A redox strategy to tailor the release properties of Fe(III)-alginate aerogels for oral drug delivery

Iron(III)-crosslinked alginate aerogel beads (d = 3-5 mm) were prepared and loaded with ibuprofen by using the technique of adsorptive deposition from supercritical CO2. Additional formulations were prepared where the aerogels were co-impregnated by ibuprofen and ascorbic acid. The release of ibuprofen from the Fe(III)-alginate is much faster in pH = 7.4 (PBS) than in pH = 2.0 (HCl), which can be explained by the faster dissolution and higher swelling of the alginate matrix in PBS. By decreasing the size of the beads and using a higher G content alginate the release rate could be slightly increased. A marked acceleration of drug release was achieved in both HCl and PBS by incorporating ascorbic acid into the Fe(III)-alginate aerogel preparations. The explanation is that in aqueous media ascorbic acid in situ reduces the crosslinking Fe(III) to Fe(II). The latter does not interact strongly with alginate, which promotes the hydration of the chains, thus the erosion and dissolution of the carrier matrix.