Uptake and controlled release of a dye from thermo-sensitive polymer P(NIPAM-co-Vim)

Copolymers of N-isopropylacrylamide (PNIPAM) are one of the most promising microgel materials for medical applications, especially as a drug carrier. PNIPAMs present unique properties, such as size variation with changing pH and/or temperature. The results of a study on the uptake and release of a dye (Orange II) by microgels of N-isopropylacrylamide copolymer with 1-vinylimidazole (P(NIPAM-co-Vim) are presented. The dye was used as a model low-molecular substance. Hydrodynamic radius (Rh) of P(NIPAM-co-Vim) particles was measured by dynamic light scattering as a function of temperature in two pH environments: acidic and basic. The dye particles contraction was monitored as a function of temperature at pH 4. The measurements of the zeta potential indicated a positive charge of P(NIPAM-co-Vim) particles at pH 4 and a negative one at pH 9. The key experiments were the internalization and the release of the dye. The effectiveness of this process was measured by UV-Vis spectroscopy on the supernatant derived from centrifuged P(NIPAM-co-Vim) suspension. At room temperature the efficiency of trapping of the dye by the microgel at pH 4 was 87%. Changing pH of a sample initially saturated with the dye from 4 to 9 led to a complete release of the trapped dye.