Control of release characteristics in pH‐sensitive poly(vinyl alcohol)/poly(acrylic acid) microcapsules containing chemically treated alumina core

The pH‐sensitive poly(vinyl alcohol)/poly(acrylic acid) hydrogel microcapsules containing vitamin B₁₂‐loaded Al₂O₃ core were prepared with a three‐step emulsion polymerization. Al₂O₃ was chemically treated with HCl or NaOH solutions at room temperature for 24 h to modify the binding properties with vitamin B₁₂. The colon‐targeted release characteristics of vitamin B₁₂ from the microcapsules were evaluated at different pHs. These microcapsules showed the faster and larger release of vitamin B₁₂ due to the high swelling of microcapsule shell as the pH was changed into more basic condition. However, these microcapsules showed the slower and less release of vitamin B₁₂ as the acid value of Al₂O₃ increased due to the strong binding interaction between Al₂O₃ core and vitamin B₁₂ even though the initial loading of vitamin B₁₂ was higher. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010