5 research outputs found

    Synthesis and Characterization of Well-Defined PEGylated Polypeptoids as Protein-Resistant Polymers

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    Well-defined polypeptoids bearing oligomeric ethylene glycol side chains (PNMe­(OEt)<sub><i>n</i></sub>G, <i>n</i> = 1–3) with a controlled molecular weight (3.26–28.6 kg/mol) and narrow molecular weight distribution (polydispersity index, PDI = 1.03–1.10) have been synthesized by ring-opening polymerization of the corresponding <i>N</i>-carboxyanhydrides having oligomeric ethylene glycol side chains (Me­(OEt)<sub><i>n</i></sub>-NCA, <i>n</i> = 1–3) using primary amine initiators. Kinetic studies of polymerization revealed a first-order dependence on the monomer concentration, consistent with living polymerization. The obtained PEGylated polypeptoids are highly hydrophilic with good water solubility (>200 mg/mL) and are amorphous, with a glass transition temperature in the −41.1 to +46.4 °C range that increases with increasing molecular weight and decreasing side chain length. DLS and SANS analyses revealed no appreciable adsorption of lysozyme to PNMeOEtG. PNMeOEtG having different molecular weights exhibited minimal cytotoxicity toward HEp2 cells. These combined results suggest the potential use of PEGylated polypeptoids as protein-resistant materials in biomedical and biotechnological fields

    Dynamically Cross-Linked Self-Assembled Thermoresponsive Microgels with Homogeneous Internal Structures

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    The internal morphology of temperature-responsive degradable poly­(<i>N</i>-isopropylacrylamide) (PNIPAM) microgels formed via an aqueous self-assembly process based on hydrazide and aldehyde-functionalized PNIPAM oligomers is investigated. A combination of surface force measurements, small angle neutron scattering (SANS), and ultrasmall angle neutron scattering (USANS) was used to demonstrate that the self-assembled microgels have a homogeneously cross-linked internal structure. This result is surprising given the sequential addition process used to fabricate the microgels, which was expected to result in a densely cross-linked shell–diffuse core structure. The homogeneous internal structure identified is also significantly different than conventional microgels prepared via precipitation polymerization, which typically exhibit a diffuse shell–dense core structure. The homogeneous structure is hypothesized to result from the dynamic nature of the hydrazone cross-linking chemistry used to couple with the assembly conditions chosen that promote polymer interdiffusion. The lack of an internal cross-linking gradient within these degradable and monodisperse microgels is expected to facilitate more consistent drug release over time, improved optical properties, and other potential application benefits

    Phase Separation and Stack Alignment in Aqueous Cellulose Nanocrystal Suspension under Weak Magnetic Field

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    Isotropic–nematic (I–N) transitions in cellulose nanocrystal (CNC) suspension and self-assembled structures in the isotropic and nematic phases were investigated using scattering and microscopy methods. A CNC suspension with a mass fraction of 7.4% spontaneously phase separated into an isotropic phase of 6.9% in the top layer and a nematic phase of 7.9% in the bottom layer. In both the phases, the CNC particles formed stacks with an interparticle distance being of ≈37 nm. One-dimensional small-angle neutron scattering (SANS) profiles due to both phases could be fitted using a stacking model considering finite particle sizes. SANS and atomic force microscopy studies indicate that the nematic phase in the bottom layer contains more populations of larger particles. A weak magnetic field of ≈0.5 T was able to induce a preferred orientation of CNC stacks in the nematic phase, with the stack normals being aligned with the field (perpendicular to the long axis of CNC particles). The Hermans orientation parameter, ⟨<i>P</i><sub>2</sub>⟩, was ≈0.5 for the nematic phase; it remained unchanged during the relaxation process of ≈10 h. The fraction of oriented CNC populations decreased during the relaxation; dramatic decrease occurred in the first 3 h. The top layer remained isotropic in the weak field. Polarized microscopy studies revealed that the nematic phase was chiral. Adjacent particles in a stack form a twisting angle of ≈0.6 °, resulting in a helix pitch distance of ≈22 μm

    Nanoscale Lipid/Polymer Hybrid Vesicles: Effects of Triblock Copolymer Composition and Hydrophilic Weight Fraction

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    Hybrid vesicles resulting from combined self-assembly of polymers and lipids have gained interest in recent years as drug delivery systems, biosensors, and model systems for structural scaffolds as artificial organelles. So far, in the literature, more attention has been given to study how the discrepancy of chemical compositions and hydrophobic segment sizes between polymers and lipids affect the vesicle’s nature. In this study, we focused on how the hydrophilic blocks impact the vesicle’s morphology. Therefore, we developed hybrid lipid/polymer vesicle systems with lipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and amphiphilic triblock copolymers composed of poly(ethylene glycol)–poly(dimethylsiloxane)–poly(ethylene glycol) (PEG–PDMS–PEG). Three types of hybrid vesicle systems were investigated in a systematic manner by changing the hydrophilic block length and the polymer–lipid composition. From the data obtained from cryo-transmission electron microscopy (cryo-TEM) and small-angle neutron scattering, we observed that the hydrophilic mass fraction of an amphiphilic polymer can affect the membrane thickness, size polydispersity, and lamellarity of polymer/lipid hybrid vesicles

    Dynamics of Phospholipid Membranes beyond Thermal Undulations

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    We investigated the molecular dynamics of unilamellar liposomes by neutron spin echo spectroscopy. We report the first experimental evidence of a short-range motion at the length scale of the size of the headgroup of a lipid. The associated mean squared displacement shows a <i>t</i><sup>0.26</sup> dependence in the pico- to nanosecond region that indicates another process beyond the predictions of the Zilman–Granek (ZG) model (<i>t</i><sup>0.66</sup>) and translational diffusion (<i>t</i><sup>1</sup>). A comparison with theory shows that the observed low exponent is associated with a non-Gaussian transient trapping of lipid molecules in a local area and supports the continuous time random walk model. The analysis of the mean squared displacement leads to the important conclusion that the friction at the interface between water and liposomes plays a minor role. Center of mass diffusion of liposomes and transient trapping of lipids define the range in which the ZG model can be applied to analyze membrane fluctuations
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