Journal of Microencapsulation, 2013; 30(7): 657–666
ß 2013 Informa UK Ltd.
ISSN 0265-2048 print/ISSN 1464-5246 online
DOI: 10.3109/02652048.2013.774445
RESEARCH ARTICLE
Enhanced payload of lipid nanocarriers using supersaturated
solution prepared by solvent-mediated method
1
School of Life Sciences and Biotechnology, Korea University, Seoul, South Korea, 2Central Research Institute,
Kyung-Nong Co. Ltd., Kyungju, South Korea, 3Kolon Life Science Research Institute, Kyunggi, South Korea, and
4
Department of Packaging Science, Clemson University, Clemson, SC 29634-0370, USA
Abstract
With the aim to effectively enhance the payload for nanocarriers, supersaturated deltamethrin (SSD) solution was prepared using the solvent-mediated method to produce lipid nanocarriers by a combination
method of homogenization and sonication. In this study, deltamethrin was used as an active ingredient,
corn oil was used as a lipid medium, soybean lecithin and Tween-80 were used as surfactants. At 25 C, the
solubility of deltamethrin in SSD solution prepared by solvent-mediated method was 3.4 times and 1.5
times higher than that in saturated deltamethrin (SD) solution and that in SSD solution prepared by
thermal-mediated method, respectively. Therefore, compared to the use of SD solution for the production
of nanocarriers, the use of SSD solution significantly enhanced the payload, while keeping the encapsulation efficiency high. Particularly, nanocarriers produced from SSD solution prepared by solvent-mediated
method had the higher payload of 2.1 times and 4.4 times compared with preparations using SSD solution
prepared by thermal-mediated method and SD solution, respectively.
Keywords: corn oil, deltamethrin, soybean lecithin, supersaturated deltamethrin solution, payload
Introduction
having a mean diameter of 50–1000 nm, and being more
advantageous in general compared to the traditional colloidal carriers such as emulsions, liposomes, polymeric
microparticles and nanoparticles (Müller et al., 2000;
Wissing and Müller, 2002). SLN combines the advantages
of polymeric nanoparticles such as the control of drug
release and avoidance of drug leakage, and the advantages
of emulsions and liposomes such as low toxicity, good biocompatibility and higher bioavailability (Yuan et al., 2007).
However, SLNs also have a limited payload for active ingredients (Wissing and Müller 2002; Kheradmandnia et al.,
2010; Feng et al., 2011). Recently, nanostructured lipid
carriers, which are the second generation of lipid nanoparticles, have been developed to overcome some of the
limitations associated with SLNs. This was done by incorporating liquid lipids into the solid matrix of SLNs (Nam
et al., 2011). However, the amount of incorporated liquid
lipids was limited and the payload of nanocarriers was not
significantly improved (Yuan et al., 2007; Shen et al., 2010).
Nanocarrier systems provide stability to compounds that
are otherwise sensitive to conditions including ultraviolet
(UV) light or oxidation (Anton et al., 2008), and control the
release rate of incorporated compounds (Liu and Park,
2009). Therefore, nanocarriers are widely used in the cosmetics and so on (Mozafari et al., 2008). Especially, lipid
nanoparticles have received increased attention over the
last years based on their uniform size, shape, water-based
technology (avoidance of organic solvents), very high longterm stability and high and enhanced drug content (Patidar
et al., 2010). Moreover, lipid nanoparticles can control and
target drug release, improve the stability of pharmaceuticals, enhance oral bioavailability, reduce plasma profile
variability, and are easy to scale up and sterilize (Patidar
et al., 2010; Ekambaram et al., 2012). In particular, solid
lipid nanoparticles (SLNs) have been used based on their
attributes such as the property of a physical sunscreen,
20
13
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H. M. Nguyen1, I. C. Hwang2, D. K. Kweon3 and H. J. Park1,4
Address for correspondence: Professor Hyun-Jin Park, School of Life Sciences and Biotechnology, Korea University, 5 Ka, Anam-Dong, Sungbuk-Ku, Seoul
136-701, South Korea. Tel: þ82 2 3290 3450. Fax: þ82 2 953 5892. E-mail: [email protected]
(Received 28 Jun 2012; accepted 28 Jan 2013)
http://www.informahealthcare.com/mnc
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H. M. Nguyen et al.
Therefore, any other method that can effectively enhance
the payload of nanocarriers is needed.
Recently, supersaturated solution was used to enhance
the yield of synthetic reactions (Millqvist-Fureby et al.,
1998; Lee et al., 2008; Ha et al., 2010). Supersaturation is
defined as the solution that contains more dissolved solute
than its solubility limit (Lee et al., 2008). Some studies have
mentioned that supersaturated solutions could be prepared by thermal-mediated method and water-mediated
method (Lee et al., 2008; Ha et al., 2010). Thermalmediated method is used to obtain a supersaturated solution by having the saturated solution of active compound
at high temperature slowly cooled to a lower temperature
(Lee et al., 2008). In the water-mediated method, an active
compound is first dissolved in water, followed by mixing it
to a hydrophilic non-volatile medium such as hydrophilic
ionic liquids ([Emin][TfO], 1-ethyl-3-methylimidazolium
trifluoromethanesulfonate; [Bmim][TfO], 1-butyl-3-methylimidazolium trifluoromethanesulfonate). The water in the
resulting mixture is removed by the process of vacuum
evaporation at high temperature followed by slowly cooling
the mixture to a lower temperature to obtain a supersaturated solution (Ha et al., 2010). Consequently, the preparation of nanocarriers from supersaturated solutions using
the thermal-mediated method and water-mediated
method might improve the payload of nanocarriers.
Furthermore, these studies have also indicated that
water-mediated method gives higher solubility of active
compounds than thermal-mediated method (Lee et al.,
2008). However, supersaturation by water-mediated
method was only used for hydrophilic active compounds
and hydrophilic non-volatile medium (Lee et al., 2008;
Ha et al., 2010). As a result, a modified method which
is suitable for hydrophobic active compounds and hydrophobic non-volatile medium (such as vegetable oils) is
needed.
Deltamethrin, [(S)--3-phenoxybenzyl-(1R)-cis-3-(2,2dibromovinyl)-2,2-dimethylcyclopropane carboxylate], a
synthetic type II pyrethroid insecticide and one of the
most potent insecticides known (Ding et al., 2004), was
used as the hydrophobic active compound (core material)
in this work. In addition, corn oil, which is widely used in
the food industry and the pharmaceutical industry to manufacture resins, plastics, lubricants and fuels (Abdulkadir
and Abubakar, 2011), was used as the lipid medium for the
preparation of deltamethrin solution and production of
nanocarriers.
With the aim to establish a novel method to effectively
enhance the payload of nanocarriers in this study, they
were produced from supersaturated deltamethrin (SSD)
solution which was prepared by solvent-mediated
method. Encapsulation efficiency, payload and characteristics of nanocarriers produced from SSD solution prepared
by solvent-mediated method were compared to the
nanocarriers produced from saturated deltamethrin (SD)
solution (conventional method) and nanocarriers produced from SSD solution prepared by thermal-mediated
method.
Materials and methods
Materials
Soybean lecithin (Junsei Chemical Co. Ltd., Tokyo, Japan)
and Tween-80 (Samchun Pure Chemical, Seoul, Korea)
were used as surfactants. Corn oil (Sigma-Aldrich,
St. Louis, MO) was used as a lipid medium. Deltamethrin
(99%) was obtained from Kyung-Nong (Kyungju,
Kyungsangbuk-do, South Korea). All the other chemicals
were of analytical grade.
Effect of dissolution temperature on the solubility of
deltamethrin in corn oil
An excess amount of deltamethrin was added into corn oil
and stirred (approximately 500 rpm) at a specific temperature (25 C, 40 C, 45 C, 60 C, 80 C, 85 C) for 12 h. The
resulting solution was centrifuged at 3500 rcf for 1 min
(model HS-8, Hanil Science Industrial Co. Ltd., Daejeon,
Korea). The supernatant was obtained and diluted with
tetrahydrofuran (THF) in the appropriate ratio (v/v) to
determine the concentration of deltamethrin in corn oil.
This was done using the reverse-phase high-performance
liquid chromatography (HPLC) with a model 2690 pump
(Waters, Milford, MA), model 996 photodiode array detector (Waters, Milford, MA) and a Kromasil C18 column
(250 mm 4.6 mm; EKA Chemicals AB, Bohus, Sweden),
packed with 5 mm diameter particles. The mobile phase
was a mixture of acetonitrile and water (90:10, v/v).
The flow rate was 1 mL min1 at room temperature. The
detection wavelength of deltamethrin was 230 nm
(Nguyen et al., 2012).
Preparation of SD solution at 25 C
An excess amount of deltamethrin was added into corn oil
and stirred at 25 C for 24 h to get a saturated solution
(based on Figure 3(a), after 24 h, the increase of stirring
time did not significantly increase the solubility of deltamethrin). The resulting solution was centrifuged at 3500 rcf for
1 min (model HS-8, Hanil Science Industrial Co. Ltd,
Daejeon, Korea). The supernatant was obtained and
diluted with THF in the appropriate ratio (v/v) to determine the concentration of deltamethrin in corn oil. This
was done using HPLC with the same conditions as
described in section ‘‘Effect of dissolution temperature on
the solubility of deltamethrin in corn oil’’.
Preparation of SSD solution at 25 C using
thermal-mediated method
As shown in Figure 1(a), the excess amount of deltamethrin
was added into corn oil and stirred at 60 C for 24 h. The
SD solution at 60 C was slowly cooled to 25 C using model
BS-10 water bath (Jeio Tech, Seoul, Korea) at a rate of 1 C
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Enhanced payload of lipid nanocarriers
659
Figure 1. Scheme of preparation of SSD solutions. (a) Thermal-mediated method, (b) solvent-mediated method.
per 3 min and then incubated at 25 C for 1 h. After centrifugation at 3500 rcf for 1 min (model HS-8, Hanil Science
Industrial Co. Ltd., Daejeon, Korea), the supernatant
(supersaturated solution) was obtained to analyse the
deltamethrin content and was also used for production
of lipid nanocarriers or stability study of SSD solution
(referred as 0 h for re-crystallization observation).
Preparation of SSD solution at 25 C using solvent-mediated
method
As shown in Figure 1(b), first deltamethrin was fully dissolved in acetone at 25 C. Corn oil was then added to this
solution in the ratio of 1:1 (v/v), followed by mixing them
together at room temperature. After the clear solution was
obtained, acetone was removed using a rotary vacuum
evaporator (RE200, Yamato Scientific America Inc., Santa
Clara, CA) at 50 C for 30 min. The solution after evaporation was slowly cooled to 25 C using model BS-10 water
bath (Jeio Tech, Seoul, Korea) at rate of 1 C per 3 min and
then it was incubated at 25 C for 1 h. After centrifugation at
3500 rcf for 1 min (model HS-8, Hanil Science Industrial Co.
Ltd., Daejeon, Korea), the supernatant (supersaturated
solution) was obtained to analyse the deltamethrin content
and also used for the production of lipid nanocarriers or
stability study of SSD solution (referred as 0 h for re-crystallization observation).
Measurement of the remaining acetone in solution after
evaporation in supersaturation by solvent-mediated
method
Acetone was added into corn oil in the ratio of 1:1 (v/v),
followed by stirring to obtain a clear solution. Acetone contained in the resulted solution was removed using a rotary
vacuum evaporator with conditions as described in section
‘‘Preparation of SSD solution at 25 C using solventmediated method’’. At a defined time, the sample was withdrawn and diluted with THF for HPLC analysis. The HPLC
analysis was performed with the same conditions as
described in section ‘‘Effect of dissolution temperature on
the solubility of deltamethrin in corn oil’’. The detection
wavelength of acetone was 254 nm.
Production of lipid nanocarriers using deltamethrin solution
prepared by different methods
Lipid nanocarriers were produced using a combined
method of hot homogenization and sonication. Briefly,
250 mg of soybean lecithin and 250 mg of Tween-80 were
added to 48.5 mL of distilled water and stirred at 80 C for
1 h using model MS-3026 hot magnetic stirrer (Misung
Scientific Co. Ltd., Seoul, Korea). After stirring, the surfactant solution was cooled to 30 C. One and a half millilitres
of the prepared deltamethrin solution (SD solution or SSD
solution by thermal-mediated method or solvent-mediated
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H. M. Nguyen et al.
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method) were added to the surfactant solution. It is important to note that the SSD solution used for the production
of lipid nanocarriers was the SSD solution immediately
obtained after incubation at 25 C for 1 h and followed by
the removal of undissolved deltamethrin molecules using
the centrifuge (Figure 1). The resulting solution was homogenized using Ultra-TurraxÕ T 25 basic homogenizer
(IKAÕ -Werke, Staufen, Germany) at 19 000 rpm for 5 min
followed by sonication using a VCX 750 ultrasonic processor (Sonics & Materials, Newtown, CT) at 20 W for 8 min.
The resulting dispersion was poured in cooled water
(approximately from 22 C to 23 C) in the ratio of 1:9
(v/v) with stirring at 500 rpm to form lipid nanocarriers.
Measurement of particle size and zeta potential
Eindhoven, Holland). TEM studies were conducted at
KSBI (Seoul, Korea).
Release study
The lipid nanocarrier dispersions were kept in a model BS10 shaking water bath (Jeio Tech, Seoul, Korea) at 25 C and
80 rpm. At defined times the samples were withdrawn and
filtered through a 1 mm pore size cellulose ester membrane
filter. The residual amount of deltamethrin in the lipid
nanocarriers was determined by HPLC with the same
conditions as described in section ‘‘Effect of dissolution
temperature on the solubility of deltamethrin in corn oil’’.
Storage stability
The mean particle size, polydispersity index (PDI) and zeta
potential of lipid nanocarriers were determined using a
Nano-ZS nano size analyser (Malvern Zetasizer, Nano
Z-S; Malvern Instruments, Malvern, UK). Samples were
quickly diluted 20 times with distilled water (pH 5.9–6.1).
This resulting dispersion was added to a polystyrene latex
cell. The measurements were carried out at 25 C with a
detector angle of 90 .
The lipid nanocarrier dispersions were kept in an incubator
at 25 C. At defined times the samples were withdrawn and
filtered through a 1 mm pore size cellulose ester membrane
filter. The mean particle size, PDI and zeta potential of
lipid nanocarriers were determined using a Nano-ZS
nano size analyser (Malvern Zetasizer, Nano Z-S; Malvern
Instruments, Malvern, UK) with the same conditions as
described in section ‘‘Measurement of particle size and
zeta potential’’.
Encapsulation efficiency and payload
Data analysis
After being prepared, the lipid nanocarrier dispersions
were filtered using a cellulose ester membrane with a
1 mm pore size to remove unencapsulated deltamethrin
that had precipitated in the solution (Nguyen et al.,
2012). The dispersion after filtration was dissolved in THF
in the ratio of 1:3 (v/v). The encapsulated deltamethrin was
determined by HPLC with the same conditions as
described in section ‘‘Effect of dissolution temperature
on the solubility of deltamethrin in corn oil’’. The encapsulation efficiency and payload were calculated using the
following equations:
Encapsulation efficiency ð%Þ
Deltamethrin in nanoparticles ðmgÞ
100
¼
Initial added deltamethrin ðmgÞ
Payload ð%Þ
Deltamethrin in nanoparticles ðmgÞ
¼
100
Amount of nanoparticles ðmgÞ
ð1Þ
ð2Þ
Transmission electron microscopy (TEM)
After preparation, approximately 15 mL of the nanocarrier
dispersions were dropped onto the carbon-coated grids
for a brief period and the excess was drawn off with
filter paper. This step was repeated twice. Finally, the
grids were dried overnight and imaged using a TECNAI
G2 F30 transmission electron microscope (Philips-FEI,
The values are expressed as mean standard deviation.
Mean and standard deviation of the results from at least
three independent experiments were calculated using
Microsoft Excel software (Desai and Park, 2006). The significance of each mean property value was determined
with Duncan’s multiple range test using the SPSS software
version 16.0 (IBM SPSS, Armonk, NY) (p 5 0.05). Any two
means in the same figure followed by the same superscript
letter are not significantly different by Duncan’s multiple
range test.
Results and discussion
Effect of dissolution temperature of deltamethrin in corn oil
on payload of lipid nanocarriers
In this work, deltamethrin was first dissolved in corn oil at
different temperatures. After removing the undissolved
molecules by centrifugation, these resulting deltamethrin
solutions were used to produce lipid nanocarriers. The
production temperature of lipid nanocarriers was 5 C
higher than the dissolution temperature. As shown in
Figure 2(a,b), the dissolution temperatures gave a ‘‘direct
effect’’ on the solubility of deltamethrin in corn oil and
an ‘‘indirect’’ effect on the payload of lipid nanocarriers
produced using these deltamethrin solutions. As shown
in Figure 2(a), after stirring for 12 h, the concentration of
Enhanced payload of lipid nanocarriers
1400
1200
1000
800
600
400
a
80
a
c
30
20
40
10
20
b
200
a
a
0
20
30
40
50
60
70
80
40
60
0
90
0
20
40
60
80
100
0
120
Dissolution temperature (°C)
Dissolution temperature (°C)
Figure 2. (a) Effect of dissolution temperatures on solubility of deltamethrin in corn oil, (b) indirect effect of dissolution temperatures of deltamethrin in
corn oil on the encapsulation efficiency and the payload of lipid nanocarriers. Conditions: 1.5 mL of the prepared deltamethrin–corn oil solution, 250 mg of
soybean lecithin and 250 mg of Tween-80, 48.5 mL of distilled water. Data are plotted as the mean standard deviation (n ¼ 3).
(b) 3.5
(a) 250
Dissolution at 25°C
Remaining aceton in corn oil (%, v/v)
Deltamethrin concentration in corn oil (mM)
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a
Encapsulation efficiency
Payload
a
Payload (%)
(b) 100
Encapsulation efficiency (%)
Solubility of deltamethrin in corn oil (mM)
(a) 1600
661
Crystallization (thermal mediated method) at 25°C
200
Crystallization (solvent mediated method) at 25°C
Crystallization (solvent mediated method) at 45°C
150
100
50
0
0
20
40
60
Time (h)
80
3.0
2.5
2.0
1.5
1.0
0.5
0.0
10
20
30
40
50
60
70
Evaporation time (min)
Figure 3. (a) Effect of preparation methods, incubation time and incubation temperatures on the solubility and re-crystallization of deltamethrin in corn
oil. (b) Effect of evaporation time on the remaining concentration of acetone in supersaturation by solvent-mediated method. Data are plotted as the
mean standard deviation (n ¼ 3).
deltamethrin was only 37.5 0.8 mM at 25 C, while it was
245.4 39.4 mM and 1347 62.7 mM at 60 C and 85 C,
respectively. This indicated that the rise in the dissolution
temperature led to an increase in the solubility of deltamethrin in corn oil. Moreover, the higher solubility of deltamethrin in corn oil at a higher dissolution temperature
resulted in the higher payload of lipid nanocarriers produced from these solutions (Figure 2b). Particularly, the
payload of lipid nanocarriers was approximately 27 times
higher from the deltamethrin solution dissolved at 85 C
than the deltamethrin solution dissolved at 25 C
(28.74 0.79% and 1.08 0.03%). This is due to the fact
that the solubility of deltamethrin in corn oil at 85 C was
about 35 times higher than that at 25 C (Figure 2a). The
above results implied that the concentration of deltamethrin (core material) in corn oil (lipid matrix) strongly
affected the payload of nanocarriers. However, as evident
in Figure 2(b), the encapsulation efficiency was not greatly
affected by the production temperature of lipid nanocarriers and deltamethrin concentrations. Therefore, the preparation methods of deltamethrin solution played an
important role in enhancing the payload of nanocarriers,
since it resulted in the high solubility of deltamethrin in
corn oil.
Effect of preparation methods on solubility and
re-crystallization of deltamethrin in corn oil
In this study, three different methods were used to prepare
the deltamethrin solutions. In particular, the dissolution
method was used to obtain SD solution; thermal-mediated
method and solvent-mediated method were used to obtain
SSD solution. As shown in Figure 3(a), at 25 C, the concentration of deltamethrin in the saturated solution was
only 38.3 1.9 mM, while it was 84.5 6.4 mM and
130.5 8.14 mM in supersaturated solutions prepared by
thermal-mediated method and solvent-mediated method,
respectively, at time 0 h. Moreover, Figure 3(a) also indicates that after 2 days of incubation, the solubility of deltamethrin in supersaturated solutions prepared by solventmediated method was still higher than that of the saturated
solution, although re-crystallization happened and
decreased the solubility of deltamethrin in SSD solution
which may lead it to SD solution if it was incubated for
662
H. M. Nguyen et al.
Table 1. Solubility of deltamethrin in pure acetone, corn oil and corn oil
containing 0.49% (v/v) acetone at 25 C after stirring for 24 h.
Solution
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Pure acetone
Corn oil
Corn oil containing
0.49% (v/v) acetone1
Solubility of deltamethrin at 25 C
after stirring for 24 h (mM)
820.5 18.2
37.5 2.2
41 1.9
1
Experimental design: 49 mL of acetone was added into a vial containing
10 mL corn oil to form corn oil solution containing 0.49% (v/v) acetone.
Excess amount of deltamethrin was added into 0.49% (v/v) acetone-corn
oil solution and the vial was carefully covered with paraffin. After stirring
at 25 C for 24 h, the resulting solution was centrifuged at 3500 rcf for
1 min. The supernatant was obtained and diluted with THF in the appropriate ratio (v/v) to determine the concentration of deltamethrin in the
solution. This was done using HPLC with the same conditions as
described in section ‘‘Effect of dissolution temperature on the solubility
of deltamethrin in corn oil’’.
the longer time. However, this phenomenon (SSD solution
changed to SD solution) could be delayed due to the relatively high viscosity of corn oil, which can decrease the
diffusion rate from the bulk solution at the crystal/solution
interface and decrease the collision probability of deltamethrin molecules, leading to the slow re-crystallization of
‘‘excess’’ deltamethrin molecules in the supersaturated
solution (Mathlouthi and Genotelle, 1998; Lee et al.,
2008). Particularly, in the supersaturation by thermalmediated method, SD solution at high temperature
(60 C) was slowly cooled to low temperature (25 C).
Hence, SSD solution was obtained due to the difference
in solubility of deltamethrin at two different temperatures
and also due to the relatively high viscosity of corn oil,
which delayed the re-crystallization of deltamethrin as
explained above. In the supersaturation by solventmediated method, deltamethrin and corn oil were fully
dissolved in a solvent (acetone), followed by removal of
acetone using vacuum evaporation. The reason why a
mediator (acetone) was used was explained by the following reasons. Firstly, the dissolution of deltamethrin in corn
oil is simply understood by the detachment of deltamethrin
molecules from the solid surface at the solid–liquid interface and the transport of deltamethrin molecules from the
solid–liquid interface to the bulk corn oil solution (Lee
et al., 2008). Since considerable time was required to dissolve deltamethrin in corn oil, an alternative dissolution
process that used solvent (acetone) as mediator was used
to overcome this drawback. In this case, the dissolution
rate and solubility of deltamethrin in solvent should be
higher than in corn oil and the oil should be nonvolatile for the solvent removing step. Practically, at 25 C,
the solubility of deltamethrin in corn oil was 38.3 mM,
while it was approximately 21.4 times higher in acetone
(Table 1). Moreover, corn oil was non-volatile, which
was suitable for the evaporation step to remove acetone,
and had relatively high viscosity, which delayed the
re-crystallization of deltamethrin molecules. Therefore,
solvent-mediated method could be used to obtain an extremely supersaturated deltamethrin solution. As it is also
shown in Figure 3(a), in the supersaturation by solventmediated method, the incubation temperatures also
affected the solubility of deltamethrin in corn oil. During
incubation, the solubility of deltamethrin in SSD solution
incubated at 45 C was always higher than that incubated at
25 C. Moreover, this figure also indicated that the solubility
of deltamethrin in SSD solution prepared by the solventmediated method was approximately 2.5 times higher than
that prepared by thermal-mediated method. In addition,
further investigation was carried out to determine whether
the high solubility of deltamethrin in SSD solution prepared by solvent-mediated method was induced by the
remaining acetone in the solution after evaporation. As
shown in Figure 3(b), the remaining acetone was only
0.49% (v/v) after 30 min of evaporation. In addition, as
shown in Table 1, the solubility of deltamethrin in corn
oil containing 0.49% (v/v) acetone at 25 C after stirring
for 24 h was only 41 1.9 mM, while the practical result
of solubility of deltamethrin in SSD solution prepared by
solvent-mediated method was very high (130.5 mM). This
indicated that the additional solubility of deltamethrin in
the remaining acetone (0.49% (v/v)) was not a reason that
caused the extremely high solubility of deltamethrin in SSD
solution prepared by solvent-mediated method. As per the
results, the high solubility of deltamethrin in SSD solution
prepared by solvent-mediated method was only based on
the method.
Effects of deltamethrin solution prepared by different
methods on characteristics, encapsulation efficiency and
payload of lipid nanocarriers
Deltamethrin solutions prepared by different methods
were used to produce lipid nanocarriers. As shown in
Figure 4(a), the solubility of deltamethrin in SSD solution
prepared by solvent-mediated method at 25 C (the
supernatant immediately obtained after centrifugation in
Figure 1b) was 1.5 times and 3.4 times higher than that in
SSD solution prepared using thermal-mediated method
(the supernatant immediately obtained after centrifugation
in Figure 1a) and that in SD solution, respectively, at the
same temperature. In addition, as shown in Figure 3(a),
the SSD solution was stable enough for the production
of lipid nanocarriers because the total time taken for the
preparation was about 13 min (5 min for homogenization
and 8 min for sonication). However, Figure 4(b,c) indicates
that the preparation method of deltamethrin solution did
not greatly affect the characteristics of lipid nanocarriers
produced from these solutions. Particularly, the mean
particle size and zeta potential were in the range of
168–174 nm and 44 to 47 mV, respectively. Moreover,
as shown in Figure 5(a–c), most of lipid nanocarriers in
each figure had a relatively spherical shape with a size of
approximately 200 nm. This implied that the deltamethrin
solutions prepared by different methods did not greatly
affect the morphology of lipid nanocarriers.
However, the preparation method of deltamethrin solutions strongly affected the payload of lipid nanocarriers. As
Enhanced payload of lipid nanocarriers
(b)
200
120
100
b
80
60
40
a
a
a
150
a
a
Mean particle size
PDI
0.3
a
a
0.2
PDI
c
140
Mean particle size (nm)
Solubility of deltamethrin at 25°C (mM)
(a) 160
663
100
0.1
50
20
0
0
Dissolution
Thermal
mediation
Solvent
mediation
0.0
Dissolution
Thermal
mediation
Solvent
mediation
-50
a
a
a
Zeta potential (mV)
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(c) -60
-40
-30
-20
-10
0
Dissolution
Thermal
mediation
Solvent
mediation
Figure 4. (a) Effect of preparation methods on the solubility of deltamethrin in corn oil at 25 C. (b) Effect of deltamethrin solutions prepared by different
methods on mean particle size and PDI of lipid nanocarriers. (c) Effect of deltamethrin solutions prepared by different methods on zeta potential of lipid
nanocarriers. Conditions: 1.5 mL of the prepared deltamethrin–corn oil solution, 250 mg of soybean lecithin and 250 mg of Tween-80, 48.5 mL of distilled
water. Data are plotted as the mean standard deviation (n ¼ 3).
shown in Figure 6, the payload of lipid nanocarriers produced from SSD solution prepared by solvent-mediated
method (3.95 0.12%) was 2.1 times and 4.4 times higher
than that produced from SSD solution prepared by thermal-mediated method (1.92 0.11%) and that produced
from SD solution (0.89 0.01%), respectively. This was
due to the higher concentration of deltamethrin in SSD
solution prepared by solvent-mediated method compared
to that of SSD solution prepared by thermal-mediated
method and that of SD solution. According to the method
that incorporated liquid lipids into the solid matrix of SLN
to provide more space to accommodate active-ingredient
molecules and lead to an improved payload, a higher payload (only 1.42 times) was achieved (Shen et al., 2010),
while by using SSD solution prepared by solvent-mediated
method, the payload was significantly enhanced (4.4 times)
when compared to that of lipid nanocarriers produced
from SD solution.
in case of lipid nanocarriers produced from SSD solution
prepared by solvent-mediated method, the release rate
was the fastest. After 72 h, approximately 34.9% of deltamethrin was released from lipid nanocarriers produced from
SSD solution prepared by solvent-mediated method compared to 32.9% of lipid nanocarriers produced from SSD
solution prepared by thermal-mediated method and only
29.1% of lipid nanocarriers produced from SD solution.
A reasonable explanation is that the higher payload of
lipid nanocarriers produced from SSD solution will lead
to an increase in deltamethrin distribution nearby the
surface of nanocarriers (Yuan et al., 2007). Therefore, the
release rate of deltamethrin in lipid nanocarriers produced
from SSD solution was faster compared to that of lipid
nanocarriers prepared from SD solution.
Release study of lipid nanocarriers produced from SSD
solution (or SD solution)
Storage stability of lipid nanocarriers produced from SSD
solution or SD solution was carried out at 25 C. After 14
days of storage, the mean particle size of lipid nanocarriers
produced from SSD solution or SD solution was only
slightly reduced (Figure 8a). Particularly, the mean particle
size of lipid nanocarriers produced from SSD solution prepared by solvent-mediated method decreased from
178.4 1.1 nm to 163.2 2.3 nm after 14 days of storage,
Lipid nanocarriers produced from SSD solution or SD
solution were kept in a shaking water bath at 25 C and
80 rpm. As shown in Figure 7, the release rate of deltamethrin from lipid nanocarriers produced from SSD solution
or SD solution was gradual and relatively low. However,
Storage stability of lipid nanocarriers produced from SSD
solution (or SD solution)
H. M. Nguyen et al.
Figure 5. Transmission electron microscopy of lipid nanocarriers produced from deltamethrin solutions prepared by different methods. (a) Lipid nanocarriers produced from SD solution, (b) lipid nanocarriers produced from SSD solution prepared by thermal-mediated method, (c) lipid nanocarriers
produced from SSD solution prepared by solvent-mediated method. Conditions: 1.5 mL of the prepared deltamethrin–corn oil solution, 250 mg of soybean
lecithin and 250 mg of Tween-80, 48.5 mL of distilled water.
40
Dissolution (Saturation)
Thermal mediation
Solvent mediation
Deltamethrin release (%)
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664
30
20
10
0
0
Figure 6. Effect of deltamethrin solutions prepared by different methods
on encapsulation efficiency and payload of lipid nanocarriers.
Conditions: 1.5 mL of the prepared deltamethrin–corn oil solution,
250 mg of soybean lecithin and 250 mg of Tween-80, 48.5 mL of distilled
water. Data are plotted as the mean standard deviation (n ¼ 3).
while the mean particle size of lipid nanocarriers produced
from SD solution decreased from 177.2 1.7 nm to
165.2 1.9 nm. This could be due to the fact that the
release of deltamethrin molecules from lipid nanocarriers
resulted in the decrease in the mean particle size. In
20
40
Time (h)
60
80
Figure 7. Release profiles of lipid nanocarriers produced from deltamethrin solution prepared by different methods. Conditions: 1.5 mL of the
prepared deltamethrin–corn oil solution, 250 mg of soybean lecithin and
250 mg of Tween-80, 48.5 mL of distilled water. Data are plotted as the
mean standard deviation (n ¼ 2).
addition, during the study period, the PDI of lipid nanocarriers produced from SSD solution or SD solution did not
significantly change and the value was still small (Figure
8b). This implies that the lipid nanocarriers were prevented
Enhanced payload of lipid nanocarriers
665
(b) 0.35
(a) 200
180
0.30
0.25
140
120
0.20
PDI
Mean particle size (nm)
160
100
0.15
80
60
0.10
40
Dissolution (Saturation)
Thermal mediation
Solvent mediation
20
Dissolution (Saturation)
Thermal mediation
Solvent mediation
0.05
0.00
0
0
2
4
6
8
10
12
14
16
0
2
4
6
8
10
12
14
16
Storage time (day)
Storage time (day)
-40
Zeta potential (mV)
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For personal use only.
(c) -50
-30
-20
-10
Dissolution (Saturation)
Thermal mediation
Solvent mediation
0
0
2
4
6
8
10
Storage time (day)
12
14
16
Figure 8. Storage stability at 25 C of lipid nanocarriers produced from deltamethrin solution prepared by different methods. (a) Mean particle size, (b) PDI,
(c) Zeta potential. Conditions: 1.5 mL of the prepared deltamethrin–corn oil solution, 250 mg of soybean lecithin and 250 mg of Tween-80, 48.5 mL of
distilled water. Data are plotted as the mean standard deviation (n ¼ 2).
from flocculation and fusion (which forms a single larger
nanocarrier from two smaller nanocarriers), and the lipid
nanocarrier dispersions were stable during storage. As
also shown in Figure 8(c), the zeta potential of lipid nanocarriers produced from SSD solution prepared by solventmediated method decreased from 46.9 0.8 mV to
39.3 0.6 mV after 14 days of storage, while the zeta
potential of lipid nanocarriers produced from SD solution
decreased from 46.3 0.5 mV to 40.6 0.3 mV.
Although the zeta potential of the lipid nanocarriers produced from SSD solution or SD solution was slightly
decreased during storage, the remaining zeta potential
was still relatively high. This indicates that the electrostatic
repulsive force was still strong enough to maintain the stability of lipid nanocarriers. The results from Figure 8(a–c)
imply that the lipid nanocarriers produced from SSD solution or SD solution were stable under storage conditions,
and the lipid nanocarriers produced from SSD solution
prepared by solvent-mediated method were as stable as
the lipid nanocarriers produced from SD solution.
oil compared to that of saturated solution and also higher
than that of supersaturation by thermal-mediated method.
Therefore, by using the SSD solution prepared using solvent-mediated method for producing lipid nanocarriers,
the payload of lipid nanocarriers was 4.4 times higher
than that using SD solution, while the encapsulation efficiency was still relatively high. As a result, this is a very
probable method for enhancing the payload of nanocarriers. Moreover, by changing the active compounds (core
materials), this method also can be widely applied in other
fields such as food, cosmetics and pharmaceutical
industries.
Declaration of interest
The authors report no conflicts of interest. The authors
alone are responsible for the content and writing of the
article. This study was partly supported by a Grant of
Kyung-Nong Company and Korea University, Republic of
Korea.
Conclusions
In summary, SSD solution was successfully prepared by
solvent-mediated method and thermal-mediated method.
Particularly, supersaturation by solvent-mediated method
gave the extremely higher solubility of deltamethrin in corn
References
Abdulkadir M, Abubakar GI. Production and refining of corn oil from
hominy feed: A by-product of dehulling operation. J Eng Appl Sci,
2011;6:22–8.
Journal of Microencapsulation Downloaded from informahealthcare.com by Korea University on 01/03/14
For personal use only.
666
H. M. Nguyen et al.
Anton N, Benoit JP, Saulnier P. Design and production of nanoparticles
formulated from nano-emulsion templates. J Controlled Release,
2008;128:185–99.
Desai KG, Park HJ. Effect of manufacturing parameters on the characteristics of vitamin C encapsulated tripolyphosphate-chitosan microspheres prepared by spray-drying. J Microencapsulation, 2006;
23:91–103.
Ding Y, White CA, Muralidhara S, Bruckner JV, Bartlett MG. Determination
of deltamethrin and its metabolite 3-phenoxybenzoic acid in male rat
plasma by high-performance liquid chromatography. J Chromatogr B
Anal Technol Biomed Life Sci, 2004;810:221–7.
Ekambaram P, Abdul-Hasan-Sathali A, Riyanka K. Solid lipid nanoparticles: A review. Sci Revs Chem Commun, 2012;2:80–102.
Feng F, Zheng D, Zhang D, Duan C, Wang Y, Jia L, Wang F, Liu Y,
Gao Q, Zhang Q. Preparation, characterization and biodistribution
of nanostructured lipid carriers for parenteral delivery of bifendate.
J Microencapsulation, 2011;28:280–5.
Ha SH, Nguyen HM, Koo YM. Enhanced production of fructose palmitate
by lipase-catalyzed esterification in ionic liquids. Biotechnol Bioprocess
Eng, 2010;15:126–30.
Kheradmandnia S, Vasheghani-Farahani E, Nosrati M, Atyabi F.
Preparation and characterization of ketoprofen-loaded solid lipid nanoparticles made from beeswax and carnauba wax. Nanomedicine,
2010;6:753–9.
Lee SH, Dang DT, Ha SH, Chang WJ, Koo YM. Lipase-catalyzed synthesis of
fatty acid sugar ester using extremely supersaturated sugar solution in
ionic liquids. Biotechnol Bioeng, 2008;99:1–8.
Liu N, Park HJ. Chitosan-coated nanoliposome as vitamin E carrier.
J Microencapsulation, 2009;26:235–42.
Mathlouthi M, Genotelle J. Role of water in sucrose crystallization.
Carbohydr Polym, 1998;37:335–42.
Millqvist-Fureby A, Gao C, Vulfson EN. Regioselective synthesis of ethoxylated glycoside esters using -glucosidase in supersaturated solution and
lipases in organic solvents. Biotechnol Bioeng, 1998;59:747–53.
Mozafari MR, Johnson C, Hatziantoniou S, Demetzos C. Nanoliposomes
and their applications in food nanotechnology. J Liposome Res,
2008;18:309–27.
Müller HR, Mäder K, Gohla S. Solid lipid nanoparticles (SLN) for controlled
drug delivery – A review of the state of the art. Eur J Pharm Biopharm,
2000;50:161–77.
Nam SH, Ji XY, Park JS. Investigation of tacrolimus loaded nano-structured
lipid carriers for topical drug delivery. Bull Korean Chem Soc,
2011;32:956–60.
Nguyen HM, Hwang IC, Park JW, Park HJ. Enhanced payload and photoprotection for pesticides using nanostructured lipid carriers with corn oil
as liquid lipid. J Microencapsulation, 2012;29:596–604.
Patidar A, Thakur DS, Kumar P, Verma J. A review on novel lipid based
nanocarriers. Int J Pharm Pharm Sci, 2010;2:30–5.
Shen J, Sun M, Ping Q, Ying Z, Liu W. Incorporation of liquid lipid in lipid
nanoparticles for ocular drug delivery enhancement. Nanotechnology,
2010;21:025101.
Wissing SA, Müller RH. Solid lipid nanoparticles as carrier for sunscreens:
In vitro release and in vivo skin penetration. J Controlled Release,
2002;81:225–33.
Yuan H, Wang LL, Du YZ, You J, Hu FQ, Zeng S. Preparation
and characteristics of nanostructured lipid carriers for controlreleasing progesterone by melt-emulsification. Colloids Surf B,
2007;60:174–9.