Textural Properties of Carbopol® Gel with Curcumin and Curcumin–HPβCD Inclusion Complex and Biological Activities

The aim of this study was to prepare curcumin/2-hydroxypropyl-β-cyclodextrin (HPβCD) inclusion complex, evaluate the antioxidant and antimicrobial activities of curcumin and curcumin in inclusion complex, as well as to examine the effect of curcumin and curcumin inclusion complex on the textural properties of Carbopol^® gel mixture. Curcumin/2-hydroxypropyl-β-cyclodextrin inclusion complex was prepared using the co-precipitation method in a molar ratio of 1:1. The antioxidant activity of curcumin and curcumin in inclusion complex was determined using DPPH, ABTS, and FRAP methods. The micro-dilution method was used to examine in vitro the antimicrobial activity of curcumin and curcumin in inclusion complex. The textural, rheological, and morphological properties of the samples (Gel 1- Carbopol^® gel; Gel 2- Carbopol^® gel with dispersed curcumin inclusion complex; Gel 3- Carbopol^® gel with dispersed curcumin) were examined. The textural properties were evaluated using a texturometer CT3 Texture Analyzer by means of a Texture Profile Analysis (TPA) test. The results showed that curcumin in inclusion complex had higher antioxidant and antimicrobial activity. The SEM confirms the presence of curcumin and inclusion complex in Carbopol^® gel. The rheological analysis confirmed that the structural integrity of Carbopol^® gel was preserved. The highest swelling degree is achieved by Gel 3 formulation. The in vitro release of curcumin from Gel 2 and Gel 3 occurs at the rates of 0.414 µg/h·g_gel and 0.376 µg/h·g_gel, respectively. The textural analysis showed that adding curcumin or its inclusion complex did not significantly change the properties of Carbopol^® gel, indicating potential for topical use.