in living tissues, given that the size of the molecule is similar to the size of other chemotherapeutic drugs. Methylene blue has played a key function in microbiology and pharmacology such as staining living organisms, treating methemoglobinemia, and its recent reconsiderations as a drug in photodynamic therapy. For instance, Orth and coauthors’ findings, indicate that methylene blue administered through intratumoral injection alongside an illumination by argon-pumped dye lasers do kill xenotransplanted tumors found in animals as well as recurrent esophageal tumors in patients. This study investigates methylene blue diffusion in agar phantoms using optical absorption techniques.

Genina, et al. conducted a study on the diffusion of aqueous methylene blue solutions into agar gels using novel optical techniques as well as photoacoustic spectroscopy. The authors performed an optic study illuminated with a transparent tube with samples of agar. The authors also carried out data acquisition in transmission using eight photodiodes. The authors used this technique to facilitate the measuring of methylene blue’s diffusion into agar, functioning as positioning and time. The authors monitored the diffusion process using the photoacoustic technique and a modification of Rosenwaig’s photoacoustic cell. The sample was illuminated using modulated red laser beams functioning at fixed frequency. In both techniques a simple theoretical analyses facilitated the determination of effective optical properties and its evolution. The stabilization time was also investigated, with the study findings revealing that the characteristic time for stabilizing the dye diffusion process increased with agar concentration.

The study findings confirms previous study findings revealing that an increase in agar concentration in water by five times increases the stabilization rate by 10%, a behavior that is expected in low agar concentrations. Yet on high agar concentrations, the stabilization process takes longer time intervals. In both concentrations, the link in agar molecules generates strong structures that are harder for dyes to penetrate. Furthermore, using both measurements facilitated the production of an integrated analysis of the diffusion process. The optical technique provides useful information on the wavelengths to be used in illuminating lasers. In methylene blue’s case, the use of a red laser monitoring explains the good quality of the resultant experimental data. Contrastingly, the photoacoustic technique is useful in the study of living tissue samples where lateral profiles of practical measurements are possible.

The optical measurement facilitates the obtaining of direct results as well as the observing of optical absorption coefficients as positional functions. The study findings reveal a close relationship of concentration with optical absorption coefficients. This allows us to infer that a direct measurement of dye concentration and time and positions functions are possible. This study investigates the diffusion process of methylene blue agar gel phantoms using photoacoustic spectroscopy and an optical methodology using conventional cells. The techniques offer a useful analysis of the diffusion process as both studies indicate that an increase in agar concentrations slows down the diffusion process of methylene blue.


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