Effect of carboxylated carbon nanotubes on physicochemical and drug release properties of oleogels

Abstract

Oleogels have attracted considerable attention as a matrix for the delivery of the varied range of pharmaceutical agents. In the present study, we have prepared oleogel systems based on shea butter (SB) (oleogelator) and wheat-germ oil (WGO) (liquid phase). Carboxylated carbon nanotubes (cCNTs) were incorporated within the oleogels in different proportions (1-20 mg) as the crystallization modifier of SB. The oleogels were characterized using various techniques such as microscopy, IR-spectroscopy, X-ray diffraction, thermal studies (gelation kinetics, differential scanning calorimetry (DSC)), and rheology. The crystallized SB/WGO oleogels assumed dark and black hue with the incorporation of the cCNTs. Microscopic imaging of the oleogels showed that an increment in the content of cCNTs promoted the agglomeration of the gelator crystals. The changes in the molecular interactions among the oleogel components were too weak to be detected by FTIR spectroscopy owing to the very low concentration of cCNTs. X-ray diffractograms revealed that SB in the oleogels was crystallized in its most stable β-polymorphic form. The crystallinity of the oleogel formulation SW4 (cCNTs; 10 mg) was observed to be the highest among all the formulations. Gelation kinetics confirmed that the cCNTs modified the crystallization kinetics of the oleogels in a composition-dependent manner. The thermograms correlated well with the XRD observations and demonstrated that SB in all the oleogels was predominantly crystallized in its β-polymorphic form. Moreover, the thermal stability of SW4 oleogel was observed to be the highest, which can be accounted to the presence of the large crystallite size of SB crystals. Rheological studies demonstrated that cCNTs increased the brittle nature of the cCNT-loaded oleogels. The in vitro release studies of the Ciprofloxacin HCl-loaded oleogels exhibited Fickian diffusion-mediated drug release. In summary, cCNTs exhibit the great potential to be utilized as an additive to modify the physicochemical and drug release behavior of the lipid-based systems.