2 research outputs found
Fine Adjustment of Interfacial Potential between pH-Responsive Hydrogels and Cell-Sized Particles
We
quantitatively determined interfacial potentials between cell-sized
particles and stimulus-responsive hydrogels using a microinterferometer.
The hydrogel is based on physically interconnected ABA triblock copolymer
micelles comprising an inner biocompatible PMPC block and two outer
pH-responsive PDPA blocks. The out-of-plane temporal fluctuation in
the position of the cell-sized particles was calculated from changes
in the interference pattern measured by Reflection Interference Contrast
Microscopy (RICM), thus yielding the particle-substrate interaction
potential <i>V</i> (Ī<i>h</i>). Measurements
in pH buffers ranging from 7.0 to 7.8 resulted in a systematic reduction
in height of the potential minima āØĪ<i>h</i>ā© and a concomitant increase in the potential curvature <i>V</i>ā³ (Ī<i>h</i>). The experimental
data were analyzed by applying the modified Ross and Pincus model
for polyelectrolytes, while accounting for gravitation, lubrication
and van der Waals interactions. Elastic moduli calculated from <i>V</i>ā³ (Ī<i>h</i>) were in good agreement
with those measured by Atomic Force Microscopy. The ability to fine-tune
both the gel elasticity and the interfacial potential at around physiological
pH makes such triblock copolymer hydrogels a promising biocompatible
substrate for dynamic switching of cellāmaterial interactions
Emergence of Strong Nonlinear Viscoelastic Response of Semifluorinated Alkane Monolayers
Viscoelasticity
of monolayers of fluorocarbon/hydrocarbon tetrablock
amphiphiles diĀ(<i>FnHm</i>) ((C<sub><i>n</i></sub>F<sub>2<i>n</i>+1</sub>CH<sub>2</sub>)Ā(C<sub><i>m</i>ā2</sub>H<sub>2<i>m</i>ā3</sub>)ĀCHāCHĀ(C<sub><i>n</i></sub>F<sub>2<i>n</i>+1</sub>CH<sub>2</sub>)Ā(C<sub><i>m</i>ā2</sub>H<sub>2<i>m</i>ā3</sub>)) was characterized by interfacial dilational rheology
under periodic oscillation of the moving barriers at the air/water
interface. Because the frequency dispersion of the response function
indicated that diĀ(<i>FnHm</i>) form two-dimensional gels
at the interface, the viscosity and elasticity of diĀ(<i>FnHm</i>) were first analyzed with the classical KelvināVoigt model.
However, the global shape of stress response functions clearly indicated
the emergence of a nonlinearity even at very low surface pressures
(Ļ ā 5 mN/m) and small strain amplitudes (<i>u</i><sub>0</sub> = 1%). The Fourier-transformed response function of
higher harmonics exhibited a clear increase in the intensity only
from odd modes, corresponding to the nonlinear elastic component under
reflection because of mirror symmetry. The emergence of strong nonlinear
viscoelasticity of diĀ(<i>FnHm</i>) at low surface pressures
and strain amplitudes is highly unique compared to the nonlinear viscoelasticity
of other surfactant systems reported previously, suggesting a large
potential of such fluorocarbon/hydrocarbon molecules to modulate the
mechanics of interfaces using the self-assembled domains of small
molecules