Formation and characterization of light-responsive TEMPO-oxidized konjac glucomannan microspheres

A light-responsive delivery system has been developed. It consists of gelly microspheres made of TEMPO-oxidized Konjac glucomannan (OKGM) polymers where the carboxyl (COO(-)) groups are cross-linked via ferric ions (Fe(3+)) and in which functional ingredients may be incorporated. By irradiation with (simulated) sunlight, the microspheres degrade, thereby releasing the encapsulated component(s). The degree of oxidation (DO) of the OKGM polymers could be well-controlled between 15 and 80%, as confirmed by proton titrations and FT-IR spectroscopy. OKGM of DO 80% was selected to prepare the microspheres because the high COO(-) content leads to a high density of cross-links, yielding a strong gel. The electrokinetic potential of the OKGM particles increases with increasing pH and decreasing salt concentration. Mössbauer and FT-IR spectroscopy revealed that the cross-links are formed through two modes of COO(-)-Fe(3+) coordination, that is, 68.4% by bridging and 31.6% by unidentate binding. Thus, the unique properties of the OKGM microspheres make them potentially applicable as light-controlled biocompatible delivery systems.