Synthesis and characterization of pH-responsive sodium alginate/humic acid composite hydrogels for sustained drug release of l-ascorbic acid.

Addressing the challenges of poor biocompatibility and degradability of artificial drug carriers and poor stability of natural monomer gels in the current pharmaceutical market, this study utilized green natural sodium alginate (SA) and humic acid (HA) as raw materials. SA/HA-Ca hydrogel spheres were prepared using Ca as a crosslinking agent and loaded with l-ascorbic acid (L-AA), and the drug-retardation study was conducted using the droplet method. Various analysis techniques confirmed the formation of a three-dimensional network structure through coordination between HA, SA, and Ca, resulting in hydrogel spheres with good thermal stability. Meanwhile, the drug-loading rate, swelling, and in vitro drug release of SA/HA-Ca gel spheres were investigated. Results showed that the hydrogel spheres exhibited strong pH responsiveness and satisfactory pore structure favorable for the loading of L-AA. The solubility of the SA/HA-Ca hydrogel in buffer solutions at pH = 1.4 and 7.4 was 1.7315 and 5.1235 g/g, respectively, while the swelling kinetics followed a second-order swelling kinetic equation; the maximum release of L-AA was 23.67 % and 82.64 %. The release profiles of L-AA from different drug-loaded gels conformed to Langmuir's quasi-primary and quasi-secondary kinetic models. In conclusion, this study provides a theoretical basis for achieving slow drug release using SA/HA-Ca.