5 research outputs found
Two-Level Shape Changes of Polymeric Microcuboids Prepared from Crystallizable Copolymer Networks
Polymeric microdevices bearing features
like nonspherical shapes
or spatially segregated surface properties are of increasing importance
in biological and medical analysis, drug delivery, and bioimaging
or microfluidic systems as well as in micromechanics, sensors, information
storage, or data carrier devices. Here, a method to fabricate programmable
microcuboids with shape-memory capability and the quantification of
their recovery at different levels is reported. The method uses the
soft lithographic technique to create microcuboids with well-defined
sizes and surface properties. Microcuboids having an edge length of
25 μm and a height of 10 μm were prepared from cross-linked
poly[ethylene-<i>co</i>-(vinyl acetate)] (cPEVA) with different
vinyl acetate contents and were programmed by compression with various
deformation degrees at elevated temperatures. The microlevel shape-recovery
of the cuboidal geometry during heating was monitored by optical microscopy
(OM) and atomic force microscopy (AFM) studying the related changes
in the projected area (PA) or height, while the nanolevel changes
of the nanosurface roughness were investigated by <i>in situ</i> AFM. The shape-memory effect at the microlevel was quantified by
the recovery ratio of cuboids (<i>R</i><sub>r,micro</sub>), while at the nanolevel, the recovery ratio of the nanoroughness
(<i>R</i><sub>r,nano</sub>) was measured. The values of <i>R</i><sub>r,micro</sub> could be tailored in a range from 42
± 1% to 102 ± 1% and <i>R</i><sub>r,nano</sub> from 89 ± 6% to 136 ± 21% depending on the applied compression
ratio and the amount of vinyl acetate content in the cPEVA microcuboids
Noncontinuously Responding Polymeric Actuators
Reversible
movements of current polymeric actuators stem from the continuous
response to signals from a controlling unit, and subsequently cannot
be interrupted without stopping or eliminating the input trigger.
Here, we present actuators based on cross-linked blends of two crystallizable
polymers capable of pausing their movements in a defined manner upon
continuous cyclic heating and cooling. This noncontinuous actuation
can be adjusted by varying the applied heating and cooling rates.
The feasibility of these devices for technological applications was
shown in a 140 cycle experiment of free-standing noncontinuous shape
shifts, as well as by various demonstrators
Reversible Actuation of Thermoplastic Multiblock Copolymers with Overlapping Thermal Transitions of Crystalline and Glassy Domains
Polymeric
materials possessing specific features like programmability,
high deformability, and easy processability are highly desirable for
creating modern actuating systems. In this study, thermoplastic shape-memory
polymer actuators obtained by combining crystallizable poly(ε-caprolactone)
(PCL) and poly(3<i>S</i>-isobutylmorpholin-2,5-dione)
(PIBMD) segments in multiblock copolymers are described. We designed
these materials according to our hypothesis that the confinement of
glassy PIBMD domains present at the upper actuation temperature contribute
to the stability of the actuator skeleton, especially at large programming
strains. The copolymers have a phase-segregated morphology, indicated
by the well-separated melting and glass transition temperatures for
PIBMD and PCL, but possess a partially overlapping <i>T</i><sub>m</sub> of PCL and <i>T</i><sub>g</sub> of PIBMD in
the temperature interval from 40 to 60 °C. Crystalline PIBMD
hard domains act as strong physical netpoints in the PIBMD−PCL
bulk material enabling high deformability (up to 2000%) and good elastic
recoverability (up to 80% at 50 °C above <i>T</i><sub>m,PCL</sub>). In the programmed thermoplastic actuators a high content
of crystallizable PCL actuation domains ensures pronounced thermoreversible
shape changes upon repetitive cooling and heating. The programmed
actuator skeleton, composed of PCL crystals present at the upper actuation
temperature <i>T</i><sub>high</sub> and the remaining glassy
PIBMD domains, enabled oriented crystallization upon cooling. The
actuation performance of PIBMD-PCL could be tailored by balancing
the interplay between actuation and skeleton, but also by varying
the quantity of crystalline PIBMD hard domains via the copolymer composition,
the applied programming strain, and the choice of <i>T</i><sub>high</sub>. The actuator with 17 mol% PIBMD showed the highest
reversible elongation of 11.4% when programmed to a strain of 900%
at 50 °C. It is anticipated that the presented thermoplastic
actuator materials can be applied as modern compression textiles
Toward Anisotropic Hybrid Materials: Directional Crystallization of Amphiphilic Polyoxazoline-Based Triblock Terpolymers
We present the design and synthesis of a linear ABC triblock terpolymer for the bottom-up synthesis of anisotropic organic/inorganic hybrid materials: polyethylene-<i>block</i>-poly(2-(4-(<i>tert</i>-butoxycarbonyl)amino)butyl-2-oxazoline)-<i>block</i>-poly(2-<i>iso</i>-propyl-2-oxazoline) (PE-<i>b</i>-PBocAmOx-<i>b</i>-P<i>i</i>PrOx). The synthesis was realized <i>via</i> the covalent linkage of azide-functionalized polyethylene and alkyne functionalized poly(2-alkyl-2-oxazoline) (POx)-based diblock copolymers exploiting copper-catalyzed azide–alkyne cycloaddition (CuAAC) chemistry. After purification of the resulting triblock terpolymer, the middle block was deprotected, resulting in a primary amine in the side chain. In the next step, solution self-assembly into core–shell-corona micelles in aqueous solution was investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Subsequent directional crystallization of the corona-forming block, poly(2-<i>iso</i>-propyl-2-oxazoline), led to the formation of anisotropic superstructures as demonstrated by electron microscopy (SEM and TEM). We present hypotheses concerning the aggregation mechanism as well as first promising results regarding the selective loading of individual domains within such anisotropic nanostructures with metal nanoparticles (Au, Fe<sub>3</sub>O<sub>4</sub>)
Star-Shaped Drug Carriers for Doxorubicin with POEGMA and POEtOxMA Brush-like Shells: A Structural, Physical, and Biological Comparison
The
synthesis of amphiphilic star-shaped poly(ε-caprolactone)-<i>block</i>-poly(oligo(ethylene glycol)methacrylate)s ([PCL<sub>18</sub>-<i>b</i>-POEGMA]<sub>4</sub>) and poly(ε-caprolactone)-<i>block</i>-poly(oligo(2-ethyl-2-oxazoline)methacrylate)s ([PCL<sub>18</sub>-<i>b</i>-POEtOxMA]<sub>4</sub>) is presented.
Unimolecular behavior in aqueous systems is observed with the tendency
to form loose aggregates for both hydrophilic shell types. The comparison
of OEGMA and OEtOxMA reveals that the molar mass of the macromonomer
in the hydrophilic shell rather than the mere length is the crucial
factor to form an efficiently stabilizing hydrophilic shell. A hydrophilic/lipophilic
balance of 0.8 is shown to stabilize unimolecular micelles in water.
An extensive in vitro biological evaluation shows neither blood nor
cytotoxicity. The applicability of the polymers as drug delivery systems
was proven by the encapsulation of the anticancer drug doxorubicin,
whose cytotoxic effect was retarded in comparison to the free drug