Strain maps characterize the symmetry of convergence and extension patterns during zebrafish gastrulation

During gastrulation of the zebrafish embryo, the cap of blastoderm cells organizes into the axial body plan of the embryo with left–right symmetry and head–tail, dorsal–ventral polarities. Our labs have been interested in the mechanics of early development and have investigated whether these large-scale cell movements can be described as tissue-level mechanical strain by a tectonics-based approach. The first step is to image the positions of all nuclei from mid-epiboly to early segmentation by digital sheet light microscopy, organize the surface of the embryo into multi-cell spherical domains, construct velocity fields from the movements of these domains and extract strain rate maps from the change in density of the domains. During gastrulation, tensile/expansive and compressive strains in the axial and equatorial directions are detected as anterior and posterior expansion along the anterior–posterior axis and medial–lateral compression across the dorsal–ventral axis and corresponds to the well characterized morphological movements of convergence and extension. Following gastrulation strain is represented by localized medial expansion at the onset of segmentation and anterior expansion at the onset of neurulation. In addition to linear strain, symmetric patterns of rotation/curl are first detected in the animal hemispheres at mid-epiboly and then the vegetal hemispheres by the end of gastrulation. In embryos treated with C59, a Wnt inhibitor that inhibits head and tail extension, the axial extension and vegetal curl are absent. By analysing the temporal sequence of large-scale movements, deformations across the embryo can be attributed to a combination of epiboly and dorsal convergence-extension.

Poly(etheretherketone)/Poly(ethersulfone) Blends with Phenolphthalein: Miscibility, Thermomechanical Properties, Crystallization and Morphology

Polyetheretherketone (PEEK)/polyethersulfone (PES) blends are initially not miscible, except when the blends are prepared by solvent mixing. We propose a route to elaborate PEEK/PES blends with partial miscibility by melt mixing at 375 °C with phenolphthalein. The miscibility of blends has been examined using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMTA). When adding phenolphthalein to PEEK/PES blends, the glass transitions are shifted inward as an indication of miscibility. We suggest that phenolphthalein acts as a compatibilizer by creating cardo side groups on PEEK and PES chains by nucleophilic substitution in the melted state, although this condensation reaction was reported only in the solvent until now. In addition, phenolphthalein acts as a plasticizer for PES by decreasing its glass transition. As a consequence, the PEEK phase is softened which favors the crystallization as the increase of crystalline rate. Due to aromatic moieties in phenolphthalein, the storage modulus of blends in the glassy region is kept identical to pure PEEK. The morphological analysis by SEM pictures displays nano- to microsized PES spherical domains in the PEEK matrix with improved PEEK/PES interfacial adhesion.

ANALYSIS OF LIQUID MEDIATED CONTACT OF GLASS COLLOIDAL PARTICLE WITH POLYSTYRENE COATED SURFACE

Spin coating has been widely used for obtaining uniform thin polymeric coating over glass surfaces. Previous studies have shown that the thin-coated film can deform and bulge out upon immersion in liquid. Such deformations can affect various properties of the films. In this study, we have analyzed the interaction of glass colloidal particle and the polystyrene (PS) spin-coated surface immersed in deionized (DI) water. It was found that the glass colloidal particle interacts with the surface in dissimilar way at various locations on the surface. A sudden reduction in the forces was also observed at different locations on the same surface. The separation distances at which the sudden change in the force occurred was closer to the height of the spherical domains. Therefore, the change could be attributed to the presence of blisters on the surface formed due to permeation of water into the thin film-substrate interface.

Ductility and Toughness Improvement of Injection-Molded Compostable Pieces of Polylactide by Melt Blending with Poly(ε-caprolactone) and Thermoplastic Starch

The present study describes the preparation and characterization of binary and ternary blends based on polylactide (PLA) with poly(ε-caprolactone) (PCL) and thermoplastic starch (TPS) to develop fully compostable plastics with improved ductility and toughness. To this end, PLA was first melt-mixed in a co-rotating twin-screw extruder with up to 40 wt % of different PCL and TPS combinations and then shaped into pieces by injection molding. The mechanical, thermal, and thermomechanical properties of the resultant binary and ternary blend pieces were analyzed and related to their composition. Although the biopolymer blends were immiscible, the addition of both PCL and TPS remarkably increased the flexibility and impact strength of PLA while it slightly reduced its mechanical strength. The most balanced mechanical performance was achieved for the ternary blend pieces that combined high PCL contents with low amounts of TPS, suggesting a main phase change from PLA/TPS (comparatively rigid) to PLA/PCL (comparatively flexible). The PLA-based blends presented an “island-and-sea” morphology in which the TPS phase contributed to the fine dispersion of PCL as micro-sized spherical domains that acted as a rubber-like phase with the capacity to improve toughness. In addition, the here-prepared ternary blend pieces presented slightly higher thermal stability and lower thermomechanical stiffness than the neat PLA pieces. Finally, all biopolymer pieces fully disintegrated in a controlled compost soil after 28 days. Therefore, the inherently low ductility and toughness of PLA can be successfully improved by melt blending with PCL and TPS, resulting in compostable plastic materials with a great potential in, for instance, rigid packaging applications.

Stable Frank–Kasper phases of self-assembled, soft matter spheres

Single molecular species can self-assemble into Frank–Kasper (FK) phases, finite approximants of dodecagonal quasicrystals, defying intuitive notions that thermodynamic ground states are maximally symmetric. FK phases are speculated to emerge as the minimal-distortional packings of space-filling spherical domains, but a precise measure of this distortion and how it affects assembly thermodynamics remains ambiguous. We use two complementary approaches to demonstrate that the principles driving FK lattice formation in diblock copolymers emerge directly from the strong-stretching theory of spherical domains, in which a minimal interblock area competes with a minimal stretching of space-filling chains. The relative stability of FK lattices is studied first using a diblock foam model with unconstrained particle volumes and shapes, which correctly predicts not only the equilibrium σ lattice but also the unequal volumes of the equilibrium domains. We then provide a molecular interpretation for these results via self-consistent field theory, illuminating how molecular stiffness increases the sensitivity of the intradomain chain configurations and the asymmetry of local domain packing. These findings shed light on the role of volume exchange on the formation of distinct FK phases in copolymers and suggest a paradigm for formation of FK phases in soft matter systems in which unequal domain volumes are selected by the thermodynamic competition between distinct measures of shape asymmetry.

Thermoplastic films containing lignin and their optical polarization properties

A soda lignin, Protobind 2400, was blended at ratios up to thirty weight percent with polyolefins or the aliphatic-aromatic copolyester Ecoflex and films were cast with a twin-screw extruder. The mechanical properties, structure, and optical properties of the resultant films were characterized by tensile tests and microscopy. Films for all blends of this modified lignin were successfully cast without operational issues. Film elongation was maintained for both the polyolefins and Ecoflex. Lignin significantly increased the modulus of the polyethylene films but decreased the modulus of the polypropylene and Ecoflex films. Lignin was found as lamellae oriented in the machine direction of the polyolefin films, but as spherical domains in the Ecoflex film. It was concluded that the oriented lamellar structure was critical to the behavior of the polyolefin-lignin blends as optical polarization films (OPFs). Additional development around improvement of this property, which for the prototypes produced here was about one-tenth the efficiency of commercially available OPFs, to produce a sustainable OPF was recommended.