ABSTRACT
Ionotropically crosslinked alginate beads suffer generally from poor drug loading, poor stability in biorelevant media and hence fast (i.e. uncontrolled) drug release profiles. Therefore, the present work aims at addressing these drawbacks by enhancing the stability of these metal ion-crosslinked alginate complexes via the incorporation of terephthalic acid which is proposed to act as a bridging crosslinking aid. In addition to the effect of terephthalic acid, we investigated the effect of curing temperature (4, 25 and 40 degrees C) and curing cross-linking metal ions (zinc, calcium and aluminum) on the characteristics of the resulting beads, i.e., drug loading and release profiles. Methylene blue (MB) was used as loaded drug model. The resulting beads were chemically and physically probed using infrared spectroscopy and differential scanning calorimetry. Interestingly, all prepared alginate-terephthalate beads (i.e., cured with zinc, calcium and aluminum) illustrated higher MB loadings and accessed controlled release profiles compared to their corresponding terephthalate-free alginate counterparts. Calcium-crosslinked alginate-terephthalate beads illustrated enteric release behavior regardless of their curing temperature. On the other hand, zinc-crosslinked alginate-terephthalate beads accessed enteric-like release profiles when only cured at 40 degrees C. However, aluminum-crosslinked alginate-terephthalate beads yielded interesting zero order release profiles regardless of their curing temperatures.
