“Smart Nanoparticles”
Stimuli Sensitive Hydrogel Particles
L. Andrew Lyon, Associate Professor
School of Chemistry and Biochemistry
Georgia Institute of Technology
Hydrogels
Crosslinked water soluble polymers – a physically
restricted, dimensionally-stable, polymer solution
Responsive Hydrogels
Polymeric gels can be designed to undergo
environmentally-initiated phase separation
events (volume phase transition).
Change in local environment
pH, Photons,Temperature, Ionic Strength,
Electric Fields, Pressure, [Analyte]
Collapsed state
Chain-chain
interactions
dominate
Swollen state
Solvent-chain
interactions
dominate
Typical Responsive Gel
poly(N-isopropylacrylamide) (pNIPAm) – Thermoresponsive Gel
(
H
O
HN
H
H
H O
H O
H
H
H
O
H
O H
O
H
H
H
)
H O
H
O
H
H
O
H
O
H
O HN
H
(
H
H O
H
H
O
O H
H
H O
H
H
O
H
O
H
H
H
O
O
H
)
Swollen/Hydrophilic
H O
H
31 °C
H
O
H
H O
H
H H
O
(
)
HN
H
O
O H
H
O
H
H
HN
H
O H
H
H
O
H
O
H
O
(
H
O
)
H
O
H
O
H
H O
H
H
H
H O
H
Collapsed/Hydrophobic
O
H
Polymer Phase Separation
Phase separation of poly-N-isopropylacrylamide occurs via an
entropically-driven coil to globule transition.
Xiaohui Wang; Xingping Qiu; Chi Wu
Macromolecules, 1998, 31 (9), 2972 –2976.
Responsive Hydrogels
A change in osmotic
pressure on either side of
the interface induces a
solvation/desolvation
response
π
k BT
=
π el + π M
k BT
Decrease Solvent Quality/Increase χ
0.8
Osmotic Pressure
Volume phase transitions
in simple gels can be
modeled as a crosslinked
polymer in a vdW fluid.
0.4
0.5
0.0
1
-0.4
2
0.1
4
6 8
2
4
1
log [G el Volume]
1
⎡
⎤
3
n0 ⎢ 1 ⎛ n ⎞ ⎛ n ⎞ ⎥ 1
⎜⎜ ⎟⎟ − ⎜⎜ ⎟⎟ − ln (1 − nv ) + nv + χn 2 v 2
=
N x ⎢ 2 ⎝ n0 ⎠ ⎝ n0 ⎠ ⎥ v
⎢⎣
⎥⎦
[
]
“Smart” Polymers
endoglucanase 12A
web.mit.edu/physics/tanaka/bac
kground/patterns.html
Chen, Park, and Park J. Biomed. Mat.
Res. 1999, 44(1), 53-62.
Shimoboji, Larenas, Fowler,
Hoffman, and Stayton Bioconj.
Chem. 2003, 14(3), 517-525.
Asher, Sharma, Goponenko, and Ward Anal.
Chem. 2003, 75(7), 1676-1683.
pNIPAm Microgel/Nanogel Synthesis
O
O
HN
HN
+
+
HN
SDS
70 oC
APS
>4 hrs.
O
X
O
Precipitation Polymerization
Oligoradical
Precursor
Particle
Growing
Particle
Microgel
Controllable Parameters:
particle porosity/solvent content (crosslinker identity/conc.)
size – 50 nm to 5 μm (initiator, surfactant conc.)
phase transition magnitude
volume phase transition shape
Hydrogel Design
Particle design via copolymerization
O
O
HN
O
HO
O
HN
O
HN
N
O
S
O
HO
H2N
pH sensitive/polyelectrolytes
O
O
O
thermosensitive
O
O
Crosslinker length
O
O
N
Hydrogel Design:
Responsivity/Sensitivity
Electric Field
O
Light
O
HN
HN
HN
O
Metal Ions
HN
O
O
S
O
HO
O
H2N
O
HO
N
N
O
O
O
O
O
Hydrogel Particle Characteristics
Highly Monodisperse
Infinite Spherical
Network
High water content (90-99% v/v)
a microgel is effectively all surface area
Volume Phase Transitions
2 mol%
crosslinked
pNIPAm in
water
Dynamic Light Scattering (Photon Correlation Spectroscopy)
Multiresponsive Hydrogels
pNIPAm-co-Acrylic Acid – pH and temperature
dependent
Core/Shell Synthesis
+ Shell
70 °C
Swollen
Core
Collapsed
Core
25 °C
Collapsed
Core/Shell
Swollen
Core/Shell
Collapsed core particles act as preexisting hydrophobic
nuclei onto which growing polymer (the shell) adds.
Must control hetero-nucleation vs. homonucleation to
achieve monodisperse populations.
Core/Shell Particle Characterization
100
p-NIPAm
% Intensity
1 μm
p-NIPAm-co-AAc
Core
80
Core-Shell
60
40
20
0
0
50
100
250
Radius (nm)
Light scattering data typically show an
increase in particle size between core and
core/shell with invariant polydispersity.
300
Multiresponsive Core-Shells
1
2
3
4
p-NIPAm Core
p-NIPAm -co-AAc Shell
pH 6.5
Radius, nm
160
1
140
2
120
3
100
4
80
30
40
50
o
Temperature, C
Jones, C. D., Lyon, L. A. Macromolecules, 2000, 33, 8301-8306.
Phase Transition Tuning
Phase transition temperature determined by
hydrophilic/hydrophobic balance.
O
O
HN
HN
+
+
HN
SDS
70 oC
APS
>4 hrs.
O
X
O
X=N-tert-butyl
Ratio of N-isopropyl to N-tert-butyl determines
transition point.
Phase Transition Tuning
(○) 1 mol-%, (z) 5 mol-%, (□) 10 mol-%, („) 20 mol-% and (U) 40 mol-% TBAm
Debord, J. D.; Lyon, L. A. Langmuir, 2003, 19, 7662-7664.
Phase Transition Tuning – pH and
Hydrophobicity
Poly(N-isopropyl
acrylamide-co-N-tertbutyl acrylamide-coacrylic acid) microgels
– electrostatic repulsion
mediates hydrophobic
collapse.
pH 8.0
pH 3.5
Multi-Functional Nanogels
PEG-grafted “core” and core/shell particles
How does PEG-grafting impact protein adsorption?
Multi-Functional Nanogels
“Bare” pNIPAm
microgels (no PEG)
display strong Tdependent protein
adsorption. Below
phase transition =
hydrophilic; above
phase transition =
hydrophobic.
40 °C
25 °C
Multi-Functional Nanogels
PEG-Modification renders collapsed particles hydrophilic.
Gan, D.; Lyon, L. A. Macromolecules, 2002, 35, 9634-9639.
Multi-Functional Nanogels
NMR Analysis indicates a relative change in polymer
hydration – PEG “core” phase separates to shell surface.
Polyelectrolyte/Microgel Multilayers
=Anionic Microgel
=Polycation (PAH)
(
H2N
)
Microgel Film Formation
Passive Adsorption
Spin Coating
1 layer
1 layer
3 layer
3 layer
pNIPAm-AAc = polyanion
poly(allylamine)•HCl (PAH) = polycation
Serpe, M. J.; Jones, C. D.; Lyon, L. A. Langmuir, 2003, 19, 8759-8764.
Co-Deposition of Macromolecules
Insulin-impregnated films obtained via
incubation of particle solution with peptide.
Labeled Insulin Incorporation
Linear increase in
insulin content with
particle layer number.
Nolan, C. M.; Serpe, M. J.; Lyon, L. A. Biomacromolecules 2004, in press.
Pulsatile Insulin Release
Medium Replacement
Heat to 40 C
9-layer film in
0.02M PBS
pH=7.4
Fast, pulsatile insulin release during film deswelling.
Bio-Functional Nanogels with
Designed Topology
Cleavable diol
crosslinks (DHEA)
Biotinylated core beneath a shell with tunable pore size.
Bio-Functional Nanogels with
Designed Topology
HABA assay for biotin-avidin binding
Avidin-HRP binding
(~150 kDa)
“Bare” Cores
Biotin Cores
Avidin binding
(~60 kDa)
Partially degraded shell Æ MW dependent binding.
Towards a Smarter Nanogel
Drug/Gene/RNA delivery
Goals:
1. Long Circulation Time
2. Cell-Specific Targeting
3. Receptor Mediated
Endocytosis
4. Endosomal Escape
5. Cytosolic or NucleusLocalized Release
These steps comprise a state-dependent “program”
Cancer Targeting with Nanogels
Folic acid - an effective ligand for targeting solid tumors.
Fluorescent
Hydrogel Core
Folate(-) Nanogels
Folate Labeled
Shell
Folate(+) Nanogels
Cancer Targeting with Nanogels
Dual staining (particle+lysotracker) illustrates
endosomal escape.
Nayak, S.; Lee, H.; Chmielewski, J.; Lyon, L. A., submitted.
Cancer Targeting with Nanogels
Thermal trigger induces cytotoxicity
Other Stimuli: Photons
Photosensitive microgels via T-jump dyes
ε = 150,000; φ = 0
Photosensitive Microgels
Increasing
T(bath)
Increasing dye
concentration =
greater
photoheating.
Hydrogel Micro-Optics
Substrate-supported microgels behave as microlenses.
SEM
DIC
LENS
LENS
Serpe, M. J.; Kim, J.; Lyon, L. A. Advanced Materials, 2004, 16, 184-187.
Tunable Aqueous Microlenses
pH 3.0
pH 6.5
pNIPAm-co-AAc –
temperature and pH
tunable lensing.
Photoswitchable Microlenses
Laser heating of gold nanoparticles provides route to
photoswitching
OFF ON
Acknowledgements
The Group
Justin Debord (g) – Bioconjugates
Clint Jones (g) – Core-Shell/Crystals (now at PSU)
Christine Nolan (g) – Thin Films/Insulin Delivery
Satish Nayak (g) – Bioconjugates
SaetByul (Stella) Debord (g) – Colloidal Crystals
Mike Serpe (g) –Thin Films/Lenses/Drug Delivery
Jonathan McGrath (g) – Templated Microgels
Jongseong Kim (g) – Films/Polyelectrolytes/Lenses
Ashlee St.John (g) – Colloidal Crystals
Bart Blackburn (g) – Cell Targeting
Neetu Singh (g) – Bioconjugates
Ryan Mulkeen (ug) – Colloidal Crystals
Collaborators
Victor Breedveld (GT-ChE)
Mohan Srinivasarao (GT-PTFE)
Jean Chmielewski (Purdue-Chem)
Mike Ogawa (BGSU-Chem)
Joe LeDoux (GT-BME)
Support
NSF-CAREER
NSF-DMR
NSF-STC (MDITR)
Office of Naval Research
DARPA (BOSS)
Beckman Foundation
Sloan Foundation
Dreyfus Foundation
GT Blanchard Fellowship