Nanostructured lipid carriers (NLCs) represent a promising delivery system for poorly soluble drugs. Liquid lipids enhance the drug loading capacity of NLCs by enabling the formation of an amorphous matrix within the solid lipid, which is the main advantage over solid lipid nanoparticles. In a previous study, NLCs with incorporated model active pharmaceutical ingredient X (API X) were developed, but they were not stable. Therefore, the purpose of this master's thesis was to determine the reason for the instability and to optimize the composition of NLCs so that they retain drug loading in an isotonic environment for at least 7 days.
NLCs were made from Compritol 888 ATO, Captex 200, PEG 2000 DSPE, and API X using the homogenization method. The parameters size, polydispersity index (PI), zeta potential (ZP), encapsulation efficiency (EE), and drug loading were evaluated. In the design of experiments (DOE), we varied the parameters Captex 200, Kolliphor HS 15, and API X with the aim of optimizing the NLC composition. In DOE2, smaller quantities of Captex 200, Kolliphor HS 15, and API X were incorporated into NLCs compared to DOE1. In both experiments, the stability of NLCs and their parameters were characterized.
NLCs in an isotonic medium were similar in size to those prepared in demineralized water, and a significant decrease in EE was observed for both samples after 4 days of storage. We found that API X started to crystallize from the NLCs within one day and that NLC are physically unstable. The success of incorporation is significantly influenced by excipients, so we evaluated the solubility of API X in various lipids and found that it has the highest solubility in a mixture of Captex 200 and Kolliphor HS 15 in a ratio of 1:3, and the second highest in Captex 200. The DOE1 samples were as large as 179.5 nm with a PI below 0.3, a ZP of up to –20.71 mV, and an EE of 70–80%. Since the EE dropped significantly in all samples after the first day, we reduced the amount of excipients used in DOE2. This resulted in smaller particles with a higher EE of up to 95.87%, which were stable for 7 days. We found that NLCs can incorporate a certain amount of drug, and when this amount is exceeded, it crystallizes within a few days and precipitates out of the NLCs. With the optimized composition, we produced NLCs with a size below 100 nm, a PI below 0.3, a ZP of around –16 mV, and an EE of 90–97%. Particles were stable after 2 days, with EE decreasing by approximately 3%.
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