Because the number of variables in SLN preparation is very high and the development of an optimized method needs many experiments, we useda series of screening tests by varying only one factor at a time to reduce thenumber of independent variables and experiments.
Theresults of the screening tests indicated thatthis system was highly influenced by microemulsion temperature duringthe production. We set the temperature 5 0Cabove melting point of the lipid. A decreasein applying temperature can increase particlesize. On the other hand, the upper temperatures can decompose curcumin readily(31).The effect offour different lipids, glycerylmonosterate, cetyl palmitate, stearic acid and beeswax,was studied on particle size(nm),PDI and stability of SLNs (Table 2).
Cetylpalmitate was chosen due to the smaller particle size and narrow sizedistribution and most stability of SLNs(32).The effect of probe sonication on size, PDI and %LE of Cur-SLNs wasstudied by varying amplitude and sonication time (Table 3). The best resultswere observed in 30% amplitude at 5 min sonication time. Increased in size andPDI was observed when the amplitude of probe sonication increased to 40%.
It was observed that the application of higher amplitude or sonication time caused the formation of unstable SLNs, increasingparticle size and PDI, which was the result of the destruction of surfactantcoatings because of more kinetic energy. We also investigatedinfluence of homogenization time, mechanical stirring intensity (rpm) and timeon the particle size (nm) and PDI of SLNs and fixed them in 8min, 1000rpm and30 min respectively. Homogenization was performed at 10000 rpm for fivedifferent time intervals 2, 5, 8 , 10 and 15 min.
Dcreased in size and PDI was observed when homogenization time increased from 2 to 8 min while at 10 min both size and PDI wereincreasing. Homogenization is one of the important strategies of applying kinetic energy to achieve lower size and PDI. Applying high kinetic energy for longer time may lead to instability of formed lipidic structures thereby resulting into aggregation and formation of larger particles.
Size and PDI were higher at 2 and 5 min when compared to 8 min due to insufficient homogenization. Therefore, anoptimum duration of homogenization will result in formation of stable particleswith uniform size distribution (Table 4)