Particles 2009, Berlin
Mechanical characterization of microcapsules
using AFM force spectroscopy
Andreas Fery
University of Bayreuth
F
Faculty
lt off Biology,
Bi l
Ch
Chemistry
i t and
dG
Geosciences
i
Department Physical Chemistry II
Bayreuth Center for Colloids and Interfaces
BZKG
Microcapsules
Encapsulation :
pharmaceutics, cosmetics,
food design,….
Biosystems :
abundance of capsules
(bacterial and viral
capsids,…)
Mechanical properties
• Stability
• Insight in physical state of the wall material
• Stimulus sensitivity
• Transport properties in flow, Rheology
p y mechanics-surface forces))
• Adhesion ((interplay
New tools for
Investigations on
Single microcapsule
level needed
Combination of AFM
with optical micoscopy
Layer-by-layer
Layer
by layer
capsules
Microballoons
hthin
VAir-Burst
2 RSwell
2 Zburst
AFM schematically
Photodiode
Laserdiode
Mirror
Sample
Feedback
XYZ Piezo-Scanner
Force detection or imaging possible
AFM: Force information
Usage of colloidal probe-cantilever1
ensures wellll defined
d fi d deformationd f
ti
geometry
1Butt
HJ.
HJ Biophysical Journal 1991; 60 (6):
1438-1444.
Colloidal probe
Microcapsule,
Mi
l axiosymmetric
i
ti
deformation
RICM: Shape Reconstruction
Reflection Interference Contrast
Microscopy (RICM)
allows
reconstruction of shape
Interferences
J. Rädler, E. Sackmann; J. Phys France II 3: 727 (1993)
Dubreuil, F., N. Elsner, A. Fery Europhys. J. E 12(2) 215 (2003)
Single Microcapsule Deformation : Method
H2O
Atomic Force Microscopy (AFM)
• Solvent, Temperature, … variable
• Force resolution < 10 pN
• Force range: 100pN – 100nN
• Deformation Resolution <1nm
MicroMi
scope.
Optical Microscopy
Image
Processing
• Shape information
• Contact areas
• Fluorescence
Europhys. J. E, 12 (2), 215-221 (2003)
review article :
Polymer, 48 7221-7235 (2007)
Microcapsule Systems
Polyelectrolyte Multilayer
C
Capsules
l
Polyelectrolyte Multilayer
T b 1
Tubes
Micro –Bubbles
Pickering
Emulsions2
1
: R. Müller & al. Polymer 48 2520 (2007); R. Müller et al. J. Phys. Chem. B 111 8547 (2007)
2 : Russell et. al. Angew. Chem. Int. Ed. 44 2420 (2005); Ferri et al. Soft Matter 11 2259
(2008)
Combination of AFM
with optical micoscopy
Layer-by-layer
Layer
by layer
capsules
Microballoons
hthin
VAir-Burst
2 RSwell
2 Zburst
PE-Multilayer capsules
LbL
Core
dissolution
E. Donath, G. B. Sukhorukov, F. Caruso, S. A. Davis and H. Möhwald, Angewandte Chemie,
International Ed.
Ed in English.
English 37,
37 2202-2205,
2202 2205 (1998)
wall properties
(thickness composition)
(thickness,
defined by multilayer
shape
(size, monodispersity)
d fi d b
defined
by ttemplate
l t particle
ti l
Qualitative look at PEM capsule deformation
F=k*x
Buckling transition from spherical shape to
indented sphere
Eur. Phys. J. E 12(2): 215 (2003)
Prog. Coll. Pol. Sci. 132: 117 (2006)
Small Deformation Approach
Playing Ping-Pong :
Deformations on the
order of the
membrane thickness 1,2 :
Ping Pong Ball : plastic deformation
f
and no volume conservation
F
d
h
d
F ∝ Eh 2
R
E : Young‘s modulus
R : radius of curvature
h : membrane thickness
R
Material of Young‘s modulus E
1:
L. Pauchard and S. Rica Philosophical Magazine B 78 225-233 (1998)
2: E. Reissner J. Mat. Phys. 25 80 (1946)
Wall-thickness effect and Young‘s modulus
System : Polystyrenesulfonate (PSS) / Polyallylamine (PAH) in water
400
350
kshell in m
mN/m
N
300
250
20
18
16
14
12
10
8
6
4
2
0
0
1
k ∝ Eh 2
R
Young‘s modulus
E = 294 ± 94 * 106 Pa
100 200 300 400 500 600
kshell in mN/m
200
Diffusion-coefficient
D< 10-15 cm2/sec
150
100
immobile chains,
glasslike material
50
0
Capsule stiffness can be
controlled by wall thickness
0
500 1000 1500 2000 2500 3000
2
2
h in nm
New Journal of Physics 6 18 (2004)
Stimulus sensitivity : Temperature
incubation time: 20 min
Capsule dia
ameter / μm
4,5
Effect of temperature ( T > 35°C ) :
System Poly-diallyl-dimethyl-ammonium /PSS
4,0
3,5
A
3,0
B
C
2,5
2,0
1,5
10
20
30
40
50
60
70
80
Incubation temperature / °C
90
100
Shrinking and thickness increase
(irreversible)
Köhler, K.; Shchukin, D. G.; Sukhorukov, G. B.; Möhwald, H. J. Phys. Chem. B 109, 18250-18259 (2005)
Change of Young‘s Modulus with temperature
stiffness
s k [pN/nm
m]
10000
Upon, cooling,
U
li
shape
h
iis
frozen
blue : room temperature
red : at 70 °C
1000
Change in k ~ Change in E
100
E changes by two
orders of magnitude
g
upon cooling,
E is in MPa range at
high temperature
10
0
10
20
30
40
time [min]
R. Müller, K. Köhler, R. Weinkamer, G. B. Sukhorukov and A. Fery Macromolecules 38 9766-9771 (2005)
Rate dependency of elastic constants
7
open symbols :
high temperature,
pronounced rate
dependency
norm
malized stiffn
ness
6
5
4
3
2
1
0
0,1
1
10
extension/retraction rate [Hz]
Transition from frozen to viscoelastic state
filled symbols:
low temperature,
li l variation
little
i i
over 2 decades
of deformation rate
Gold-NP containing capsules
System: Sukhorukov, Skirtach
Au-NP
PDADMAC/PSS
Talk M. Bedard Tue, 15:30
for details
Here : Shrinking process
stops at well defined radius,
depending on Au-NP content
1. Bedard MF, Munoz-Javier A, Muller R, del Pino P, Fery A, Parak WJ, Skirtach AG
and Sukhorukov GB. Soft Matter 2009; 5 (1): 148-155.
Mechanical characterization
(nN
N)
Nonlinear dependency
Of mechanical properties
on Au-NP content
• Regime 1: gold embedded in PDADMAC/PSS matrix,
surface tension dominates
• Regime
R i
2
2: gold
ld NPs
NP percolate,
l t
shrinking stops
Combination of AFM
with optical micoscopy
Layer-by-layer
Layer
by layer
capsules
Microballoons
hthin
VAir-Burst
2 RSwell
2 Zburst
Microballoons in Theragnostics
Micro-balloons = gas filled microcapsules
Micro-balloons act as strong scatterers for
ultrasound in the body (large density difference)
• contrast
t t enhancement
h
t
• therapy by encapsulation and
release of therapeutic gases
PVA Microballoons
Microballoon Synthesis (G. Paradossi / F. Cavallieri)
Polymerization of poly(vinyl alcohol) under agitation
Macroscopic
M
i creaming
i
Shelf lifetime months
Cavalieri, Hamassi, Chiessi
C
C
and Paradossi, Langmuir 2005, 21, 8758
Soft X-ray Microscopy: Langmuir 2008, 24, 13677; Soft Matter 2008, 4, 510
Micro-Balloon Deformation - Bursting
Gas filled MB
(strong scattering)
Same MB after
Bursting
(weak scattering)
Force (μN
N)
De
eflection
(µN)
3.0
<<< trace
>>> retrace
Bubble
Burst
2.5
2.0
1.5
1.0
hthin
0.5
VAir-Burst
0.0
6
7
8
Piezo Displacement
(μm) (µm)
Piezo Displacement
9
10
2 RSwell
2 Zburst
Deformation rate dependency
1.0
10 Hz
8 Hz
6 Hz
4 Hz
2 Hz
1 Hz
0.5 Hz
0.05 Hz
Large deformation:
pronounced rate dependency
Permeability effects ?
Force (µN)
0.8
0.6
0.4
Small deformation:
Weak rate dependency
0.2
00
0.0
2.0
1.5
1.0
0.5
Deformation (µm)
0.0
-0.5
-1.0
Conclusions
Combination RICM-AFM:
• Shape information can be obtained in situ
• Fewer assumptions on deformation
Mechanism necessary
PE-Multilayer capsules:
• deformation described by shell theory
• shrinking
g effects upon
p „melting“
g
• composite shells show two destinct regimes
Deflection (µN)
3.0
<<< trace
>>> retrace
2.5
Bubble
Burst
2.0
1.5
1.0
Microballoons:
• gas release can be monitored in situ
• Compressible interior,
interior volume forces dominant
05
0.5
0.0
6
7
8
Piezo Displacement (µm)
9
10
Coworkers :
Cooperations :
F. Dubreuil (microcapsule mechanics)
F
R. Müller (microcapsule T-effects)
N. Elsner (microcapsule pH-effects)
P Fernandes,
P.
Fernandes M
M. Pretzl,
Pretzl C.
C Hanske
(Micro-balloons)
PE Capsules:
p
G.B. Sukhorukov (Queen Mary Coll.)
H. Möhwald, A. Skirtach (MPI Golm)
Micro-balloons:
G. Paradossi, F. Cavallieri (University of Rome
‚Tor Vegata‘): MB preparation
Financial support : DFG, European Framework Program 6
Thank you for your attention !