Investigation of the swelling response and drug loading of ionic microgels: The dependence on functional group composition

Spherical micron-sized (4-7 mu m diameter) poly(methacrylic acid-co-nitroph enyl acrylate) microgels were synthesized by precipitation polymerization a nd selectively derivatized with carboxylic acid, glutamic acid, hydroxamic acid, sulfonic acid, and ethanol functional groups in five separate postpol ymerization reactions. The pH and NaCl induced swelling response, drug load ing, capacity ("capacity" = total number of functional ionic groups that bi nd protons), and density of the five different composition anionic microgel s, each containing a different functional group as well as a baseline of ca rboxylic acid groups, were measured. Using the micropipet flow technique, i t was found that the pH range of the swelling response for the five differe nt microgel compositions shined by an amount that was proportional to the s olution pK(a)'s of their functional groups. The degree of drug loading incr eased in proportion to the microgels' capacity. However, the drug loading d id not decrease proportionately when the capacity was lowered.