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>_r,micro), while at the nanolevel, the recovery ratio of the nanoroughness (<i>R</i>_r,nano) was measured. The values of <i>R</i>_r,micro could be tailored in a range from 42 ± 1% to 102 ± 1% and <i>R</i>_r,nano 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>_m of PCL and <i>T</i>_g 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>_m,PCL). 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>_high 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>_high. 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, Fe₃O₄)

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 ([PCL₁₈-<i>b</i>-POEGMA]₄) and poly­(ε-caprolactone)-<i>block</i>-poly­(oligo­(2-ethyl-2-oxazoline)­methacrylate)­s ([PCL₁₈-<i>b</i>-POEtOxMA]₄) 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