Green Synthesis of Soy Protein Nanocomposites: Effects of Cross-Linking and Clay Nanoparticles on the Mechanical Performance.

A green synthesis scheme was adopted for preparation of soy-protein-based clay nanocomposites, in which soy protein isolates (SPIs) were utilized as the biodegradable resin and clay nanoparticles (CNPs) were used as the nanoreinforcing phase. Cross-linking of the SPIs was realized through an aqueous reaction scheme with oxidized sugars (e.g., glucose and sucrose as the typical constituents of soy flours) as the cross-linkers. Toughening effects of the cross-linkers, process parameters, and CNPs on the mechanical properties (e.g., tensile strength, stiffness, strain at break, and toughness) of the resulting SPI-based clay nanocomposites were examined by micromechanical tensile testing. The cross-linking and toughening mechanisms of the SPI-based nanocomposites were evaluated by Fourier transform infrared spectroscopy, sol-gel and color characterization, scanning differential calorimetry, and transmission electron microscopy. Thermal stability of the cross-linked SPIs was evaluated by thermogravimetric analysis. Experimental results show that cross-linking can noticeably improve both the tensile strength and tensile modulus of the resulting SPI films, and a small quantity of CNPs can obviously alter the mechanical properties of the resulting clay nanocomposite films. The present study indicates that defatted soy flours can be directly utilized for developing low-cost, SPI-based nanocomposites without the need for external plasticizers, and the entire synthesis is completely green without involvement of any petroleum-based organic solvents, polymers, and metallic catalysts. Such biodegradable SPI-based green nanocomposites have the potential to substitute fossil-based plastics and polymer composites for use in various industrial products and house utilities.

Circumferential wrinkling of polymer nanofibers.

Surface wrinkles are commonly observed in soft polymer nanofibers produced in electrospinning. This paper studies the conditions of circumferential wrinkling in polymer nanofibers under axial stretching. A nonlinear continuum mechanics model is formulated to take into account the combined effects of surface energy and nonlinear elasticity of the nanofibers on wrinkling initiation, in which the soft nanofibers are treated as incompressible, isotropically hyperelastic neo-Hookean solid. The critical condition to trigger circumferential wrinkling is determined and its dependencies upon the surface energy, mechanical properties, and geometries of the nanofibers are examined. In the limiting case of spontaneous circumferential wrinkling, the theoretical minimum radius of soft nanofibers producible in electrospinning is determined, which is related closely to the intrinsic length l_{0}=γ/E of the polymer (γ: the surface energy; E: a measure of the elastic modulus), and compared with that of spontaneous longitudinal wrinkling in polymer nanofibers. The present study provides a rational understanding of surface wrinkling in polymer nanofibers and a technical approach for actively tuning the surface morphologies of polymer nanofibers for applications, e.g., high-grade filtration, oil-water separation, tissue scaffolding, etc.

Spatial Distribution and Solvent Polarity-Triggered Release of a Polypeptide Incorporated into Invertible Micellar Assemblies.

Extracting, stabilizing, or delivering biomacromolecules such as proteins and peptides in organic phases have potential applications in biocatalysis, protein extraction, and food antioxidation. However, most current delivery/stabilization platforms face various limitations such as protein/peptide molecular size, platform stability/reusability, and/or potential damage to the cargos. A potential solution to these problems is micellar self-assemblies from amphiphilic invertible polymers, which have recently been demonstrated to be powerful as molecular hosts to deliver both small molecular drugs and functional polypeptides in the aqueous phase. To better understand the function of biomacromolecules and predict the usefulness of the formed invertible micellar assemblies (IMAs) as biomacromolecular hosts in organic phases, it is critical to characterize the spatial distribution, structure, and dynamics of biomacromolecules in the IMA including those upon release. However, the background signals of the IMAs limit the application of most peptide characterization approaches. In this work, we overcome the technical barriers by using site-directed spin labeling electron paramagnetic resonance to probe the spatial arrangement and release of a model, the hemagglutinin (HA) peptide, in the IMAs formed from two different amphiphilic invertible polymers. By site-specifically probing three residues along the peptide chain, for the first time, we depict the possible spatial distribution of HA within the IMAs. By triggering the disassembly of the IMAs with a thermodynamically good solvent (in this study, acetone), we detailed the stability of IMAs in toluene and the peptide release conditions once the polarity of the medium changes. Our findings are important for the application of peptides/proteins at the polar-nonpolar interface or using this interface to extract or deliver biomacromolecules. Our work also demonstrates the power of SDSL-EPR on probing peptide or micelle dynamics, which can be generalized to understand proteins or other biomacromolecules in micellar polymer assemblies in varied applications.

An amphiphilic invertible polymer as a delivery vehicle for a M2e-HA2-HA1 peptide vaccine against an Influenza A virus in pigs.

Influenza A viruses (IAVs) are a group of genetically diverse and economically important zoonotic pathogens. Despite decades of research, effective and broadly protective vaccines are yet to be developed. Recent breakthroughs in epitope-based immunization for influenza viruses identify certain conserved regions of the HA2 and M2e proteins as capable of inducing broad protection against multiple influenza strains. The M2e and HA2 peptides have been evaluated in mice but not as a combination in pigs, which play an important role in the transmission and evolution of IAV. Peptides are inherently weak immunogens; and effective delivery of peptide antigens is challenging. To enhance the delivery and immunogenicity of peptide-based vaccines, the conserved M2e and HA2 and a strain-specific HA1 epitope of Influenza A (H1N1) pdm09 were expressed as a chain in a bacterial expression system and entrapped in a novel amphiphilic invertible polymer made from polyethyelene glycol (PEG, molecular weight 600 g/mol) and polytetrahydrofuran (PTHF, molecular weight 650 g/mol), PEG600PTHF650. Piglets vaccinated with polymeric peptide vaccine mounted significantly stronger antibody responses against the peptide construct when compared to piglets immunized with the multi-epitope peptide alone. When vaccinated pigs were challenged with Influenza A (H1N1) pdm09, viral shedding in nasal secretions and lung lesion scores were significantly reduced when compared to the unvaccinated controls and pigs vaccinated with the peptide alone at six days post-challenge. Thus, the combination of the PEG600PTHF650 polymer and trimeric peptide construct enhanced delivery of the peptide antigen, acted as an adjuvant in stimulating strong antibody responses, reduced the effects of viral infection in vaccinated pigs.

Macromolecular inversion-driven polymer insertion into model lipid bilayer membranes.

Macromolecules of amphiphilic invertible polymers (AIPs) are capable of self-assembly into micellar assemblies of various morphologies in solvents of different polarities. The micellar assemblies in aqueous media are capable of encapsulating poorly aqueous soluble cargo and can undergo inverse conformational change and cargo release in contact with non-polar media, including potentially, cell membranes. Thus, invertible micellar assemblies have significant potential in drug delivery and related domains. However, to date there have been few investigations into their interactions with lipid membranes. Herein, we investigate the interactions of three recently developed AIPs of varying hydrophobicity/hydrophilicity balance with a highly fluidic microcavity supported 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipid bilayer. We combined electrochemical impedance spectroscopy (EIS) with fluorescence correlation spectroscopy (FCS) to understand how the AIP micellar assemblies impacted bilayer permeability and fluidity respectively, across polymer concentrations above and below their critical micelle concentrations (cmcs). At concentration as above their cmcs, all of the AIPs explored increased permeability and decreased the fluidity of the lipid membrane. The extent of impact depended on the hydrophobicity of the AIP. PEG600-PTHF650, the most hydrophobic of the polymers, synthesized from PEG (molecular weight 600 g/mol) and PTHF (molecular weight 650 g/mol) exerted the greatest influence on the bilayer's physical properties and fluorescence imaging and correlation data indicate that PEG600-PTHF650 micelles loaded with BODIPY probes adsorb and invert at the lipid membrane with release of cargo into the bilayer. This study should help inform future advancement of AIPs for membrane molecular delivery.