Refine
Has Fulltext
- no (191)
Year of publication
Document Type
- Article (191) (remove)
Is part of the Bibliography
- yes (191) (remove)
Keywords
- biomaterials (8)
- Polymer (6)
- shape-memory effect (6)
- Hydrogel (5)
- biomaterial (5)
- electrospinning (5)
- polymer (5)
- stimuli-sensitive polymers (5)
- Biomaterial (4)
- multiblock copolymer (4)
- shape memory (4)
- Biomaterials (3)
- Degradation (3)
- Langmuir monolayer (3)
- Polymers (3)
- cell adhesion (3)
- endothelial cells (3)
- hemocompatibility (3)
- mesenchymal stem cells (3)
- microparticles (3)
- microstructure (3)
- morphology (3)
- poly(ether imide) (3)
- shape-memory polymers (3)
- Biomimetic (2)
- Biopolymer (2)
- Degradable (2)
- Depsipeptide (2)
- Gelatin (2)
- Hyaluronic acid (2)
- Membrane (2)
- Mesenchymal stem cells (2)
- Molecular modeling (2)
- Nanostructure (2)
- Oligo(epsilon-caprolactone) (2)
- Phase morphology (2)
- Poly(epsilon-caprolactone) (2)
- Rheology (2)
- Shape-memory effect (2)
- Shape-memory polymer (2)
- Temperature-memory effect (2)
- Thin film (2)
- actuation (2)
- artificial muscles (2)
- atomic force microscopy (2)
- crystallization (2)
- crystallization behavior (2)
- degradation (2)
- ellipsometry (2)
- gelatin (2)
- hydrogel (2)
- hydrogels (2)
- mechanical (2)
- migration (2)
- multifunctional polymers (2)
- oligodepsipeptides (2)
- phase morphology (2)
- platelets (2)
- poly(epsilon-caprolactone) (2)
- poly(ethylene glycol) (2)
- polyester (2)
- polyesterurethanes (2)
- polyglycerol (2)
- properties (2)
- protein adsorption (2)
- ring-opening polymerization (2)
- soft actuators (2)
- soft robotics (2)
- spectroscopic ellipsometry (2)
- stem cell adhesion (2)
- surface functionalization (2)
- (NMR) (1)
- 2D materials (1)
- 3D-printing (1)
- 4D-actuation (1)
- Actuation (1)
- Actuators (1)
- Additive manufacturing (1)
- Adipocyte (1)
- Adsorption of uremic toxins (1)
- Aerophobicity (1)
- Ageing (1)
- Air bubble repellence (1)
- Angle-dependent X-ray induced photoelectron spectroscopy (1)
- Biocompatibility testing (1)
- Biocompatible polymers (1)
- Biomolecules coupling (1)
- Biopolymer material (1)
- Biopolymers (1)
- Brewster angle microscopy (1)
- Cartilage repair (1)
- Chondrocytes (1)
- Chronic kidney disease (1)
- Chronic kidney disease (CKD) (1)
- Cinnamylidene acetic acid (1)
- Click chemistry (1)
- Collagen-binding peptide (1)
- Composite (1)
- Crosslinking (1)
- Deformation (1)
- Docking study (1)
- Drug delivery systems (1)
- Drug loading (1)
- Electrospinning (1)
- Endothelial cells (1)
- Endothelialization (1)
- Energy (1)
- Energy storage (1)
- Enzymatic degradation (1)
- Enzymatic polymer degradation (1)
- FAK-MAPK (1)
- Fastener (1)
- Fiber (1)
- Function by design (1)
- Functionalization (1)
- Gripper (1)
- HDAC1 (1)
- High-throughput (1)
- Hydrogels (1)
- Hydrolytic degradation (1)
- Hydrolytic stability (1)
- Hydroxyapatite (1)
- Hypoxia (1)
- In situ (1)
- Inflammation (1)
- Ink (1)
- Ki67 (1)
- Langmuir layers (1)
- Langmuir monolayer degradation technique (1)
- Langmuir monolayers (1)
- Langmuir technique (1)
- Langmuir thin-films (1)
- Langmuir-Schaefer method (1)
- Langmuir-Schafer films (1)
- Macrophage (1)
- Magnetic composites (1)
- Magnetite nanoparticles (1)
- Mass spectrometry (1)
- Matrix metalloproteinase (1)
- Mechanical properties (1)
- Methacrylate (1)
- Microindentation (1)
- Microstructure (1)
- Modeling (1)
- Modelling (1)
- Molecular (1)
- Molecular dynamics simulation (1)
- Molecular interaction design (1)
- Molecular orientation (1)
- Molecular weight (1)
- Morpholindione (1)
- Multiblock copolymer (1)
- Multiblock copolymers (1)
- Multifunctional polyester networks (1)
- Multifunctionality (1)
- NICE-2014 (1)
- Nanofiber (1)
- Nanoparticle (1)
- Nanoparticles (1)
- Near infrared light triggered shape-recovery (1)
- Negative control (1)
- Nuclear magnetic resonance (1)
- OEG-OPG-OEG triblock copolymer (1)
- Oligo(ethylene glycol) (1)
- Oligo(ethylene glycol) derivatization (1)
- Oligo(omega-pentadecalactone) (1)
- Oligodepsipeptide (1)
- Oligoglycerols (1)
- On-demand release (1)
- PDLLGA (1)
- PHA-depolymerases (1)
- Packaging (1)
- Particle shape (1)
- Particle size (1)
- Phagocytosis (1)
- Photoresponsive polymers (1)
- Physical Network (1)
- Platelet (1)
- Poly(carbonate-urea-urethane)s (1)
- Poly(epsilon-caprolactone) networks (1)
- Poly(ether imide) (1)
- Poly(n-butyl acrylate) (1)
- Poly[acrylonitrile-co-(N-vinyl pyrrolidone)] (1)
- Polyesterurethane (1)
- Polyether ether ketone (1)
- Polylactide stereocomplex (1)
- Polymer architecture (1)
- Polymer functionalization (1)
- Polymer micronetwork colloids (1)
- Polymer network properties (1)
- Polymer networks (1)
- Polymeric substrate (1)
- Porous poly(ether imide) microparticulate absorbers (1)
- Protein (1)
- Proteins (1)
- RGD peptides (1)
- RGD-peptide (1)
- RUNX2 (1)
- Raman spectroscopy (1)
- Random copolymer (1)
- Rheological characterization (1)
- Ring-opening polymerization (1)
- Robotic synthesis (1)
- Robotics (1)
- SAXS (1)
- Scaffold contraction (1)
- Scaffold degradation (1)
- Scaffold stiffness (1)
- Scanning probe microscopy (SPM) (1)
- Sequence structure (1)
- Shape memory (1)
- Shape-memory (1)
- Simulation (1)
- Skin absorption (1)
- Sn(IV) alkoxide (1)
- Submicron particles (1)
- Surface functionalization (1)
- Surface reaction (1)
- Surfactants (1)
- Switchable wettability (1)
- TCP (1)
- THP-1 cells (1)
- Telechel (1)
- Thermo-responsive polymer (1)
- Thermomechanical history (1)
- Tin octanoate (1)
- UV crosslinking (1)
- Uremic toxins (1)
- VEGF (1)
- WAXS (1)
- Water (1)
- X-ray scattering (1)
- actin cytoskeleton (1)
- active polymer (1)
- active scaffold (1)
- adipogenic differentiation (1)
- adipose tissue regeneration (1)
- adsorber materials (1)
- amide ligand (1)
- amorphous polymers (1)
- assembly capabilities (1)
- atomic force microscopy (AFM) (1)
- basement membrane (1)
- beta-galactosidase (1)
- biocompatibility (1)
- biodegradable polymers (1)
- biofunctionalization (1)
- bioinspired materials (1)
- bioinstructive implants (1)
- biological applications of polymers (1)
- biological membrane (1)
- biomaterial-tissue interface (1)
- biomedical (1)
- biomimetic (chemical reaction) (1)
- biopolymer (1)
- bioprinting (1)
- blend (1)
- block copolymers (1)
- body temperature (1)
- brewster angle microscopy (1)
- broad melting temperature range (1)
- calcium influx (1)
- capsule formation (1)
- cardiovascular disease (1)
- cardiovascular implant (1)
- catalyst (1)
- cavitation-based mechanical force (1)
- cell culture (1)
- cell culture device (1)
- cell cycle inhibitors (1)
- cell encapsulation (1)
- cell selectivity (1)
- cell-material interaction (1)
- cells (1)
- chain-extended (1)
- chemical synthesis (1)
- chronic kidney disease (CKD) (1)
- co-expression (1)
- cold (1)
- collagen (1)
- collagen-IV (1)
- composite (1)
- controlled release (1)
- coordination bonds (1)
- copolymer networks (1)
- copper-catalyzed alkyne-azide cycloaddition (1)
- critical micellation temperature (1)
- cross-linking (1)
- crosslinking (1)
- crystal structures (1)
- crystalline (1)
- crystallinity (1)
- cyclic olefin copolymer (1)
- cyclic thermomechanical testing (1)
- cyclodextrin (1)
- cytokine release (1)
- cytokines/chemokines (1)
- cytotoxicity (1)
- dedifferentiation (1)
- degradable (1)
- degradable polyester (1)
- degradable polymer (1)
- degradable polymers (1)
- dendritic cells (1)
- differentiation (1)
- diffusion (1)
- drug eluting stent (1)
- efficient (1)
- elastomers (1)
- electron microscopy (1)
- electrospun scaffold (1)
- ellipsometric mapping (1)
- endothelial basement membrane (1)
- engineering (1)
- enzymatic-degradation (1)
- enzyme (1)
- excimer UV light (1)
- extracellular matrix modifying enzymes (1)
- fiber actuators (1)
- fiber meshes (1)
- fibers (1)
- fibrinogen (1)
- fibroblast (1)
- fibronectin (1)
- fluorescence stimuli‐ responsivity (1)
- foam (1)
- focal adhesion (1)
- foreign body giant cells (1)
- form stability (1)
- functional (1)
- functionalization of polymers (1)
- gelatin based scaffold (1)
- gelatin-based hydrogels (1)
- gels (1)
- gene delivery (1)
- glass (1)
- hemodialysis (1)
- human monocytic (THP-1) cells (1)
- hydrophobic uremic toxins (1)
- immunogenicity (1)
- in vitro synthesized mRNA (1)
- in vitro thrombogenicity testing (1)
- in vivo study (1)
- inclusion complex (1)
- induced pluripotent stem cells (1)
- integrated co-transfection (1)
- inverse (1)
- iron (1)
- langmuir monolayer (1)
- libraries (1)
- library (1)
- life cycle assessment (1)
- lipase release (1)
- lipases (1)
- lipid (1)
- lipoplexes (1)
- liquid-crystalline polymers (1)
- macrophage subsets (1)
- magnetic (1)
- magnetic nanoparticles (1)
- magnetosensitivity (1)
- materials science (1)
- matrix elasticity (1)
- mechanical property (1)
- mechanotransduction (1)
- mediated delivery (1)
- mercury intrusion porosimetry (1)
- microgels (1)
- microporous (1)
- molecular dynamics simulations (1)
- molecular modeling (1)
- multiblock copolymers (1)
- multiple functions (1)
- nanocomposites (1)
- nanoparticle characterization (1)
- nanostructure (1)
- network structure (1)
- networks (1)
- on demand particle release (1)
- optical imaging (1)
- orientational memory (1)
- osteogenic differentiation (1)
- oxygen plasma (1)
- p16 (1)
- p21 (1)
- parallel co-transfection (1)
- particulate (1)
- pathways (1)
- peptides (1)
- photoinduced radical polymerization (1)
- platelet activation (1)
- platelet adhesion (1)
- platelet aging (1)
- platelet function (1)
- platelet rich plasma (1)
- platelet storage (1)
- platelet-rich plasma (1)
- polarization (1)
- poly(e-caprolactone) (1)
- poly(epsilon-caprolactone) methacrylate (1)
- poly(ether imide) microparticles (1)
- poly(n-butyl acrylate) (1)
- poly(tetrafluoroethylene) (1)
- poly[(rac-lactide)-co-glycolide] (1)
- polyamines (1)
- polycaprolactone (1)
- polydepsipeptide (1)
- polyesters (1)
- polyesterurethane (1)
- polyhydroxyalkanoates (PHA) (1)
- polyimides (1)
- polymer actuators (1)
- polymer foams (1)
- polymer surface (1)
- polymer-based biomaterials (1)
- polymers (1)
- polysiloxanes (1)
- population doubling time (1)
- pore-size distribution (1)
- porosity (1)
- porous microparticles (1)
- precondition (1)
- processing (1)
- protein (1)
- protein-protein interactions (1)
- reactive oxygen species (ROS) (1)
- reference (1)
- renewable (1)
- reshaping abilities (1)
- resistive heating (1)
- responsive (1)
- reversible bidirectional shape-memory polymer (1)
- reversible shape-memory actuator (1)
- reversible shape-memory effect (1)
- rheology (1)
- rhodium(I)– phosphine (1)
- rhodium-phosphine coordination bonds (1)
- ring opening polymerization (1)
- root mean square roughness (1)
- scaffold (1)
- self-healing (1)
- semi-IPN hydrogels (1)
- semi-crystalline (1)
- senescence-associated (1)
- sequence structures (1)
- shape change (1)
- shape shifting materials (1)
- shape-memory (1)
- shape-memory hydrogel (1)
- shape-memory polymer (1)
- shape-memory polymer actuators (1)
- shape-memory properties (1)
- shape‐memory polymer actuators (1)
- side reaction (1)
- side-chains functionalization (1)
- silicone (1)
- sirna transfection (1)
- soft matter micro- and nanowires (1)
- solvent resistance (1)
- stent coatings (1)
- stereocomplexes (1)
- stimuli-sensitive materials (1)
- successive (1)
- supramolecular polymer network (1)
- surface chemistry (1)
- surface coating (1)
- surface properties (1)
- sustainability (1)
- switch (1)
- telechelics (1)
- temperature (1)
- temperature-memory effect (1)
- temperature-memory polymers (1)
- therapeutics (1)
- thermal properties (1)
- thermal treatments (1)
- thermo-sensitivity (1)
- thermomechanical properties (1)
- thermoplastic elastomer (1)
- thermoplastics (1)
- thermoresponsive polymers (1)
- thermosensitive (1)
- thrombocyte adhesion (1)
- thrombogenicity (1)
- tin(II) 2-ethylhexanoate (1)
- tissue (1)
- transfection (1)
- transfection methods (1)
- triple-shape effect (1)
- two dimensional network (1)
- ultrasound (1)
- uremia (1)
- vascular graft (1)
- vascular grafts (1)
- vascularization (1)
- viability (1)
- whole blood (1)
- wide angle x‐ ray scattering (1)
Institute
Polymeric devices capable of releasing submicron particles (subMP) on demand are highly desirable for controlled release systems, sensors, and smart surfaces. Here, a temperature-memory polymer sheet with a programmable smooth surface served as matrix to embed and release polystyrene subMP controlled by particle size and temperature. subMPs embedding at 80 degrees C can be released sequentially according to their size (diameter D of 200 nm, 500 nm, 1 mu m) when heated. The differences in their embedding extent are determined by the various subMPs sizes and result in their distinct release temperatures. Microparticles of the same size (D approximate to 1 mu m) incorporated in films at different programming temperatures T-p (50, 65, and 80 degrees C) lead to a sequential release based on the temperature-memory effect. The change of apparent height over the film surface is quantified using atomic force microscopy and the realization of sequential release is proven by confocal laser scanning microscopy. The demonstration and quantification of on demand subMP release are of technological impact for assembly, particle sorting, and release technologies in microtechnology, catalysis, and controlled release.
Maximizing the efficiency of nanocarrier-mediated co-delivery of genes for co-expression in the same cell is critical for many applications. Strategies to maximize co-delivery of nucleic acids (NA) focused largely on carrier systems, with little attention towards payload composition itself. Here, we investigated the effects of different payload designs: co-delivery of two individual "monocistronic" NAs versus a single bicistronic NA comprising two genes separated by a 2A self-cleavage site. Unexpectedly, co-delivery via the monocistronic design resulted in a higher percentage of co-expressing cells, while predictive co-expression via the bicistronic design remained elusive. Our results will aid the application-dependent selection of the optimal methodology for co-delivery of genes.
The shape and the actuation capability of state of the art robotic devices typically relies on multimaterial systems from a combination of geometry determining materials and actuation components. Here, we present multifunctional 4D-actuators processable by 3D-printing, in which the actuator functionality is integrated into the shaped body. The materials are based on crosslinked poly(carbonate-urea-urethane) networks (PCUU), synthesized in an integrated process, applying reactive extrusion and subsequent water-based curing. Actuation capability could be added to the PCUU, prepared from aliphatic oligocarbonate diol, isophorone diisocyanate (IPDI) and water, in a thermomechanical programming process. When programmed with a strain of epsilon(prog) = 1400% the PCUU networks exhibited actuation apparent by reversible elongation epsilon'(rev) of up to 22%. In a gripper a reversible bending epsilon'(rev)((be)(nd)()) in the range of 37-60% was achieved when the actuation temperature (T-high) was varied between 45 degrees C and 49 degrees C. The integration of actuation and shape formation could be impressively demonstrated in two PCUU-based reversible fastening systems, which were able to hold weights of up to 1.1 kg. In this way, the multifunctional materials are interesting candidate materials for robotic applications where a freedom in shape design and actuation is required as well as for sustainable fastening systems.
Collagen-based biomaterials with oriented fibrils have shown great application potential in medicine. However, it is still challenging to control the type I collagen fibrillogenesis in ultrathin films. Here, we report an approach to produce cohesive and well-organized type I collagen ultrathin films of about 10 nm thickness using the Langmuir-Blodgett technique. Ellipsometry, rheology, and Brewster angle microscopy are applied to investigate in situ how the molecules behave at the air-water interface, both at room temperature and 37 degrees C. The interfacial storage modulus observed at room temperature vanishes upon heating, indicating the existence and disappearance of the network structure in the protein nanosheet. The films were spanning over holes as large as 1 mm diameter when transferred at room temperature, proving the strong cohesive interactions. A highly aligned and fibrillar structure was observed by atomic force microscopy (AFM) and optical microscopy.
The degradation of polymers is described by mathematical models based on bond cleavage statistics including the decreasing probability of chain cuts with decreasing average chain length. We derive equations for the degradation of chains under a random chain cut and a chain end cut mechanism, which are compared to existing models. The results are used to predict the influence of internal molecular parameters. It is shown that both chain cut mechanisms lead to a similar shape of the mass or molecular mass loss curve. A characteristic time is derived, which can be used to extract the maximum length of soluble fragments l of the polymer. We show that the complete description is needed to extract the degradation rate constant k from the molecular mass loss curve and that l can be used to design polymers that lose less mechanical stability before entering the mass loss phase.
Soft actuator performance can be tuned by chemistry or mechanical manipulation, but this adjustability is limited especially in view of their growing technological relevance. Inspired from textile engineering, we designed and fabricated fiber mesh actuators and introduced new features like anisotropic behavior and soft-tissue like elastic deformability. Design criteria for the meshes are the formation of fiber bundles, the angle between fiber bundles in different stacked layers and covalent crosslinks forming within and between fibers at their interfacial contact areas. Through crosslinking the interfiber bond strength increased from a bond transmitting neither axial nor rotational loads (pin joint) to a bond strength capable of both (welded joint). For non-linear elastic stiffening, stacked fiber bundles with four embracing fibers were created forming microstructural rhombus shapes. Loading the rhombus diagonally allowed generation of “soft tissue”-like mechanics. By adjustment of stacking angles, the point of strong increase in stress is tuned. While the highest stresses are observed in aligned and crosslinked fiber mats along the direction of the fiber, the strongest shape-memory actuation behavior is found in randomly oriented fiber mats. Fiber mesh actuators controlled by temperature are of high significance as soft robot skins and as for active patches supporting tissue regeneration.
Tissue reconstruction has an unmet need for soft active scaffolds that enable gentle loading with regeneration-directing bioactive components by soaking up but also provide macroscopic dimensional stability. Here microporous hydrogels capable of an inverse shape-memory effect (iSME) are described, which in contrast to classical shape-memory polymers (SMPs) recover their permanent shape upon cooling. These hydrogels are designed as covalently photo cross-linked polymer networks with oligo(ethylene glycol)-oligo(propylene glycol)-oligo(ethylene glycol) (OEG-OPG-OEG) segments. When heated after deformation, the OEG-OPG-OEG segments form micelles fixing the temporary shape. Upon cooling, the micelles dissociate again, the deformation is reversed and the permanent shape is obtained. Applicability of this iSME is demonstrated by the gentle loading of platelet-rich plasma (PRP) without causing any platelet activation during this process. PRP is highly bioactive and is widely acknowledged for its regenerative effects. Hence, the microporous inverse shape-memory hydrogel (iSMH) with a cooling induced pore-size effect represents a promising candidate scaffold for tissue regeneration for potential usage in minimally invasive surgery applications.
In vivo endothelialization of polymer-based cardiovascular implant materials is a promising strategy to reduce the risk of platelet adherence and the subsequent thrombus formation and implant failure. However, endothelial cells from elderly patients are likely to exhibit a senescent phenotype that may counteract endothelialization. The senescence status of cells should therefore be investigated prior to implantation of devices designed to be integrated in the blood vessel wall. Here, human umbilical vein endothelial cells (HUVEC) were cultivated up to passage (P) 4, 10 and 26/27 to determine the population doubling time and the senescence status by four different methods. Determination of the senescence-associated beta-galactosidase activity (SA-beta-Gal) was carried out by colorimetric staining and microscopy (i), as well as by photometric quantification (ii), and the expression of senescence-associated nuclear proteins p16 and p21 as well as the proliferation marker Ki67 was assessed by immunostaining (iii), and by flow cytometry (iv). The population doubling time of P27-cells was remarkably greater (103 +/- 65 h) compared to P4-cells (24 +/- 3 h) and P10-cell (37 +/- 15 h). Among the four different methods tested, the photometric SA-beta-Gal activity assay and the flow cytometric determination of p16 and Ki67 were most effective in discriminating P27-cells from P4- and P10-cells. These methods combined with functional endothelial cell analyses might aid predictions on the performance of implant endothelialization in vivo.
The production and consumption of commodity polymers have been an indispensable part of the development of our modern society. Owing to their adjustable properties and variety of functions, polymer-based materials will continue playing important roles in achieving the Sustainable Development Goals (SDG)s, defined by the United Nations, in key areas such as healthcare, transport, food preservation, construction, electronics, and water management. Considering the serious environmental crisis, generated by increasing consumption of plastics, leading-edge polymers need to incorporate two types of functions: Those that directly arise from the demands of the application (e.g. selective gas and liquid permeation, actuation or charge transport) and those that enable minimization of environmental harm, e.g., through prolongation of the functional lifetime, minimization of material usage, or through predictable disintegration into non-toxic fragments. Here, we give examples of how the incorporation of a thoughtful combination of properties/functions can enhance the sustainability of plastics ranging from material design to waste management. We focus on tools to measure and reduce the negative impacts of plastics on the environment throughout their life cycle, the use of renewable sources for their synthesis, the design of biodegradable and/or recyclable materials, and the use of biotechnological strategies for enzymatic recycling of plastics that fits into a circular bioeconomy. Finally, we discuss future applications for sustainable plastics with the aim to achieve the SDGs through international cooperation. <br /> Leading-edge polymer-based materials for consumer and advanced applications are necessary to achieve sustainable development at a global scale. It is essential to understand how sustainability can be incorporated in these materials via green chemistry, the integration of bio-based building blocks from biorefineries, circular bioeconomy strategies, and combined smart and functional capabilities.
Ethylene oxide sterilization of electrospun poly(L-lactide)/poly(D-lactide) core/shell nanofibers
(2021)
The application of polymers in medicine requires sterilization while retaining material structure and properties. This demands detailed analysis, which we show exemplarily for the sterilization of PLLA/PDLA core-shell nanofibers with ethylene oxide (EtO). The electrospun patch was exposed to EtO gas (6 vol% in CO2, 1.7 bar) for 3 h at 45 degrees C and 75% rel. humidity, followed by degassing under pressure/vacuum cycles for 12 h. GC-MS analysis showed that no residual EtO was retained. Fiber diameters (similar to 520 +/- 130 nm) of the patches remained constant as observed by electron microscopy. Young's modulus slightly increased and the elongation at break slightly decreased, determined at 37 degrees C. No changes were detected in H-1-NMR spectra, in molar mass distribution (GPC) or in crystallinity measured for annealed samples with comparable thermal history (Wide Angle X-Ray Scattering). Altogether, EtO emerged as suitable sterilization method for polylactide nanofibers with core-shell morphology.
The Venus flytrap is a fascinating plant with a finely tuned mechanical bi-stable system, which can switch between mono- and bi-stability. Here, we combine geometrical design of compliant mechanics and the function of shape-memory polymers to enable switching between bi- and mono-stable states. Digital design and modelling using the Chained Beam Constraint Model forecasted two geometries, which were experimentally realized as structured films of cross-linked poly[ethylene-co-(vinyl acetate)] supported by digital manufacturing. Mechanical evaluation confirmed our predicted features. We demonstrated that a shape-memory effect could switch between bi- and mono-stability for the same construct, effectively imitating the Venus flytrap.
Shape-memory polymers designed in view of thermomechanical energy storage and conversion systems
(2021)
Oligodepsipeptides (ODPs) attract increasing attention as degradable materials in controlled drug delivery or as building blocks for nano-carriers. Their strong intermolecular interactions provide high stability. Tailoring the side groups of the amino acid repeating units to achieve a strong affinity to particular drugs allows a high drug-loading capacity. Here we describe synthesis and characterization of dihydroxy terminated teroligodepsipeptides (ter-ODPs) by ring-opening copolymerization (ROP) of three different morpholine-2,5-diones (MDs) in bulk in order to provide a set of teroligomers with structural variation for drug release or transfection. Ter-ODPs with equivalent co-monomer feed ratios were prepared as well as ter-ODPs, in which the co-monomer feed ratio was varied between 9 mol% and 78 mol%. Ter-ODPs were synthesized by ROP using 1,1,10,10-tetra-n-butyl-1,10-distanna-2,9,11,18-tetraoxa-5,6,14,15-tetrasulfur-cyclodecane (tin(IV) alkoxide) that was obtained by the reaction of dibutyl tin(II) oxide with 2-hydroxyethyl disulfide. The number average molecular weight (M-n) of ter-ODPs, determined by H-1 NMR and gel permeation chromatography (GPC), ranged between 4000 g center dot mol(-1) and 8600 g center dot mol(-1). Co-monomer compositions in ter-ODPs could be controlled by changing the feed ratio of co-monomers as observed by H-1 NMR spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The amount of remaining monomers as determined by H-1 NMR could be kept below 1 wt%. Macrocycles as main sources of byproducts as determined from MALDI-TOF-MS measurements were significantly lower as compared to polymerization by Sn(Oct)(2). Glass-transition temperature (T-g) of ter-ODPs ranged between 59 degrees C and 70 degrees C.
The chemical nature, the number length of integrated building blocks, as well as their sequence structure impact the phase morphology of multiblock copolymers (MBC) consisting of two non-miscible block types. It is hypothesized that a strictly alternating sequence should impact phase segregation. A library of well-defined MBC obtained by coupling oligo(epsilon-caprolactone) (OCL) of different molecular weights (2, 4, and 8 kDa) with oligotetrahydrofuran (OTHF, 2.9 kDa) via Steglich esterification results in strictly alternating (MBCalt) or random (MBCran) MBC. The three different series has a weight average molecular weight (M-w) of 65 000, 165 000, and 168 000 g mol(-1) for MBCalt and 80 500, 100 000, and 147 600 g mol(-1) for MBCran. When the chain length of OCL building blocks is increased, the tendency for phase segregation is facilitated, which is attributed to the decrease in chain mobility within the MBC. Furthermore, it is found that the phase segregation disturbs the crystallization by causing heterogeneities in the semi-crystalline alignment, which is attributed to an increase of the disorder of the OCL semi-crystalline alignment.
Complexes from catalysts and initiator can be used to insert a specific number of additional chemical functional groups in (co)polymers prepared by ring-opening polymerization (ROP) of lactones. We report on the synthesis of cooligomers from sec-butyl-morpholine-2,5-dione (SBMD) and para-dioxanone (PDX) by ROP with varied feed ratios in the bulk using the catalyst complex SnOct(2)/2-hydroxyethyl sulfide. M-n of the cooligomers (determined by GPC) decreased with decreasing SBMD feed ratio from 4200 +/- 420 to 800 +/- 80 g mol(-1). When the feed ratio was reduced from 80 to 50 mol% the molar ratio of SBMD of the cooligomers (determined by H-1-NMR) remained nearly unchanged between 81 and 86 mol% and was attributed to a higher reactivity of SBMD. This assumption was confirmed by fractionation of GPC, in which an increase of SBMD with increasing molecular weight was observed. The catalyst/initiator system provides a high potential to create orthogonal building blocks by cleavage of the sulfide bond.
Fibrous shape-memory polymer (SMP) scaffolds were investigated considering the fiber as basic microstructural feature. By reduction of the fiber diameter in randomly oriented electrospun polyetherurethane (PEU) meshes from the micro-to the nano-scale, we observed changes in the molecular orientation within the fibers and its impact on the structural and shape-memory performance. It was assumed that a spatial restriction by reduction of the fiber diameter increases molecular orientation along the orientation of the fiber. The stress-strain relation of random PEU scaffolds is initially determined by the 3D arrangement of the fibers and thus is independent of the molecular orientation. Increasing the molecular orientation with decreasing single fiber diameter in scaffolds composed of randomly arranged fibers did not alter the initial stiffness and peak stress but strongly influenced the elongation at break and the stress increase above the Yield point. Reduction of the single fiber diameter also distinctly improved the shape-memory performance of the scaffolds. Fibers with nanoscale diameters (< 100 nm) possessed an almost complete shape recovery, high recovery stresses and fast relaxation kinetics, while the shape fixity was found to decrease with decreasing fiber diameter. Hence, the fiber diameter is a relevant design parameter for SMP.
High crystallization rate and thermomechanical stability make polylactide stereocomplexes effective nanosized physical netpoints. Here, we address the need for soft, form-stable degradable elastomers for medical applications by designing such blends from (co)polyesters, whose mechanical properties are ruled by their nanodimensional architecture and which are applied as single components in implants. By careful controlling of the copolymer composition and sequence structure of poly[(L-lactide)-co-(epsilon-caprolactone)], it is possible to prepare hyperelastic polymer blends formed through stereocomplexation by adding poly(D-lactide) (PDLA). Low glass transition temperature T-g <= 0 degrees C of the mixed amorphous phase contributes to the low Young's modulus E. The formation of stereocomplexes is shown in DSC by melting transitions T-m > 190 degrees C and in WAXS by distinct scattering maxima at 2 theta = 12 degrees and 21 degrees. Tensile testing demonstrated that the blends are soft (E = 12-80 MPa) and show an excellent hyperelastic recovery R-rec = 66-85% while having high elongation at break epsilon(b) up to >1000%. These properties of the blends are attained only when the copolymer has 56-62 wt% lactide content, a weight average molar mass >140 kg center dot mol(-1), and number average lactide sequence length >= 4.8, while the blend is formed with a content of 5-10 wt% of PDLA. The devised strategy to identify a suitable copolymer for stereocomplexation and blend formation is transferable to further polymer systems and will support the development of thermoplastic elastomers suitable for medical applications.
The hierarchical design approach provides various opportunities to adjust the structural performance of polymer materials. Electrospinning processing techniques give access to molecular orientation as a design parameter, which we consider here in view of the shape-memory actuation performance. The aim of this work is to investigate how the reversible strain epsilon'(rev) can be affected by a morphology change from a bulk material to an electrospun mesh. epsilon'(rev) could be increased from 5.5 +/- 0.5% to 15 +/- 1.8% for a blend from a multiblock copolymer with poly(epsilon-caprolactone) (PCL) and poly(L-lactide) (PLLA) segments with oligo(D-lactide) (ODLA). This study demonstrates an effective design approach for enhancing soft actuator performance, which can be broadly applied in soft robotics and medicine.
Active fibers can serve as artificial muscles in robotics or components of smart textiles. Here, we present an origami hand robot, where single fibers control the reversible movement of the fingers. A recovery/contracting force of 0.2 N with a work capacity of 0.175 kJ kg(-1) was observed in crosslinked poly[ethylene-co-(vinyl acetate)] (cPEVA) fibers, which could enable the bending movement of the fingers by contraction upon heating. The reversible opening of the fingers was attributed to a combination of elastic recovery force of the origami structure and crystallization-induced elongation of the fibers upon cooling.
Shape-memory polymer micronetworks (MN) are micrometer-sized objects that can switch their outer shape upon external command.This study aims to scale MN sizes to the low micrometer range at very narrow size distributions. In a two-step microfluidic strategy, the specific design of coaxial class capillary devices allowed stabilizing the thread of the dispersed phase to efficiently produce precursor particles in the tip-streaming regime at rates up to similar to 170 kHz and final sizes down to 4 mu m. In a subsequent melt-based microfluidic photocrosslinking of the methacrylate-functionalized oligo(epsilon-caprolactone) precursor material, MN could be produced without particle aggregation. A comprehensive analysis of MN properties illustrated successful crosslinking, semi-crystalline morphology, and a shape-switching functionality for all investigated MN sizes (4, 6, 9, 12, 22 mu m). Such functional micronetworks tailored to and below the dimension of cells can enable future applications in technology and medicine like controlling cell interaction.