Controlled Release of Model Substances from pH–Sensitive Hydrogels

David Quintanar–Guerrero,¹ Briza Nadyr Zorraquín–Cornejo,¹ Adriana Ganem–Rondero,¹ Elizabeth Piñón–Segundo,^1* María Guadalupe Nava–Arzaluz,¹ and José Manuel Cornejo–Bravo²

¹ División de Estudios de Posgrado (Tecnología Farmacéutica), Facultad de Estudios Superiores Cuautitlán, Universidad Nacional Autónoma de México. Av. 1° de Mayo s/n, Cuautitlán Izcalli, Estado de México, México, C. P. 54140.^* Responsible author: elizabeth.pinonsegundo@gmail.com

² Facultad de Ciencias Químicas e Ingeniería, Universidad Autónoma de Baja California, Tijuana, Baja California, México, C.P. 22300.

Received October 21, 2008 ]]> Accepted December 19, 2008

Abstract

pH–Sensitive hydrogels of the poly(methacrylic acid–co–methyl methacrylate) (MAA/MMA) type, 22/18 molar % with different cross–linking percentages (0.3 and 0.5%) were synthesized. These gels were loaded with a model hydrophilic compound (dichlorobro–mophenol blue dye, DCBFB) with the aim of evaluating its release at different pH values (1.2, 5.0, 6.8, 1.4). The swelling degree and the release from these hydrogels are highly dependent on the pH of the dissolution medium and on the cross–linking degree. Scanning electron microscopy and differential scanning calorimetry studies demonstrated that part of the dye is embedded in crystal form within the hydrogel. The release profiles of the hydrogels assessed at pH = 6.8 and 1.4 were adjusted to the Higuchi model, regarding them as matrix delivery systems.

Keywords: Hydrogels, pH–sensitive polymers, Methacrylates, poly(methacrylic acid–comethyl methacrylate).

Resumen

Se sintetizaron hidrogeles pH–sensibles del tipo poli(ácido metacrílico–co–metacrilato de metilo) (MAA/MMA) 22/18 % molar con diferentes porcentajes de entrecruzamiento (0.3 y 0.5%). Estos geles fueron cargados con un compuesto hidrofílico modelo (azul de diclorobromofenol), con la finalidad de evaluar su liberación a diferentes pH's (1.2, 5.0, 6.8, 1.4). El grado de hinchamiento y la liberación a partir de estos hidrogeles presenta alta dependencia al pH del medio de disolución y al grado de entrecruzamiento. Estudios de microscopía electrónica de barrido y calorimetría diferencial de barrido demostraron que parte del colorante se encuentra embebido en forma de cristales dentro del hidrogel. Los perfiles de liberación de los hidrogeles evaluados a pH = 6.8 y 1.4 fueron ajustados al modelo de Higuchi, considerándolos como sistemas de liberación matriciales.

Palabras clave: Hidrogeles, polímeros pH–sensibles, metacrilatos, poli(ácido metacrílico–co–metil metacrilato).

Acknowledgements

The authors would like to acknowledge the technical assistance of Rodolfo Robles in the scanning electron microscopy studies.

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