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

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>_g’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