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Many new therapeutic candidates and active pharmaceutical ingredients (APIs) are poorly soluble in an aqueous environment, resulting in their reduced bioavailability. A promising way of enhancing the release of an API and, thus, its bioavailability seems to be the use of liquid oil marbles (LOMs). An LOM system behaves as a solid form but consists of an oil droplet in which an already dissolved API is encapsulated by a powder. This study aims to optimize the oil/powder combination for the development of such systems. LOMs were successfully prepared for 15 oil/powder combinations, and the following properties were investigated: particle mass fraction, dissolution time, and mechanical stability. Furthermore, the release of API from both LOMs and LOMs encapsulated into gelatine capsules was studied.
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Pharmaceutics, Drug Delivery and Pharmaceutical Technology
Liquid Oil Marbles: Increasing the Bioavailability of Poorly
Water-Soluble Drugs
Petra Jansk
a, Ond
rej Rychecký, Ale
s Zadra
zil, Franti
anek, Jitka
Department of Chemical Engineering, Chemical Robotics Laboratory, University of Chemistry and Technology Prague, Technick
a 5, 166 28 Prague 6,
Czech Republic
article info
Article history:
Received 18 December 2018
Revised 23 January 2019
Accepted 28 January 2019
Available online 2 February 2019
liquid oil marbles
enhanced release
Many new therapeutic candidates and active pharmaceutical ingredients (APIs) are poorly soluble in an
aqueous environment, resulting in their reduced bioavailability. A promising way of enhancing the release
of an API and, thus, its bioavailability seems to be the use of liquid oil marbles (LOMs). An LOM system
behaves as a solid form but consists of an oil droplet in which an already dissolved API is encapsulated by a
powder. This study aims to optimize the oil/powder combination for the development of such systems.
LOMs were successfully prepared for 15 oil/powder combinations, and the following properties were
investigated: particle mass fraction, dissolution time, and mechanical stability. Furthermore, the release of
API from both LOMs and LOMs encapsulated into gelatine capsules was studied.
©2019 American Pharmacists Association
. Published by Elsevier Inc. All rights reserved.
During recent years, the number of poorly water-soluble drugs
increased signicantly.
The solubility in water is, however, one of
the most important parameters of drug usage and drug delivery.
For some substances, it is possible to obtain a pharmacological
response even at a very low concentration (e.g., hormones),
whereas for the others (antibiotics, etc.), higher concentrations are
required. Hence, the solubility issue emerges. Low bioavailability of
newly discovered active pharmaceutical ingredients (APIs) is one of
the most challenging pursuits in pharmaceutical development,
especially for orally administered drugs.
The bioavailability of such
APIs is mostly limited during their release followed by the ab-
sorption in the gastrointestinal tract. Several approaches, mostly
based on physical and chemical modication of the drug sub-
stances, have been reported to enhance their solubility and thus
bioavailability. The physical modication includes particle size
reduction (micronization, nanosuspension),
crystal modication
(amorphous form, co-crystallization),
and drug dispersion (solid
Changing pH, salt formation, and complexation are
techniques that belong to the category of chemical modication.
Another technique for dissolution enhancement of poorly
water-soluble drugs is liquisolid technique.
This technique is
described as the incorporation of active substances as a liquid phase
(solution, suspension, or emulsion) into highly porous support
(solid state) to form a dry nonsticking powder with properties
suitable for further processing. The advantages of such a technique
are the low production cost, increased bioavailability, and the
possibility to prepare pharmaceutical forms with controlled release
ability and pH-independent drug release prole.
On the other
hand, this technique is not suitable for drugs with a high dose of API
because the oil content is only 17%-36% and thus a large tablet must
be manufactured.
Incorporating a poorly soluble drug into liquid phase and
transforming this system into a solid form represents a novel
approach to increase its bioavailability. Liquid oil marbles (LOMs)
can be considered as such incorporation, where the LOM is formed
from liquid droplet covered by powder. Liquid marbles (LMs) were
rst presented in 2001 by Aussillous and Qu
who introduced
aqueous LMs. The LMs behave as soft solids, which gives them
excellent nonwetting and nonadhesive properties in contact with
various surfaces. Particles of the coating powders do not absorb
inside of the liquid core and stay on the surface in comparison with
liquisolid formulation.
In recent years, aqueous LMs have been intensively studied.
On the contrary, only a few reports exist about LMs with encap-
sulated oil instead of aqueous phase. The preparation of LOMs is a
much more challenging task than liquid aqueous marbles
due to the relatively low surface tension of many oils and relatively
high surface energy of many solid particles. Potential uses of LMs
Abbreviations used: API, active pharmaceutical ingredient; LM, liquid marble;
LOM, liquid oil marble; PTFE, polytetrauoroethylene; SEM, scanning electron
This article contains supplementary material available from the authors by request
or via the Internet at
*Correspondence to: Jitka
a (Telephone: þ420 220444460).
E-mail address: (J.
Contents lists available at ScienceDirect
Journal of Pharmaceutical Sciences
journal homepage:
0022-3549/©2019 American Pharmacists Association
. Published by Elsevier Inc. All rights reserved.
Journal of Pharmaceutical Sciences 108 (2019) 2136-2142
have been studied and tested for a variety of applications such as
microuidics, miniature reactors, sensors, accelerometers, and gas
storage and pressure-sensitive adhesives because of their ability to
encapsulate functional materials.
The LOMs are different in the
ratio between the solid and liquid phases by comparison with LMs.
The LOMs can contain around 10%-15% of oils relative to the total
mass, whereas LMs can contain up to 90% of aqueous phase.
The main goal of this article was to design and prepare a capsule
containing LOMs with a poorly water-soluble drug (API). A wide
range of materials, both oils and powders, were tested to fabricate
stable LOMs (stability regarding at least a few weeks). Based on the
characterization of oils and powders concerning the preparation of
LOMs, the best combination was chosen to fabricate a gelatine
capsule with encapsulated LOMs.
Materials and Methods
The following powders were used for fabrication of the LOMs:
agarose, aluminum hydroxide, calcium carbonate, carbon SLG,
carboxymethylcellulose, D-sorbitol, dextran, gelatine, glucose,
hydroxypropyl methylcellulose, chitosan, lactose, maltodextrin,
methylcellulose, polytetrauoroethylene (PTFE, 35
m), and yeast
extract (all from Sigma-Aldrich), wheat our (Penam, Brno, Czech
Republic), sodium alginate (SAFC), starch (Natura, Czech Republic),
glycine and sodium hydroxide (Penta, Prague, Czech Republic). As
oil phase, rapeseed oil (Br
olio), macadamia oil (Saloos, Opava, Czech
Republic), and castor oil (Saloos) were used. Other chemicals used
for the experiments were sodium uoride (Penta), Avicel (Fluka),
ethanol (Sigma-Aldrich), potassium chloride (Lachner, Neratovice,
Czech Republic), and gelatine capsules (Zentiva, Praha-Dolní
echolupy, Czech Republic).
Liquid Oil Marble Preparation
The preparation procedure for LOMs was as follows. The solid
powders were spread on a Petri dish, and a single oil droplet was
dropped onto it (10, 20, 50, and 100
L). A positive displacement
pipette (Gilson Microman Positive Displacement M50 or M1000)
was used for handling viscous oils. The oil droplet (placed on the
powder) was gently shaken in a circular motion to ensure complete
coverage of the oil droplet surface by the particles of the powder (to
form liquid oil marble), and the fabricated LOM was carefully
transferred to a separate Petri dish.
Oil Characterization
The physical properties of oils (viscosity, density, and surface
tension) were characterized. The rheological properties of oils
were determined by the rotational viscometer Rheolab QC (Anton
Paar) at 25
C, over a wide range of shear rates (from 10 to 160 s
corresponding to 2.32 to 37.14 rpm, respectively). The shear
stress, shear rate, viscosity, and velocity were also measured. The
drop shape analysis method (Theta; Biolin Scientic) was used to
determine the surface tension (oil-air interface), and the surface
tension was calculated using the Young-Laplace t. The loading
capacity of API in oils was experimentally measured as follows: 1
g of APIs was mixed with 9 g of oil for 2 h on a magnetic stirrer
(at 600 rpm). In the next step, 0.5 g of API was added and mixed
at 600 rpm for 2 h, and if the API was completely dissolved, this
step was repeated until the maximal loading capacity of the oil
was reached.
Particle Characterization
The size distribution of particles was measured by static light
scattering in a ow cell (Horiba Partica LA 950V2) and evaluated
using the Fraunhofer kernel. Ethanol was used as a disperse phase
for the measurement as the particles are not soluble in ethanol.
Particles morphology was investigated by scanning electron
microscopy (SEM; Jeol JCM-5700). The samples were coated with
5-nm-thin gold layer, to prevent charging during SEM measure-
ment, using the sputter coater Emitech K550X.
Particle-Oil Interactions
The drop shape analysis system (Theta; Biolin Scientic) was
used to determine the time-dependent contact angle between
liquid (castor, macadamia, and rapeseed oils) and powders
(aluminum hydroxide, lactose, methylcellulose, starch, and yeast
extract). A pellet (10 mm in diameter, applied pressure of 7 metric
tons) was made from each powder using the Carver 4350 Bench Top
Laboratory Pellet Press.
Mass Fraction of Solid Particle Evaluation
The pipetted volume used for formation of liquid oil droplet was
weighted ðm
Þto precisely dene the mass of the oil core (each
measurement was repeated 10 times); 10 LOMs were fabricated
and weighted ðm
Þ. The total mass of LOMs was evaluated, and
mass fraction was calculated according to Equation 1:
where ðm
Þis the mass of the particles, m
is the
mass of the LOMs, and w
is the mass fraction of adhered and
absorbed particles in the oil droplet.
The size of the LOMs was evaluated using image analysis (NIS-
Elements). The picture of a Petri dish with LOMs was taken from the
top view using the camera (digital camera Olympus E-620).
The Stability of Liquid Oil Marbles
The mechanical stability and elasticity of LOMs were analyzed
by the texture analyzer (Brookeld CT3, TA44)d10 samples for a
given combination of oil and powder. The texture analyzer was set
to press the LOMs to the 50% of their size, the test speed was set to
0.1 mm/s and the distance traveled by the probe as a function of the
load was recorded. The stability of LOMs in time was also tested.
Fabricated LOMs were placed into the Petri dish (laboratory con-
ditions, 25
C), and every day, LOMs were observed, shaken, and a
picture of them was taken to investigate their long-term stability.
Dissolution Study of APIs From the Liquid Oil Marbles
The dissolution study of LOMs formed from 10
L of the oil
phase with dissolved APIs was performed. For release experiments,
an LOM was placed in a vessel tted with 200 mL of hydrochloric
acid-potassium chloride buffer (pH 1.4) and kept at 37 ±0.5
C with
rotating speed of 120 rpm. The hydrochloric acid-potassium chlo-
ride buffer was prepared by mixing 50 mL of 0.2M potassium
chloride with 41.4 mL of 0.2M hydrochloric acid. The API release
from LOMs was measured at a specic wavelength of given API
(250 nm) by time-dependent UV/vis spectrophotometry (Pion
DISS Proler). The release rate from the LOMs was compared to
the dissolution rate of pure APIs in the buffer. The dissolution study
was performed in triplicates.
P. Jansk
a et al. / Journal of Pharmaceutical Sciences 108 (2019) 2136-2142 2137
Capsules Containing Liquid Oil Marbles
The LOMs (10
L of the oil phase with dissolved APIs) were lled
into hard gelatine capsules and put into the dissolution vessels. The
composition of the gelatine capsule was gelatine (44%), glycerol
(24%), and water (32%), and the internal volume of the gelatine
capsule was 0.81 mL (size 0). Hydrochloric acid-potassium chloride
buffer (100 mM, pH 1.4) was used as a medium for dissolution
experiments. A single capsule was placed in 1000 mL of hydro-
chloric acid-potassium chloride buffer and kept at 37 ±1
C with a
rotating speed of 120 rpm. The time-dependent UV/vis spectrum
was measured. The dissolution study was performed in triplicates.
Results and Discussion
In this study, LOMs are demonstrated as a new approach to
increasing the dissolution rate and, thus, the bioavailability of a
poorly soluble drug. Suitable combinations of oil and powder for
the fabrication of LOMs were experimentally investigated with the
aim of enhancing drug release after oral administration.
The Interaction Between Powders and Oils: An Initial Parametric
Our initial parametric study was performed with 20 different
powders, including PTFE, the most common material for the
preparation of aqueous LMs, and rapeseed oil. The handbook of
pharmaceutical excipients
was used to identify suitable powder
candidates for the fabrication of drug carriers for in vivo use. When
an oil droplet was dropped onto the powder and followed by gentle
shaking, 4 different cases were observed (see Fig. 1).
Case 1 represented the formation of a perfectLOM and was only
observed for PTFE powder. The LOM was stable, and the volume of
the oil phase leaked out when the LOM was cut in half. This indicates
that the PTFE particles were not present in the oil phase. Thus, PTFE
particles are an ideal material for the fabrication of LOMs. PTFE
particles are commonly used for the preparation of LMs (with an
aqueous core) because of their hydrophobic character. Furthermore,
PTFE particles are also known as a material that repels oils because of
their oleophobic properties
; however, PTFE microparticles are not
approved by the Food and Drug Administration as excipients for oral
delivery and thus were excluded from our further studies.
In case 2, rapeseed oil soaked through the layer of particles and
no LOM or any other structured particle was formed. This was
observed for carbon SLG, carbopol, carboxymethylcellulose,
glycine, maltodextrin, and sodium alginate. Consequently, these
powders were also excluded from our further investigations.
In case 3, an LOM was formed; however, after cutting the LOM
with a scalpel (at room temperature), a large number of particles
were found to be present in the oil phase. Case 3 was observed for
aluminum hydroxide, dextran, our, lactose, starch, and yeast
In case 4, similar marbles as in case 3 were formed. Moreover,
there was swelling of the whole LOM. Case 4 was observed for the
following powders: agarose, Avicel, calcium carbonate, D-sorbitol,
gelatine, glucose, hydroxypropyl methylcellulose, chitosan, potas-
sium chloride, and sodium uoride.
Although cases 3 and 4 did not correspond to perfectLOMs
(i.e., a liquid-oil core covered by a shell consisting of solid particles
as in case 1) and the coating particles were also present inside the
oil core, it still fullled the requirement that the oil was encapsu-
lated within the powder and that the whole structure behaves as a
soft solid without any leakage of the oil content. Therefore, selected
powders from cases 3 and 4 were chosen for LOM preparation.
From 3 groups of chemical structures (inorganic, high molecular
weight, and sugar), 5 powders were chosen. Based on interaction
with oils, at least one representative powder was chosen from each
group. From the rst group, the inorganic compound aluminum
hydroxide was chosen. From the highemolecular weight group,
methylcellulose and starch were chosen. Lactose was selected from
the third group. Although yeast extract does not t into the dened
groups, it was chosen for further studies because of its interesting
behavior in our preliminary studies.
Oil Characterization: Castor Oil or Macadamia Oil as Potential
The basic physicochemical properties are the key parameters of
a liquid core used in the fabrication of LOMs. Because of this,
Figure 1. Four cases observed during LOM preparation. (a) Case 1, liquid oil marble in
which the particles cover only the droplet surface. (b) Case 2, no liquid oil marble
formation. (c) Case 3, liquid oil marble with some particles dispersed in the oil phase.
(d) Case 4, liquid oil marble with some particles dispersed in the oil phase combined
with its swelling.
Table 1
Summary of Density, Loading Capacity of API in Oils, Surface Tension, and Viscosity
of Oils
Physical Properties of Oils Castor Oil Macadamia Oil Rapeseed Oil
Density (kg/m
) 966 915 920
Loading capacity of API (g API/g oil) 0.72 0.44 0.28
Surface tension (mN/m) 34.0 30.4 31.9
Viscosity (mPa s) 401 40.1 45.9
Figure 2. Size distribution of the particles dispersed in ethanol.
P. Jansk
a et al. / Journal of Pharmaceutical Sciences 108 (2019) 2136-21422138
3 different types of oils (castor, macadamia, and rapeseed) were
chosen for the investigation. All of them are used in the pharma-
ceutical industry.
Their key physicochemical parameters were
measured (Table 1, data obtained at an ambient temperature of
C). In accordance with the literature,
as viscosity increased,
the coverage of the aqueous LM by powders decreased. Moreover,
the solubility of an API in an appropriate oil is an important
parameter that plays a key role in the mass ratio of the API in the
nal product. Both surface tension and loading capacity provided
clear evidence that castor oil was the most appropriate oil for the
fabrication of LOMs.
Optimal Physical Properties of Powders Used for LOMs' Fabrication
Size, morphology, and wettability are the key parameters of
powders used in the fabrication of LOMs. According to McEleney
et al.,
particle size affects the preparation of LMs such that the
attainable surface coverage decreases as the particle mass increases.
Figure 3. Scanning electron microscope images of particles used for LOM preparation. Left column: magnication 100. Right column: magnication 1000(acceleration voltage
20 kV).
P. Jansk
a et al. / Journal of Pharmaceutical Sciences 108 (2019) 2136-2142 2139
The authors also reported that a large particle size leads to a high
ratio of powder mass per surface area. Therefore, particle size dis-
tribution was measured (Fig. 2) and SEM was used to investigate the
microstructure of the particles (Fig. 3.) It has been reported
ne particles move around easily and envelope the liquid core,
thereby maintaining the integrity of the shell; however, because
large particles are more rigid and inexible, they do not protect the
internal phase against contact with the support. In the case of an oil-
air system, partially oleophobic particles are important for stabili-
zation of the oil-in-air materials, such as LOMs.
Therefore, the
wettability between oil and powders is likely to be a key parameter
in the formation of LMs. Compared with the other powders initially
tested, aluminum hydroxide had the lowest contact angles with
castor, macadamia, and rapeseed oils (Table S2); aluminum hy-
droxide was the material most wetted by the oils. This may be due to
the narrow particle size distribution and smooth surface of
aluminum hydroxide powder. On the other hand, yeast extract
reached very high contact angles, (especially with castor oil) which
could be inuenced by the irregular morphology of its grain surface.
Characterization of Liquid Oil Marbles: Best Combinations of Powder
and Oil for LOM Preparation
Mechanical Stability of LOMs
Four different oil-phase volumes (10, 20, 50, and 100
L) were
used to fabricate LOMs. Although the LOMs formed from the
smallest volume were stable in all cases (see Fig. S1), those con-
taining a higher oil volume (50 or 100
L) were not always stable.
In fact, at 100
L, the oil leaked out and the investigated LOMs
(all oil/powder combinations) collapsed. This led us to conclude
that stable LOMs require an oil volume of 20
L or less.
Long-term stability tests of the 20
L LOMs (1, 20 and 30 days,
Fig. S2) showed that they remained stable during the investigated
time frame. Unlike aqueous LMs, within which evaporation of the
aqueous core takes place, LOMs remained stable for a longer time.
Although, under some conditions, degradation/oxidation of the oil
may occur (see Mechanical Stability of LOMs Under External Force),
the stability of LOMs appears to make them suitable candidates for
application in drug formulation.
Mechanical Stability of LOMs Under External Force
Because the ability to ll LOMs into a gelatine capsule is desired,
information about their mechanical stability under force is crucial to
identifying the most favorable oil/powder combinations. The me-
chanical stability of LOMs during their handling before usage, stor-
age, and transportation depends on their hardness. The hardness of
LOMs was measured by using the texture analyzer where the load
required to squeeze an LOM in half was evaluated (see The Stability
of Liquid Oil Marbles). During the compressive stress tests, 2
different responses of the LOMs were observed (see Fig. 4).
In the rst case, an LOM crushed before squeezing into the half
of the original size. Such results were observed for LOMs fabricated
from aluminum hydroxide. The maximum loads for crushing these
LOMs were found to be 98, 72, and 73 mN with castor oil, macad-
amia oil, and rapeseed oil, respectively; however, after crushing, no
oil was visible inside the LOMs because of the chemical reaction
that takes place between the aluminum hydroxide and the oils.
Castor oil reacts with aluminum hydroxide to produce glycerol and
castor acid aluminum salt. Rapeseed oil is more complex because it
contains more acids, primarily through oleic acids. Hence, the re-
action between triacylglycerol and aluminum hydroxide leads to
the production of glycerol and oleic acid aluminum salt. In the case
of macadamia oil, the main ingredient is also triacylglycerol.
Overall, these results suggest that LOMs containing aluminum hy-
droxide are not suitable potential candidates for use as API carriers.
In the second case, the LOMs were squeezed by the texture
analyzer to half of their original size while remaining compact
(Fig. 5) and the force response of the LOMs to the deformation was
measured. The LOMs prepared from methylcellulose and rapeseed
oil required the highest load (332 mN ±87 mN) compared with
aluminum hydroxide (with all types of oils), which required load of
around 80 mN. Because methylcellulose has a wide particle size
distribution and rough particle surface, a much higher load is
required (200-300 mN depending on the oil) to squeeze the LOMs.
On the other hand, aluminum hydroxide has the smallest particles
(mean size of approximately 9
m) of all of the investigated pow-
ders. It also has a narrow particle size distribution and smooth
particle surface (Fig. 3) compared with the other powders. These
properties resulted in a much smaller load (72 mN ±10 mN) being
required to crush LOMs made from aluminum hydroxide.
Mass Fraction of Particles Stabilizing the LOMs
The composition of the LOMs was experimentally investigated
with the aim of determining the mass fraction of particles adhered
to and absorbed on/in them (see Fig. 6). For their application, LOMs
must have the smallest mass fraction of particles possible, and
leakage of the oil phase must be avoided. According to the litera-
LMs could contain up to 98% liquid phase. Nquyen et al.
reported that particles smaller than 50
m form multilayers,
whereas large/rigid particles form monolayers around the oil
droplet. Likewise, Eshtiaghi et al.
found that surface coverage
decreases as particle size increases. This means that the mass
fraction of particles in LOMs could also be inuenced by particle
size distribution. On the other hand, a multilayer surface helps the
Figure 4. Liquid oil marbles after squeezing: (a) crushing of a liquid oil marble from macadamia oil and aluminum hydroxide and (b) squeezing of a liquid oil marble from
macadamia oil and yeast extract.
P. Jansk
a et al. / Journal of Pharmaceutical Sciences 108 (2019) 2136-21422140
liquid core to avoid contact with the wetting surface as this makes
the powder shell dense. Methylcellulose was identied as the most
suitable powder for the preparation of LOMs.
Release Efciency of Model Drug From LOMs
The release efciencies of our LOMs were compared to the
dissolution rates of pure APIs in an aqueous environment. As a
reference dissolution time, 90% API dissolution in 60 ±5 min was
used. The time required for the release of 90% of the available API
content is summarized in Table 2, and examples of the full release
curves presented in Figure S3. The available API content was
dened as the amount when the released API amount becomes
constant in time. Some amount of the API remains in the oil phase
because of the higher solubility of API in oils than in the aqueous
The fastest API release was observed in the case of yeast
extract with castor oil (90% API release within 6 min). Conversely,
the release of the API from LOMs composed of lactose took
approximately 40 min. The release rate from aluminum hydroxide
was approximately 1.5 times slower than the dissolution of the API
in aqueous buffer. Again, this shows that LOMs prepared from
aluminum hydroxide are not suitable for further testing and usage.
In conclusion, 15 combinations of LOMs were fabricated and
characterized, with the focus on their mechanical and long-term
stability, on the mass fraction of solid particles in the LOMs, and
on their ability to carry and release poorly water-soluble APIs.
The LOM combinations were plotted using a spider diagram
(Fig. S4). The following LOMs covered the largest area: methyl-
cellulose/rapeseed oil and methylcellulose/macadamia oil. Over-
all, methylcellulose/macadamia oil appears to be the best
candidate for the fabrication of LOMs because of (1) high solu-
bility of APIs in macadamia oil and (2) mass fraction of particles
in these LOMs was lower than that in the methylcellulose/rape-
seed combination.
Table 2
Time Required for Release of 90% of the API From LOMs
Powder Castor Oil
) [min]
Macadamia Oil
) [min]
Rapeseed Oil
) [min]
Aluminum hydroxide 95 ±28 101 ±689±2
Lactose 37 ±249±840±9
Methylcellulose 39 ±131±850±15
Starch 70 ±14 50 ±739±1
Yeast extract 6 ±234±448±10
The oil-phase volume was 10
L, and initial API concentrations were 0.72, 0.44, and
0.28 API (g)/oil (g) in castor, macadamia, and rapeseed oils, respectively.
Figure 6. Mass fraction of particles adhered to and adsorbed in/on LOMs (volume of
the oil phase was 10
L). The error bars were evaluated from 10 experiments with the
indicated oil types.
Figure 5. (a) Example of the displacement curve of methylcellulose with macadamia
oil (the dashed line represents the LOM compression, and the solid line represents the
retraction). (b) Maximum load required for compressing the LOM in half.
Figure 7. Example of release from capsule containg 10 LOMs (macadamia oil and
methylcellulose) or pure API.
P. Jansk
a et al. / Journal of Pharmaceutical Sciences 108 (2019) 2136-2142 2141
LOM Capsules
For use in the pharmaceutical industry, LOMs could be sealed
into a gelatine capsule. Macadamia oil and methylcellulose were
chosen to test this because of their lower mass fraction and higher
load stability when being squeezed (182 mN). Smaller LOMs
fabricated from 10
L of the mixture (macadamia oil with API) and
methylcellulose were placed in the nal dosage form. On a mass
basis, the nal composition of the LOM was 6% API, 56% macadamia
oil, and 38% methylcellulose powder. Ten LOMs were transported to
each capsule. The capsules achieved 90% API release in 59 ±14 min
(Fig. 7). By comparison, after oral administration of the API alone,
the maximum concentration is reached after 2-4 h for tablets and
1-2 h for solution form.
In this article, a novel concept of drug delivery based on LOMs
was experimentally investigated. LOMs are gaining importance in
the pharmaceutical industry. This system can increase the disso-
lution rate and bioavailability of poorly soluble drugs. We have
shown that LOMs could be an appropriate substitute for the liqui-
solid formulations as some combinations (macadamia oil with
methylcellulose) reach quite high oil content, means high dissolved
APIs. LOMs were sufciently stable to resist stress in the capsule.
Moreover, LOM composition changes the speed of API dissolution.
LOM is a promising and innovative technology because of the
simple manufacturing process, low production cost, and sustained
release formulations, having water-insoluble drug exhibit zero or-
der release. To our best knowledge, we are the rst to report the
usage of LOMs for enhancing the release rate of poorly water-
soluble APIs. Therefore, we are already working with various APIs
to verify the capability of LOMs.
C. would like to gratefully acknowledge support from the Czech
Science Foundation (17-21696Y). P.J. would like to thank the Spe-
cic University Research (MSMT No 21-SVV/2018) for nancial
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... [3], immense progress has been made in terms of applications. LM has successfully demonstrated a potential for many applications such as acceleration sensors [6,7], thermal sensors [8], water pollution revelation [9], pressure-sensitive adhesives [10], gas sensing [11], micro-reactors [12,13], material synthesis [14], cell culture [15], drug delivery and sensitivity test [16,17], compound lenses [18] and many more. ...
Particle-coated liquid entities are the basis of many useful products, such as foams, emulsions, bijels, and liquid marbles. Particles stabilized at the liquid-air interface have been widely explored during the past two decades. Such interfaces usually consist of micro- to nano-sized particles that often tend to aggregate and lose transparency as well as the smoothness of the interface. Recently, these obstacles have been overcome by using sol-gel-derived silica nanoparticle coating. Sol-gel-derived nanoparticles offer a monolayer structure at the interface with high transparency and reproducibility. This paper critically reviews three sol-gel-derived liquid entities: Liquid marbles, Liquid plasticine, and nanoparticle-coated flat interface. Liquid marble, a particle-covered droplet, was significantly explored for its application as a container in many biological and chemical processes. Unlike powder-derived liquid marble, sol-gel-derived liquid marble can be formed into any desired shape, commonly known as liquid plasticine. Monolayer-covered sol-gel entities also offer a simple physical platform for investigating many fundamental properties of particle-coated interfaces. In the present review, starting from its preparation to the application, all critical aspects are summarized. Some unaddressed issues compared to the powder LM are also discussed for future research.
... Poorly soluble or insoluble drugs result in low absorption, which certainly affects drug bioavailability, especially in oral drug delivery [1][2][3][4][5]. Therefore, many formulation strategies have been developed to overcome the limitations of these drugs [6][7][8][9][10]. ...
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Physicochemical characterization is a crucial step for the successful development of solid dispersions, including the determination of drug crystallinity and molecular interactions. Typically, the detection of molecular interactions will assist in the explanation of different drug performances (e.g., dissolution, solubility, stability) in solid dispersions. Various prominent reviews on solid dispersions have been reported recently. However, there is still no overview of recent techniques for evaluating the molecular interactions that occur within solid dispersions of poorly water-soluble drugs. In this review, we aim to overview common methods that have been used for solid dispersions to identify different bond formations and forces via the determination of interaction energy. In addition, a brief background on the important role of molecular interactions will also be described. The summary and discussion of methods used in the determination of molecular interactions will contribute to further developments in solid dispersions, especially for quick and potent drug delivery applications.
Encapsulation of active compounds into liquid marbles (LMs) represents an emerging technology with potential applications in several fields including food, cosmetics and pharmaceutics. However, existing methods for the preparation of LMs are either based on manual one-by-one fabrication or on batch processes such as high-shear granulation, which lack the required precision in LM size distribution. We present a device capable of continuous LM production with high reproducibility, control over the LM properties and production rate flexibility. The device utilizes droplet impact onto a continuously moving powder bed on a belt conveyor with subsequent product separation by sieving. The device has been applied for fabricating LMs from various combinations of coating powders and core liquids including water- and oil-based systems as well as melts. Monodisperse populations of all three LM types were obtained in the range of 2.0–3.5 mm depending on the nozzle setting, and the maximum productivity of the device was up to 50 LMs per second. The effect of process parameters was investigated and guidelines for defect-free production were obtained. We0.5Re0.25 above a critical value was found to indicate the onset of undesirable satellite droplet generation or interface jamming upon the droplet impact; the critical value was also found to depend on the thickness of the moving powder bed. Surprisingly, the minimum safe interval between consecutive LMs that was necessary to avoid coalescence was found to be invariable with respect to both LM type and diameter. The device was capable of laboratory-scale LM production for a range of product testing and prototyping purposes and provided useful data for subsequent process scale-up.
The study of liquid marbles (LMs) composed of stabilizing liquid droplets with solid particles in a gaseous environment has matured into an established area in surface and colloid science. The minimized "solid-liquid-air" triphase interface enables LMs to drastically reduce adhesion to a solid substrate, making them unique non-wetting droplets transportable with limited energy. The small volume, enclosed environment, and simple preparation render them suitable microreactors in industrial applications and processes such as cell culture, material synthesis, and blood coagulation. Extensive application contexts request precise and highly efficient manipulations of these non-wetting droplets. Many external fields, including magnetic, acoustic, photothermal, and pH, have emerged to prepare, deform, actuate, coalesce, mix, and disrupt these non-wetting droplets. Electric fields are rising among these external stimuli as an efficient source for manipulating the LMs with high controllability and a significant ability to contribute further to proposed applications. This Feature Article attempts to outline the recent developments related to LMs with the aid of electric fields. The effects of electric fields on the preparation and manipulation of LMs with intricate interfacial processes are discussed in detail. We highlight a wealth of novel electric field-involved LM-based applications and beyond while also envisaging the challenges, opportunities, and new directions for future development in this emerging research area.
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Liquid marbles allow for quantities of various liquids to be encapsulated by hydrophobic particles, thus ensuring isolation from the external environment. The unique properties provided by this soft solid has allowed for use in a wide array of different applications. Liquid marbles do however have certain drawbacks, with lifetime and robustness often being limited. Within this review, particle characteristics that impact liquid marble stability are critically discussed, in addition to other factors, such as internal and external environments, that can be engineered to achieve a robust long‐lived liquid marble. New emerging applications, which will benefit from this improvement, are explored such as unconventional computing, cell mimicry, and soft lithography. Incorporation of liquid marbles and liquid crystal technologies shows promise in utilizing structural color for optical display applications, and within green and environmental applications, liquid marble technology is increasingly adapted for use in energy conversion, heavy metal recovery, CO2 capture, and oil removal. Liquid marbles offer unique and desirable properties for numerous applications. This review focuses on their more recent incorporation within green applications, such as carbon dioxide and oil capture. It considers how their lifetime and robustness can be improved to be better suited to real life functions, to ensure a more long‐lived and useful device.
Abiraterone acetate has limited bioavailability in the fasted state and exhibits a strong positive food effect. We present a novel formulation concept based on the so-called oil marbles (OMs) and show by in vitro and in vivo experiments that the food effect can be suppressed. OMs are spherical particles with a core-shell structure, formed by coating oil-based droplets that contain the dissolved drug by a layer of powder that prevents the cores from sticking and coalescence. OMs prepared in this work contained abiraterone acetate in the amorphous form and showed enhanced dissolution properties during in vitro experiments when compared with originally marketed formulation of abiraterone acetate (Zytiga®). Based on in vitro comparison of OMs containing different oil/surfactant combinations, the most promising formulation was chosen for in vivo studies. To ensure relevance, it was verified that the food effect previously reported for Zytiga® in humans was translated into the rat animal model. The bioavailability of abiraterone acetate formulated in OMs in the fasted state was then found to be enhanced by a factor of 2.7 in terms of AUC and by a factor of 4.0 in terms of Cmax. Crucially, the food effect reported in the literature for other abiraterone acetate formulations was successfully eliminated and OMs showed comparable extent of bioavailability in a fed-fasted study. Oil marbles therefore seem to be a promising formulation concept not only for abiraterone acetate but potentially also for other poorly soluble drugs that reveal a positive food effect.
Particle size reduction to sub-micrometer dimensions in stirred media mills is an increasingly common formulation strategy used for improving the bioavailability of poorly aqueous soluble active pharmaceutical ingredients (APIs). Due to their hydrophobic character, the API particles need to be stabilised by a surfactant in order to form a stable nano-suspension. This work is concerned with the understanding of an undesired phenomenon often encountered during the development and scale-up of wet nano-milling processes for hydrophobic APIs - the formation of foams. We investigate the microstructure, rheology and stability of these foams, and find them to be Pickering foams stabilised by solid particles at the gas-liquid interface rather than by a surfactant. By exploring the effect of surfactant concentration on the on-set of foaming in conjunction with the milling kinetics, we find a relationship between the specific surface area of the nano-suspension, the quantity of surfactant present in the formulation and the occurrence of foaming. We propose a mechanistic explanation of foam formation, and find that in order to prevent foaming, a large surfactant excess of approx. 100x above the critical micelle concentration has to be present in the solution in order to ensure a sufficiently rapid coverage of freshly exposed hydrophobic surfaces formed during the wet nano-milling process.
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We consider the flotation of deformable, non-wetting drops on a liquid interface. We consider the deflection of both the liquid interface and the droplet itself in response to the buoyancy forces, density difference and the various surface tensions within the system. Our results suggest new insight into a range of phenomena in which such drops occur, including Leidenfrost droplets and floating liquid marbles. In particular, we show that the floating state of liquid marbles is very sensitive to the tension of the particle-covered interface and suggest that this sensitivity may make such experiments a useful assay of the properties of these complex interfaces.
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A novel, supersaturable self-microemulsifying drug delivery system (S-SMEDDS) was successfully formulated to enhance the dissolution and oral absorption of valsartan (VST), a poorly water-soluble drug, while reducing the total quantity for administration. Poloxamer 407 is a selectable, supersaturating agent for VST-containing SMEDDS composed of 10% Capmul® MCM, 45% Tween® 20, and 45% Transcutol® P. The amounts of SMEDDS and Poloxamer 407 were chosen as formulation variables for a 3-level factorial design. Further optimization was established by weighting different levels of importance on response variables for dissolution and total quantity, resulting in an optimal S-SMEDDS in large quantity (S-SMEDDS_LQ; 352 mg in total) and S-SMEDDS in reduced quantity (S-SMEDDS_RQ; 144.6 mg in total). Good agreement was observed between predicted and experimental values for response variables. Consequently, compared with VST powder or suspension and SMEDDS, both S-SMEDDS_LQ and S-SMEDDS_RQ showed excellent in vitro dissolution and in vivo oral bioavailability in rats. The magnitude of dissolution and absorption-enhancing capacities using quantity-based comparisons was in the order S-SMEDDS_RQ > S-SMEDDS_LQ > SMEDDS > VST powder or suspension. Thus, we concluded that, in terms of developing an effective SMEDDS preparation with minimal total quantity, S-SMEDDS_RQ is a promising candidate.
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Most of the newly developed drug candidatesare lipophilic and poorly water-soluble. Enhancing the dissolution and bioavailability of these drugs is a major challenge for the pharmaceutical industry. Liquisolid technique, which is based on the conversion of the drug in liquid state into an apparently dry, non-adherent, free flowing and compressible powder, is a novel and advanced approach to tackle the issue. The objective of this article is to present an overview of liquisolid technique and summarize the progress of its applications in pharmaceutics. Low cost, simple processing and great potentials in industrial production are main advantages of this approach. In addition to the enhancement of dissolution rate of poorly water-soluble drugs, this technique is also a fairly new technique to effectively retard drug release. Furthermore, liquisolid technique has been investigated as a tool to minimize the effect of pH variation on drug release and as a promising alternative to conventional coating for the improvement of drug photostability in solid dosage forms. Overall, liquisolid technique is a newly developed and promising tool for enhancing drug dissolution and sustaining drug release, and its potential applications in pharmaceutics are still being broadened.
Liquid marbles show promising potential application in the microreactor field. It is of great importance to control the coalescence between two or multiple liquid marbles, however, it is highly difficult to successfully merge two isolated marbles due to their mechanically robust particle shells. In this work, we accomplished the coalescence of multiple liquid marbles via acoustic levitation. The dynamic behaviors of the liquid marbles were monitored by a high-speed camera to find that driven by the sound field, the liquid marbles moved towards each other, collided, and eventually coalesced into a larger single marble. The underlying mechanisms of this process were probed via sound field simulation and acoustic radiation pressure calculation; the results indicate that the pressure gradient on the liquid marble surface favors the formation of a liquid bridge between the liquid marbles resulting in their coalescence. A preliminary indicator reaction was induced by the coalescence of dual liquid marbles, which suggests that expected chemical reactions can be successfully triggered with multiple reagents contained in isolated liquid marbles via acoustic levitation.
In the present work, milled nanocrystals of a poorly soluble compound using different stabilizers were prepared and characterized. The aim of the study was to evaluate a fundamental set of properties of the formulations prior to i.v. injection of the particles. Two polyethylene oxide containing stabilizers; (distearoyl phosphatidylethanol amine (DSPE)) −PEG2000 and the triblock copolymer Pluronic F127, were investigated, with and without polyvinylpyrrolidone K30/Aerosol OT (PVP/AOT) present. The solubility in water was around 10 nM for the compound, measured from nanocrystals, but 1000 times higher in 4% human serum albumin. The particles were physically stable during the time investigated. The zeta potential was around −30 and −10 mV for DSPE-PEG2000 and Pluronic F127 stabilized particles, respectively, at the conditions selected. The dissolution rate was similar for all four formulations and similar to the theoretically predicted rate. Critical micelle concentrations were determined as 56 nM and 1.4 μM for DSPE-PEG2000 and Pluronic F127, respectively. The adsorption isotherms for the PEG lipid showed a maximum adsorbed amount of about 1.3 mg/m², with and without PVP/AOT. Pluronic F127 showed a higher maximum amount adsorbed, at around 3.1 mg/m², and marginally lower with PVP/AOT present. Calculated data showed that the layer of Pluronic F127 was thicker than the corresponding DSPE-PEG2000 layer. The total amount of particles distributed mainly to the liver, and the hepatocellular distribution in vitro (Liver sinusoidal endothelial cells and Kupffer cells), differed depending on the stabilizing mixture on the particles. Overall, DSPE-PEG2000 stabilized nanocrystals (with PVP/AOT) accumulated to a larger degree in the liver compared to particles with Pluronic F127 on the surface. A theoretical model was developed to interpret in vivo pharmacokinetic profiles, explaining the balance between dissolution and liver uptake. With the present, fundamental data of the nanocrystal formulations, the platform for forthcoming in vivo studies was settled.
The ability to simulate the 3D structure of a human body is essential to increase the efficiency of drug development. In vivo conditions are significantly different in comparison to in vitro conditions. A standardly used cell monolayer on tissue culture plastic (2D cell culture) is not sufficient to simulate the transfer phenomena occurring in living organisms, therefore, cell growth in a 3D space is desired. Drug absorption, distribution, metabolism, excretion and toxicity could be tested on 3D cell aggregates called spheroids, decrease the use of animal models and accelerate the drug development. In this work, the formation of spheroids from HT-29 human colorectal adenocarcinoma cells was successfully achieved by means of the so-called liquid marbles, which are liquid droplets encapsulated by a hydrophobic powder. During the cultivation in the medium inside the liquid marbles, cells spontaneously formed spherical agglomerates (spheroids) without the need of any supporting scaffold. The study focused on the influence of different parameters—namely liquid marble volume, seeding cell density and time of cultivation—on the final yield and quality of spheroids. This work has shown that using liquid marbles as microbioreactors is a suitable method for the cultivation of HT-29 cells in the form of spheroids.
Highly soluble cocrystals can be used to improve bioavailability of a poorly soluble drug, through generating supersaturation, when absorption is limited by drug dissolution. Dihydromyricetin (DMY) is a biopharmaceutics classification system (BCS) IV drug, exhibiting dissolution limited absorption. Two novel soluble cocrystals of (±)DMY with caffeine and urea were prepared, and their physicochemical properties were evaluated for suitability in formulation development. Although having a much higher solubility than (±)DMY, both cocrystals undergo rapid precipitation during dissolution and form the poorly soluble (±)DMY dihydrate in aqueous media. This negates the potential advantage offered by the high solubility of the two cocrystals in enhancing the dissolution rate and in vivo bioavailability. To solve this problem, we have systematically evaluated suitable crystallization inhibitors to maintain the supersaturation generated by cocrystals dissolution over a prolonged period of time. At 37 °C, an approximately five fold enhancement in oral bioavailability of (±)DMY was achieved when both cocrystals were dosed with 2.0 mg/mL polyvinylpyrrolidone K30 solution than (±)DMY dihydrate suspended in 0.5 mg/mL carboxymethylcellulose sodium solution. This study demonstrates that the use of a highly soluble cocrystal along with an appropriate crystallization inhibitor is a potentially effective formulation strategy for improving oral bioavailability of poorly soluble BCS IV drugs.
Background: The trend towards the consumption of functional foods that aid in the maintenance of human health has increased in recent decades. In this way, macadamia nut contains bioactive compounds and high levels of monounsaturated fatty acids that are beneficial to health and can be minimally processed or industrialized for the production of oil and defatted flour. Scope and approach: The extraction of macadamia oil is commonly performed by cold pressing; however, the process presents low extraction yields, generating partially defatted meal as a byproduct, which can be subjected to further processing to increase the yield of oil extraction. Thus, studies about different methods of extraction and evaluation of the defatted material properties, such as color, water and oil holding capacity and solubility of the protein fraction were considered in this work. Key findings and conclusions: It was found that the fatty acid composition of macadamia oil allows for its diverse use in many industries, i.e. cosmetics and pharmaceutical, while evaluation of the functional properties of the protein fraction of the defatted meal have shown that this byproduct can be used in food industry. Subsequent studies of the macadamia oil extraction process should enable the preservation of oil quality, in terms of fatty acid composition and bioactive compounds, and the functional properties of the defatted meal.
PURPOSE: The aim of this work was to develop a microbioreactor using liquid marble (LM) as a novel system for oocyte in vitro maturation (IVM) in small volumes. METHODS: Cumulus-oocyte complexes (COCs) obtained from slaughterhouse sheep ovaries were in vitro matured in a LM system prepared by placing a drop (30 μl containing 10 COCs) suspended in TCM 199 supplemented with 10 % (v/v) oestrus sheep serum (OSS) and 0.1 IU FSH and LH onto a polytetrafluoroethylene (PTFE) particle bed (LM group). As a control group (CTRL group), COCs were in vitro matured in standard volume and conditions (600 μl of IVM medium in a four-well dish). After 24-h culture at 38.5 °C in 5 % CO2 in air, COCs were released from LM and the following parameters were evaluated: (a) percentage of MII oocytes, (b) oocyte developmental competence following in vitro fertilization (IVF) or parthenogenetic activation (PA) and embryo culture for 8 days in synthetic oviductal fluid (SOF) medium at 38.5 °C in 5 % O2, 5 % CO2, and 90 % N2. RESULTS: The results indicated similar percentage of MII oocytes in LM and CTRL groups (88.0 vs. 92.0 %). No differences were observed in blastocyst rate after IVF (LM 47.5 % vs. CTRL 50.2 %, P=0.637) or PA (LM 44.4 % vs. CTRL 48.3 %, P=0.426). CONCLUSIONS: The results indicate that LM microbioreactor is a viable technique that provides a suitable microenvironment to induce oocyte in vitro maturation.
Poor water solubility of current active pharmaceutical ingredients (APIs) and new chemical entities (NCEs) is a major hurdle in the development of pharmaceutical dosage forms. More (APIs) and new chemical entities (NCEs) are a major hurdle in the development of pharmaceutical dosage forms. More than 40% of NCEs fall into Biopharmaceutical Classification System (BCS) class II category having a dissolution rate limited bioavailability. A 50%-attrition rate among drugs in development has been reported to result from poor biopharmaceutical properties, including water insolubility. From the perspective of medical professionals and patients, this means missing out on new potential and efficacious treatments to combat diseases and illnesses. For the pharmaceutical industry, this translates into a loss in potential revenue due to longer developmental time to formulate new products and a delay in transitioning them to the market. Among strategies to enhance bioavailability, amorphization by destroying or preventing long-range crystalline molecular order in solid-state drug compounds has been seen as a potentially “universal” method that can be applied to many APIs. It is not unusual to observe an increase in dissolution rate by several orders of magnitude. Since the amorphous form is meta-stable, it suffers from the drawback of returning to the crystalline state over time and thereby losing out on the enhancement in bioavailability. Stabilization of the amorphous form for an acceptable shelf-life remains a formidable technical challenge. Through bio-enhancement, the new amorphous formulations are expected to improve the efficacy of the solid dosage form and reduce the dosage of API required to produce a therapeutic effect at the required site of action. In terms of manufacturing and environmental considerations, there is a reduction in the material and energy consumption in the API production process by minimizing the “wastage of drugs” that is currently needed to ensure adequate exposure for a therapeutic benefit. In this review paper, we discuss the need for APIs in the amorphous state, use of several techniques to amorphize APIs and enhance the stability of the amorphous form under stress test conditions. Hot melt extrusion, co-precipitation using supercritical anti-solvent process and using functionalized excipients are a few methods of amorphous form stabilization that are discussed. The pivotal role of various pharmaceutically acceptable excipients that are used for stability enhancement and the mechanism therein are also discussed.