Thermo/hydration responsive shape memory polymers with enhanced hydrophilicity for biomedical applications Page: 3
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Smart Mater. Struct. 32 (2023) 015006
Tg and E' under wet conditions with an increasing DAc ratio. 0
A comparison with SMPs modified with phenethyl acrylam- HS O- N N" O SH
ide (PAc), which has the same chemical structure as DAc 0 NH
except it lacks two adjacent hydroxyl groups, clearly showed O N O
enhanced hydrophilicity and reduced Tg and E' contributed to
the improved recovery effect. Here, we optimize the hydro- o SH
philicity and thermomechanical properties of SMPs by incor- ' OH
porating a hydrophilic monomer to make SMP substrates more OH
advantageous for biomedical applications. TMICN DAc2. Materials and methods
2.1. Materials
Triallyl-1,3,5-triazine-2,4,6-trione (TATATO), tris[2-(3-
mercaptopropionyloxy)ethyl] isocyanurate (TMICN), dopam-
ine hydrochloride, phenethylamine, acryloyl chloride, and
2,2-dimethoxy-2-phenylacetone (DMPA) were purchased
from Sigma-Aldrich and used without further purification.
Triethylamine (TEA) was purchased from Sigma-Aldrich and
purified by drying with calcium hydride, followed by vacuum
distillation. Anhydrous grade tetrahydrofuran, dimethylform-
amide, methanol, and ethyl acetate were purchased and used
as received. DAc and PAc were synthesized from dopamine
hydrochloride and phenethylamine, respectively, by reacting
with acryloyl chloride [27, 28]. The detailed procedure is
available in the supporting information with the correspond-
ing NMR spectra (figures S1 and S2). All monomers used in
this work are shown in figure 1.
2.2. Synthesis of thiol-ene/acrylamide SMP films
Using trifunctional monomers TMICN and TATATO and
monofunctional acrylamides DAc and PAc, thiol-ene/
acrylamide SMPs were synthesized by photopolymerization.
Thiol, alkene, each acrylamide monomer, and 1 wt% DMPA
of total monomer weight were dissolved in a glass vial using a
spin mixer. DAc and PAc were counted as alkene components,
and their monomer ratios varied from0 to 40 mol% at 10 mol%
increments. The stoichiometric balance between thiol and ene
was maintained by correcting the number of functional groups
in each monomer, as described in table 1. The monomer solu-
tion was encased between two glass slides spaced by 30 ,pm
thick plastic shims of varying thickness to accommodate for
different tests, then polymerized in a 254 nm UV curing cham-
ber for 2 h. The cured polymer was heated in a vacuum oven
at 120 C and 150 mmHg for 24 h to complete the reaction.
2.3. Dynamic mechanical analysis (DMA)
DMA measurements were performed under tensile mode
using an RSA-G2 (TA Instruments) with a maximum strain
of 0.275%, deformation frequency of 1 Hz, and ramp rate of
2 C min-1 in air (dry conditions) or in phosphate-buffered
saline (PBS) (soaked/wet conditions). The test samples were
cut into a rectangle 30 ,pm in thickness, 15 mm in length,0
TATATOO NH
PAcFigure 1. Chemical structures of monomers.
and 3 mm in width using a CO2 laser. Dry DMA experi-
ments were performed from 5 C to 100 C. Soaked exper-
iments consisted of two steps with the immersion system of
the DMA instrument filled with PBS [29]. The first step was
the complete immersion of the polymer. The temperature was
raised from room temperature 22 C to 37 C, then main-
tained for 60 min. In this process, the softening kinetics were
evaluated, and the completion of softening process was con-
firmed through a steady modulus. The second step included
cooling to 15 C, followed by heating from 15 C to 80 C
to observe the thermomechanical properties under wet condi-
tions after the polymer is plasticized. All measurements were
performed for three independent specimens to obtain mean
value and standard deviation; however, only representative
measurements are shown in the graphics. The glass transition
temperature (Tg) was evaluated at the tan 6 peak. Values are
displayed as mean standard deviation.
2.4. Tensile tests
Stress-strain curves were obtained using a universal test-
ing machine (Lloyd LR5K Plus), which has a temperature-
controlled chamber. Polymer samples were made according to
the previously described procedure as 1.25 mm thick sheets.
The sheets were cut into ASTM D638 Type V dogbones via
a CO2 laser. Each sample was tested at Tg + 20 C, and
all samples were heated in the chamber at the corresponding
temperature for 10 min prior to the measurements. The res-
ults were recorded using a 50 N load cell at a strain rate of
0.87%/s (5 mm min-1 extension speed). Each polymer was
measured five times, and values including fracture strain (Ef)
and Young's modulus (E) at Tg + 20 C were averaged.
2.5. Shape memory tests
A. Dry conditions: To test shape memory behavior, samples
were cut by a carbon dioxide (CO2) laser from thin polymerY Suzuki et al
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Suzuki, Yuta; Hu, Qichan; Batchelor, Benjamin; Voit, Walter & Ecker, Melanie. Thermo/hydration responsive shape memory polymers with enhanced hydrophilicity for biomedical applications, article, December 5, 2022; (https://digital.library.unt.edu/ark:/67531/metadc2179416/m1/3/: accessed July 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT College of Engineering.