Hindawi Publishing Corporation
BioMed Research International
Volume 2013, Article ID 569470, 16 pages
A Novel Multilayered Multidisk Oral Tablet for
Chronotherapeutic Drug Delivery
Zaheeda Khan,1Yahya E. Choonara,1Pradeep Kumar,1Lisa C. du Toit,1
Valence M. K. Ndesendo,2and Viness Pillay1
1Department of Pharmacy and Pharmacology, Faculty of Health Sciences, University of the Witwatersrand,
7 York Road, Parktown, Johannesburg 2193, South Africa
2Department of Pharmaceutics and Formulation Sciences, St John’s University of Tanzania, Dodoma, Tanzania
Correspondence should be addressed to Viness Pillay; email@example.com
Received 30 April 2013; Accepted 15 July 2013
Academic Editor: Sanyog Jain
Copyright © 2013 Zaheeda Khan et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
A Multilayered Multidisk Tablet (MLMDT) comprising two drug-loaded disks enveloped by three drug-free barrier layers was
developed for use in chronotherapeutic disorders, employing two model drugs, theophylline and diltiazem HCl. The MLMDT was
designed to achieve two pulses of drug release separated by a lag phase. The polymer disk comprised hydroxyethylcellulose (HEC)
and ethylcellulose (EC) granulated using an aqueous dispersion of EC. The polymeric barrier layers constituted a combination of
pectin/Avicel (PBL) (1st barrier layer) and hydroxypropylmethylcellulose (HPMC) (HBL1 and HBL2) as the 2nd and 3rd barrier
layers, respectively. Sodium bicarbonate was incorporated into the diltiazem-containing formulation for delayed drug release.
Erosion and swelling studies confirmed the manner in which the drug was released with theophylline formulations exhibiting
a maximum swelling of 97% and diltiazem containing formulations with a maximum swelling of 119%. FTIR spectra displayed no
interactions between drugs and polymers. Molecular mechanics simulations were undertaken to predict the possible orientation
of the polymer morphologies most likely affecting the MLMDT performance. The MLMDT provided two pulses of drug release,
separated by a lag phase, and additionally it displayed desirable friability, hardness, and uniformity of mass indicating a stable
formulation that may be a desirable candidate for chronotherapeutic drug delivery.
Biological processes, namely heart rate, fibrinolytic activity,
gastric motility, are known to follow the timed daily scale [1–
5]. In addition symptoms of diseases such as hypertension,
coronary heart disease, asthma, arthritis, osteoarthritis, and
duodenal ulcers also fluctuate with the time of the day [6–
20]. These diseases, although usually treated with sustained
ery where drug is released at predetermined time intervals
after a lag phase. Pulsatile drug delivery offers the follow-
ing advantages: (i) extended daytime or nighttime activ-
ity, (ii) reduced side effects, (iii) reduced dosing frequency,
(iv) reduction in dose size, (v) improved patient compliance,
addition to the use in these disorders, pulsatile drug delivery
olism as well as to target drugs to a specific site within the
gastrointestinal tract [21–24].
Numerous research works have been published on pul-
satile drug delivery [22, 25–30]. Among these is a “tablet in
capsule” device used to provide a three-pulse drug release
. The capsule consists of an impermeable capsule body
and a soluble cap. The capsule is loaded with a three-layer-
ed tablet which serves to provide the first two pulses and
a double-layered tablet which serves to provide the third
pulse. Additional pulsatile drug delivery systems intended
for chronotherapy include capsules [14, 21, 32], tablets [33–
35], and low density carriers [16, 36]. Marketed chronother-
apeutic drug delivery systems include OROS (Alza Cor-
poration, Mountain View, CA, USA), CEFORM (Biovail
Corporation, Mississauga, ON, Canada), CODAS (Elan Cor-
poration, Gainesville, FL, USA), Egalet (Egalet a/s, Vaerlose,
2BioMed Research International
Copenhagen, Denmark), CONTIN (Purdue Pharma, Pick-
ering, ON, Canada), Pulsincaps (R.P. Scherer Corporation,
PA, USA), and TIMERx (Penwest Pharmaceutical Company,
Danbury, CT, USA).
The characterization of the biological rhythms is usually
(2) the levels conferring to the rhythmic variation baseline,
(3) the amplitudes depicting the extent of variability, and
(4) the phases involving peaks and troughs corresponding
to the respective time scale [5, 37]. The circadian rhythms
can further be differentiated based on small amplitudes
(e.g., heart rate) or high amplitudes (e.g., blood cortisol
concentrations) [5, 38]. The above mentioned characteristics
may be used as a reference towards the determination of the
influence of “circadian rhythm” on the physiological systems
and the physiology of diseased states .
loaded disks that serve as the two pulsatile doses. These disks
were enveloped between three polymeric barrier layers. The
in an immediate pulse of drug release. The second and third
barrier layers (middle and bottom) swell and protect the
has to self-administer the MLMDT after dinner, the first
dose will provide immediate release and will persist until the
patient retires to bed. Drug release will then “turn off” whilst
the patient is asleep and then “turn on” before awakening
when the controlled release disk is activated. This coincides
with the body’s natural circadian rhythm and delivers drug
when it is mainly needed.
The purpose of this study therefore was to explore
the design and development of the MLMDT for use in
chronotherapeutic disorders. Theophylline (THP) and dil-
tiazem hydrochloride (DTZ) were employed as the model
drugs to develop two separate formulations, showing the
versatilityof the MLMDT when incorporatedwith prototype
water insoluble and water soluble drugs. In addition to the
experimental studies, the incorporation of EC along with
HEC, pectin and Avicel was mechanistically elucidated using
mechanistic modeling of the three-dimensional architecture
of the respective saccharide molecular complexes for the
prediction of the relative orientation of the polymer mor-
phologies affecting the MLMDT performance.
2. Materials and Methods
2.1. Materials. Materials employed include ethylcellulose
(THP), and diltiazem hydrochloride (DTZ) that were pur-
chased from Sigma Aldrich (Sigma Aldrich, MO, USA) as
well as hydroxypropyl methylcellulose (HPMC) (methocel
K4M CR, surelease), ethylcellulose (EC aqueous disper-
sion)(sureteric) (ColorconLimited,Kent, UnitedKingdom);
hydroxyethylcellulose (HEC) (degree of molar substitution =
(degree of esterification 38%, Mw = 80g/mol) (Herbstreith
and Fox GmbH, Werder/Havel, Germany). Lactose and
sodium bicarbonate (Saarchem, Krugersdorp, South Africa)
as well as microcrystalline cellulose (Avicel 101) (FMC Bio-
polymer, Drammen, Norway) were used as excipients. All
other reagents used were of analytical grade and were em-
ployed as purchased.
2.2.1. Preparation of the Multilayered Multidisk
(1) Preparation of Disk One (Lactose Disk). Lactose and either
THP or DTZ (30% of total drug) were measured, blended,
and directly compressed at 5 tons using a Karnavati Mini
Press II (Rimek Products, Gujarat, India) loaded with punch
and dies with a diameter of 10mm.
(2) Preparation of Disk Two (Polymer Disk). Quantities of
drug (70% of total drug) and polymer (either HEC or EC)
Surelease was prepared as per manufacturer instruction by
measuring a 60% 푤/V of the solution and adding 40% 푤/V
Sureteric was reconstituted to a 15% solid suspension using
deionized water (Milli-Q Millipore, Billerica, MA, USA)
to which 0.33% of an antifoaming agent was added. The
polymer were blended using a cube blender (Erweka Appa-
ratebau, Heusenstamm, Germany) to which the granulating
fluid was then added to produce a wet mass. The wet mass
The granules were placed in an oven at 37∘C until dry. The
granules were weighed and compressed in a disk at 5 tons
using a Karnavati Mini Press II.
of deionized water (Milli-Q Millipore, Billerica, MA, USA).
The solution was then agitated for 40 minutes prior to use.
was then passed through a 2휇m aperture sieve and collected.
(3) Preparation of the Multilayered Multidisk Tablet
(MLMDT). A schematic of the MLMDT is shown in
Figure 1. Briefly, the barrier layers comprised a pectin/Avicel
blend as the first upper barrier layer and HPMC as the
middle and bottom barrier layers. DTZ formulations
contained sodium bicarbonate combined with HPMC in
various regions. Table 1 expands on the specific quantities
In order to combine the MLMDT, a barrier layer was
added to the 13mm punch and die, and after leveling out
the powder blend, a disk was added and then centered using
the tip of a needle. The next barrier layer was added and
lastly the third barrier layer. The punch was then inserted
and the tablet was compressed at 5 tons using a Beckman
hydraulictablet press(Beckman Instruments,Inc., Fullerton,
CA, USA), fitted with a flat-faced punch and die (diameter
13mm). To minimize processing variables, all tablets were
tablets was performed in triplicate.
BioMed Research International3
Pectin/avicel barrier layer
HPMC barrier layer
HPMC barrier layer
consisting of two drug disks surrounded by barrier layers (PBL1,
HBL1, and HBL2).
Table 1: Mass constituents comprising the MLMDT for both DTZ
and THP formulations.
Pectin barrier layer (PBL)
HPMC middle barrier
layer 1 (HBL1)
HPMC outer barrier
layer 2 (HBL2)
Polymer disk (EC/HEC)
Total weight of tablet
1The DTZ MLMDT includes an additional 100mg of sodium bicarbonate in
the HPMC layers.
2.2.2. In-Process Validation Tests on the MLMDT. Friability,
hardness, thickness, and uniformity of mass analyses were
performed on both disks as well as the MLMDT. A sample
of 10 units each was examined to ensure reproducibility of
the tablet making process. Analyses were performed on a
Hardness Tester (Pharma Test, Hainburg, Germany) while
friability was determined on a Friabilator (Erweka D-63150,
Heusenstamm, Germany) at 25rpm for 4 minutes with
1% set as the upper limit of acceptability. The weight of
each MLMDT was determined using an analytical digital
balance (Mettler, Model AE 240, Griefensee, Switzerland)
with readings recorded to 2 decimal places. A digital caliper
(25 × 0.01mm capacity) (Taizhou hangyu tools gauge and
blades Co., Ltd., Wenqiao, Zhejiang, China) was used to
determine the thickness of both the disks and the MLMDT.
2.2.3. Computational Modeling to Obtain an Optimized For-
The major aim of this phase of the study was to obtain the
desired drug release profile (i.e., pulsatile drug release) as
modeled in Figure 2. By preventing drug release from the
polymer disk for the first 12–15 hours, this lag phase may be
achieved. Preliminary studies suggested that the duration of
of the polymer disk with HPMC, EC, and HEC displaying
optimum properties. ANN was explored as an optimization
option based on its robustness of convergence algorithms
05 10 1520
Drug release (%)
First phase of
of drug release
Figure 2: Schematic model depicting a representative ideal drug
release profile from the MLMDT.
for complex formulations that have diverse variables in
optimization model was employed to appropriately optimize
the MLMDT performance.
Based on this analogy, 21 formulations with variations in
the quantities of HPMC, EC, and HEC were evaluated for
drug release. Table 2(a) depicts 11 THP formulations while
Table 2(b) illustrates 10 DTZ formulations. Although HPMC
proved to be a suitable candidate when formulating THP
devices, this was not the case for DTZ formulations and
disk and the barrier layers.
was used to construct a Multilayer Perceptron (MLP) as
an ANN approach in order to generate an optimized for-
mulation. MLPs are layered feedforward networks typically
trained with static back propagation. These networks have
found their way into countless applications requiring static
pattern classification. Their main advantage is that they can
approximate any input/output map. The key disadvantages
are that they train slowly and require lots of training data
(typically requiring three times more training samples than
network weights). A generalized feedforward (GFF) network
over one or more layers (Figure 3). In theory, MLP can solve
any problem that a generalized feedforward network cannot
often solve the problem much more efficiently.
the Sigmoid Axon transfer function and Conjugate Gradient
learning rule were employed. A maximum of 10000 epochs
were run on NeuroSolutions version 4.32 (NeuroDimension
Inc., Gainsville, FL, USA) to ensure optimal training of data.
This study utilized a GFF model to predict the drug release.
studies were performed using a USP dissolution apparatus II
(Erweka, Heusenstamm, Germany) equipped with paddles.
Dissolution was performed in 900mL simulated human
4 BioMed Research International
Table 2: Experimental formulation investigations showing (a) polymers, granulating, and bulking agents employed for THP formulations
and (b) polymers, granulating, and bulking agents employed for DTZ formulations.
FormulationHEC (mg) EC (mg)HPMC (mg)
FormulationHEC (mg)EC (mg)Surelease
Polymer disk (mg)
1HBL1: HPMC middle barrier layer.
Sureteric: polyvinyl acetate phthalate.
2HBL2: HPMC outer barrier layer.
Figure 3: Schematic representing a Multilayer Perceptron (MLP)
with two hidden layers.
gastrointestinal fluid (SHGF) pH 1.2  for the first 2 hours
and simulated human intestinal fluid (SHIF) pH 6.8  for
the remainder of the study. Where sodium bicarbonate was
used, formulations were tested in pH 1.2 only. The MLMDT
was placed on a ring wire mesh assembly . The wire mesh
fits into the lower portion of the glass vessels and prevents
tablets from sticking to the vessel, allowing the full surface
area of the tablet to be exposed to the dissolution medium.
Dissolution studies were performed at a paddle speed of
50rpm and at a temperature of 37 ± 0.5∘C. Sampling of 5mL
was replaced with an equal amount of the simulated fluid
such that the volume of the simulated fluid in the dissolution
medium remained constant. The drug content was analyzed
was undertaken every 1 hour for 12 hours and thereafter at
the 24th hour. The withdrawn quantity of sample (i.e., 5mL)
by UV spectrophotometer at 휆280nmfor THP and 휆238nmfor
DTZ and computed from a standard linear curve of drug
BioMed Research International
in SHGF and SHIF (푅2> 0.99). Photographs of the tablets
tablets during dissolution by recording the aerial view of the
at certain dissolution time were captured using a camera
(Samsung NV15, Korea) to obtain changes of the dry-coated
2.2.5. Polymer Swelling Studies. The rate of water uptake was
determined by the equilibrium weight gain method .
tus II in the same way as described in Section 2.2.4 at pH 6.8
the MLMDTs were removed, blotted with absorbent sheets
to remove excess fluid, and reweighed. The percentage water
uptake,which isthedegreeof swelling,was estimatedat each
time point using (1) as follows:
% water uptake =푊푠− 푊푖
since the experiment was performed in triplicate.
initial weight of the matrix, and 푊푝is the weight of polymer
in the matrix. The polymer swelling or water uptake data
2.2.6. Matrix Erosion Studies. Erosion studies were under-
testing study described earlier. MLMDTs were subjected to
analysis using USP dissolution apparatus II 2 at 50rpm. At
predetermined time intervals, the MLMDTs were removed
and dried to constant weight in a thermofan oven. The per-
matrix erosion (%) =푊푖− 푊푡
centage matrix erosion (퐸) at time 푡 was estimated using (2)
where 푊푖is the initial starting weight of the matrix and 푊푡
is the weight of matrix subjected to erosion, for time 푡. The
matrix erosion data was obtained by calculating the mean of
2.2.7. Textural Analysis. Textural analysis was used to eval-
uate energy of deformation and indentation hardness of the
MLMDT which was converted to Brinell Hardness Number
(BHN). A calibrated texture analyzer (TA.XTplus, Stable
(2mm diameter) was employed for energy of matrix defor-
mation and a ball probe (2mm diameter) for indentation
hardness. Hardness was measured as the force (N) required
to indent the matrices to a set distance (mm). This force was
then converted to BHN using (3). Data was captured at a
rate of 200 points per second via texture exponent software
(version 3.2). The employed settings are shown in Table 3.
All experiments were conducted in triplicate. Consider the
where 퐹 is the force generated from indentation, 퐷 is the
diameter of spherical probe indenter (3.175mm), and 푑 is the
indentation depth (1.563mm).
2.2.8. Determination of Polymeric Structural Variations
molecular structures of the native polymers, the drug-poly-
mer granulated blend, and the compressed drug-loaded
MLMDT were analyzed using FTIR spectroscopy (Perkin
variations in vibrational frequencies and subsequent poly-
meric structure as a result of drug-polymer or even polymer-
polymer interactions. Changes in the polymeric backbone
erties of the polymer and therefore such changes need to be
determined. Analyses were performed in triplicate.
2.2.9. Surface Morphological Analysis. The surface morphol-
ogy of the MLMDT was observed using Scanning Electron
Microscopy (SEM). Samples of the MLMDT layers were
sectioned using a surgical scalpel (to minimize interference)
and mounted onto stubs and sputter coated with gold in a
USA) and then photographed using a bench-top scanning
electron microscope (Phenom Fei Company, OR, USA).
2.2.10. Atomistic Molecular Structural Mechanics Simulations.
Molecular mechanics computations in vacuum, which in-
cluded the model building of the energy-minimized struc-
tures of multipolymer complexes, were performed using the
HyperChem 8.0.8 Molecular Modeling System (Hypercube
of ethylcellulose (EC), hydroxyethylcellulose (HEC), pectin
(PEC), and Avicel (cellulose, AVC) (4 saccharide units each)
were built from standard bond lengths and angles using the
sugar builder module on HyperChem 8.0.8. The generation
of the overall steric energy associated with the energy-mini-
mized structures was initially executed via energy minimiza-
tion using MM+ force field and the resulting structures were
again energy minimized using the AMBER 3 force field. A
complex of one molecule with another was assembled by
disposing them in a parallel way, and the same procedure
of energy minimization was repeated to generate the final
models: EC-HEC and PEC-AVC. Full geometry optimiza-
tions were carried out in vacuum employing the Polak-
Ribiere conjugate gradient method until an RMS gradient
of 0.001kcal/mol was reached. Force field options in the
AMBER (with all H-atoms explicitly included) and MM+
(extended to incorporate nonbonded limits and restraints)
methods were the HyperChem 8.0.8 defaults. For computa-
tions of energy attributes, the force fields were utilized with
a distance-dependent dielectric constant scaled by a factor of
1. The 1–4 scale factors are the following: electrostatic 0.5 and
Van der Waals 0.5 .
3. Results and Discussion
in mass, each having an average weight of 99.6 ± 0.4mg
3.1. In-Process Validation Tests. The MLMDTs were uniform
0.03mm while friability was at an average of 0.5 ± 0.03%
(Table 4). The thickness ranged from 1.78 ± 0.02 to 5.18 ±
6 BioMed Research International
Table 3: Textural settings employed for the determination of deformation energy and matrix hardness.
Table 4: Friability, thickness, and mass uniformity for the DTZ and THP-loaded formulations (푁 = 10).
THP lactose disk0.9
THP polymer disk0.5
DTZ lactose disk0.8
DTZ polymer disk 0.4
Friability (%)Thickness (mm)
1.78 ± 0.02
2.14 ± 0.04
Uniformity of mass1(%)
99.6 ± 0.4
4.82 ± 0.03
1.78 ± 0.02
99.6 ± 0.4
99.9 ± 0.1
99.4 ± 0.6
99.5 ± 0.5
2.08 ± 0.02
5.18 ± 0.03 99.7 ± 0.3
1Expressed as a percentage of the theoretical weight.
Sensitivity about the mean
Figure 4: A typical bar chart portraying the ANN-derived sensitiv-
ity of HEC, EC, and sodium bicarbonate on 푘3.
(i.e., within the set limit 1%) (Table 4), demonstrating desir-
able matrix compressibility.
3.2. Employment of an ANN Approach for Formulation Opti-
mization. Results obtained from the model including the
average of the MSE values for all the training runs and the
best network run out of 10,000 epochs are highlighted in
Tables 5(a) and 5(b), respectively. The correlation coefficient
between the desired output and actual output of 푘3suggests
tiated in the profile shown in Figure 5(a) which showed a lin-
ear curve for HEC, suggesting that the concentration of HEC
of 푅2= 0.98 (Table 5(c)) determined from the comparison
Results from sensitivity testing suggested that the quan-
that the employed training model was extremely efficient.
of EC had a minor effect on the drug release. The quantity
of sodium bicarbonate present in the DTZ formulation also
affected the drug release profile as illustrated in Figure 5(b).
There was a linear increase in the sensitivity of the MLMDT
as the concentration of sodium bicarbonate increased up
to 50mg. However, at concentrations greater than 50mg
per layer, sodium bicarbonate had no longer a beneficial
matrix-stiffening effect on the formulation. This suggested
that 50mg per layer was the optimum concentration. The
compositions of the optimized formulation as determined
by the ANN approach are depicted in Table 5(d), while
drug release profiles are depicted in Figure 6. All further
experiments were performed on the optimized THP-loaded
and DTZ-loaded formulations.
3.3. In Vitro Drug Release Studies. Based on previous pre-
liminary studies, drug release profiles were separated into
four phases, namely, the initial phase, the first pulse of drug
release, the lag phase, and second phase of drug release
(Figure 2). Consequently, the rate release constant (푘) for
The rate constant, pertaining to the initial lag phase, first
(4) describing drug release from simple swellable matrix
where 푀푡/푀∞is the fraction of drug released at time 푡, 푘 is
the release rate constant, and 푛 is the release rate exponent.
release were termed 푘1, 푘2, 푘3, and 푘4, respectively. Ideally 푘3
should be 0. Table 6 highlights the rate constants of the 21
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Table 5: ANN results showing (a) data training diagnostics, (b) the
best network run, (c) the ANN model fit parameters and, (d) com-
bination of polymers to produce the optimum 푘3.
Average of final
Min abs error
Max abs error
4.51퐸 − 06
Correlation coefficient 푅2
1HBL1: HPMC middle barrier layer.
2HBL2: HPMC outer barrier layer.
Drug release profiles indicate that the formulations dis-
layers surrounding the disks. Thereafter there was a rapid
increase in drug release which was due to erosion of the
PBL and the subsequent exposure of the lactose disk to the
media. After complete release of drug from the lactose disk,
drug release from all the formulationsslowed down and then
gradually increased. The release of drug from the polymer
disk was controlled by the barrier layers and the type of
polymer in the polymer disk. Due to the high hydrophobic
nature of EC, formulations containing pure EC (F numbers
3, 4, 5, 6, 8 and 12) displayed reduced drug release (<50%)
(F numbers 1, 2, 7 and 9) demonstrated higher rates of drug
release. However, instead of a lag phase, biphasic release was
observed (Figures 7(a) and 7(c)). Utilizing both hydrophobic
and hydrophilic polymers (F numbers 10, 11, 13, 14, 15, 16, 17,
over the 24-hour period (Figures 7(a), 7(b), and 8(a)).
Varied polymer input
Varied salt input
0 2040 6080100
Figure 5: (a) Profiles showing the effect of EC and HEC on 푘3; (b)
profile showing the influence of sodium bicarbonate on 푘3.
was fairly controlled.
3.3.1. The Effect of Sodium Bicarbonate on Drug Release from
DTZ-Loaded MLMDTs. DTZ is known for its high water
solubility (>50% 푤/푤 at 25∘C) making controlled release
to control the rate of release of DTZ as demonstrated by the
mechanism proposed by Pillay and Fassihi, 1999 . The
a challenge. To counteract this challenge, an electrolyte
sodium bicarbonate was incorporated into the formulation
8BioMed Research International
Fractional drug release
Fractional drug release
Figure 6: Drug release profiles of optimized (a) THP and (b) DTZ-
loaded MLMDT formulations.
location and quantity of sodium bicarbonate in the MLMDT
significantly affected the rate of drug release as demonstrated
by F numbers 14–20 (Figures 8(a), 8(b), and 8(c)). Higher
concentrations of sodium bicarbonate (F numbers 17 and
18) reduced drug release to a level sufficient for incomplete
release after the 24-hour period. Formulations that served as
controls, that is, had no sodium bicarbonate (F numbers 12
and 21), displayed biphasic release instead of the desired lag
3.4. Swelling and Erosion Studies. In order to obtain further
evidence for the observed drug release kinetics, swelling
and erosional studies were performed on the optimized for-
mulations. Figure 9 shows the relationship between swelling
and erosion on (a) THP and (b) DTZ MLMDTs. The THP
formulation swelled to 80% of the original size within the
It is this initial swelling that contributed to the lag phase
Table 6: The rate constants of the various formulations.
seen in the drug release profiles (Figure 7(a)). After 4 hours
though, there was a sharp decrease in the % of water intake
(i.e., swelling). This may be ascribed to the erosion of the
upper PBL layer. This was further substantiated by the digital
images taken at 푡 = 4 hours, which showed the absence of
erosion rate remained reasonably constant. This accounted
for the lag phase observed in the drug release profile. At 12
hours there was an increase in swelling, and at 24 hours a
to approximately 60%. The MLMDT was relatively intact
(Figure 10(a) (G)) after 24 hours, and this may explain the
incomplete drug release that was obtained.
Swelling and erosion results from DTZ formulations
display different results even though the same polymers
were used. This was attributed to the inclusion of sodium
of an alkaline salt to an acidic drug resulted in a buffering
effect that inhibited drug release . There was an increase
in swelling within the first 2 hours contributing to the initial
lag phase (Figure 8(a)). Subsequently, there was a drop in
the swelling percentage similar to the THP-loaded MLMDTs
due to the erosion of the upper PBL layer and the lactose
the upper layer and the lactose disk (Figure 10(a) (B)). After
6 hours, the HBL1 and HBL2 layers swelled steadily while the
disk. The DTZ formulation swelled >100% in the first 2
matrix swelling. Thereafter there was a constant increase in
the swelling behaviour as well as the erosion over the next
10 hours. This was confirmed by the digital images as shown
in Figure 10(b). Despite the fact that there was an increase in
swelling, minimal drug was released confirming that sodium
bicarbonate does in fact inhibit drug release. After 12 hours,
hours compared with the THP formulation. This suggested
that the inclusion of sodium bicarbonate resulted in high
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Fractional drug release
Fractional drug release
Fractional drug release
Figure 7: Drug release profiles of THP-loaded MLMDTs in pH 1.2 (2hrs) and pH 6.8 (3 hours onwards).
there was a sharp decrease in swelling which may be justified
by the decreased rate in drug release (Figures 8(b) and 8(c)).
was 20% 푤/푤 only indicating that most of the drug had
been released thus correlating with the drug release profiles
3.5. Textural Analysis on the MLMDT. Textural analysis was
performed to determine the indentation hardness which was
converted to BHN. Since the MLMDTs comprised different
polymers on the top and bottom layers (Figure 11), hardness
was determined on both sides (top and bottom layers) of the
MLMDT. According to the obtained results, the HBL2 layer
Textural analysis was also employed to measure alter-
ations to swelling behavior. Force-displacement profiles for
Table 7: Brinell Hardness Numbers for the MLMDTs.
THP MLMDT layer one (PBL)
THP MLMDT layer three (HBL2)
DTZ MLMDT layer one (PBL)
DTZ MLMDT layer three (HBL2)
optimized DTZ- and THP-loaded formulations were ob-
tained using the texture exponent software V2 (Figures 12(a)
and 12(b)). Figure 12(a) illustrates the force-displacement
placement profiles for THP-loaded formulations exposed to
pH 1.2 and 6.8, while Figure 12(b) displays the profile for
DTZ-loaded formulations exposed to pH 1.2. The upward
the swollen matrix, with a smaller force needed to penetrate
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Fractional drug release
05 101520 2530
Fractional drug release
0510 1520 25
Fractional drug release
Figure 8: Drug release profiles of DTZ-loaded MLMDTs in pH 1.2.
the gel layer which increased once the probe penetrated the
tion of the probe from the swollen matrix (Figures 12(a) and
the erosion of the PBL layer. The MLMDT swelled progres-
sively with the final measurement at 24 hours demonstrating
a decline in size. These sequential events coincide with the
shape of the digital images obtained in the % of water uptake
(swelling) studies (Figure 12(a)). DTZ-loaded formulations
displayed a considerable increase in swelling during the first
2 hours. This was followed by an increase in swelling up to
10 hours after which there was a decline in the swelling as
erosion increased. The DTZ-loaded MLMDT swelled to a
greater degree than the THP-loaded MLMDT. This may be
ascribed to inclusion of sodium bicarbonate in the DTZ-
loaded formulations and corresponds with the shape of the
digital images obtained in Figure 12(b).
3.6. Determination of Polymeric Structural Variations Using
Fourier Transmission Infrared Spectroscopy (FTIR). FTIR
spectroscopy was carried out on the native polymer and
drug as well as the granulated (not shown) and compressed
forms of the formulation. The spectra were then evalu-
ated to determine if any changes in any of the structures
occurred. FTIR spectra of both the compressed THP for-
mulation (Figure 13(a)) and the compressed DTZ formula-
tion (Figure 13(b)) show no change in the structure of the
BioMed Research International 11
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05 1015 202530
Figure 9: Correlation of swelling and erosion profiles of (a) THP-loaded and (b) DTZ-loaded MLMDTs.
(D) (E) (F)
Figure 10: Digital images depicting (a) swollen THP-loaded MLMDTs and (b) swollen DTZ-loaded MLMDTs at (A) 2, (B) 4, (C) 6, (D) 8,
(E) 10, (F) 12, and (G) 24 hours, respectively.
Figure 11: The MLMDT tablet showing the difference between the
top and bottom layers of the device as based on the different poly-
mers employed in the layers.
compressed final tablet in comparison with that of the native
polymer and drug. Both figures illustrated characteristic
1054cm−1typical of EC, HPMC, and HEC. Figure 13(a)
shows the native THP peaks which were observed between
and at 700cm−1, and they were unchanged in the com-
pressed formulation. Similarly Figure 15(b) highlights the
cellulose bands occurring at 3476cm−1, 2934cm−1, and
characteristic DTZ bands observed between 1600cm−1and
in the amide group, which was present in the compressed
tablet. Thus, the observed spectrum could be regarded as
a simple superimposition between the native polymers and
drug, suggesting that no interaction occurred between the
polymer and the drug.
1800cm−1, indicative of the stretching of the carbonyl bond
SEM was conducted on the compressed MLMDT to observe
in Figure 14, there was a distinct difference in the surface
structure of the PBL and HBL1 layers. This variation in
structure accounted for the different rates of erosion and
swelling and consequently the drug release kinetics.
3.8. Molecular Mechanics Assisted Model Building
and Energy Refinements
3.8.1. Molecular Mechanics Energy Relationship Analysis. The
analytico-mathematical illustration of the potential energy
values, in the form of molecular mechanics energy rela-
tionship (MMER) analysis, was employed to gain mecha-
nistic information involved in the bonding and nonbond-
ing contributors. Blended-polysaccharide morphologies and
interactions were explained with reference to valence terms,
coulombic terms, and London dispersion forces. The MMER
12BioMed Research International
Figure 12: Typical force-displacement profiles for (a) THP-loaded MLMDTs in pH 1.2 and 6.8 and (b) DTZ-loaded MLMDTs in pH 1.2.
model for the various steric energy factors inherent to the
molecular complexes can be written as (5)–(7). Consider the
퐸molecule/complex= 푉∑= 푉푏+ 푉휃+ 푉휑+ 푉푖푗+ 푉hb+ 푉el⋅⋅⋅ ,
+ 8.746푉푖푗− 0.209푉hb+ 0.691푉el⋅⋅⋅ ,
퐸EC/HEC= 115.616푉∑= 7.861푉푏+ 72.277푉휃+ 44.159푉휑
퐸EC= 72.116푉∑= 3.551푉푏+ 32.878푉휃+ 26.457푉휑
+ 10.28푉푖푗− 0.231푉hb+ 0.863푉el⋅⋅⋅ ,
+ 7.085푉푖푗− 3.399푉hb− 75.157푉el⋅⋅⋅ ,
퐸PEC/AVC= −65.913푉∑= 3.824푉푏+ 28.882푉휃+ 40.252푉휑
퐸HEC= 130.862푉∑= 4.017푉푏+ 35.115푉휃+ 80.816푉휑
+ 10.968푉푖푗− 2.578푉hb− 17.072푉el⋅⋅⋅ ,
퐸PEC= −25.743푉∑= 2.030푉푏+ 16.827푉휃+ 26.87푉휑
+ 6.145푉휑+ 13.110푉푖푗− 34.094푉el⋅⋅⋅ ,
퐸AVC= −4.641푉∑= 1.477푉푏+ 8.718푉휃
+ 7.804푉푖푗− 4.933푉hb− 141.745푉el⋅⋅⋅ ,
where 푉∑= total steric energy for an optimized structure,
푉푏= bond stretching contributions, 푉휃= bond angle con-
tributions, 푉휑= torsional contributions, 푉푖푗= van der Waals
3.8.2. Geometrical Optimizations for Composite Polysac-
charide Morphologies. The molecular geometry minimized
structures of the EC-HEC and PEC-AVC after static lattice
atomistic iterations were modeled as depicted in Figures
15(a)–15(d), and the respective steric energy values to which
they will be responsive are listed in (7). Molecular modeling
studies may assist in determination of the specific interac-
tions among component polymer segments and may further
provide estimation towards the compatibility of the blending
polymers. Our theoretical foundation for this method relies
of the interactions acting locally among the segments of the
polymer chains involved in modeling computations .
The total steric energy value for the EC-HEC complex
(representing base disc) is stabilized by a binding energy of
∼87kcal/mol (Δ퐸BINDING = −87.362kcal/mol; (6)). On a
related to the negative free energy of mixing, that is, –ve
theoretical basis, the mandatory condition determining the
compatibility and miscibility of a blend of two polymers is
Δ퐸 . This energy minimization in case of EC-HEC was
strain due to steric interactions. These torsional strains were
however dismissed by the introduction of bond length and
bond angle alterations with respect to the systems’ degrees of
freedom. As obvious from comparisonbetween Figures 15(a)
and 15(b), the lowering of the energetic obstructions leads
to a substantial change from the initial starting geometry.
interacting monosaccharide residues producing rotational
BioMed Research International 13
Figure 13: FTIR spectra depicting (a) pure THP and compressed
THP MLMDT and (b) pure DTZ and compressed DTZ-loaded
The pendent groups (ethyl and hydroxylethyl) moved to
their “nearest minimum downhill” from the starting point
during minimization and hence causing the molecules to
pass through unfavorable regions. The steric modulations
further assist the pendent groups to overcome the tor-
sional barriers presenting a larger accessible potential energy
62kcal/mol) contributed mainly to the finally stabilized
surface . This torsional energy stabilization (Δ퐸푉휑
geometrical configurations. These energy optimizations are
(Δ퐸푉el∼ 20kcal/mol) between the two 4-saccharide units
sugar molecules. Furthermore, regarding the spatial prefer-
ence of EC with HEC, as depicted by the dots rendering in
Figure 14: SEM image illustrating morphology of the pectin/Avicel
(PBL) and HPMC (HBL1) layers (magnification 355x).
in form of H-bonding and those closely sharing the van der
These underlying weak chemical interactions may not
cause a structural change in the polymers but may initiate
containaliphaticside chains, hencecreatingrelocalizedareas
with density and refractive index different from the initial
values. Additionally, the hydroxyl group induced inter- and
intramolecular hydrogen bonding in EC-HEC (≈10 times
causing a “notable increase in the amount of drug released
over a given period” as explained earlier in the paper. This
release pattern may be attributed to the modified matrix
hydration process of EC (hydrogen bonding induced by the
presence of the HEC) and continued retarded release of drug
due to the entanglement of saccharide chains which in turn
lead to a high BHN of layer 3 as shown in Table 7.
Similarly, the molecular mechanistically minimized
energy value for PEC-AVC complex (representing layer 1) is
influence the hydration process of the EC polymer matrix
stabilized by a binding energy of ∼35kcal/mol (Δ퐸BINDING=
where the molecular models can be developed for the
1996 . Additionally, in case of PEC-AVC, the pectin’s
interaction model with cellulose was generated by trying
various helix translations along the axis and different mutual
rotational orientations with the helices within van der Waals
radius (Figures 15(c) and 15(d)). For efficient packing, low
energy of stabilization was supported by the rotations caused
by the coupled individual chains. These very rotations
caused the formation of bonding interactions in the form of
interactions (∼30kcal/mol) leading to the formation of a
−35.529kcal/mol; (7)). Molecular modeling proved to be a
powerful tool for studying the orientation of polysaccharides
torsional energy minimization (∼10kcal/mol), the formation
14BioMed Research International
Figure 15: Energy minimized geometrically constrained models of the following. (a) Ethylcellulose and hydroxyethylcellulose before
(red), and hydrogen (white). (c) Avicel (cellulose) and pectin before complexation; (d) PEC-AVC complex derived from MM computations.
The atoms in close interaction proximity are emphasized by space filling model (dots) where the yellow dots depict atoms involved in H-
bonding. Color codes for elements are carbon (cyan), nitrogen (blue), oxygen (red), and hydrogen (white).
rotational screw axis as depicted in Figures 15(c) and 15(d).
The aforementioned interactions involving the nonbonded
forces may cause the formationof induced dipoles within the
complex. Additionally, the binding energy changes should
be proportional to the polarizability of the substituents,
which in turn may lead to the formation of a dense polymer
network responsible for prolonged release of the bioactives
(Figures 15(c) and 15(d)).
The higher energy of stabilization (Δ퐸BINDING) of EC-
AVC being a less stabilized molecular complex is anticipated
to erode faster than EC-HEC leading to the release of drug
from layer 1 earlier than that from base disc. Hence, the
present modeling and computation method involving four
polysaccharides provided a justification of using a definite
delivery system with desired release profile (DDSDRP).” This
MLMDT and subsequent modeling system may act as a tem-
plate for the future applications employing various drug and
HEC as compared to PEC-AVC corroborated with the
chronotherapeutic strategy explained in this research. PEC-
polymer combination strategies involving chronotherapeutic
and DDSDRP requirements.
The MLMDT was successfully developed and characterized.
The system comprised two drug-loaded disks enveloped
by barrier layers. Friability, hardness, and uniformity of
mass were all within the specified limits depicting desirable
manufacturing settings. The MLMDT provided two pulses
of drug release, separated by a lag phase. The lag phase was
the concentrations of HEC and sodium bicarbonate being
the most important factors in producing the lag phase. The
experimental results were well corroborated by the molecu-
lar mechanics computations. Overall, the MLMDT showed
much promise as a chronotherapeutic drug delivery system.
Conflict of Interests
The authors declare that there is no conflict of interests.
BioMed Research International 15
This research was funded by the National Research Founda-
tion (NRF) of South Africa and the Technology Innovation
Agency (TIA) of South Africa.
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