4 research outputs found
Immobilized Multifunctional Polymersomes on Solid Surfaces: Infrared Light-Induced Selective Photochemical Reactions, pH Responsive Behavior, and Probing Mechanical Properties under Liquid Phase
Fixing polymersomes onto surfaces
is in high demand not only for the characterization with advanced
microscopy techniques but also for designing specific compartments
in microsystem devices in the scope of nanobiotechnology. For this
purpose, this study reports the immobilization of multifunctional,
responsive, and photo-cross-linked polymersomes on solid substrates
by utilizing strong adamantane−β-cyclodextrin host–guest
interactions. To reduce nonspecific binding and retain better spherical
shape, the level of attractive forces acting on the immobilized polymersomes
was tuned through poly(ethylene glycol) passivation as well as decreased β-cyclodextrin
content on the corresponding substrates. One significant feature of
this system is the pH responsivity of the polymersomes which has been
demonstrated by swelling of the immobilized vesicles at acidic condition
through in situ AFM measurements. Also, light responsivity has been
provided by introducing nitroveratryloxycarbonyl (NVOC) protected
amine molecules as photocleavable groups to the polymersome surface
before immobilization. The subsequent low-energy femtosecond pulsed
laser irradiation resulted in the cleavage of NVOC groups on immobilized
polymersomes which in turn led to free amino groups as an additional
functionality. The freed amines were further conjugated with a fluorescent
dye having an activated ester that illustrates the concept of bio/chemo
recognition for a potential binding of biological compounds. In addition
to the responsive nature, the mechanical stability of the analyzed
polymersomes was supported by computing Young’s modulus and
bending modulus of the membrane through force curves obtained by atomic
force microscopy measurements. Overall, polymersomes with a robust
and pH-swellable membrane combined with effective light responsive
behavior are promising tools to design smart and stable compartments
on surfaces for the development of microsystem devices such as chemo/biosensors
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Reversible Thermosensitive Biodegradable Polymeric Actuators Based on Confined Crystallization
We
discovered a new and unexpected effect of reversible actuation of
ultrathin semicrystalline polymer films. The principle was demonstrated
on the example of thin polycaprolactone-gelatin bilayer films. These
films are unfolded at room temperature, fold at temperature above
polycaprolactone melting point, and unfold again at room temperature.
The actuation is based on reversible switching of the structure of
the hydrophobic polymer (polycaprolactone) upon melting and crystallization.
We hypothesize that the origin of this unexpected behavior is the
orientation of polycaprolactone chains parallel to the surface of
the film, which is retained even after melting and crystallization
of the polymer or the “crystallization memory effect”.
In this way, the crystallization generates a directed force, which
causes bending of the film. We used this effect for the design of
new generation of fully biodegradable thermoresponsive polymeric actuators,
which are highly desirable for bionano-technological applications
such as reversible encapsulation of cells and design of swimmers
Shape Memory Properties of Epoxy/PPO–PEO–PPO Triblock Copolymer Blends with Tunable Thermal Transitions and Mechanical Characteristics
In
this paper, we report a simple method to prepare novel, transparent,
hard-tough and hard-flexible shape memory, and soft-flexible epoxy
polymers based on poly(propylene glycol)-<i>block</i>-poly(ethylene
glycol)-<i>block</i>-poly(propylene glycol) (PPO–PEO–PPO)
triblock copolymer (TBCP) and diglycidyl ether of bisphenol A (DGEBA)/4,4′-diaminodiphenylmethane
(DDM) system. The PPO–PEO–PPO triblock copolymer was
used to tailor cross-link density and flexibility in epoxy thermosets
and thereby their glass transition temperatures (<i>T</i><sub>g</sub>’s). The formed blends exhibit a phase-separated
morphology. The phase separation was initiated by immiscible PPO blocks
via self-assembly. Three types of shape memory polymers, viz., stiff,
intermediate, and soft-flexible epoxy systems, with entirely different
physical and mechanical properties were prepared only by adjusting
the blend composition. All the blends were UV resistant, were thermally
and dimensionally stable, and could be used for various outdoor applications.
To the best of our knowledge, no work has been reported on the shape
memory properties of epoxy modified block copolymers
PEG-<i>ran</i>-PPG Modified Epoxy Thermosets: A Simple Approach To Develop Tough Shape Memory Polymers
In
this work, we prepared thermoresponsive shape memory epoxy thermosets
by blending epoxy resin with poly(ethylene glycol-<i>ran</i>-propylene glycol) random copolymer (PEG-<i>ran</i>-PPG
or RCP). Incorporation of RCP precisely tuned the temperature showing
the shape memory effect of epoxy thermoset, which was established
by dynamic mechanical analysis (DMA) and fold-deploy test. FTIR spectroscopy
confirmed that the compatibility of the system is caused by intermolecular
hydrogen bonding and only at high RCP concentration some phase separation
starts. DMA and thermomechanical analysis provided evidence for the
interactions of RCP chains with epoxy thermoset. The impact strength
considerably increased especially for 30 and 40 wt % RCP modified
blends. Furthermore, the blends exhibited good thermal stability in
conjunction with excellent UV resistance