Core−Shell chitosan microcapsules for programmed sequential

Research Article
www.acsami.org

Core−Shell Chitosan Microcapsules for Programmed Sequential
Drug Release
Xiu-Lan Yang,† Xiao-Jie Ju,*,†,‡ Xiao-Ting Mu,† Wei Wang,† Rui Xie,† Zhuang Liu,† and Liang-Yin Chu†,‡
†

School of Chemical Engineering and ‡State Key Laboratory of Polymer Materials Engineering, and Collaborative Innovation Center
for Biomaterials Science and Technology, Sichuan University, Chengdu 610065, P. R. China
S Supporting Information
*

ABSTRACT: A novel type of core−shell chitosan microcapsule with programmed sequential drug release is developed
by the microfluidic technique for acute gastrosis therapy. The
microcapsule is composed of a cross-linked chitosan hydrogel
shell and an oily core containing both free drug molecules and
drug-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles. Before exposure to acid stimulus, the resultant
microcapsules can keep their structural integrity without
leakage of the encapsulated substances. Upon acid-triggering,
the microcapsules first achieve burst release due to the acidinduced decomposition of the chitosan shell. The encapsulated
free drug molecules and drug-loaded PLGA nanoparticles are
rapidly released within 60 s. Next, the drugs loaded in the
PLGA nanoparticles are slowly released for several days to achieve sustained release based on the synergistic effect of drug
diffusion and PLGA degradation. Such core−shell chitosan microcapsules with programmed sequential drug release are
promising for rational drug delivery and controlled-release for the treatment of acute gastritis. In addition, the microcapsule
systems with programmed sequential release provide more versatility for controlled release in biomedical applications.
KEYWORDS: microcapsulesc, chitosan, PLGA, nanoparticles, programmed sequential drug release

1. INTRODUCTION
The incidence of gastropathy increases every year because of

unreasonable eating and living habits, the abuse of drugs, or
inherited factors.1,2 Acute gastritis attacks rapidly, and often
causes dehydration and acid−base disturbance. Without
treatment in time, acute gastritis can even bring a variety of
complications, which will badly endanger the health of patients.
Traditional dosage forms, such as tablets, capsules, and
granules, for gastroenteritis treatment have many disadvantages,
such as frequent drug administration, large fluctuation of
plasma drug concentration, untargeted action, and low
bioavailability.3,4 Considering the characteristics of acute
gastroenteritis and the clinical needs, controlled drug release
systems are expected to obtain more effective treatment. When
gastroenteritis attacks, it is desired that the plasma drug
concentration could immediately reach to the treatment level
and that the drug could quickly take effect after administration.
Thus, the burst-release mode with large drug dose is more
appropriate in this case. After the first burst release, it is desired
that the drug dose could be constantly supplied to keep the
plasma drug concentration within safe and effective range for a
long time, which can maintain therapeutic effect and restrain
complications. Thus, the sustained-release mode is more
suitable in this case. If burst-release and sustained-release
modes are orderly combined into a single drug carrier to
achieve sequential release behaviors, i.e., burst release first and
© 2016 American Chemical Society

then sustained release, it would be very beneficial to more
rational and effective therapy for gastroenteritis. Therefore, the
design and preparation of drug delivery systems with
programmed sequential release ability, which can reduce the

frequency of administration and increase patient compliance,
are of great scientific and technological importance.
Microcapsules, which can encapsulate various active
substances to protect them from the surrounding environment,
are of great interest for many applications, especially in the drug
delivery field.5,6 Recently, microcapsules with various structures
and functions are developed to achieve programmed sequential
release, and they are considered to be very applicable as drug
delivery carriers. These functional microcapsules are mainly
divided into two categories. One is the stimuli-responsive
microcapsule with a programmed pulsed-release ability based
on a repeated “on−off” mechanism.7−16 However, triggered by
such a programmable pulse-type external stimulus, the drug
release from the microcapsules is either in an “on” state or in an
“off” state, so the drug release mode is relative simplex.7,8 The
other category is the core−shell-structured microcapsule with
drugs loaded in different layers, so that the drugs can be
released sequentially.17−23 The drugs loaded in outer shell are
Received: January 31, 2016
Accepted: April 7, 2016
Published: April 7, 2016
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Scheme 1. Schematic Illustration of the Programmed Sequential Drug Release from Core−Shell Chitosan Microcapsule: (A)
First, Burst Release of Free Drug Molecules and Drug-Loaded PLGA Nanoparticles from the Microcapsule Can Be Achieved via
the Rapid Decomposition of Chitosan Shell in Acidic Solution, and (B) Second, Sustained-Release of Drugs from the PLGA
Nanoparticles Can Be Achieved via Drug Diffusion and PLGA Degradation

first released when the shell layer is eroded, swelled, or
decomposed, and then the drugs in the core layer diffuse out to
achieve the second-stage release. However, these sequential
release manners are usually both sustained-release mode, so
that the plasma drug concentration cannot immediately reach
effective value after the first dosing.17 Furthermore, drug
leakage problems exist before these core−shell microcapsule
carriers reach the targeted sites. To the best of our knowledge,
drug-loaded microcapsules that can achieve burst release first
and then sustained release have not been reported yet. Previous
studies inspired us to design a kind of microcapsule with special
core−shell structure and a stimuli-responsive property to
achieve the programmed sequential drug release that we expect.
Here, we report on a novel type of core−shell microcapsule
with programmed sequential drug release, i.e., burst release in
the stomach first and then sustained release in the gastrointestinal tract. As illustrated in Scheme 1A1, the proposed
microcapsule is composed of a cross-linked chitosan hydrogel
shell and an oily core. Particularly, the oily core contains both
free drug molecules and drug-loaded poly(lactic-co-glycolic
acid) (PLGA) nanoparticles. Because of the existence of an
oil−water interface between the inner oily core and the hydrous
chitosan shell, there will be no-leakage of the encapsulated
drugs before these microcapsule carriers reach the stomach. In
our previous studies, we find that chitosan hydrogels prepared

using terephthalaldehyde as the cross-linker exhibit a great acidinduced dissolution property.24,25 There is an obvious change
in pH along the gastrointestinal tract, and the stomach is a
special acidic environment with low pH value (pH 1−3).26
Therefore, the encapsulated free drug molecules with large dose
can be suddenly released due to the decomposition of the
chitosan shell under the unique acidic condition of the stomach
(Scheme 1A2,A3). Simultaneously, the coencapsulated drugloaded PLGA nanoparticles are also released out, which could
provide a second, sustained release based on the synergistic
effect of drug diffusion and PLGA degradation,27,28 as shown in
Scheme 1B1−B3. The first burst-release mode can make the
plasma drug concentration rapidly reach the treatment level,
which can relieve the symptoms of acute gastritis quickly. The

second sustained-release mode can constantly supply drug
dosage to keep the plasma drug concentration within a safe and
effective range for a long time, which can cure acute gastritis
and suppress complications. That is, this kind of novel core−
shell microcapsule, which can achieve programmed sequential
drug release, is of great potential to realize more rational drug
administration for the treatment of acute stomach illness. In
addition, these microcapsules provide more flexibility for
versatile loading of different drugs, such as oleophilic drugs,
hydrophilic drugs, and multiple drugs with synergistic efficacy.

2. EXPERIMENTAL SECTION
2.1. Materials. Water-soluble chitosan (CS, Mw = 5000, degree of
deacetylation = 85%) is provided by Ji’nan Haidebei Marine
Bioengineering Co., Ltd. PLGA (≥99%, lactide/glycolide = 50/50,
Mw = 20 000) is purchased from Sichuan Dikang Sci & Tech
Pharmaceutical Co., Ltd. Soybean oil (Kerry Oils & Grains) is used as

the oil phase. Oleophilic curcumin (HPLC ≥ 98%, Chengdu
Herbpurify), hydrophilic catechin (HPLC ≥ 98%, Chengdu
Herbpurify), and hydrophilic Rhodamine B (RhB, ≥ 99%, Chengdu
Kelong Chemicals) are all used as model drugs. Poly(vinyl alcohol)
(PVA, ≥97%, Chengdu Kelong Chemicals) is used as emulsion
stabilizer for preparation of drug-loaded PLGA nanoparticles. Pluronic
F127 (Bio-Reagent, Sigma-Aldrich) and polyglycerol polyricinoleate
(PGPR, ≥99.8%, Danisco) are used as surfactants in aqueous phase
and organic phase, respectively. Hydroxyethylcellulose (HEC, ≥98%,
Lingxianzi Cellulose) is used for viscosity adjustment. Terephthalaldehyde (≥98%, Sinopharm Chemical Reagent) is used as cross-linker. All
other chemicals are of analytical grade and used as received. Deionized
water (18.2 MΩ, 25 °C) from a Millipore Milli-Q Plus water
purification system is used throughout the experiments.
2.2. Preparation of Drug-Loaded PLGA Nanoparticles. In this
work, oleophilic curcumin and hydrophilic catechin, which are both
typical gastrointestinal drugs with good anti-inflammatory effect, are
used as model drugs to prepare different drug-loaded PLGA
nanoparticles.
Curcumin-loaded PLGA nanoparticles (Cur−PLGA-NPs) are
prepared by a modified emulsion solvent evaporation method.29,30
Briefly, PLGA (300 mg) and curcumin (40 mg) are dissolved in a
mixed organic solvent (10 mL) of dichloromethane and ethyl acetate
(3:2, v/v) as the oil phase. Thirty milliliters of PVA aqueous solution
(1.0%, w/v) is used as the water phase. The oil phase is dropwise
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added into the water phase under agitation (300 rpm) for 10 min,
followed by homogeneous emulsification (19 000 rpm) for 2 min
using a BRT homogenizer (B25, 10 mm head) to obtain oil-in-water
(O/W) emulsions. Next, the O/W emulsions are transferred into
deionized water and stirred overnight at room temperature for
complete evaporation of the organic solvent. The solidified nanoparticles are purified by repeated centrifugation with deionized water.
Catechin-loaded PLGA nanoparticles (C−PLGA-NPs) are prepared
by a similar emulsion solvent evaporation process as mentioned above,
except water-in-oil-in-water (W1/O/W2) double emulsions are used
as the synthesis templates.31 Briefly, ethanol (1 mL) containing
catechin (40 mg) is dispersed in organic solution (10 mL) containing
PLGA to obtain W1/O primary emulsions. Then, the primary
emulsions are dropwise added into aqueous solution (30 mL)
containing PVA (2.0%, w/v) under agitation to prepare the double
emulsion templates. The increase of PVA concentration is to improve
the loading capacity of catechin. Next, after complete solvent
evaporation and centrifugation-based purification, C−PLGA-NPs are
obtained. Because the color and fluorescence of catechin are difficult to
observe, RhB with similar hydrophilicity property and molecular
weight is used as the model hydrophilic drug instead of catechin for
optical and fluorescent characterization. Thus, RhB-loaded PLGA
nanoparticles (RhB−PLGA-NPs) are also prepared using the same
method as for C−PLGA-NPs.
To maintain the drug activity and avoid PLGA hydrolysis, the drugloaded PLGA nanoparticles are freeze-dried and then stored in a dry
cabinet at 4 °C.
2.3. Characterization of Drug-Loaded PLGA Nanoparticles.
The chemical compositions of Cur−PLGA-NPs, C−PLGA-NPs, and

RhB−PLGA-NPs are confirmed by Fourier transform infrared
spectroscopy (FT-IR, IR Prestige-21, Shimadzu) using the KBr disk
technique. The morphologies of the drug-loaded PLGA nanoparticles
in the dried state are observed by scanning electron microscopy
(SEM) (JSM-7500F, JEOL), and their morphologies in water and oil
solutions are observed by confocal laser scanning microscopy (CLSM)
(SP5-II, Leica). Moreover, the size and size distribution of the drugloaded PLGA nanoparticles are measured by dynamic light scattering
(DLS) (Zetasizer Nano ZS90-ZEN3690, Malvern).
The drug-loading capacity and encapsulation efficiency of PLGA
nanoparticles are measured by UV−visible spectrophotometry (UV−
vis) (UV-1700, Shimadzu). A given amount of freeze-dried nanoparticles (2 mg for Cur−PLGA-NPs or 5 mg for C−PLGA-NPs/
RhB−PLGA-NPs) is dissolved in 2 mL of methanol, and then the
solution is treated with ultrasonic oscillation for 4 h to ensure the
complete extraction of the loaded drugs. The methanol solution is
centrifuged at 12 000 rpm and the supernatant is collected. After
dilution, the drug concentration in the supernatant is determined by
UV−vis at a specific wavelength (435 nm for curcumin and 278 nm for
catechin). The drug-loading capacity (LCNP) and encapsulation
efficiency (EENP) of PLGA nanoparticles are calculated as follows:

LC NP =

mass of drug in nanoparticles
× 100%
total mass of nanoparticles

EE NP =

mass of drug in nanoparticles
total mass of drug used for nanoparticle preparation

× 100%

burst release. Taking these factors into consideration and to have
comparability, the flow rates of three-phase fluids and the size of the
microfluidic device have been optimized and fixed to use in this work.
Briefly, a mixture of soybean oil and benzyl benzoate (1:1, v/v)
containing free drug molecules (3 mg/mL), drug-loaded PLGA
nanoparticles (3 mg/mL), terephthalaldehyde (2.4 wt %), and PGPR
(8.0%, w/v) is used as the inner oil phase. Soybean oil is used as the
oily solvent, and benzyl benzoate is added to adjust the density and
viscosity of the inner oil phase. Deionized water containing chitosan
(2.0%, w/v), F127 (1.5%, w/v), and HEC (2.0%, w/v) is used as the
middle aqueous phase. The outer oil phase is soybean oil containing
PGPR (8.0%, w/v). The flow rates of the inner, middle, and outer
fluids are QI = 400 μL/h, QM = 800 μL/h, and QO = 5000 μL/h,
respectively. The obtained O/W/O emulsions are collected in a glass
container and left for 10 h at room temperature to ensure the
complete cross-linking of the chitosan in the water phase. Here, we
present several kinds of composite core−shell microcapsules
containing different free drug molecules and different drug-loaded
PLGA nanoparticles. Moreover, other kinds of chitosan microcapsules
are also prepared by the same method except that the inner cores
contain only free drug molecules or only drug-loaded PLGA
nanoparticles. Generally, the prepared microcapsules can be placed
in a small amount of soybean oil for storage. Before characterization,
these prepared microcapsules are washed with a mixture of acetone
and deionized water (1:1, v/v) to remove the outer oil and
simultaneously to keep the inner cores still inside the microcapsules.
2.5. Characterization of O/W/O Emulsions and Microcapsules. The morphologies of O/W/O emulsions are characterized
by optical microscopy (BX 61, Olympus). The size and size

distribution are calculated on the basis of the obtained optical
micrographs using analytic software (Tiger 3000, Chongqing
Xinminfeng Instruments). The morphologies of resultant core−shell
chitosan microcapsules are observed by CLSM (SP5-II, Leica).
Furthermore, to confirm that there is no leakage of drug molecules
from the microcapsules before they reach the stomach, the stability of
composite core−shell microcapsules in neutral environment is
investigated by recording the variation of the relative fluorescence
intensity of the inner cores.
2.6. Programmed Sequential Drug Release of Microcapsules. The whole release behavior of the core−shell chitosan
microcapsules is a programmed combination of, first, burst release of
free drug molecules and, second, sustained release from drug-loaded
PLGA nanoparticles.
The acid-triggered burst-release behavior of the microcapsules is
monitored by CLSM (SP5-II, Leica). First, the composite core−shell
microcapsules are equilibrated in a small amount of deionized water in
a transparent glass container. To change the ambient solution into an
acidic medium, excess HCl solution (pH 1.5) is added into the
container rapidly. All experiments on burst-release behaviors of
microcapsules are performed at room temperature.
After acid-triggered burst release, the free drug molecules and drugloaded PLGA nanoparticles in inner cores are both released and
dispersed in the surrounding solution. That is, the following sustainedrelease behavior is similar to the simple drug release from PLGA
nanoparticles. To verify our hypotheses, the sustained-release
behaviors of curcumin and catechin directly from PLGA nanoparticles
are studied first. These release experiments are carried out in
phosphate-buffered saline (PBS, pH 7.4) at 37 °C using a waterbathing shaker at 100 rpm. Because of the poor water solubility of
curcumin, PBS containing ethanol (5%, v/v) is employed for Cur−
PLGA-NPs to increase the solubility of curcumin. Each sustainedrelease experiment is performed in triplicate at the same time and
under sink condition. In detail, 12 mL of PBS containing 18 mg of
drug-loaded nanoparticles is divided equally into three parts and then

separately placed into three centrifuge tubes. At predetermined time
intervals, the nanoparticle suspensions are centrifuged at 12 000 rpm
for 10 min, and then 3 mL of supernatant is removed and replaced
with fresh PBS. Drug concentrations of these supernatants are
determined by UV−vis to calculate the released amount of drug at
different time intervals.

(1)

(2)

2.4. Preparation of Core−Shell Chitosan Microcapsules. The
core−shell chitosan microcapsules containing both free drug
molecules and drug-loaded PLGA nanoparticles are prepared with
oil-in-water-in-oil (O/W/O) emulsions as templates, which are
fabricated by the capillary microfluidic technique according to our
published method.24
The microfluidic technique is an excellent method to prepare
multiple emulsions with precisely controlled size. To better achieve
our proposed design purpose, first the formed O/W/O emulsion
templates and as-prepared microcapsules should be stable; moreover,
the prepared microcapsules with large inner volume and proper
membrane thickness are good for loading more drugs and for rapid
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To display the entire programmed sequential drug release process, a
continuous release experiment combining, first, burst release and,
second, sustained release is also studied. Before adding acid, the
prepared composite core−shell microcapsules (1 mL) are immersed
into 4 mL of ethanol for ∼10 min. Then, the pH value of the ethanol
solution is adjusted to 1.5 by immediately adding hydrochloric acid.
The drug concentrations in ethanol solution before and after adding
acid are measured by UV−vis to determine the amount of released
drugs. After complete decomposition of the chitosan shell for burst
release, the drug-loaded PLGA nanoparticles are also released into the
ethanol solution. These drug-loaded PLGA nanoparticles are collected
by centrifugation at 12 000 rpm for 10 min and then dispersed into
PBS solution (pH 7.4) to investigate further the second, sustained
release by conducting experiments similar to the above-mentioned
simple sustained-release experiment of drug-loaded PLGA nanoparticles. The use of ethanol for the first burst release is to ensure that,
the free drug molecules including both oleophilic curcumin and
hydrophilic catechin can be rapidly dispersed into the surrounding
solution from oily cores. This process is similar to the actual situation
in which the free drug molecules can be immediately dispersed in
gastric fluid when composite core−shell microcapsules reach stomach.
The drug-loading capacity of the composite microcapsules (LCMC)
is defined as the ratio of the total drug-loading amount to the mass of
microcapsules. The total drug-loading amount in the microcapsules is
the sum of the amounts of the encapsulated free drugs and the drugs
contained in the encapsulated PLGA nanoparticles. To calculate the
drug-loading capacity of the microcapsules, a certain amount of
microcapsules are immersed into a given volume of ethanol solution
(pH 1.5). Due to the acid-induced decomposition of chitosan shell,

free drug molecules and drug-loaded nanoparticles are all dispersed in
ethanol solution. Then, the ethanol solution is ultrasonically treated
for 2 h to ensure the maximum dissolution of drug molecules in the
ethanol solution. After that, the ethanol solution is centrifuged (12 000
rpm) for 10 min and the supernatant solution is collected. The drug
concentration in the supernatant solution is measured by UV−vis. To
completely extract drugs from the nanoparticles, the precipitant is
redispersed in a given volume of ethanol solution, followed with
repeated ultrasonic treatment and centrifugation until the drug
concentration in the supernatant solution cannot be detected. The
sum of the drug amounts in all supernatant solutions is the total drugloading amount in the microcapsules.

Figure 1. FT-IR spectra of blank PLGA nanoparticles (A), curcumin
drug (B), Cur−PLGA-NPs (C), catechin drug (D), C−PLGA-NPs
(E), RhB model drug (F), and RhB−PLGA-NPs (G).

spectra of Cur−PLGA-NPs (curve C), C−PLGA-NPs (curve
E), and RhB−PLGA-NPs (curve G). All the results confirm
that curcumin, catechin, and RhB are successfully encapsulated
in PLGA nanoparticles.
SEM images of Cur−PLGA-NPs, C−PLGA-NPs, and RhB−
PLGA-NPs clearly show that all drug-loaded nanoparticles
show good spherical shape and uniform size (Figure 2). CLSM
is used to observe the dispersibility and morphology of the
drug-loaded PLGA nanoparticles in water. As shown in Figure
3A1, PLGA nanoparticles containing oleophilic curcumin
exhibit obvious green fluorescence due to the autofluorescence
of curcumin. Because catechin has nearly no fluorescence, C−
PLGA-NPs do not exhibit fluorescence under CLSM
observation (Figure 3A2). For better observation, RhB−

PLGA-NPs are used as a substitute sample for PLGA
nanoparticles containing hydrophilic drugs, because they
display obvious red fluorescence from the RhB dye (Figure
3A3). It can be seen that these three kinds of nanoparticles are
well-dispersed in water without bulk aggregation, which
benefits the drug release from the nanoparticles. The DLS
results show that the average sizes of Cur−PLGA-NPs, C−
PLGA-NPs, and RhB−PLGA-NPs are 551.6, 478.4 and 466.6
nm, respectively. The polydispersity index (PDI) values of
Cur−PLGA-NPs, C−PLGA-NPs, and RhB−PLGA-NPs are
0.122, 0.114, and 0.091, respectively, indicating the good
monodispersity of these nanoparticles. A uniform size for
polymer particles is crucial for their use as drug delivery
carriers, since it allows precise manipulation of the drug-loading
amount, optimization of the release kinetics, and repeatability
of the release profiles.32 The dispersibility of drug-loaded PLGA
nanoparticles in oil solution is also studied. As shown in Figure
S1 (Supporting Information), Cur−PLGA-NPs, C−PLGANPs, and RhB−PLGA-NPs also exhibit good dispersibility in
soybean oil without bulk aggregation, which benefits the
generation of O/W/O emulsion templates in microfluidic
devices without clogging the microchannel.

3. RESULTS AND DISCUSSION
3.1. Composition and Morphology of Nanoparticles.
FT-IR spectra of different drug-loaded PLGA nanoparticles are
shown in Figure 1. Specifically, the characteristic bands of
curcumin molecule (curve B), including a wide peak around
3400 cm−1 for the O−H stretching vibration of the phenol
group, three peaks at 1625−1500 cm−1 for the CC skeletal
stretching vibration in the benzene ring, and two peaks at 860−

800 cm−1 for the C−H bending vibration of the benzene ring,
are all found in the FT-IR spectrum of Cur−PLGA-NPs (curve
C). Similarly, the characteristic bands of catechin (curve D),
including a wide peak around 3380 cm−1 for the O−H
stretching vibration of the phenol group, three peaks at 1625−
1500 cm−1 for the CC skeletal stretching vibration of the
benzene ring, and two peak at 860−800 cm−1 for the C−H
bending vibration of the benzene ring, are all found in the FTIR spectrum of C−PLGA-NPs (curve E). For RhB−PLGANPs, the characteristic bands of RhB (curve F), including the
characteristic peak at 1700 cm−1 for the CO stretching
vibration of the carboxyl group and two peaks at 1650−1550
cm−1 for the CC skeletal stretching vibration of the benzene
ring, can also be found in the FT-IR spectrum of RhB−PLGANPs (curve G). Furthermore, the characteristic peak at 1750
cm−1 for the CO stretching vibration of the ester bond in
PLGA nanoparticles (curve A) can be found in the FT-IR
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Figure 2. SEM images of Cur−PLGA-NPs (A), C−PLGA-NPs (B), and RhB−PLGA-NPs (C).

Figure 3. CLSM images (A) and size distributions (B) of Cur−PLGA-NPs (A1, B1), C−PLGA-NPs (A2, B2), and RhB−PLGA-NPs (A3, B3) in
water.

drug molecules and PLGA nanoparticles with the same drug

molecules. Such kind of microcapsule is demonstrated by
preparing microcapsules containing free oleophilic curcumin
and Cur−PLGA-NPs and microcapsules containing free
hydrophilic catechin and C−PLGA-NPs. This kind of microcapsule is used to prove that the same drugs can be released in a
programmed sequential release manner to reduce the frequency
of drug administration. The other kind of the microcapsules
contain free drug molecules and PLGA nanoparticles with
different drug molecules. This is demonstrated by preparing
microcapsules containing free curcumin and C−PLGA-NPs
and microcapsules containing free catechin and Cur−PLGANPs. Such type of microcapsule is used to verify that multiple
drugs with synergistic efficacy35,36 can be sequentially released
to enhance the therapeutic effect.
O/W/O emulsions are used as templates to prepare the
designed core−shell chitosan microcapsules. Figure 4A−H
shows the optical micrographs of different kinds of O/W/O
emulsions prepared by the microfluidic method. These
emulsions all show clear and stable core−shell structures.
Similarly, since catechin exhibits no color and no fluorescence,
RhB is used instead of catechin as the hydrophilic model drug
for optical characterization. Curcumin has a bright-yellow color
and RhB is a red dye. As a result, different O/W/O emulsions
have different colors in the inner cores. Figure 4A−D shows the
control groups with inner cores containing only free drugs or

The drug-loading capacities of Cur−PLGA-NPs and C−
PLGA-NPs are 12.87% and 3.23%, respectively, and their
encapsulation efficiencies are 64.76% and 66.85%, respectively.
The loading capacity of hydrophilic catechin is smaller than that
of oleophilic curcumin. The reason is that a large number of
catechin is lost during the nanoparticle preparation process.

Hydrophilic drug molecules can easily diffuse from the organic
phase into the outer aqueous phase during the solvent
evaporation process, which results in small drug-loading
capacity.33 Similarly, the drug-loading capacity and encapsulation efficiency of RhB−PLGA-NPs is 2.94% and 60.23%.
Certainly, the loading capacity of hydrophilic drugs in PLGA
nanoparticles can be improved by various methods through
changing the preparation parameters.34
3.2. Morphologies of Emulsion Templates and Microcapsules. The purpose of this work is to develop a novel type
of core−shell microcapsule for programmed sequential drug
release. The proposed microcapsule is composed of a crosslinked chitosan shell and an oily core containing both free drug
molecules and drug-loaded PLGA nanoparticles. The microcapsules with such core−shell structures provide more
flexibility for versatile loading of different drugs, such as
oleophilic drugs, hydrophilic drugs, and multiple drugs with
synergistic efficacy. To demonstrate the feasibility of our
technique, two kinds of core−shell chitosan microcapsules are
designed in this work. One is microcapsules containing free
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Figure 4. Optical micrographs (A−H) and size distributions (E1−H1) of different O/W/O emulsions: (A) emulsions containing only free
curcumin, (B) emulsions containing only Cur−PLGA-NPs, (C) emulsions containing only free RhB, (D) emulsions containing only RhB−PLGANPs, (E, E1) emulsions containing both free curcumin and Cur−PLGA-NPs, (F, F1) emulsions containing both free curcumin and RhB−PLGANPs, (G, G1) emulsions containing both free RhB and RhB−PLGA-NPs, and (H, H1) emulsions containing both free RhB and Cur−PLGA-NPs.
Scale bars are 200 μm.

Figure 4E−H shows the optical micrographs of the final O/W/
O emulsions, which serve as templates to prepare core−shell
microcapsules containing both free drug molecules and drugloaded PLGA nanoparticles. The image of O/W/O emulsions
containing both free curcumin and Cur−PLGA-NPs (Figure
4E), which shows both bright yellow color and lots of black
dots in the inner cores, is nearly an overlay of parts A and B of
Figure 4. Similarly, the image of O/W/O emulsions containing
both free RhB and RhB−PLGA-NPs (Figure 4G) seems to be
an overlay of parts C and D of Figures 4. On the other hand,
the core color of O/W/O emulsions containing both free
curcumin and RhB−PLGA-NPs (Figure 4F) is almost a mixture

only PLGA nanoparticles with same drug molecules. The O/
W/O emulsions containing only free oleophilic curcumin
(Figure 4A) or only Cur−PLGA-NPs (Figure 4B) show
obvious yellow color in their inner cores. Specially, due to
larger amount of curcumin, the emulsions containing only free
curcumin show brighter yellow color in their inner cores than
those containing only Cur−PLGA-NPs. In addition, there are
lots of black dots in the inner cores of emulsions containing
only Cur−PLGA-NPs, which are slightly aggregated PLGA
nanoparticles. Similarly, the O/W/O emulsions containing only
free hydrophilic RhB (Figure 4C) or only RhB−PLGA-NPs
(Figure 4D) exhibit red color from RhB dye in the inner cores.
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of the colors in Figure 4A,D. A similar situation can also be
found in O/W/O emulsions containing both free RhB and
Cur−PLGA-NPs (Figure 4H). These results indicate that
different free drug molecules and drug-loaded PLGA nanoparticles are successfully encapsulated into the inner cores of
O/W/O emulsions individually or together. In addition,
encapsulated free drug molecules and drug-loaded PLGA
nanoparticles do not affect the structural integrity and stability
of the emulsions.
Figure 4E1−H1 is the corresponding size distributions of
these final O/W/O emulsions. All emulsion templates show
uniform size with a narrow size distribution. A parameter called
the coefficient of variation (CV), which is defined as the ratio of
the standard deviation of the size distribution to its arithmetic
mean, is used to evaluate the size monodispersity of the
particles and emulsions. The calculated CV values for the inner
diameters (ID) and outer diameters (OD) of O/W/O
emulsions shown in Figure 4E are 1.48% and 1.64%,
respectively, indicating the high monodispersity of these
emulsion templates. The O/W/O emulsions shown in Figure
4F also show good monodispersity, and the CV values for ID
and OD are 2.01% and 1.99%, respectively. Similarly, CV values
for ID and OD shown in Figure 4G are 1.85% and 1.2%,
respectively, and CV values for ID and OD shown in Figure 4H
are 1.67% and 1.2%, respectively.
Using the monodisperse O/W/O emulsions as templates,
core−shell chitosan microcapsules with uniform size and
structure are prepared via an interfacial cross-linking reaction.

Figure 5 shows the CLSM images of core−shell chitosan
microcapsules loading with different substrates in their inner
cores. Due to the formation of Schiff base bonds, chitosan
hydrogels cross-linked by terephthalaldehyde can exhibit
autofluorescence.24,25 Therefore, the chitosan shell layers in
these different kinds of microcapsules all display obvious green
fluorescence. Due to loading with different substrates, there
exist distinct differences in their inner cores. Because curcumin
and RhB are naturally fluorescent in the visible green and red
spectra respectively, the inner cores of microcapsules
containing only free curcumin (Figure 5A) or only free RhB
(Figure 5B) show clear green fluorescence or red fluorescence.
Similarly, microcapsules containing only Cur−PLGA-NPs
(Figure 5C) or only RhB−PLGA-NPs (Figure 5D) also show
green fluorescence or red fluorescence. Because of the higher
loading amount of free drug molecules, the microcapsules
containing only free curcumin or only free RhB have brighter
fluorescence in their inner cores compared with the microcapsules containing only Cur−PLGA-NPs or only RhB−
PLGA-NPs. Compared with those in Figure 5A,C, the
fluorescence intensity of the inner cores in microcapsules
containing both free curcumin and Cur−PLGA-NPs (Figure
5E) obviously increases. The composite core−shell microcapsules containing both free RhB and RhB−PLGA-NPs
(Figure 5G) show the same phenomenon, that the red
fluorescence intensity in the inner cores also increases
compared with that in Figure 5B,D. In addition, core−shell
microcapsules containing both free RhB and Cur−PLGA-NPs
(Figure 5H) display a mixed fluorescence color of red
fluorescence from RhB and green fluorescence from Cur−
PLGA-NPs. However, in the overlap of CLSM images on green
and red fluorescent channels, the phenomenon of mixed

fluorescence color does not appear for the microcapsules
containing both free curcumin and RhB−PLGA-NPs (Figure
5F), which just show green fluorescence. The reason is that the

Figure 5. CLSM images of different core−shell chitosan microcapsules: (A) microcapsules containing only free curcumin, (B)
microcapsules containing only free RhB, (C) microcapsules containing
only Cur−PLGA-NPs, (D) microcapsules containing only RhB−
PLGA-NPs, (E) microcapsules containing both free curcumin and
Cur−PLGA-NPs, (F) microcapsules containing both free curcumin
and RhB−PLGA-NPs, (G) microcapsules containing both free RhB
and RhB−PLGA-NPs, and (H) microcapsules containing both free
RhB and Cur−PLGA-NPs. parts A, C, and E are on a green
fluorescent channel and parts B, D, and F−H are the overlap of images
on green and red fluorescent channels. Scale bars are all 500 μm.

loading amount of RhB in the PLGA nanoparticles is much
smaller than that of free curcumin in the inner cores, so the red
fluorescence of RhB is shielded by the green fluorescence of
curcumin. All the results demonstrate that different free drug
molecules and drug-loaded nanoparticles can be successfully
encapsulated in the composite core−shell microcapsules.
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Figure 6. Relative fluorescence intensity of the inner cores at hourly intervals in neutral aqueous solution (pH 6.8, 37 °C): (A) microcapsules
containing both free oleophilic curcumin and Cur−PLGA-NPs and (B) microcapsules containing both free hydrophilic RhB and RhB−PLGA-NPs.

3.3. Stability of Drug-Loaded Microcapsules. Before
the proposed core−shell chitosan microcapsules reach the
targeted stomach site, it is vital that microcapsules can maintain
their structural integrity and prevent loaded drugs from leaking.
Therefore, no leakage of drugs from the microcapsules in
neutral medium is confirmed before the controlled-release
experiments. The core−shell chitosan microcapsules containing
both free drug molecules and drug-loaded PLGA nanoparticles
are used as the typical examples to investigate the stability of
different composite core−shell microcapsules. In order to
facilitate real-time monitoring by the CLSM method, the drug
amounts of curcumin and RhB are represented by the
fluorescence intensities of the inner cores. After the microcapsules are placed into the neutral aqueous solution (pH 6.8,
37 °C), the fluorescence intensities of the inner cores are
recorded at hourly intervals within 6 h. Relative fluorescence
intensity, which is defined as the ratio of fluorescence intensity
at a desired time to that at the initial time, is used to evaluate
the drug leakage. For microcapsules loaded with oleophilic
curcumin (Figure 6A), the relative fluorescence intensity
remains nearly unchanged at ∼1, indicating nearly no leakage
of curcumin from the microcapsules. For hydrophilic RhBloaded microcapsules (Figure 6B), the fluorescence intensity of
inner cores slightly decreases after 3 h. After being dispersed in
aqueous solution for 3 h, the chitosan shells of microcapsules
swell completely, so the pores of the cross-linked network
become larger. At this time, compared with oleophilic
curcumin, hydrophilic RhB is easier to pass through the

hydrous chitosan shell. However, such slight leakage does not
affect the actual clinical performance, because the delivery time
of the microcapsules from oral administration to stomach site is
usually less than 2 h. So, there is nearly no leakage of RhB
before the drug-loaded microcapsules reach stomach. We also
test the stabilities of the microcapsules containing only free
drug molecules, only drug-loaded nanoparticles, or other kinds
of composite core−shell microcapsules (Figure S2, Supporting
Information), which also show the similar results. These results
indicate that the loaded drug molecules scarcely escape from
microcapsules within the required time due to the oil−water
interface between the inner cores and the hydrous chitosan
shells.
3.4. Programmed Sequential Release Characteristics
of Microcapsules. The programmed sequential drug release
of our proposed core−shell chitosan microcapsules is designed
as, first, burst release in the stomach and, second, sustained
release in the gastrointestinal tract. The controlled-release

behaviors of two kinds of representative core−shell microcapsules containing both free drug molecules and PLGA
nanoparticles with same drug molecules are investigated.
First, the acid-triggered burst-release behaviors of proposed
microcapsules are studied under CLSM. Prior to tests,
microcapsule samples are immersed in deionized water. Then,
we introduce a sudden change to the pH value of their
environmental solution by quickly adding excess HCl solution
(pH 1.5). Figure 7 shows the CLSM microscope snapshots of
acid-triggered burst-release processes of these two kinds of

Figure 7. CLSM microscope snapshots of acid-triggered burst-release

processes of microcapsules containing both free curcumin and Cur−
PLGA-NPs (A, green fluorescent channel) and microcapsules
containing both free RhB and RhB−PLGA-NPs (B, overlap of images
on green and red fluorescent channels). HCl solution with pH 1.5 is
added at t = 0 s. The scale bars are all 500 μm.
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Figure 8. Cumulative releases of curcumin (A) and catechin (B) from PLGA nanoparticles in PBS (pH 7.4, 37 °C).

Figure 9. Programmed sequential release behaviors of curcumin-loaded (A) and catechin-loaded (B) composite core−shell microcapsules.

representative microcapsules. One is the microcapsules
containing both free oleophilic curcumin and curcumin-loaded
PLGA nanoparticles (Figure 7A), and another one is the
microcapsules containing both free hydrophilic RhB and RhBloaded PLGA nanoparticles (Figure 7B). The acid-induced
decomposition phenomena of chitosan shell layers for these
two kinds of microcapsules are almost the same. That is,
chitosan microcapsules maintain good spherical shape and
structural integrity in neutral medium (pH 6.8, 37 °C). Once
HCl solutions are added into the microcapsule suspensions, the
chitosan shells swell immediately at first and then a rapid and
complete decomposition is achieved within 60 s. Such

decomposition of chitosan shells in acidic solution is a result
of acid-induced hydrolysis of the Schiff base bonds between
chitosan and terephthalaldehyde.24,25 With the breakup of
chitosan shells, both free drug molecules and drug-loaded
PLGA nanoparticles are released into the surrounding medium,
along with the dispersion of inner cores. For our proposed
microcapsules, the release of free drug molecules with large
loading amount successfully first achieves the stomach-targeted
burst release that can make the plasma drug concentration
rapidly reach the treatment level. Meanwhile, the quickly
released drug-loaded nanoparticles disperse well in the aqueous
medium, which is beneficial to the following sustained drug
release from the PLGA nanoparticles. Movies of the acidtriggered burst-release processes are also shown in the
Supporting Information (Movie S1 and Movie S2).
At the first acid-triggered burst-release stage, the coencapsulated drug-loaded PLGA nanoparticles are also released from
the microcapsules, which could provide a second, sustained

release based on the synergistic effect of drug diffusion and
PLGA degradation. The sustained-release behaviors of
curcumin and catechin from PLGA nanoparticles are evaluated
under simulated physiological conditions (PBS, pH 7.4, 37 °C).
The in vitro release profiles of drugs are obtained by graphing
the accumulated release percentage of drug from PLGA
nanoparticles as a function of the time. The cumulative release
curves of oleophilic curcumin and hydrophilic catechin both
present a typical sustained-release “first-order kinetic model”. A
sustained and prolonged release of oleophilic curcumin in the
PBS for up to 28 days is observed in Figure 8A. In the initial
period of 6 h, approximately 10% of curcumin is released,
followed by a sustained drug release. Within 28 days, 63.6% of

the encapsulated curcumin is released from the nanoparticles.
Figure 8B shows the release profile of hydrophilic catechin,
which also represents a good sustained-release behavior. There
is also a relative fast release of catechin within the initial 6 h,
and 60.86% of drug is slowly released within 6 days. It is
noteworthy that the release rate and mechanism are different
between curcumin and catechin. In general, the drug release
mechanisms depend upon the solubility and diffusion of drug,
as well as the biodegradation of the matrix materials. Catechin
is a hydrophilic molecule with a greater solubility in aqueous
environment, so its drug diffusion rate through the polymeric
matrix is much faster than that of oleophilic curcumin. In
summary, the drug-loaded PLGA nanoparticles show good
second, sustained release, which can bring constant and
effective therapeutic action.
To display the entire programmed sequential drug release
process, a continuous release experiment combining, first, burst
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release stage. Simultaneously, the coencapsulated drug-loaded
PLGA nanoparticles are also released to provide the second
sustained-release stage. Respectively, about 19.3% of curcumin

and 32.3% of catechin are slowly released from PLGA
nanoparticles within 2 days. Such well-designed core−shell
chitosan microcapsules with programmed sequential drug
release are promising to achieve a more rational drug delivery
and controlled release for the treatment of acute stomach
illness. In addition, these microcapsules provide more versatility
for loading different drugs, such as oleophilic drugs, hydrophilic
drugs, and multiple drugs with synergistic efficacy. Moreover,
the results of this study also provide a versatile strategy for
designing and developing novel functional microcapsules with
various programmed sequential release properties for biomedical applications.

release and, second, sustained release is also studied. Figure 9
shows the drug release curves of two kinds of representative
core−shell microcapsules. One is for the microcapsules
containing both free oleophilic curcumin and curcumin-loaded
PLGA nanoparticles (Figure 9A), and the other one is for the
microcapsules containing both free hydrophilic catechin and
catechin-loaded PLGA nanoparticles (Figure 9B). During the
initial 10 min equilibrium time, there is nearly no leakage of
drug from the microcapsules. These data match well with the
results of stability experiments of microcapsules in Figure 7.
After adding ethanol solution containing HCl (pH 1.5), free
drug molecules are released immediately from the composite
core−shell microcapsules. Respectively, about 56.2% of
curcumin (Figure 9A) and 59.6% of catechin (Figure 9B) are
released within 60 s, which directly shows the first burst-release
performance. The following sustained-release experiments are
carried out for 2 days. Relative to the total drug-loading amount
in whole microcapsules, about 19.3% of curcumin (Figure 9A)

and 32.3% of catechin (Figure 9B) are slowly released from
PLGA nanoparticles within 2 days. The curve shapes and
tendencies for change of sustained-release parts in Figure 9 are
similar to that in Figure 8, which also present a typical
sustained-release “first-order kinetic model”. However, since the
accumulated release percentage of drug is relative to the total
drug-loading amount in the whole microcapsules, the sustainedrelease curves in Figure 9 seem to be relatively gentle compared
to those in Figure 8. The entire controlled release behaviors
fully confirm that our proposed composite core−shell microcapsules possess the programmed sequential drug release
properties for both oleophilic drugs and hydrophilic drugs.

■

ASSOCIATED CONTENT

S Supporting Information
*

The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acsami.6b01277.
CLSM images of Cur−PLGA-NPs, C−PLGA-NPs, and
RhB−PLGA-NPs in soybean oil and stabilities of the
microcapsules containing only free drug molecules or
containing only drug-loaded nanoparticle or containing
both free drug molecules and drug-loaded nanoparticles
(PDF)
The acid-triggered burst-release process of chitosan
core−shell microcapsules containing both free curcumin
and Cur−PLGA-NPs (Supplementary Movie S1) (AVI)
The acid-triggered burst-release process of chitosan

core−shell microcapsules containing both free RhB and
RhB−PLGA-NPs (Supplementary Movie S2) (AVI)

4. CONCLUSIONS
A novel type of core−shell microcapsules with programmed
sequential drug release for acute gastrosis therapy has been
successfully developed in this work. The proposed microcapsule is composed of a cross-linked chitosan hydrogel shell
and an oily core containing both free drug molecules and drugloaded PLGA nanoparticles. Oleophilic curcumin and hydrophilic catechin are used as anti-inflammatory model drugs in
this work, which also have synergistic efficacy in clinic. We have
designed and prepared several kinds of representative microcapsules. For example, the core−shell microcapsules encapsulate the same drugs (free oleophilic curcumin and curcuminloaded PLGA nanoparticles, or free hydrophilic catechin and
catechin-loaded PLGA nanoparticles), and the core−shell
microcapsules contain different drugs (free curcumin and
catechin-loaded PLGA nanoparticles, or free catechin and
curcumin-loaded nanoparticles). CLSM results confirm that
various free drug molecules and drug-loaded PLGA nanoparticles are successfully encapsulated inside the inner cores of
the microcapsules. The microcapsules can keep their structural
integrity without leakage of drugs in neutral aqueous medium
before they reach the acidic stomach environment. Controlledrelease results indicate that the proposed microcapsules with
this unique core−shell structure can successfully achieve
programmed sequential drug release, i.e., burst release in the
stomach first and then sustained release in the gastrointestinal
tract. When the microcapsules are transferred to an acidic
environment like the stomach, the encapsulated free drug
molecules are rapidly released as the first burst-release stage due
to the acid-triggered decomposition of chitosan shell. About
56.2% of curcumin and 59.6% of catechin are respectively
released from the microcapsules within 60 s at the first burst-

■

AUTHOR INFORMATION

Corresponding Author

*E-mail:
Author Contributions

The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS
The authors gratefully acknowledge support from the National
Natural Science Foundation of China (21322605, 21276002,
81321002), the Training Program of Sichuan Province
Distinguished Youth Academic and Technology Leaders
(2013JQ0035), and the State Key Laboratory of Polymer
Materials Engineering (sklpme2014-3-02).

■

REFERENCES

(1) Siegel, R.; Ma, J. M.; Zou, Z. H.; Jemal, A. Cancer Statistics, 2014.
Ca-Cancer J. Clin. 2014, 64, 9−29.

(2) Sinha, M.; Gautam, L.; Shukla, P. K.; Kaur, P.; Sharma, S.; Singh,
T. P. Current Perspectives in NSAID-Induced Gastropathy. Mediators
Inflammation 2013, 2013, 258209.
(3) den Hollander, W. J.; Kuipers, E. J. Current Pharmacotherapy
Options for Gastritis. Expert Opin. Pharmacother. 2012, 13, 2625−
2636.

10533

DOI: 10.1021/acsami.6b01277
ACS Appl. Mater. Interfaces 2016, 8, 10524−10534


Research Article

ACS Applied Materials & Interfaces

(25) Wang, X. X.; Ju, X. J.; Sun, S. X.; Xie, R.; Wang, W.; Liu, Z.;
Chu, L. Y. Monodisperse Erythrocyte-Sized and Acid-soluble Chitosan
Microspheres Prepared via Electrospraying. RSC Adv. 2015, 5, 34243−
34250.
(26) Evans, D. F.; Pye, G.; Bramley, R.; Clark, A. G.; Dyson, T. J.;
Hardcastle, J. D. Measurement of Gastrointestinal pH Profiles in
Normal Ambulant Human Subjects. Gut 1988, 29, 1035−1041.
(27) Danhier, F.; Ansorena, E.; Silva, J. M.; Coco, R.; Le Breton, A.;
Preat, V. PLGA-Based Nanoparticles: An Overview of Biomedical
Applications. J. Controlled Release 2012, 161, 505−522.
(28) Panyam, J.; Labhasetwar, V. Biodegradable Nanoparticles for
Drug and Gene Delivery to Cells and Tissue. Adv. Drug Delivery Rev.
2012, 64, 61−71.

(29) Yallapu, M. M.; Gupta, B. K.; Jaggi, M.; Chauhan, S. C.
Fabrication of Curcumin Encapsulated PLGA Nanoparticles for
Improved Therapeutic Effects in Metastatic Cancer Cells. J. Colloid
Interface Sci. 2010, 351, 19−29.
(30) Pillai, J. J.; Thulasidasan, A. K. T.; Anto, R. J.; Devika, N. C.;
Ashwanikumar, N.; Kumar, G. S. V. Curcumin Entrapped Folic Acid
Conjugated PLGA-PEG Nanoparticles Exhibit Enhanced Anticancer
Activity by Site Specific Delivery. RSC Adv. 2015, 5, 25518−25524.
(31) Pool, H.; Quintanar, D.; Figueroa, J. D.; Marinho Mano, C.;
Bechara, J. E. H.; Godinez, L. A.; Mendoza, S. Antioxidant Effects of
Quercetin and Catechin Encapsulated into PLGA Nanoparticles. J.
Nanomater. 2012, 2012, 145380.
(32) De La Vega, J. C.; Elischer, P.; Schneider, T.; Hafeli, U. O.
Uniform Polymer Microspheres: Monodispersity Criteria, Methods of
Formation and Applications. Nanomedicine 2013, 8, 265−285.
(33) Jain, R. A. The Manufacturing Techniques of Various Drug
Loaded Biodegradable Poly(lactide-co-glycolide) (PLGA) Devices.
Biomaterials 2000, 21, 2475−2490.
(34) Astete, C. E.; Sabliov, C. M. Synthesis and Characterization of
PLGA Nanoparticles. J. Biomater. Sci., Polym. Ed. 2006, 17, 247−289.
(35) Aditya, N. P.; Aditya, S.; Yang, H.; Kim, H. W.; Park, S. O.; Ko,
S. Co-Delivery of Hydrophobic Curcumin and Hydrophilic Catechin
by a Water-in-Oil-in-Water Double Emulsion. Food Chem. 2015, 173,
7−13.
(36) Manikandan, R.; Beulaja, M.; Arulvasu, C.; Sellamuthu, S.;
Dinesh, D.; Prabhu, D.; Babu, G.; Vaseeharan, B.; Prabhu, N. M.
Synergistic Anticancer Activity of Curcumin and Catechin: An In Vitro
Study Using Human Cancer Cell Lines. Microsc. Res. Tech. 2012, 75,
112−116.

(4) Rakatansky, H. Review article: Gastroenterology and the
Pharmaceutical Industry. Aliment. Pharmacol. Ther. 2002, 16, 1859−
1866.
(5) Bysell, H.; Mansson, R.; Hansson, P.; Malmsten, M. Microgels
and Microcapsules in Peptide and Protein Drug Delivery. Adv. Drug
Delivery Rev. 2011, 63, 1172−1185.
(6) Lensen, D.; Vriezema, D. M.; van Hest, J. C. M. Polymeric
Microcapsules for Synthetic Applications. Macromol. Biosci. 2008, 8,
991−1005.
(7) Sukhorukov, G.; Fery, A.; Mohwald, H. Intelligent Micro- and
Nanocapsules. Prog. Polym. Sci. 2005, 30, 885−897.
(8) Kost, J.; Langer, R. Responsive Polymeric Delivery Systems. Adv.
Drug Delivery Rev. 2012, 64, 327−341.
(9) Wang, C. Y.; Yang, C. H.; Lin, Y. S.; Chen, C. H.; Huang, K. S.
Anti- Inflammatory Effect with High Intensity Focused UltrasoundMediated Pulsatile Delivery of Diclofenac. Biomaterials 2012, 33,
1547−1553.
(10) Long, Y.; Liu, C. Y.; Zhao, B.; Song, K.; Yang, G. Q.; Tung, C.
H. Bio-Inspired Controlled Release through Compression-Relaxation
Cycles of Microcapsules. NPG Asia Mater. 2015, 7, e148.
(11) Chu, L. Y.; Yamaguchi, T.; Nakao, S. A Molecular-Recognition
Microcapsule for Environmental Stimuli-Responsive Controlled
Release. Adv. Mater. 2002, 14, 386−389.
(12) Chu, L. Y.; Liang, Y. J.; Chen, W. M.; Ju, X. J.; Wang, H. D.
Preparation of Glucose-Sensitive Microcapsules with a Porous
Membrane and Functional Gates. Colloids Surf., B 2004, 37, 9−14.
(13) Yang, W. C.; Xie, R.; Pang, X. Q.; Ju, X. J.; Chu, L. Y.
Preparation and Characterization of Dual Stimuli-Responsive Microcapsules with a Superparamagnetic Porous Membrane and ThermoResponsive Gates. J. Membr. Sci. 2008, 321, 324−330.
(14) Masoud, H.; Alexeev, A. Controlled Release of Nanoparticles
and Macromolecules from Responsive Microgel Capsules. ACS Nano
2012, 6, 212−219.

(15) Zheng, C. L.; Ding, Y. F.; Liu, X. Q.; Wu, Y. K.; Ge, L. Highly
Magneto-Responsive Multilayer Microcapsules for Controlled Release
of Insulin. Int. J. Pharm. 2014, 475, 17−24.
(16) Jeong, W. C.; Kim, S. H.; Yang, S. M. Photothermal Control of
Membrane Permeability of Microcapsules for On-Demand Release.
ACS Appl. Mater. Interfaces 2014, 6, 826−832.
(17) Stubbe, B. G.; De Smedt, S. C.; Demeester, J. Programmed
Polymeric Devices” for Pulsed Drug Delivery. Pharm. Res. 2004, 21,
1732−1740.
(18) De Cock, L. J.; De Koker, S.; De Geest, B. G.; Grooten, J.;
Vervaet, C.; Remon, J. P.; Sukhorukov, G. B.; Antipina, M. N.
Polymeric Multilayer Capsules in Drug Delivery. Angew. Chem., Int. Ed.
2010, 49, 6954−6973.
(19) Li, D.; Zhang, Y. T.; Jin, S.; Guo, J.; Gao, H. F.; Wang, C. C.
Development of a Redox/pH Dual Stimuli-Responsive MSP@
P(MAA-Cy) Drug Delivery System for Programmed Release of
Anticancer Drugs in Tumour Cells. J. Mater. Chem. B 2014, 2, 5187−
5194.
(20) Windbergs, M.; Zhao, Y.; Heyman, J.; Weitz, D. A.
Biodegradable Core−Shell Carriers for Simultaneous Encapsulation
of Synergistic Actives. J. Am. Chem. Soc. 2013, 135, 7933−7937.
(21) Koppolu, B.; Rahimi, M.; Nattama, S.; Wadajkar, A.; Nguyen, K.
T. Development of Multiple-Layer Polymeric Particles for Targeted
and Controlled Drug Delivery. Nanomedicine 2010, 6, 355−361.
(22) Wang, Y. Z.; Zhang, Y. Q.; Wang, B. C.; Cao, Y.; Yu, Q. S.; Yin,
T. Y. Fabrication of Core-Shell Micro/Nanoparticles for Programmable Dual Drug Release by Emulsion Electrospraying. J. Nanopart.
Res. 2013, 15, 1726.
(23) Zhang, Y. Q.; Wang, B. C.; Wang, Y. Z.; Qiao, W. L.; Shao, P. Y.
A Novel Hypurgia for Cancer Chemotherapy: Programmable Release
of Antineoplastics and Cytothesis Agents from Core-Shell Micro-/

Nano-particles. Med. Hypotheses 2011, 76, 201−203.
(24) Liu, L.; Yang, J. P.; Ju, X. J.; Xie, R.; Liu, Y. M.; Wang, W.;
Zhang, J. J.; Niu, C. H.; Chu, L. Y. Monodisperse Core-Shell Chitosan
Microcapsules for pH-Responsive Burst Release of Hydrophobic
Drugs. Soft Matter 2011, 7, 4821−4827.
10534

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