Usnic acid-incorporated alginate and gelatin sponges prepared by freeze-drying for biomedical applications

Abstract

There is considerable interest in the pharmaceutical and biomedical areas in the use of sponges, produced with biopolymers, as matrices for the controlled release of drugs. The objective of this work was to evaluate the physicochemical characterization of alginate–gelatin (ALG–GEL) sponges containing usnic acid (UA), by thermogravimetric analysis (TG/DTG), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The macroscopic aspect showed a flexible structure, with variations in coloration depending on the concentration of UA in the sponges. The TG/DTG curves of ALG–GEL sponges and sponges containing 1 and 5 % of UA showed similar profiles and percentages of loss of mass. The DSC curves of both the sponges showed similar profiles, with two events involving a variation of enthalpy being observed, the first an endothermic event and the latter exothermic events, typical of decomposition. These curves show the absence of an endothermic peak of UA at 201 °C, indicating that the drug was present in the polymeric system. The SEM showed the ALG–GEL sponge to have the largest average pore diameter and a more heterogeneous arrangement of polymeric fibers, while sponges incorporated with UA showed more homogeneous arrangement of polymeric fibers. In conclusion, the incorporation of UA did not change the thermal stability of the sponges. Furthermore, the sponges incorporated with the drug showed a microstructural organization suitable for drug release systems.