appendix 5 micro- and nano- particle synthesis and processing...
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Appendix 5 Micro- and Nano- Particle
Synthesis and Processing for
Pharmaceutical, Biomedical, and Food
Applications (Part 3)
Chi-Hwa Wang
Department of Chemical and Biomolecular Engineering, National
University of Singapore, 4 Engineering Drive 4, Singapore,
117585, Singapore. E-mail: [email protected].
Computational fluid dynamics simulations
for drug delivery systems
Chi-Hwa Wang1,2
1 Department of Chemical and Biomolecular Engineering, National University of
Singapore, 4 Engineering Drive 4, Singapore 117576
2 Molecular Engineering of Biological and Chemical Systems, Singapore-MIT
Alliance, 4 Engineering Drive 3, Singapore 117576
Confocal fluorescence images of C6 glioma cells incubated 1 hour withcoumarin6-loaded PLGA particles (200-300nm).
Introduction
• Cancer is the number one killer in Singapore since 1996.
• Conventional post-surgery therapies for brain tumors:
Radiation & Intravenous chemotherapy.
Both methods are ineffective due to:
• Elevated interstitial pressure in the tumor center (Baxter & Jain 1989)
• Blood Brain Barrier
A novel way is the controlled drug release using polymers implanted into patients after the
surgery. Gliadel Wafers approved by FDA in 1996
Manufactured by Guilford Pharmaceuticals. Carmustine loaded polyanhydride
polymer (PCPP:SA)
6 months survival rate improved by up to 60%.
• This provides potential benefits of reduced overall toxicity to the entire body and improved survival rate.
Objectives
Current research aims at primarily:
• Developing a simulation platform which uses an engineering approach towards understanding the delivery transport mechanism.
• To derive the transient flow field that occurs after wafer implantation.
• Using simulation to study how wafer’s placement, its release profile, loading and other parameters will affect the efficiency of medical treatments.
Establishing a simulation platform, which will optimize key process
parameters to help surgeons in executing a successful treatment.
Ultimate Aim
a
Chem. Eng. Sci., 53(20), 3579-3600 (1998).
J. Controlled Release,
61 21-41 (1999).
J. Controlled Release,
61 21-41 (1999).
Temporal variation of
BCNU concentration
profiles:
(a) core implantation,
(b) tumor implantation
(c) systemic bolus
injection.
J. Controlled Release,
61 21-41 (1999).
Chem. Eng. Sci., 53(20), 3579-3600 (1998).
Chem. Eng. Sci., 53(20), 3579-3600 (1998).
Distribution of velocity and drug concentration
J. Controlled Release, 61 21-41 (1999).
Methodology
1. Construct a brain tumor geometry consisting of cavity (with wafers implanted), tumor and normal tissue zones.
2. Solving the transport equations of mass, momentum and species (drug), using Computational Fluid Dynamics Simulation to obtain a steady state condition prior to surgery.
3. Perturbing the steady state solution to simulate the transient effects:
a) assess the fluid flow pattern and its effects on the drug delivery
b) assess how different release profiles affect the efficacy of delivery
3D-Simulation of Enclosed Tumor
Model geometry developed
for the 3D simulation
incorporating 8 wafers and
the effect of gravity. The
table below shows that 2D
results are qualitatively
similar to 3D case. Gravity
does not introduce
significant change in the
flow field of the surgical
cavity.
C.S. Teo, K.H. Tan, T. Lee, and C.H. Wang, "Simulation of Drug Delivery to Brain Tumors, Effects of Transient Interstitial Fluid Flow", Chem. Eng. Sci., 60, 4803-4821
(2005).
Post-surgery Chemotherapy and
Radiotherapy
3-D Computational Geometry Pressure Distribution
Model GeometryC (cavity),T (tumor), N (normal
tissues), W (wafers)
1,2,3 – boundaries between
wafers and cavity
1, 2 – internal boundaries
3 – external boundary of
tissue.
Constructed from actual magnetic
resonance images
Governing Equations (Continued)
Adapted from Curry F E, Mechanics and thermodynamics of transcapillary
exchange in Handbook of Physiologyst, 4, 320-327, 1984, Saltzman & Radomsky,
Drugs released from Polymers: Diffusion and Elimination in Brain Tissue, Chem.
Eng. Sci. 1990, Loo T L et al., The Antitumor Agent, 1,3-Bis(2-chloroethyl)-1-
nitrosurea, J. Pharm Sci.,55, 5, 1966.
elsewhere0
tissuesnormalandtumorin
cavityin
cavityin0
tissuesandtumorin1
1
waferin/
Ck
Ck
R
e
PeCC
V
PSCF
eS
F
e
c
Pe
vvvv
t
o
sv
Steady State Fluid Profile
• A solution of the pressure and velocity profile is obtained prior to wafer implantation. This is the initial condition from which the transient profile can be derived.
• Simulation results show:
• High central interstitial pressure (1.2 kPa) agreeable with that of Baxter and Jain (1989).
• Outward flow of interstitial fluid which is detrimental to treatment based on systemic administration.
Bi-directional flow of fluid
(akin to that obtained in
the 2D simulation) in the
tumor zone at a cut section.
The tissue and tumor zones
are depicted by red and
gray meshes, respectively.
Preferential flow of
interstitial fluid around the
wafers (depicted by green
mesh) which is much less
permeable than the surgical
gel filling the cavity. This is
obtained at a cut section
midway in the z-direction.
C.S. Teo, K.H. Tan, T. Lee, and C.H. Wang, "Simulation of
Drug Delivery to Brain Tumors, Effects of Transient
Interstitial Fluid Flow", Chem. Eng. Sci., 60, 4803-4821
(2005).
0.E+00
1.E-06
2.E-06
3.E-06
4.E-06
5.E-06
6.E-06
0.0 0.3 0.6 0.9 1.2 1.5
Time (hour)
Velo
cit
y (
m/s
)
0
200
400
600
800
1000
1200
Pre
ssu
re (
Pa)
Velocity
Pressure
6.0E-9
8.0E-9
1.0E-8
1.2E-8
1.4E-8
1.2 1.3 1.4 1.5
Transient Flow Field
Transient variation of pressure and velocity in the cavity zone:
C.S. Teo, K.H. Tan, T. Lee, and C.H. Wang, "Simulation of Drug Delivery to Brain Tumors, Effects of Transient Interstitial Fluid Flow", Chem. Eng. Sci., 60, 4803-4821
(2005).
C.S. Teo, K.H. Tan, T. Lee, and C.H. Wang, "Simulation of Drug Delivery to Brain Tumors, Effects of Transient
Interstitial Fluid Flow", Chem. Eng. Sci., 60, 4803-4821 (2005).
Chemotherapy for Brain Tumor
C.S. Teo, K.H. Tan, T. Lee, and C.H. Wang, "Simulation of Drug Delivery to Brain Tumors, Effects of Transient Interstitial Fluid
Flow", Chem. Eng. Sci., 60, 4803-4821 (2005).
Chemotherapy for Brain Tumor
C.S. Teo, K.H. Tan, T. Lee, and C.H. Wang, "Simulation of Drug Delivery to Brain Tumors, Effects of Transient
Interstitial Fluid Flow", Chem. Eng. Sci., 60, 4803-4821 (2005).
Chemotherapy for Brain Tumor
C.S. Teo, K.H. Tan, T. Lee, and C.H. Wang, "Simulation of Drug Delivery to Brain Tumors, Effects of Transient Interstitial Fluid Flow", Chem. Eng. Sci., 60,
4803-4821 (2005).
3D-Simulation of Enclosed Tumor
Model geometry developed
for the 3D simulation
incorporating 8 wafers and
the effect of gravity. The
table below shows that 2D
results are qualitatively
similar to 3D case. Gravity
does not introduce
significant change in the
flow field of the surgical
cavity.
Cavity Tumor Normal Tissue
3D1 3D2 2D 3D1 3D2 2D 3D1 3D2 2D
Pressure
(kPa)
1.0 1.0 1.1 1.0 1.0 1.1 0.90 0.90 0.95
Velocity (m/s)
5 x 10-9
4 x 10-9
7 x 10-9
2 x 10-10
2 x 10 -10
2 x 10-10
1 x 10-10
1 x 10-10
3 x 10-10
The superscripts 1 and 2 refer to gravity in the z (as shown in above figure) and x directions, respectively.
C.S. Teo, K.H. Tan, T. Lee, and C.H. Wang,
"Simulation of Drug Delivery to Brain Tumors,
Effects of Transient Interstitial Fluid Flow",
Chem. Eng. Sci., 60, 4803-4821 (2005).
Temporal Evolution of Drug
Concentration
Tumor Wafer
Drug distribution at a cut
section in the z-direction
with partial display of the
wafers for clearer
visualization. (Time = 20
hours)
Distribution of drug in the
wafers.
K.H. Tan, F.J. Wang, T. Lee and C.H. Wang, “Delivery
of Etanidazole to Brain Tumor from PLGA Wafers: A
Double Burst Release System”, Biotechnology and
Bioengineering 82(3), 278-288 (2003).
0
2
4
6
8
10
12
0 15 30 45 60 75Time (day)
Th
era
pe
uti
c I
nd
ex
A
B
0
2
4
6
8
10
12
14
16
0 15 30 45 60 75Time (day)
Pe
ne
tra
tio
n D
ista
nc
e (
mm
)
B
A
Legend:
(A) Linear release
(B) Double burst
As shown in these figures,
linear release devices
achieve better therapeutic
index and penetration
depth (14 mm) than its
double burst counterpart.
K.H. Tan, F.J. Wang, T. Lee and C.H. Wang, “Delivery of Etanidazole to Brain Tumor from PLGA Wafers: A Double Burst Release
System”, Biotechnology and Bioengineering 82(3), 278-288 (2003).
0.0E+00
2.0E-09
4.0E-09
6.0E-09
8.0E-09
1.0E-08
1.2E-08
0 15 30 45 60 75
Time (day)
Co
nc
en
tra
tio
n (
mo
l/c
m3) A
B
However, in comparison with a double release wafer (B), linear release (A)
faces:
• a delay of several days in the tumor attaining therapeutic threshold level
(represented by dashed line in Fig LR-2). This is crucial to killing the
malignant cells.
• accumulation of drug concentration leading to increasing drug toxicity
towards later stages of treatment.
Fig
ure
LR
-2
K.H. Tan, F.J. Wang, T. Lee and C.H. Wang, “Delivery of Etanidazole to Brain Tumor from PLGA Wafers: A Double Burst Release
System”, Biotechnology and Bioengineering 82(3), 278-288 (2003).
2
T
N
C
1
3
N1
N2
N3
1 mm
W1
1
C/T
C/N
E
B
AF
Open Tumor: Transient Variations
Model Geometry used for open tumor
simulation
0.0E+00
1.0E-10
2.0E-10
3.0E-10
4.0E-10
5.0E-10
6.0E-10
7.0E-10
8.0E-10
9.0E-10
1.0E-09
0.00 0.20 0.40 0.60 0.80 1.00Time (hour)
Ve
locit
y (
m/s
)
550
600
650
700
750
800
850
900
950
1000
1050
1100
1150
1200
Pre
ssu
re (
Pa
)
Pressure
Velocity
Transient variation of
velocity and pressure in
the tumor zone,
summarizing the
developing transient
profiles of the open
tumor.
K.H. Tan, T. Lee, and C.H. Wang, “Simulation
of Intra-tumoral Release of Etanidazole: Effects
of the Size of Surgical Opening”, J. Pharm. Sci.
92(4) 773-789 (2003).
At the onset, fluid flows into
the cavity zones, causing a
pressure depression in all
zones.
However, the high
interstitial central pressure
which is crucial for efficient
drug delivery is never
restored, undermining the
efficacy of the treatment.
Pressure slowly equilibrates
leading to a bi-directional flow
of fluid in the tumor zone
which persisted for the
remaining part of the
simulation.
(All units in Pa) K.H. Tan, T. Lee, and C.H. Wang, “Simulation of Intra-tumoral
Release of Etanidazole: Effects of the Size of Surgical Opening”,
J. Pharm. Sci. 92(4) 773-789 (2003).
Velocity vector plot showing the
leakage of interstitial fluid in the
newly-attained steady state. Such
leakage causes uneven drug
distribution as well as transporting
the drug through the opening.
(Units in m/s)
Open Tumor: Effects on Treatment Efficacy
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0.00 0.50 1.00 1.50 2.00 2.50 3.00Time (hr)
Ra
tio
(
/P
e)
0
2
4
6
8
10
12
14
16
18
20
Ra
tio
(P
e)
Pe
/Pe j j
Temporal variation of the normalized
ratio of Pe and j/Pe in the Cavity.
Ratio(j/Pe) is defined as (j/Pe)op/(j/Pe)cl
and Ratio(Pe) is defined as (Pe)op/(Pe)cl,
where the subscripts “op” and “cl” refer
to the open and enclosed tumor
respectively. The opening has led to
increased convective effect.
K.H. Tan, T. Lee, and C.H. Wang, “Simulation of Intra-tumoral Release of
Etanidazole: Effects of the Size of Surgical Opening”, J. Pharm. Sci. 92(4)
773-789 (2003).
0.0E+00
5.0E-09
1.0E-08
1.5E-08
2.0E-08
2.5E-08
3.0E-08
3.5E-08
4.0E-08
4.5E-08
5.0E-08
0 5 10 15 20% Opening
Mass L
oss (
kg
/s)
0.E+00
1.E-09
2.E-09
3.E-09
4.E-09
5.E-09
6.E-09
7.E-09
8.E-09
Velo
cit
y (
m/s
)
3.64E-10 kg/s
Mass Loss
Velocity
Open Tumor: Effects of Opening Sizes
Drug contour plot showing the
uneven drug distribution in the
tumor zone due to the tumor
opening.
0
200
400
600
800
1000
1200
0.00 0.25 0.50 0.75 1.00 1.25 1.50
Time (Hr)
Pre
ss
ure
(P
a)
Closed
3.75%
6.19%
11.98%
17.99%
Transient variation of pressure in the
cavity due to different opening sizes
Mass loss and fluid flow velocity through the
opening with varying opening sizes
Mass
fraction
K.H. Tan, T. Lee, and C.H. Wang, “Simulation of Intra-tumoral Release of Etanidazole: Effects of the Size of Surgical Opening”, J. Pharm. Sci. 92(4)
773-789 (2003).
Design Strategy
• The double concentration peaks suggested that new formulation strategies are required to optimize the treatment against brain tumor.
Controlled Release of Etanidazole From
Double Walled Microspheres
Fabrication involves a hybrid process that incorporates phase separation
phenomenon when two polymer solutions were mixed and solvent
evaporation. Hence, microspheres with two distinct polymer layers were
formed in the process and were dried through solvent evaporation.
Water + Poly Vinyl Alcohol
(PVA)
Ultrasonication
Solvent Evaporation
Filtration + Freeze Drying
PLGA
Etanidazole + DCM
Ultrasonication
PLLA + DCM
Consistent and reproducible drug loaded double walled microspheres
has been produced in the study. It has also been successful in
manipulating the thickness of the shell wall and core diameter
through the control of the mass ratio of the two polymers. (i.e.
PLLA/PLGA)
A: PLLA/PLGA 1:1; B,C: PLLA/PLGA 2:1; D: PLLA/PLGA 2.5:1
A B
C D
T.H. Lee, J.J. Wang and C.H. Wang.
“Double-walled Microspheres for
Sustained Release of Highly Water
Soluble Drugs: Characterization and
Irradiation Studies”, J. Controlled
Release, 83, 437-452 (2002).
SEM showing microspheres with dissolved cores, ascertained that the core
was made up of PLGA while the shell of PLLA. A: PLLA/PLGA 2:1; B:
PLLA/PLGA 1:1.
•Differentiation by Solubility
PLGA is soluble in organic solvent Ethyl Acetate while PLLA is not. By
dissolving the cross sectional cuts of the microspheres and observing the
resultant structure, the configuration of the 2 polymers in the microspheres can
be determined.
A B
T.H. Lee, J.J. Wang and C.H. Wang. “Double-walled Microspheres for
Sustained Release of Highly Water Soluble Drugs: Characterization and
Irradiation Studies”, J. Controlled Release, 83, 437-452 (2002).
In Vitro Release: With Irradiation
50 Gy
0 Gy
30 kGy
14 days
t50
T.H. Lee, J.J. Wang and C.H. Wang.
“Double-walled Microspheres for
Sustained Release of Highly Water
Soluble Drugs: Characterization and
Irradiation Studies”, J. Controlled
Release, 83, 437-452 (2002).
Transcatheter oily chemoembolizationTreatment Procedure
Liver
Hepatoma
Tube
Majorartery
TubeHepatoma
Doxorubicin droplets
Blood capillaries
Maximum interstitial pressure occurs in the core, reaching a value of 1.55 kPa, in contrast to the value of 1.53 kPa reported by Baxter and Jain (1989)
Radially outward fluid velocity
Pressure and VelocityDistribution
0 153 307 460 613 766 920 1070 1230 1380 1530
(Pa)
Hepatoma
Drug Concentration
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0 2 4 6 8 10 12 14 16 18 20
t (h)
(kg/m3)
Tumor
Core
Tissue
i C
Baseline case:
Hepatoma
F.Y.M. Goh, H.L. Kong, and C. H. Wang, “On the Delivery of Doxorubicin to Hepatoma”,
Pharmaceutical Research, 18(6) 761-770 (2001).
1 minute
kg/m3
Hepatoma
F.Y.M. Goh, H.L. Kong, and C. H. Wang, “On the Delivery of Doxorubicin to Hepatoma”,
Pharmaceutical Research, 18(6) 761-770 (2001).
15 minutes
kg/m3
Hepatoma
F.Y.M. Goh, H.L. Kong, and C. H. Wang, “On the Delivery of Doxorubicin to Hepatoma”,
Pharmaceutical Research, 18(6) 761-770 (2001).
30 minutes
kg/m3
Hepatoma
F.Y.M. Goh, H.L. Kong, and C. H. Wang, “On the Delivery of Doxorubicin to Hepatoma”,
Pharmaceutical Research, 18(6) 761-770 (2001).
1 hour
kg/m3
Hepatoma
F.Y.M. Goh, H.L. Kong, and C. H. Wang, “On the Delivery of Doxorubicin to Hepatoma”,
Pharmaceutical Research, 18(6) 761-770 (2001).
Hepatoma
Effect of S/V Ratio
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 2 4 6 8 10 12 14 16 18 20
t (h)
Tumor
Core
tissue
0CC /
Lower S/V ratio:
F.Y.M. Goh, H.L. Kong, and C. H. Wang, “On the Delivery of Doxorubicin to Hepatoma”,
Pharmaceutical Research, 18(6) 761-770 (2001).
Varying injection volume does not alter amount and distribution of drug significantly
Changing dosage leads to corresponding change in drug concentration
- high dosage gives high concentration in tumor- low dosage gives lower toxicity in tissueoptimal dosage can be found
Lower vascular exchange area leads to lower concentration
Lymphatic drainage in tumor does not result in significant decrease in concentration
Cellular metabolism reduces drug concentration
Summary
Computer Simulation of Delivery
of Gentamicin to Bone
for The Treatment of Osteomyelitis
Osteomyelitis: bone infection commonly
caused by Staphylococcus aureus.
Present treatment involves the use of
antibiotics impregnated in
polymethylmethacrylate (PMMA) beads.
Problem: PMMA beads are non-
biodegradable.
Proposed solution: Biodegradable drug
disc.
PMMA beads
Implantation of PMMA
beads into the tibia
In vivo results
6-week PMMA PLGA disc
Bone formation after a period of 6-weeks
PMMA beads removed after 2-weeks to allow
for tissue growth before PLGA discs are
implanted
PLGA discs being implanted in rabbit femur.
P.K. Naraharisetti, C.G. Lee, Y.C. Fu, D.J. Lee, and C.H. Wang “In Vitro and In Vivo Release of Gentamicin from Biodegradable Discs”, Journal of
Biomedical Materials Research: Part B: Applied Biomaterials, 77B, 329-337, (2006).
Geometry used for simulation
Drug disc dimension: 5 mm diameter, 7 mm length
Surgical opening dimension: 10 mm by 5 mm
Surgical
Opening
(clot)
Marrow
Drug disc
Cortical bone
Periosteum
A
Marrow
Drug
Disc
xy-plane
Results I (Baseline Simulation)
Time = 10 min Time = 1 hour Time = 1 day
1500 Pa 0 Pa
Pressure contour for the yz-plane at different time.
1.27 x 10-1 m/s 2.89 x 10-8 m/s
Velocity vector for the yz-plane at t = 10 min
10 min 1 hour 1 day
C.G. Lee, YC Fu, and C.H. Wang, “Simulation of
Gentamicin Delivery for the Local Treatment of
Osteomyelitis”, Biotechnology and Bioengineering,
91, 622-635 (2005).
Results I (Baseline Simulation)
10 mins 1 hr
1 day 10 days
20 days 40 days
Change in gentamicin concentration with time (yz-plane):
(Coloured regions have concentration to bacteria MIC)
927 mg/ml 0.25 mg/ml
C.G. Lee, YC Fu, and C.H. Wang, “Simulation of Gentamicin Delivery for the Local Treatment of
Osteomyelitis”, Biotechnology and Bioengineering, 91, 622-635 (2005).
Results I (Baseline Simulation)
Mean gentamicin concentration in different region
Drug concentration rises
to a maximum 2 days after
implantation before
decreasing exponentially.
Decrease in concentration
is brought about by a
decrease in drug flux with
time and systemic
circulation serving as a
drug sink.
Pressure induced
convective transport also
results in rapid clearance
of drug through surgical
opening initially.
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
0 10 20 30 40 50
Time (Day)
Co
nc
(m
g/m
l)
marrow
clot
cortical bone
C.G. Lee, YC Fu, and C.H. Wang, “Simulation of Gentamicin Delivery for the Local
Treatment of Osteomyelitis”, Biotechnology and Bioengineering, 91, 622-635 (2005).
Results II (Comparison with PMMA beads)
0%
20%
40%
60%
80%
100%
0 20 40 60 80 100Time (Day)
Re
lea
se
of
ge
nta
mic
in (
%)
Experimental
Fitted Curve
Source: Wahlig et. al, The Release Of Gentamicin From
Polymethylmethacrylate Beads, J Bone and Joint Surgery, 60B(2), 1978
Experimental in-vitro drug release profile
from PMMA beads.
Cortical
Bone
PMMA
beads
Surgical Opening
(clot)
Marrow
Periosteum
Marrow
Geometry used incorporating
PMMA beads
(bead diameter = 5mm)
y =0.28823 t 0.2839
Results II (Comparison with PMMA beads)Change in gentamicin concentration with time (yz-plane):
(Coloured regions have concentration to bacteria MIC)
10 mins 1 hr
1 day 10 days
20 days 40 days
1391 mg/ml 0.25 mg/ml
C.G. Lee, YC Fu, and C.H. Wang, “Simulation of Gentamicin Delivery for the Local Treatment of Osteomyelitis”, Biotechnology and Bioengineering, 91, 622-635 (2005).
Summary
Continuous drainage of interstitial fluid from surgical opening in
the initial period of treatment causes drug concentration in marrow
to decrease exponentially.
Increasing clotting duration further depresses the mean drug
concentration in the marrow.
Drug release profile showing double burst exhibits a longer period
of drug concentration above MIC during the second burst.
While using PMMA beads results in an overall increase in drug
concentration, their non-biodegradable nature makes them less
appealing than biodegradable disc. A possible link between carrier
geometry and drug concentration may exist.