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Because the number of variables in SLN preparation is very high and the development of an optimized method needs many experiments, we used
a series of screening tests by varying only one factor at a time to reduce the
number of independent variables and experiments. The
results of the screening tests indicated that
this system was highly influenced by microemulsion temperature during
the production. We set the temperature 5 0C
above melting point of the lipid. A reduction
of temperature can increase particle size.
On the other hand, the upper temperatures can decompose curcumin partly (31).The effect of
four different lipids, glyceryl
monosterate, cetyl palmitate, stearic acid and beeswax,
was studied on particle size(nm),PDI and stability of SLNs (Table 2). Cetyl
palmitate was chosen due to the smaller particle size and narrow size
distribution and most stability of SLNs(32).The effect of probe sonication on size, PDI and %LE of Cur-SLNs was
studied by varying amplitude and sonication time (Table 3). The best results
were observed in 30% amplitude at 5 min of sonication time. Increased in size
and PDI was observed when the amplitude of probe sonication increased to 40%. Applying higher amplitude or sonication time causes the formation of
unstable SLNs. This phenomenon is because of increasing particle size and PDI,
which was the result of the destruction of surfactant coatings due to apply higher
kinetic energy.
In addition the influence of homogenization time, mechanical stirring intensity
(rpm) and time of stirring on the particle size (nm) and PDI of SLNs have been
investigated. Then the mentioned parameters were fixed in 8min, 1000 rpm and 30
min respectively. Homogenization was performed at 10000 rpm for five different
time intervals (2, 5, 8 , 10 and 15  min).
Decreased in size and PDI was observed when 
homogenization time increased 
from  2  to 
8  min  while at 
10 min  both size and PDI were
increased. Homogenization is  one  of 
the  important  strategies 
of  applying  kinetic 
energy in order to  achieve  lower 
size  and  PDI. 
Applying  high  kinetic 
energy  for  longer 
period of time  may  lead 
to  instability  of  the
system.  This phenomenon is because of 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, an
optimum duration of homogenization will result in formation of stable particles
with uniform size distribution (Table 4)

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