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November 2015
different vegetable oils. The percen- tage of lipid phase (blend of solid lipid and liquid oil) on the miniemulsions was kept constant being 5% (w/w) of the total formulation, while the liquid oil content in the lipid phase was varied in to different solid lipid to oil ratios.
The mean particle size (Z.average), the polydispersity index and zeta potential of the lipid nanocarriers are illustra- ted in Figures 1 and 2, respectively. NLCs with particle sizes ranging from 126 to 228 nm and with relatively uni- form particle size distributions (PDI of 0.145 - 0.293) were obtained. It could be observed in Figure 1, that the ave- rage size of the NLC decreases with the increase of liquid oil amount up to 80%. This may be due to that the liquid oil could be more easily dispersed into the aqueous phase and contribu- ted to smaller particles (Zheng et al. 2013). On the other hand, the diffe- rence on the fatty acid compositions of the used vegetable oils seems to has low influence on the particle size of final NLCs being this affected by the percentage of oil on the lipid ma- trix. The lowest average sizes were obtained with 40:60 and 20:80 ratios, independently of the used oil, with an exception for the 60:40 (capric acid: sunflower oil) ratio which also de- monstrated a low value.
The physical stability of colloidal sys- tems is determined in function of zeta potential, which quantifies the particle charge. In theory, higher values of zeta potential, either positive or negative, end to stabilize the suspension and aggregation phenomena are less likely to occur for charged particles with
zeta potential|
(>|30|), due to
the electros-
tatic repulsion
between par-
ticles with the
same elec-
trical charge
(Pinto et al.
2014) The de-
termined zeta
potential values
of the formula-
ted NLCs ran-
ged between −17.1 and – 23.0 mV (Fi- gure 2), which predicts a short-term stability to the particles.
Effect of fatty acid chain length of the solid lipid on NLCs size and surface charge
From the previous study it was cho- sen the more suitable percentage of vegetable oil on the lipid phase, that corresponds to the 40:60 ratio, and it was kept constant. The NLCs were prepared with saturated solid fatty acids ranging from C10 to C18, in order to study the effect of the chain length on particle size and physical stability
The particle sizes and PDI of the NLCs, assessed by DLS, are presented in Figure 3. It can be observed that in-
creasing the length of the solid fatty acid demons- trated to have low influence on NLCs size. All the formu- lations with the different vegetable oils had little variations on particle size with the in- crease of the chain length of the solid lipid. Des- pite that, lipid nanocarriers made from
sunflower oil had the lowest particle sizes which decrease with the in- crease of the solid fat chain length (136 nm with C10 and 76 nm with C18). This could be due to a higher proportion of linoleic acid, an unsaturated lipid, on sunflower oil composition when com- pared with the other oils. The polydis- persity parameter, gives an important information concerning on sample homogeneity (Pinto et al. 2014). The obtained PDI values were below 0.290, which reflects relatively homogeneous nanoparticles. Regarding the physical stability of the obtained lipid nanocar- riers, it was found that the increase in the fatty acid chain length had the same low effect that was noticed with the particles size. The zeta potential values were above -22.0 mV for all the NLCs formulations with the different vegetable oils, indicating a short-term stability to the particles and that this parameter needs to be improved.
Through this work, it could be concluded that all formulations led to the development of suitable NLCs, presenting characteristics that would render them as promising nanocar- riers with high incorporation poten- tial of active ingredients. Lipid nano- carriers with particle sizes ranging from 76 to 228 nm and with a narrow particle size distribution were obtai- ned by the miniemulsion methodo- logy. The percentage of vegetable oil in the lipids phase of the miniemul- sions demonstrated to have influence on particle size of NLCs. In a contrary way, the differences on the fatty acids composition of the vegetable oils and the fatty acid chain length of solid li- pids had a low impact in both size and surface charge of the obtained lipid nanocarriers. Negative zeta potential values above -23.0 were determined, which characterizes the particles with a short-term physical stability, being
0 -5 -10 -15 -20 -25
Fiiguurere2 2– Z–etZaeptoatepnotitael nvatliuaelsvoaflNuLeCssosfynNthLeCssizesdywnith edsiffiezreednt
with different vegetable oils and solid lipid to oil ratios.
vegetable oils and solid lipid to oil ratios
Figure 3 – Z.average and PDI data based on particle size measurements. Influence of fatty acid chain length of the solid lipid on NLCs size, with a constant oil percentage (40:60, solid lipid: vegetable oil).
80:20 60:40 40:60 20:80 0:100 80:20 60:40 40:60 20:80 0:100 80:20 60:40 40:60 20:80 0:100 80:20 60:40 40:60 20:80 0:100

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