Porous self-protonating spiropyran-based NIPAAm gels
with improved reswelling kinetics
Supporting Information
Bartosz Ziółkowski1, Larisa Florea1, Jannick Theobald1,2, Fernando Benito-Lopez1,3
and Dermot Diamond1*
1
Insight: Centre for Data Analytics, National Centre for Sensor Research, Dublin City
University, Dublin, Ireland
2
Institute of Pharmacy and Molecular Biotechnology, Division of Pharmaceutical
Biology, University of Heidelberg, Im Neuenheimer Feld 364, D-69120 Heidelberg,
Germany
3
Analytical Chemistry Department,University of the Basque Country UPV/EHU,
Vitoria-Gasteiz, Spain
Gel shrinking measurements
Since the cut gel samples are never ideal circles several diameters were measured
before light irradiation. Then as the gel shrunk, the ratio in shrinking separately for
every diameter was expressed in percent. The percentage errors were calculated
between the shrinking ratios for the given time interval (n = 3).
Table 1. Average diameter changes under different illumination conditions.
light
Blank gel
2k gel
20k gel
darkness
Time
(min)
0
5
10
20
25
30
40
50
60
70
80
Average
100.0%
90.8%
85.8%
83.6%
84.8%
86.0%
88.8%
90.9%
92.6%
94.6%
96.0%
% error
0.0%
1.8%
1.7%
0.5%
0.3%
0.3%
0.4%
0.3%
0.4%
0.4%
0.4%
Average
100.0%
93.7%
89.2%
85.1%
91.3%
93.8%
97.4%
98.7%
99.3%
99.7%
99.7%
% error
0.0%
1.1%
0.9%
0.3%
1.0%
1.4%
0.7%
0.8%
0.4%
0.3%
0.3%
Average
100.0%
92.3%
88.2%
85.0%
91.6%
94.2%
97.2%
99.0%
99.4%
99.8%
99.9%
% error
0.0%
0.4%
0.3%
0.3%
1.0%
0.4%
0.6%
0.4%
0.4%
0.1%
0.1%
FT-IR spectroscopy
The ATR-FTIR spectra were collected on a Perkin-Elmer Spectrum 100 in the range
of 650−4000 cm−1 and were obtained from 4 scans with a resolution of 2 cm−1. The
samples analysed were the PEG 2000 powder and the poly(NIPAAm-co-BSP-A-co-
AA) gel after the washing steps (Figure S1). The ATR-FTIR spectrum of the hydrogel
confirms that the PEG has been washed out following the washing protocol described.
The spectrum of pure PEG is characterized by the stretching vibration of the C–H at
2883 cm−1, the C=O stretching vibration at 1644 cm−1, the deformation vibration of
the C–H bonds at 1466 and 1341 cm−1, the bending vibration of the O–H at 1279 and
1241 cm−1 and the C–O stretching vibration at 1147 cm−1 [1]. In the spectra of the
poly(NIPAAm-co-BSP-A-co-AA) gel, most absorption peaks of the main functional
groups of PEG do not appear, except for the C=O stretching that is also present in the
hydrogel due to the presence of the C=O from the poly(NIPAM)[2]
Figure S1. ATR-FTIR spectra of PEG and porous hydrogel.
UV-Vis Spectroscopy
Changes in the absorbance spectra of the spiropyran hydrogels under different
illumination conditions were recorded in reflectance mode using two fiber-optic light
guides connected to a Miniature Fiber Optic Spectrometer (USB4000 - Ocean Optics)
and aligned using an in-house made holder (Figure S1). The in-house-designed holder
was fabricated using a 3D printer (Dimension SST 768) in black acrylonitrile
butadiene styrene co-polymer (ABS) plastic in order to minimise interferences from
ambient light. The two parts of the holder (one to be placed underneath the hydrogel,
the other one on top (Figure S2A) were designed using ProEngineer CAD/CAM
software package and fixed together to ensure no interferences from ambient light
(Fig. S2B). A white background was used under the hydrogel to improve reflectance
signal. The light source was a LS-1 tungsten halogen lamp (white light) obtained from
Ocean Optics, Inc. The light source was turned ON every ~ 2 min only when the
spectra were recorded, as continuous irradiation with the white light source will cause
the protonated merocyanine form to convert to the closed spiropyran and disturb the
reprotonation process. Data from the spectrometer was processed using Spectrasuite
software provided by Ocean Optics Inc. The normalised absorbance value at 485 nm
was plotted against time to give the BSP reprotonation kinetics for each of the
hydrogels (blank, 2k gel and 20k gel, respectively).
Figure S2. In-house designed holder used for absorbance measurements of the
spiropyran hydrogels (left) and holder with connected reflectance fiber-optic (right).
Microscopy images of poly(NIPAAm-co-BSP-A-co-AA) gels
After hydration, for microscopy imaging purposes, the hydrogels were placed in a 5
mm wide and 2 mm deep PDMS mould filled with water and covered with a ~ 150
μm thick microscope glass slide. The imaging was done with an Aigo GE-5
microscope using a 60x objective lens and the accompanying software. The white
light required for hydrogel shrinking light was provided by a Dolan-Jenner-Industrie
Fiber-Lite LMI at maximum power through two waveguide goosenecks placed 5 cm
from the sample. It was observed that after hydration the porous gels (Figure S3B and
C) are considerably more opaque in contrast to the blank gels that remain transparent
after swelling in water (Figure S3A). This effect is observed in both illumination
conditions, in the dark (Figure S3 left) and after 20 min irradiation with white light
(Figure S3 right), respectively.
Figure S3. Microscopy images of blank and porous hydrogels (PEG 2K and PEG
20K) in the dark (left) and after 20min white light irradiation (right).
References:
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Wang C, Feng L, Yang H, Xin G, Li W, Zheng J, Tian W, Li X (2012)
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[2]
Wu D, Liu X, Yu S, Liu M, Gao C (2010) Modification of aromatic polyamide
thin-film composite reverse osmosis membranes by surface coating of thermoresponsive copolymers P(NIPAM-co-Am). I: Preparation and characterization. J
Memb Sci 352: 76.