Week #7 Novel Pharmaceutical
Particles
Chi-Hwa Wang
Department of Chemical and Biomolecular Engineering, National
University of Singapore, 4 Engineering Drive 4, Singapore, 117576,
Singapore. E-mail: chewch@nus.edu.sg.
Advanced Drug Delivery Systems
Computation Simulation and Optimization
Optimized Strategy for
Cancer Therapy
Patient Specific
Treatment
Novel Fabrication of
Nano-/Micro-particles
NUS Presentation Title 2001
Novel Fabrication of Pharmaceutical Particles
Electrohydrodynamic atomization applications
Micro- and nanofibers.
Thin films.
Micro- and nanoparticles.
Microencapsulation of living cells, DNA etc.
Paclitaxel
Chemotherapy & radiotherapy for brain tumors.
Penetrates the blood-brain barrier poorly.
Ijsebaert J. C., K. B. Geerse, J. C. M. Marijnissen, J. J. Lammers, P. Zanen. Electro-hydrodynamic atomization of drug
solutions for inhalation purposes, J. Appl. Physiol. (2001) 91: 2735-2741.
Loscertales I. G., A. Barrero, I. Guerrero, R. Cortijo, M. Marquez, A. M. Ganan-Calvo. Micro/nano encapsulation via
electrified coaxial liquid jets, Science (2002) 295: 1695-1698.
Ding L. N., T. Lee, C. H. Wang. Fabrication of monodispersed Taxol-loaded particles using electrohydrodynamic
atomization, J. Control. Rel. (2005) 102(2):.395-413.
Xie J., C.M.M Jan, C.H. Wang. Microparticles developed by electrohydrodynamic atomization for the local delivery of
anticancer drug to treat C6 glioma in vitro. Biomaterials (2006) 27: 3321-3332
Xie J., C.H. Wang, “Electrospun micro- and nanofibers for sustained delivery of paclitaxel to treat C6 glioma in vitro”
Pharmaceutical Research , (2006) 23, 1817-1826.
Xie J., L.K. Lim, Y. Phua, J. Hua, C.H. Wang “Electrohydrodynamic atomization for biodegradable polymeric particle
production” J. Colloid & Interface Sci., 302, 103–112 (2006).
NUS Presentation Title 2001
Electro-hydrodynamic Atomization Process
Using electric field to break liquid drops into fine droplets
Syringe
Vn
Filter
Vr
Particles
Vacuum
pump
N2
Vn
Vr
: the trace of protective Nitrogen;
: solvent with polymer & drugs;
: volatilized solvent;
: collected polymer & drug particles;
: high voltage used to break liquid drops;
: high voltage applied to metal hoop;
NUS Presentation Title 2001
Electrohydrodynamic atomization process
Vn  Vn  Vg  Vn  0  Vn
Vr  Vr  Vg  Vr  0  Vr
Vg  0
Electrohydrodynamic atomization is an atomization method based on the application of an electrical
stress on the fluid that emerges from the tip of the nozzle. A Taylor cone, which is formed due to the
acceleration of the fluid by the applied electrical stress, reduces the diameter of the jet, so that a
thin jet is formed at the tip of the Taylor cone. Depending on the solution properties, either discrete
particles or strands of fibers can be formed using the same equipment.
Droplet Size Variation with Different Ring
Electrical Potential (Vr)
Vn=5kV, 3ml/h
140
Vn=8kV, 3ml/h
Droplet Size (micron)
120
Linear (Vn=5kV, 3ml/h)
100
Linear (Vn=8kV, 3ml/h)
80
II
60
40
20
I
0
1.5


3.5
5.5
Vr (kV)
7.5
9.5
I: changes in droplet size when Vn is kept at 5kV.
II: changes in droplet size when Vn is kept at 8kV.
Particle Size
Mass balance
Droplet Size
Modulation
Varying Vr
Taylor Cone, jet and droplet formation process
Nozzle Wall
Taylor Cone
Jet
320 micron
Droplet
Formation
The Front Tracking/Finite Difference CFD simulation was
able to replicate all observable phenomenon of the EHDA
process, including the Taylor Cone, Jet and the droplet
formation process.
Since the electrical charge resides on the surface of the
liquid, the electrical field accelerates the surface of the
liquid, and results in the formation of the circulating fluid
inside the Taylor cone.
Fluid: Dichloromethane; Flowrate: 6ml/h; Vn=8kV, Vr=8.9kV
Nozzle inner radius: 110 micron; Nozzle outer radius: 170 micron
Nozzle to Ring: 10mm; Nozzle to Ground: 100mm; Ring Diameter: 40mm
Taylor Cone, jet and droplet formation process
Nozzle Diameter ~ 340micron
Droplet Diameter ~ 50micron
A transient CFD simulation was done, so that the formation of the
Taylor Cone, jet and droplet was captured with time. Droplet
formation was also simulated and the simulated droplet size can be
obtained directly from the simulation data.
Fluid: Dichloromethane; Flowrate: 6ml/h; Vn=8kV, Vr=8.9kV
Nozzle inner radius: 110 micron; Nozzle outer radius: 170 micron
Nozzle to Ring: 10mm; Nozzle to Ground: 100mm;
Ring Diameter: 40mm
A
B
C
A: Eggers, J. Fluid. Mech., 262, 205, 1994;
B: CFD simulation results;
C: Chaudhary, J. Fluid. Mech., 96, 275, 1980
Closer look of Taylor Cone formation
CFD simulation
Experimental
The Taylor Cone is an important phenomenon in the
EHDA process, enabling the formation of thin jet
that is at least one order of magnitude smaller than
the inner diameter of the nozzle, resulting in
droplets that is smaller than the inner diameter of
the nozzle. The Taylor cone angle is also a useful
parameter for comparison between the experimental
and the simulation results.
Fluid flow field
Fluid: Dichloromethane; Flowrate: 6ml/h; Vn=8kV, Vr=8.9kV
Nozzle inner radius: 110 micron; Nozzle outer radius: 170 micron
Nozzle to Ring: 10mm; Nozzle to Ground: 100mm;
Ring Diameter: 40mm
Electrohydrodynamic Atomization
NUS Presentation Title 2001
Taylor cone
Jet
Charged droplets
J. Xie, J. C. M. Marijnissen, C. H. Wang. Biomaterials. 27: 3321-3332 (2006).
J. Xie, L. K. Lim, Y. Y. Phua, J. Hua, C. H. Wang. Journal of Colloids and Interface Science. 302, 103–112 (2006).
EHDA Microparticles
Xie J, Jan CMM, Wang CH. Microparticles
developed by electrohydrodynamic atomization
for the local delivery of anticancer drug to treat
C6 glioma in vitro. Biomaterials 2006; 27: 3321-3332
NUS Presentation Title 2001
Different polymer solution flow rates.
a: 3.0 ml/h size: 11±0.8μm;
b: 1.0 ml/h size: 6.5±0.8μm;
c: 0.5 ml/h size: 4.9±0.8μm.
d: 3ml/h size 17μm;
e: 10ml/h size 26μm;
f: 15ml/h size 32μm.
I 
KQ 
1

K: Conductivity
Q: flow rate
d: diameter of droplets
γ: surface tension I: current
(d)
(b)
(e)
(c)
(f)
2
1

4
 Q  6
0

d c
 Q1/ 2

I 2 








(a)
EHDA Microparticles
a
b
c
d
e
f
g
h
NUS Presentation Title 2001
Operating
parameters
Polymer Polymer
Polymer solution Air flow The voltage The voltage Nozzle
concentration flow rate
rate
of nozzle of ring
size
Samples
S1
S2
S3
S4
PCL
PLGA
PLGA
PLGA
6%
8%
8%
8%
3ml/h
5ml/h
5ml/h
5ml/h
25L/min
25L/min
25L/min
25L/min
9.8kV
10.0kV
10.0kV
10.0kV
7.1kV
9.0kV
9.0kV
9.0kV
0.91mm
0.91mm
0.91mm
0.91mm
Variation of operating parameters results
in controllable size and morphology of
microparticles.
Xie J, Jan CMM, Wang CH. Microparticles
developed by electrohydrodynamic atomization
for the local delivery of anticancer drug to treat
C6 glioma in vitro. Biomaterials 2006; 27: 3321-3332.
SEM images microparticles (a, b:
S1; c, d: S2; e, f: S3; g, h: S4)
EHDA Microparticles
NUS Presentation Title 2001
Characterization for samples S1 – S5.
Samples
S1
S2
S3
S4
S5
Drug loading (%) Encapsulation Efficiency (%)
8.1
7.9
8.4
15.8
0
81.3
82.3
84.1
78.1
-
Particle size (μm) ± SD
11.4 ± 0.9
15.2 ± 1.7
14.2 ± 2.2
15.1 ± 0.7
12.6 ± 0.8
S1 - Paclitaxel-loaded PCL microspheres
S2 - Paclitaxel-loaded PLGA microspheres
S3 - Paclitaxel-loaded PLGA particles of biconcave shape
S4 – Paclitaxel-loaded PLGA microspheres
S5 – Blank PLGA microspheres
Xie J, Jan CMM, Wang CH. Microparticles developed by electrohydrodynamic
atomization for the local delivery of anticancer drug to treat C6 glioma in vitro.
Biomaterials 2006; 27: 3321-3332.
EHDA Microparticles
NUS Presentation Title 2001
In vitro release
Cumulative release (%)
80
70
S1
60
S2
S1: 10% PCL Microspheres
S2: 10% PLGA Microspheres
S3
50
S4
S3: 10% PLGA Biconcave
40
S4: 20% PLGA Microspheres
30
20
Xie J, Jan CMM, Wang CH. Microparticles developed
by electrohydrodynamic atomization for the local
delivery of anticancer drug to treat C6 glioma in vitro.
Biomaterials 2006; 27: 3321-3332.
10
0
0
5
10
15
20
25
30
35
Tim e (day)
Initial burst due to dissolution and diffusion
of paclitaxel on the surface layer of the
microspheres proved by XPS results.
Paclitaxel-loaded PLGA microparticles could release faster than
paclitaxel-loaded PCL microparticles. Biconcave-shaped PLGA
microparticles may release slightly faster than PLGA microspheres.
20% paclitaxel-loaded PLGA microparticles could release slightly
faster than 10% paclitaxel-loaded samples. The total amount of
paclitaxel released seemed to be less than 60% of the total amount
of drug in the microparticles.
EHDA Microparticles
(d)
(g)
(b)
(e)
(h)
(c)
(f)
(i)
NUS (a)
Presentation Title 2001
Representative optical images of C6 glioma cells after being treated by paclitaxel-loaded PLGA microparticles
( 50μm). a, b, c: 250μg/ml 1, 2, 5 day; d, e, f: 1250μg/ml 1, 2, 5day; g, h, i: 2000μg/ml 1, 2, 5 day.
Optical microscope
EHDA Microparticles
NUS Presentation Title 2001
Cell viability
Xie J, Jan CMM, Wang CH. Microparticles developed by electrohydrodynamic
atomization for the local delivery of anticancer drug to treat C6 glioma in vitro.
Biomaterials 2006; 27: 3321-3332.
120%
120%
1day
100%
2days
100%
1day
3days
Cell viability (%)
Cell viability (%)
2days
3days
80%
4days
5days
60%
40%
40%
20%
0%
0%
20
40
60
80
100
120
140
Taxol concentration (μg/ml)
160
5days
60%
20%
0
4days
80%
0
250
500
750 1000 1250 1500 1750 2000 2250 2500 2750
Paclitaxel-loaded PLGA microparticle concentration (μg/ml)
The values of IC50 for Taxol and paclitaxel-loaded microspheres after 5days are around
14μg/ml and 160μg/ml, respectively. (Actual amount of paclitaxel: 160×10%*0.8=12.8
μg/ml). IC50 (inhibitory concentration 50%) represents the concentration of a drug that is required for 50% inhibition in vitro.
NUS Presentation Title 2001
Electrospinning
Taylor cone
Jet
Fibers
Schematic of electrospinning setup
Representative image of electrospinning jet
with the exposure time of 10ms.
0mM
1mM
5mM
Polymer NUS Presentation Title 2001
concentration
15%
0mM
1mM
5mM
10%
110±16nm
100±14nm
1mM
5mM
15mM
0mM
10mM
15mM
5%
82±11nm
Tetrabutylammonium
tetraphenylborate
(TATPB)
2%
Ionic surfactant
Increasing conductivity
45±7nm
31±5nm
Electrospun Micro- and Nano-fibers
NUS Presentation Title 2001
SEM images of paclitaxel-loaded PLGA Fibers
Cross section
10% paclitaxel-loaded
10% paclitaxel-loaded
PLGA nanofiber
PLGA microfiber
before release
Diameter: 14.5mm
Thickness: 1mm
Characterization of paclitaxel-loaded fibers
Samples
Fibers mean diameter Drug loading (%) Encapsulation efficiency (%)
PLGA MF (s1) 2.5±0.32 µm
9.9±0.1
99.0±1.0
PLGA NF (s2) 770±13 nm
9.2±0.03
92.0±0.3
http://www.drugs.com/PDR/Gliadel_Wafer.html
Results and discussion
Electrospinning
Micro- and Nano-fibers
NUS Presentation Title 2001
J. Xie, C.H. Wang, “Electrospun Micro- and Nanofibers for Sustained Delivery of Paclitaxel to Treat C6
Glioma In Vitro” Pharmaceutical Research , 23, 1817-1826 (2006).
Laser scanning confocal microscopy images
Cell morphology after 72h incubation with different formulations
Blank PLGA nanofibers
10% Paclitaxel-loaded
PLGA nanofibers
1000µg/ml
10% Paclitaxel-loaded PLGA
nanofibers 500µg/ml
10% Paclitaxel-loaded PLGA
nanofibers 2000µg/ml
10× green colour indicates living cells stained with FDA
Results and discussion
Electrospinning
Micro- and Nano-fibers
NUS Presentation Title 2001
J. Xie, C.H. Wang, “Electrospun Micro- and Nanofibers for Sustained Delivery of Paclitaxel to Treat C6
Glioma In Vitro” Pharmaceutical Research , 23, 1817-1826 (2006).
Cell viability after 72h incubation with different formulations.
120
Cell viability (%)
100
The IC50 value of paclitaxel-loaded PLGA
nanofibers was around 1200µg/well.
80
60
IC50 of paclitaxel of this formulation was
about 36µg/ml, which was comparable to
the commercial paclitaxel formulation
Taxol® (30µg/ml).
40
20
0
Control
Blank PLGA NF
PLGA NF 500
PLGA NF 1000
PLGA NF 2000
Different formulations
PLGA NF500: 500µg/ml; PLGA NF 1000: 1000µg/ml; PLGA NF 2000: 2000µg/ml.
NUS Presentation Title 2001
In-Vovo Experiment Overview: Tumor Volume Response
Subcutaneous
Inoculation with
1x 106 C6
giloma cells
Balb/c Nude mice
Disc (Surgical Implantation)
Microspheres
(Surgical Implantation)
a
Microparticles
b
Tumor _ Vol 
(Intra-tumor injection)
1
ab 2
6
After period of tumor growth,
Microparticles, Discs or
Microspheres are implanted
In-Vovo Experiment Overview: Tumor Volume Response
Representative pictures of tumours
after 21days of C6 glioma cells implantation
Blank
Microspheres
10% Taxol
loading EHDA
Microparticles
Taxol®
20% Taxol
loading EHDA
Microparticles
NUS Presentation Title 2001
Tumor volume response: Paclitaxel EHDA Microparticles
6000
Blank Microparticles
Tumor was allowed to grow for a period of 14
days before 1st injection of microparticles and
commercial taxol (for control were administered)
directly into the tumor mass.
Commercial Taxol - 1 mg Taxol
5000
Tumore volume (mm3)
Microparticle 20% Taxol Loading - 1 mg Taxol
4000
3000
20% Taxol Loading group had 1 mg taxol
administered in two doses of 0.5 mg as injection
directly into the tumor on Day 14 & 21.
2000
1000
0
0
5
10
15
20
Tim e (days)
25
30
35
40
70
EHDA Microparticles in
vitro release profile
Cumulative release (%)
60
Significant tumor growth suppression for at least
7 days after first injection (30 % in vitro release
reached).
50
Tumor volume is among lowest of treatment (see
next slide).
40
30
No significant variation of animal weight from
controls were observed. Indicating minimal or no
systemic toxicity effects.
20
10% PLGA EHDA Microparticles
10
20% PLGA EHDA Microparticles
0
0
5
10
15
20
Time (day)
25
30
35
40
NUS Presentation Title 2001
In-Vovo Experiment Overview: Tumor Volume Response
In vivo release profile of EHDA microparticles
14%
drug loaded EHDA microparticles
In vivo release profile for 14.8% Drug Loaded EHDA Microparticles
3.50
23.6 ± 6.5 ng/ml
EHDA microparticles
ng Paclitaxel/ ml Plasma
3.00
Control
EHDA Microparticles
Control
2.50
2.00
1.50
1.00
0.50
0.00
2
7
10
14
17
Days after Implantation
21
Days after implantation
28
Weight loss observed in control group
over first seven days.
No weight loss observed for EHDA
group.
Control group showed Paclitaxel
cleared from Plasma after 10 days.
Sustained delivery observed for
Experimental group for up to 28 days.
Particle Fabrication Techniques for Pharmaceutical Applications
Biomedical Devices Developed by Electrohydrodynamic Atomization (EHDA) Technique
Electrohydrodynamic atomization (EHDA) is a process, also called electrospray, where a
liquid jet breaks up into fine droplets under the influence of electrical forces. With increasing
electric forces, different spray modes can be obtained from dripping mode, single cone-jet
mode to multiple-cone mode. After the solvent evaporates, polymeric particles can be obtained.
Electrospinning of liquids involves the introduction of electrostatic charges to a stream of
polymeric fluid in the presence of strong electric field. After the fluid evaporates, fibers can be
formed.
Typical jet of electrospray and electrospinning
Representative optical images of C6 glioma cells after
being treated by different concentrations of
paclitaxel-loaded PLGA microparticles
Typical biomedical devices including gel microbeads, microparticles, films and
fibers.
Tumor volume variation with time
The research efforts of this project are to
develop various biomedical devices for
applications in controlled release of
bioactive materials using
electrohydrodynamic atomization
techniques. Through investigation of the
processing parameters during the EHDA
process, controllable size and
morphology of particles, controllable
diameters of fibers and controllable
thicknesses of films were successfully
achieved.
Singapore-MIT Alliance
Nanoparticle fabrication of
biodegradable polymers using
supercritical antisolvent: Effects of
mixing and thermodynamic
properties
Nanoparticle fabrication
Advantages of CO2
Methods of Fabrication
•“green” solvent, environmentally benign
•Readily available and inexpensive
•Low critical pressure and temperatures
Emulsion methods (O/W; W1/O/W2)
Spray drying (Microparticles)
RESS Rapid Expansion of Supercritical Solutions
(Debenedetti et al. (1993) Fluid Phase Equilibria 82, 311-321)
ASES Aerosol Solvent Extraction System
Electrohydrodynamic atomization (EHDA)
(Micro and nanopartices)
Dialysis (nanoparticles)
Supercritical fluid
techniques
(Micro and nanoparticles)
(Bleich et al. (1993) Int. J. Pharma., 97, 111-117)
SEDS Solution Enhanced Dispersion by Supercritical
Fluids
(Ghaderi et al. (1999) Pharma. Res., 16(5), 676 – 681)
SAS Supercritical AntiSolvent
(Reverchon et al. (2003) Ind. Eng, Chem. Res., 42, 6405 – 6414)
SASEM Supercritical Antisolvent with Enhanced Mass
Transfer
(Chattopadhyay et al. (2002) Ind Eng Chem Res., 41, 6049 – 6058)
Supercritical antisolvent
Most organic solvents are soluble in supercritical CO2
Low critical temperature (31.1 deg C)
Suitable for processing thermally labile pharmaceuticals
Polymer
Drug
Removal of organic solvent from product
Organic
solvent
Capillary nozzle
Small orifice
Coaxial nozzles
Assisted jet breakup
Enhanced mixing
Ultrasonic nozzles
Uniform atomization
Enhanced mass transfer in vessel
Hydrodynamics and thermodynamics
Both hydrodynamics and thermodynamics play a role in
influencing the Supercritical antisolvent process for polymer
particle formation
Diego and coworkers (2005) identified the two regimes of
particle formation for precipitation of polymers in the PCA
process
Below mixture critical pressure, the solution droplets were obtained
and mass transfer takes place between the solution droplets and CO2
Initial size of droplets influences the particle size
Above mixture critical pressure, solution enters the supercritical CO2 as
a gaseous plume
Turbulent mixing of solution and CO2
Mass transfer and mixing influence the particle size
Fibers or discrete particle may be obtained
Diego et al. (2005) Operating regimes and mechanism of particle formation during the precipitation of polymers using
the PCA process. J. Supercritical fluids, 35, 147 - 156
Hydrodynamics
Carretier and coworkers (2003) investigated the
hydrodynamics of the SAS process for precipitation of PLA
particles from methylene chloride (DCM) solution
Jet formation and breakup at supercritical pressures
Varying liquid flow rates (0.25 – 3 ml/min)
Jet breakup length dependent on the spray Reynolds number
Fibers or microparticles were obtained depending on liquid flow rates
Chattopadhyay and Gupta (2001) developed the supercritical
antisolvent with enhanced mass transfer (SASEM) for
production of uniform sized nanoparticles
Ultrasonic assisted atomization of jet
Enhanced mass transfer between organic solution and supercritical
CO2 phases
E. Carretier et al. (2003) Hydrodynamics of Supercritical Antisolvent Precipitation: Characterization and influence
on particle morphology. Ind. Eng, Chem, Res, 42, 331 – 338
P. Chattopadhyay and R. B. Gupta, Production of griseofulvin nanoparticles using supercritical CO2 antisolvent with
enhanced mass transfer. Int. J. Pharma. 228 (2001) 19 – 31
Objectives
Fabrication of nanoparticles of biodegradable polymers
Controlled release purposes
Model drug: Paclitaxel (hydrophobic)
Polymer studied: Poly L lactide (PLA)
Organic solvent used: Methylene chloride (DCM)
1.
Effect of thermodynamic conditions on particle properties
Constant operating temperature
35 deg C
Varying operating pressure
73.8 bar – 95 bar
2.
Effect of hydrodynamics
Jet formation in supercritical fluid
Jet flow rate
3.
Effect of mixing on particle formation
Supercritical antisolvent (SAS) process
Ultrasonication for mixing with the high pressure vessel
SAS setup
V1
P1
C2
F2
PI
CO2
V2
C1
P2
TC
F1
V3
Modified SASEM setup
V1
P1
C2
U1
PI
CO2
V2
C1
P2
TC
F1
U1: Ultrasonic system; Branson sonifier and converter,
Sonics and Materials probe (3/8” probe tip diameter)
F2
V3
Particle fabrication
1.
Pressurization (CO2)
2.
Spraying (Organic solution jet)
High pressure pump was used to deliver liquefied CO2 to high pressure
vessel
Temperature in high pressure vessel was maintained using circulating water
bath
High pressure liquid pump was used to deliver organic solution (Solvent +
pharmaceutical) into the high pressure vessel via a capillary nozzle
Vertical jet (SAS)
Horizontal jet (modified SASEM with ultrasonication)
Flowrate may be controlled by HPLC pump
3.
Venting
4.
Purging
Organic solvent – CO2 mixture was vented off to a fume cupboard from the
bottom of the vessel
Filter frit (0.22mm) was placed at bottom of the vessel to collect particles
Vessel was purged using fresh CO2 to remove any remaining organic solvent
SAS setup
Flow rate = 4ml/min
Reynolds number = 292
Jet breakup after
entering high
pressure CO2
Jet breakup length
is dependent on
spray Reynolds
number
No external mixing
in the high pressure
vessel during
precipitation
Effect of varying pressure
Experimental conditions
Solution flow rate was kept constant at 4ml/min
System temperature was maintained at 35 deg C
2% polymer loading in DCM
Pressure varied from 73.8 to 95 bars
73.8 bars
80 bars
Effect of varying pressure
90 bars
Smoother surface morphology particles obtained
Particle sizes were highly polydispersed
95 bars
Effect of varying pressure
Results obtained
Particle sizes of 5 – 10 mm were obtained
At 73.8 bars, particles obtained were agglomerated and surfaces were
very rough
At 80 bars and above, spherical particles with little agglomeration were
achieved
As supercritical pressure increases, particle morphology improves
For particles obtained at 90 and 95 bars, smooth surface morphology were
obtained
This suggests that as pressure increases, better mass transfer between
CO2 and DCM during the spraying process
More rapid precipitation
Less agglomeration
Effect of varying solution flowrate
Temperature: 35 deg C
Pressure: 90 bars
2% polymer loading in DCM
Solution flowrate of 2, 4, 6 ml/min
4 ml/min
2 ml/min
6 ml/min
Effect of varying solution flowrate
Count intensity (%)
12
4ml/min
10
Mean Size: 3.03 mm
SD: 2.25 mm
8
6
4
2
18
9.
6
9
8.
4
Particle size (mm)
6ml/min
16
Mean Size: 2.05 mm
SD: 1.21 mm
14
12
10
8
6
4
2
Particle size (mm)
9.
6
9
8.
4
7.
8
7.
2
6.
6
6
5.
4
4.
8
4.
2
3.
6
3
2.
4
1.
8
1.
2
0
0.
6
Count intensity (%)
7.
8
7.
2
6.
6
6
5.
4
4.
8
4.
2
3.
6
3
2.
4
1.
8
1.
2
0.
6
0
Effect of varying flowrate
Results obtained
At 90 bar and 35 deg C, powdery particles with little/no
agglomeration were obtained
Particles obtained have similar surface morphologies
Polydispersed particles
Clusters of small particles (< 2 mm)
Larger particles (2-10 mm)
Higher liquid flowrate generally decreases the particle size for
the larger particles
Shorter jet breakup length
Better mass transfer between the organic solvent and supercritical CO2
Modified SASEM setup
Jet breakup is not
due to liquid film
disintegration from
ultrasonic vibrating
surface
Enhanced
turbulence and
mixing of jet in the
high pressure cell
due to ultrasonic
vibration
Jet break up
Turbulence and mixing
Effect of ultrasonication
Comparison of SAS (No external mixing) and modified SASEM
10w/w% paclitaxel loaded PLA particles
2% polymer loading in DCM
No ultrasonication
Polydispersed
particles obtained
Mean Size: 4.13 mm
SD: 1.98 mm
Effect of ultrasonication
Particles obtained with ultrasonication
30 mm vibration amplitude
10% of maximum vibration
60 mm vibration amplitude
20% of maximum vibration
Effect of ultrasonication
Particles obtained with ultrasonication
90 mm vibration amplitude
30% of maximum vibration
120 mm vibration amplitude
40% of maximum vibration
Particle properties
Particle size and size distribution tends to decrease as vibration amplitude
increases
Recovery yield was comparable to conventional spray drying methods
Differential scanning calorimetry was performed to determine the crystalline state
of particles fabricated using the SAS/ modified SASEM setup
Encapsulation efficiency and in vitro release profile of the particles were
determined
EE% of as high as 80% were obtained
5000
90
4500
80
Encapsulatution efficiency (%)
70
3500
60
3000
(%)
Particle size (nm)
4000
Recovery yield (%)
2500
50
2000
40
1500
30
1000
20
500
10
0
0
0
30
60
90
Ultrasonic vibration amplitude (micron)
120
0
30
60
90
Ultrasonic vibration amplitude (micron)
120
Differential scanning calorimetry analysis
Thermogram analysis is an useful tool to determine whether
paclitaxel is molecularly dispersed in the polymer matrix or
phase separated as paclitaxel crystals
DSC analysis
Temperature range = 20 – 280 deg C
Temperature ramp speed = 10 deg C/min
Nitrogen flow rate = 5ml/min
Literature values
Pure paclitaxel
PLLA
Endothermic peak @ 223.0 deg C
Melting point @ 172-178 deg C
Thermogram properties
20
Raw paclitaxel
15
raw PLA (before SAS process)
Exotherm (mW)
10
Paclitaxel loaded PLA with
ultrasonication
Blank PLA with ultrasonication
5
0
-5
-10
-15
-20
0
50
100
150
200
Temperature (oC)
250
300
In vitro release profiles
Particles suspended in phosphate buffered saline (PBS)
Placed in shaker bath (120 rpm, 37 deg C)
Removed at predetermined time intervals
Solution was centrifuged and buffer solution was removed
Fresh PBS was added
Paclitaxel content in PBS was extracted and analysed using HPLC
60
Cumulative release (%)
50
40
Paclitaxel loaded PLA samples obtained using modified SASEM process
30
Sample
S1
S1
S2
S3
S4
20
S2
10
S3
0
0
5
10
15
20
25
Release time (days)
30
35
40
Ultrasonic
vibration
amplitude (mm)
0
30
60
90
Recovery
Yield (%)
Encapsulation
efficiency (%)
Size (nm)
21.1
18.1
14.6
12.8
70.0 ±3.5
67.7 ± 1.4
56.4 ± 14.4
83.5 ± 0.8
4130 ± 198
769 ± 210
506 ± 163
486 ± 134
Conclusions
We have successfully fabricated micro and nanoparticles of
PLA for potential application in controlled release purposes
The effect of thermodynamic properties and hydrodynamics
on particle formation was investigated in SAS process
Varying the operating pressure from 73.8 bar (critical pressure) to 95
bar significantly alters the surface morphology of microparticles
obtained
Increasing liquid flowrate reduces particle size and size distribution
The effect of ultrasonic vibration amplitude on particle size
and properties was investigated
Nanoparticles were obtained using the modified SASEM setup
Particle size may be altered by applying different ultrasonic vibration
amplitude
Drug Delivery Devices Developed by Supercritical Fluid Technique
A supercritical fluid is any substance at a temperature and pressure above its thermodynamic
critical point. Supercritical fluids offer favourable gas-like transport properties and liquid-like
solubility. Supercritical CO2 is used to fabricate biodegradable polymeric controlled release
devices using Poly L lactide (PLA) and Poly DL lactide-co-glycolide (PLGA). CO2 was chosen
as it has accessible critical temperature (31.1 deg C) and pressure (73.8 Bars), tunable properties
near the critical region, is inexpensive, non-flammable, and generally environmentally benign.
The supercritical fluid fabrication techniques employed in our research group include
fabrication of microparticles using supercritical antisolvent (SAS) process, and the fabrication of
micro-porous polymeric foams using supercritical gas foaming technique. In the supercritical60 bars
antisolvent process, the jet disintegration process at near critical conditions was investigated. In
vitro release profiles and other properties of the controlled release devices were also
characterized.
Phase diagram for carbon dioxide
70 bars
80 bars
SEM images of different morphology particles
obtained using SAS technique
80
Cumulative release (%)
70
60
50
40
30
S3A
20
S5A
10
S1A
0
0
5
10
15
20
Time (days)
25
30
35
Investigation of Various flow regimes of
In vitro release of paclitaxel from PLA microparticles organic solution entering supercritical CO2
PLGA foams with different mean pore sizes
achieved using Supercritical gas foaming technique
The research efforts of our group are to develop controlled-release drug delivery devices using supercritical fluid techniques for
chemotherapy to treat brain and liver cancers. Through investigation of the operating parameters of the SAS and Foaming process,
controllable particle size with anticancer drug encapsulation and foams with tailored pore size have been achieved respectively. As
such, the drug release profile may be modulated.
Contact:
Prof. Wang, Chi-Hwa
Tel: 6516-5079
E-mail: chewch@nus.edu.sg