Most of the newly discovered active substances are not soluble in water. Thus, new delivery methods of the active substances that will improve their solubility and consequent bioavailability are required. There’s been an ongoing effort to develop new such systems for many years. Recently, lipid-based systems, such as oil solutions, were identified as a promising delivery system. However, these lipid-based systems normally appear in a liquid state. This makes them more challenging to implement due to associated challenges with the patient use and handling during drug production. Oily solutions can be gelled into oleo- or organogels. In contrast to hydrogels, the potential of organogels as delivery mode of active substances is poorly understood.
In this master's project, we initiated the research into nanocrystalline cellulose (CNC) as a possible organogelator. CNC is a natural polymer made of D-glucose molecules bound by a ß (1-4) glycosidic bond. Its diameter is less than 100 nm. CNC can be isolated from various plant sources, such as wood and through recycling of already used materials. The extraction process determines the properties of the end product. We did not expect direct gelation, i.e. dissolving CNC in oil, to be successful due to the hydrophilicity of the polymer. Therefore, the organogels were prepared indirectly. We prepared solutions of various CNC concentration, lyophilized them and added oil to the lyophilisates. We showed that lyophilization of a sample of CNC is key for the preparation of the organogel. Lyophilization enables the formation of aerogel, a porous structure of CNC, which successfully binds the oil. Furthermore, we compared the CNCs of two different manufacturers, Celluforce and Nanocrystacell. Celluforce CNC proved to be more adequate as an organogelator as it can bind more than 95% of oil by weight.
We determined the properties of the organogel that CNC forms using rheometry. It is desirable that it exhibits pseudoplastic properties and that the difference between the elastic and plastic modulus is large. The rheological properties of an organogel prepared with CNC were similar to the properties of organogels from polymers already in use as organogelators (e.g. HPMC). The strength of the gel and its rheological behavior was determined by the concentration of CNC in the solution prior to lyophilization.
Using differential dynamic calorimetry and scanning electron microscopy we examined morphological and physical properties of CNC. According to the DSC thermogram, the thermal decomposition temperature of Celluforce CNC is at 291º C, which corresponds to the literature data of thermal decomposition of CNCs with a well-organized crystal structure. Morphological differences between lyophilized samples of solutions with different concentrations of Celluforce CNC were not significant. However, there were noticeable differences between samples prepared with Celluforce and Nanocrystacell CNCs. Samples from Nanocrystacell CNC had a more fragmented structure with a wrinkled and torn surface compared to samples from Celluforce CNC. In samples from Celluforce the crystals are smooth and we observed strong crosslinking. Due to differences in crosslinking, structure and organization of CNC crystals from different manufacturers, different CNCs have a greater or lesser ability to bind oil.
We were unable to prepare a porous aerogel that would successfully gel the oil after the addition of amlodipine as a model active substance (BCS I) to a solution of CNC before lyophilization. Regarding the results, we can conclude that future research should focus on the use of CNC organogels for drug delivery, with the active ingredient being dispersed in the oil phase prior to organogelation with CNC.
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