-
www.sciencemag.org/cgi/content/full/319/5868/1370/DC1
Supporting Online Material for
Stimuli-Responsive Polymer Nanocomposites Inspired by the Sea
Cucumber Dermis
Jeffrey R. Capadona, Kadhiravan Shanmuganathan, Dustin J.
Tyler,
Stuart J. Rowan,* Christoph Weder*
*To whom correspondence should be addressed. E-mail:
[email protected] (C.W.); [email protected] (S.J.R.)
Published 7 March 2008, Science 319, 1370 (2008)
DOI: 10.1126/science.1153307
This PDF file includes: Materials and Methods
Figs. S1 to 10
Table S1
References
Other Supporting Online Material for this manuscript includes
the following: (available at
www.sciencemag.org/cgi/content/full/319/5868/1370/DC1)
Movie S1
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1
Supporting Online Material for:
Stimuli-responsive polymer nanocomposites inspired by the sea
cucumber dermis Jeffrey R. Capadona,1,2,3 Kadhiravan
Shanmuganathan,1 Dustin J. Tyler,2,3 Stuart J.
Rowan,1,2,3,4* and Christoph Weder1,2,4*
1Department of Macromolecular Science and Engineering, Case
Western Reserve
University, 2Rehabilitation Research and Development, Louis
Stokes Cleveland DVA
Medical Center, 10701 East Blvd., Cleveland, OH 44106,
3Department of Biomedical
Engineering, Case Western Reserve University, 4Department of
Chemistry, Case
Western Reserve University, 10900 Euclid Avenue, Cleveland, OH
44106.
Correspondence and requests for materials should be addressed to
C. Weder ([email protected])
or S. Rowan ([email protected]).
This supplement contains:
SOM Text Fig. S1 Transmission electron microscopy image of
tunicate whiskers. Fig. S2 DMA temperature sweeps for dry
EO-EPI/whisker nanocomposites. Fig. S3 DMA temperature sweeps for
water-swollen EO-EPI/whisker nanocomposites. Fig. S4 Tensile
storage moduli of EO-EPI/whisker nanocomposites. Fig. S5
Stress-strain curves of EO-EPI and EO-EPI/whisker nanocomposite.
Fig. S6 Tensile storage moduli of EO-EPI/whisker nanocomposites.
Fig. S7 Specificity of mechanical switching. Fig. S8. DMA data of
PVAc/whisker nanocomposites. Fig. S9. Swelling of PVAc/whisker
nanocomposites. Fig. S10. DMA temperature sweeps of water-swollen
PVAc/whisker nanocomposites. Table S1 Mechanical data of
EO-EPI/whisker nanocomposites. References Movie S1 Provided as
separate file.
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2
Materials. All materials and reagents were used as received.
Organic solvents, sulfuric
acid, and potassium hydroxide, were purchased from Fisher
Scientific LLC (Hanover
Park, IL). The ethylene oxide/epichlorohydrin copolymer (EO-EPI
copolymer,
Epichlomer,® co-monomer ratio = 1:1, density = 1.39 g/mL) was
received from Daiso
Co. Ltd. (Osaka, Japan). Polyvinyl acetate (Mw = 113,000g/mol,
density = 1.19g/cm3)
was purchased from Aldrich Chemicals (Milwaukee, WI). Tunicates
(Styela clava) were
collected from floating docks in Point View Marina
(Narragansett, RI). Cellulose
whiskers were prepared as previously described (S1).
Fabrication of Whisker Nanocomposites. Lyophilized whiskers were
dispersed in
dimethyl formamide (DMF) at a concentration 5 mg/mL as
previously described (S1).
The EO-EPI copolymer or PVAc polymer was dissolved in DMF (5%
w/w) by stirring for
two days. Nanocomposites were prepared by combining the desired
amounts (to yield
materials containing 0.8% - 19% v/v whiskers) of the colloidal
whisker dispersion and
polymer solution, and solution-casting the resulting homogeneous
mixture into Teflon®
Petri dishes. The dishes were placed into a vacuum oven (60 °C,
15 mbar, EO-EPI = 48
h; PVAc = 1 week) to evaporate the solvent and dry the resulting
films, before the
material was compression-molded between spacers in a Carver
laboratory press (EO-
EPI = 80 °C at 6000 psi for 2 min; PVAc = 90 °C at 0 psi for 2
min, followed by an
increase of pressure to 3000 psi for 15 min) to yield 300-400 µm
thin nanocomposite
films.
Fabrication of Neat Cellulose Whisker Reference Film by Solution
Casting. As
reported before (S2), an aqueous dispersion containing 0.8% w/w
of cellulose whiskers
(3 mL) whiskers was cast into a Teflon® Petri dish, which was
placed into a vacuum
oven (60 °C, 15 mbar, 48 h) to evaporate the water and dry the
resulting film, which had
a thickness of ca. 70 µm.
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3
Switching Experiments with EO-EPI/whisker Nanocomposites.
Compression
molded EO-EPI/whisker nanocomposites were dried in a vacuum oven
(60 °C, 15 mbar,
48 h) to remove all water and stored in a desiccator until DMA
measurements were
made. For switching experiments, vacuum-dried EO-EPI/whisker
nanocomposites were
placed into sealed vials filled with deionized water or IPA for
48 h. The extent of
swelling was determined gravimetrically from the original mass
of the dry sample and
the mass after swelling. Swollen samples were then either
measured by DMA using a
submersion chamber filled with deionized water or IPA, or
re-dried in vacuum (60 °C, 15
mbar, 48 h) and measured by DMA to explore the reversibility of
mechanical switching.
Switching Experiments with PVAc/whisker Nanocomposites.
Compression molded
PVAc/whisker nanocomposites were dried in a vacuum oven (60 °C,
15 mbar, 48 h) to
remove all water and stored in a desiccator until DMA
measurements were made. For
switching experiments, vacuum-dried PVAc/whisker nanocomposites
were placed into
DMA using a submersion chamber filled with artificial cerebral
spinal fluid (ACSF) at
room temperature. The ACSF bath was heated at a nominal rate of
2°C/min to a
temperature of 37°C, where the sample was held. DMA measurements
were made
throughout this process. ACSF was prepared based on product
information (alzet,
Cupertino, CA).
Movies Demonstrating Switching. The movie provided as part of
the supporting
material (StiffnessChange.mpeg) illustrates the mechanical
properties of a 12.2% v/v
PVAc/whisker nanocomposite. It shows that a dry nanocomposite in
the shape of a
cortical electrode is readily inserted into a polyamic acid gel
(Solvay, Torlon AI-30,
12.5% w/w in water). The object was subsequently placed into
ACSF at 37 °C for
~15min. The movie then shows that the sample thus treated no
longer penetrates the
gel, but is bent upon insertion attempts, reflecting that the
E’c of the material is
substantially reduced.
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4
Transmission Electron Micrographs (TEMs). TEMs were acquired
using a JEOL
1200EX Transmission Electron Microscope. All samples were
prepared on carbon-
coated copper grids using a standard uranyl acetate negative
staining method (S3).
Whisker dimensions were determined by analyzing four digital TEM
images of whiskers
prepared by the reported standardized procedure (S1), with a
total of 75 whiskers
measured for diameter and 45 whiskers measured for length.
Whiskers that extended
beyond the image or could not clearly be identified as an
individual whisker were
omitted from the analysis. Dimensions are reported as average
values +/- standard
error.
Scanning Electron Micrographs (SEMs). Samples used for scanning
electron
microscopy (SEM) analysis were coated with carbon and images
were acquired with a
Hitachi S-4700 field-emission microscope.
Atomic Force Microscopy (AFM). A Dimension 3100 AFM by Digital
Instruments was
used to acquire phase images in tapping mode. The micrographs
are presented in top-
view. Samples of neat EO-EPI, and the whisker nanocomposite were
embedded into an
epoxy resin, and trimmed with an ultramicrotome to obtain smooth
surfaces for AFM
analysis. Before analysis, the samples were briefly (10 s)
immersed in tetrahydrofuran
and rinsed with IPA to partially dissolve the polymer at the
surface of the sample and to
expose the inner structure of the films.
Predicted Stiffness of EO-EPI/whisker Nanocomposites. To support
the conclusion
that the drastic change in mechanical properties of the
de-ionized water-swollen
nanocomposites is due to the change of interactions between the
cellulose whiskers
and not plasticization of the EO-EPI matrix, we used the
percolation model to quantify
changes that can result from reduction of E′s (tensile storage
modulus of the neat
polymer matrix, Fig S2). When E′s was set to zero, corresponding
to complete failure of
the mechanical integrity of the matrix polymer, E′s changes
significantly below the
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5
percolation limit (Fig. S2). However, even in this extreme
(hypothetical) case, the
moduli are nearly unchanged for compositions where percolation
of the cellulose is
reached, reflecting that in this regime the contribution of the
matrix polymer to the
overall modulus of the nanocomposite is negligible. Thus, the
key parameter to affect
the magnitude of Ec′ of nanocomposites with percolating
cellulose network is the
modulus of the rigid phase (E′r). To illustrate the importance
of this parameter, E′r was
set to 1000 times or 1/1000 times the experimentally determined
value for E′r, and a
remarkable contrast in the predicted value of E′ is evident (Fig
S2).
Thermo Mechanical Testing. DMA temperature sweeps under
oscillatory stress were
performed on rectangular films of the neat polymers or the
nanocomposites using a TA
Instruments DMA Q800 in tensile mode with an oscillation
frequency of 1 Hz, a static
force of 10 mN, an oscillation amplitude of 15.0 µm, and an
automatic tension setting of
125%. Measurements were carried out at a heating rate of 3°/min
(range of 15 – 45 °C
for EO-EPI nanocomposites). Swollen sample were measured using a
submersion
clamp, filled with the appropriate medium.
Stress-strain experiments were performed at room temperature on
rectangular
films of the neat polymers or the nanocomposites using a TA
Instruments DMA Q800 in
constant strain mode with a strain rate of 2%/min for the
nanocomposites or 2 or
20%/min for the neat polymers an initial amplitude of 15.0 (dry
samples) or 150 µm
(swollen samples). Swollen nanocomposites were measured using a
submersion
clamp, filled with deionized water.
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6
Figure S1. Transmission electron microscopy image of tunicate
whiskers.
Cellulose whiskers isolated from tunicate mantles (scale bar = 1
µm).
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7
A
-40 -20 0 20106
107
108
109
1010
E' (
Pa)
19 % v/v whiskers 14 % v/v whiskers 9.5 % v/v whiskers 4.8 % v/v
whiskers 0.95 % v/v whiskers 0 % v/v whiskers
Temperature (°C)
B
-40 -20 0 200.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
tan δ
19 % v/v whiskers 14 % v/v whiskers 9.5 % v/v whiskers 4.8 % v/v
whiskers 0.95 % v/v whiskers 0 % v/v whiskers
Temperature (°C)
Figure S2. DMA temperature sweeps for dry EO-EPI/whisker
nanocomposites.
Representative DMA traces (A) that show tensile storage moduli
E’c and loss tangents
tan δ (B) of dry EO-EPI and EO-EPI/whisker nanocomposites as a
function of whisker
content and temperature.
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8
20 30 40104
105
106
107
108
E' (
Pa)
19 % v/v whiskers 14 % v/v whiskers 9.5 % v/v whiskers 4.8 % v/v
whiskers 0.95 % v/v whiskers 0.0 % v/v whiskers
Temperature (°C)
Figure S3. DMA temperature sweeps for water-swollen
EO-EPI/whisker
nanocomposites. Representative DMA traces that show tensile
storage moduli E’c of
EO-EPI and EO-EPI/whisker nanocomposites as a function of
whisker content and
temperature. The samples were equilibrated by immersion for 48 h
in deionized water
and were measured under submersion in deionized water.
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9
0.00 0.05 0.10 0.15 0.20106
107
108
109
Dry 25 C Percolation Haplin-Tsai
E' (
Pa)
Volume Fraction Filler
Figure S4. Tensile Storage moduli of EO-EPI/whisker
nanocomposites. Tensile
storage moduli E’c of EO-EPI and EO-EPI/whisker nanocomposites
as a function of
whisker content. Lines represent values predicted by the
percolation and Halpin-Kardos
model (Eqs. 1-4 in the manuscript) for dry samples. Data points
represent averages
(number of individual measurements, N, = 3-5) +/- standard error
measurements.
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10
0 50 100 150 200 250 300 350 4000.0
0.5
1.0
1.5
2.0
2.5
0 2 4 6 8 100.0
0.5
1.0
1.5
2.0
2.5
Tens
ile S
tres
s (M
Pa)
14.3 % v/v whiskers - dry 14.3 % v/v whiskers - deionized water
swollen 0.0 % v/v whiskers - dry 0.0 % v/v whiskers - deionized
water swollen
Tensile Stress
Tens
ile S
tres
s (M
Pa)
Tensile Stress (%)
Figure S5. Stress-strain curves of EO-EPI and EO-EPI/whisker
nanocomposite.
Representative stress-strain curves of neat EO-EPI and
EO-EPI/whisker
nanocomposites containing 14.3% v/v whiskers. The materials were
conditioned by
either drying in vacuum or equilibrium swelling in de-ionized
water.
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11
0.00 0.05 0.10 0.15 0.20
106
107
108
109 Dry nanocomposites (never swollen) Swollen with deionized
water Swollen with deionized water and dried Percolation model
E' (
Pa)
Volume fraction filler
Figure S6. Tensile storage moduli of EO-EPI/whisker
nanocomposites. Tensile
storage moduli E′c of EO-EPI/whisker nanocomposites as function
of volume fraction of
cellulose whiskers. The nanocomposites were conditioned by
either drying in vacuum,
equilibrium swelling in de-ionized water, or swelling to
saturation in de-ionized water
followed by re-drying in vacuum. The data were taken from Fig.
2A, but data for the
swollen samples were plotted for their original whisker content
to allow for a direct
comparison of the E′c of dry and water-swollen composites for
the same composition.
Data points represent averages (N = 3-5) +/- standard error
measurements.
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12
0.00 0.05 0.10 0.15 0.20
106
107
108
109
1010
1011
1012 Dry 25 Es = 0 Er *1000 Er/1000
E' (P
a)
Volume Fraction Filler
Figure S7. Specificity of mechanical switching. Systematic
variations were made to
individual parameters fed into the percolation model (See
Equation 1). Lines represent
(i) the model used to fit vacuum-dried nanocomposites in Fig 2A;
(ii) same as (i) but
with E's = 0; (iii) same as (i) but with E'r x 1000; (iv) same
as (i) but with E'r / 1000.
Setting E′s to zero represents a complete failure in the
mechanical integrity of the matrix
polymer. Variations in E′r are made to investigate effects of
strengthening (1000 times),
or weakening (1/1000 times) the whisker-whisker
interactions.
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13
30 40 50
0.0
0.4
0.8
1.2
1.6
2.0 16.5 % v/v whiskers 12.2. % v/v whiskers 8.1 % v/v whiskers
4.0 % v/v whiskers 0.8 % v/v whiskers 0.0 % v/v whiskers
tan δ
Temperature (°C)
0.00 0.05 0.10 0.15105
106
107
108
109
1010 Dry nanocomposite (56 °C) Swollen with deionized water (37
°C) Percolation model Halpoin-Kardos model
E' (
Pa)
Volume fraction filler
Figure S8. DMA data of PVAc/whisker nanocomposites. (A) Loss
tangents tan δ of dry PVAc and PVAc/whisker nanocomposites as a
function of whisker content and
temperature. (B) Tensile storage moduli E’c of PVAc and
PVAc/whisker
nanocomposites (dry and water swollen) as a function of whisker
content. Lines
represent values predicted by the percolation and Halpin-Kardos
model (Eqs. 1-4 in the
manuscript) for dry and water-swollen samples, respectively.
Data points represent
averages (number of individual measurements, N ≥ 2). Water
swollen samples with
higher whisker content display decreased moduli below the
Halpin-Kardos model, most
likely due to the increased swelling at high whisker content
(Fig. S9).
A
B
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14
Figure S9. Swelling of PVAc/whisker nanocomposites. Solvent
uptake as a function
of whisker volume fraction and temperature upon immersion (to
equilibration) in de-
ionized water or ACSF. Data points represent averages (N = 4-5)
+/- standard error
measurements.
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.160
20
40
60
80
100
% S
olve
nt u
ptak
e (w
/w)
Volume fraction filler
Deionized water (23°C) Deionized water (37°C) ACSF (37°C)
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15
20 30 40 50 600
50
100
150
200
250
300
350
400
Temperature (°C)
16.5 % v/v whiskers 12.2 % v/v whiskers 8.1 % v/v whiskers 4.0 %
v/v whiskers 0.8 % v/v whiskers 0.0 % v/v whiskers
E'(M
Pa)
20 30 40 50 600
1
2
3
16.5 % v/v whiskers 12.2 % v/v whiskers 8.1 % v/v whiskers 4.0 %
v/v whiskers 0.8 % v/v whiskers 0.0 % v/v whiskers
tan δ
Temperature (°C)
Figure S10. DMA temperature sweeps for water-swollen
PVAc/whisker
nanocomposites. Representative DMA traces (A) that show tensile
storage moduli E’c
and loss tangents tan δ (B) of water-swollen PVAc and
PVAc/whisker nanocomposites
as a function of whisker content and temperature.
A
B
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16
Whisker content (%v/v)
Sample condition
Stress at yield point (MPa)
Stress at Break (MPa)
Elongation at break (%)
14.3 (N=7) Dry 1.71 +/- 0.23 0.05 +/- 0.02 6.7 +/- 0.8 14.3
(N=5) Swollen 0.37 +/- 0.11 0.29 +/- 0.7 17.8 +/- 3.9
0 (N=2) Dry Not applicable 0.27 +/- 0.04 360 +/- 20 0 (N=2)
Swollen Not applicable 0.34 +/- 0.04 263 +/- 100
Table S1. Mechanical data of EO-EPI/whisker nanocomposites.
Mechanical data
extracted from stress-strain experiments of EO-EPI/whisker
nanocomposites containing
14.3% v/v whiskers and neat EO-EPI at room temperature. The
nanocomposites were
conditioned by either drying in vacuum or equilibrium swelling
in de-ionized water. N is
the number of individual measurements and values represent
averages +/- standard
error measurements.
References:
S1. O. van den Berg, J. R. Capadona, C. Weder, Biomacromolecules
8, 1353 (2007).
S2. J. R. Capadona et al., Nat. Nanotech. 2, 765 (2007).
S3. E. Le Cam, D., Frechon, M. Barray, A. Fourcade, E. Delain,
Proc. Natd. Acad. Sci.
USA 91 11816 (1994).
