A dual responsive surface is constructed on hydrophilic polymer brushes to modulate cell migration ability on demand. The responsibility is based on the dynamic host–guest interaction between β‐CD and azobenzene. Both competitive guest molecules and UV radiation are able to release azobenzene‐REDV from the substrate, weakening the cell–substrate interaction and modulating the cell migration rate.
In
this communication, we propose a different approach for analyzing
linear viscoelastic relaxation data that is more faithful to the underlying
physics and naturally accommodates the thermorheological complexity
that is observed in glass-forming polymers. Specifically, the linear
viscoelastic behavior was evaluated for a diglycidyl ether of bisphenol-A
epoxy cured with 4,4′-methylenedianaline with a glass transition
temperature (T
g) of 101.5 °C. The
dynamic storage and loss moduli were measured from 10–2 to 101.7 Hz for 19 temperatures between 90 and 180 °C.
The experimental window was extended by two orders of magnitude using
stress relaxation experiments for temperatures between 90 and 112.5
°C. The G′ and G″responses
for this single-phase polymer are thermorheologically complex, thus
precluding the construction of master curves via time–temperature
superposition. The traditional method of determining the relaxation
spectrum implicitly assumes a constant spectral density where the
spectral strength changes with the relaxation time. An alternative
approach presented herein is to assume that individual spectral contributions
have a constant strength where the spectral density changes. This
alternative approach is in better agreement with the physics of dielectric
relaxation and readily accounts for thermorheological complexity.
Using this new approach, a relaxation map of how the individual relaxation
times change with temperature has been developed, which is the only
relaxation information that can be rationally extracted from viscoelastic
isotherms. The relaxation map for the bisphenol-A epoxy shows a smooth
transition between the high temperature α+ process, the main
α transition, and the excess wing, where none of the relaxation
regions exhibit Arrhenian behavior.
Gamma-ray irradiation, using the cobalt-60 isotope, is the most common radiation modality used for medical device and biopharmaceutical products sterilization. Although X-ray and electron-beam (e-beam) sterilization technologies are mature and have been in use for decades, impediments remain to switching to these sterilization modalities because of lack of data on the resulting radiation effects for the associated polymers, as well as a lack of education for manufacturers and regulators on the viability of these sterilization alternatives. For this study, the compatibility of ethylene vinyl acetate (EVA) multilayer films with different ionizing radiation sterilization (X-ray, e-beam, and gamma irradiation) is determined by measuring chemical and physical film properties using high performance liquid chromatography, differential scanning calorimetry, Fourier-Transform InfraRed spectroscopy (FTIR), surface energy measurement, and electron spin resonance techniques. The results indicate that the three irradiation modalities induce no differences in thermal properties in the investigated dose range. Gamma and X-Ray irradiations generate the same level of reactive species in the EVA multilayer film, whereas e-beam generates a reduced quantity of reactive species.
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