Application of degradation kinetics to the rheology of poly(hydroxyalkanoates)

The time‐dependent rheological behavior of a series of 3‐hydroxybuytrate‐based semicrystalline copolymers is employed to determine the expected rheological curves that would be generated in the absence of any polymer degradation. Both dynamic frequency sweep and shear rate sweep experiments were analyzed. A model for the degradation kinetics, coupled with standard rheological relationships, was employed to extrapolate the measured sweeps to predicted curves at time zero, prior to degradation. The model is broadly applicable over a wide range of frequencies or shear rates, and generates a single degradation rate constant k for each polymer studied. A similar, although ad hoc, procedure was applied to the dynamic storage and loss moduli. The model provides a method for determining the rheological behavior of degrading polymers over a time interval, typically found in processing applications. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1794–1802, 2006     

Thermal degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)

The degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), a member of the Nodax family of polymers, were investigated using transient constant shear rate and dynamic time sweep rheological tests. The rate of chain scission at several times and temperatures was correlated with viscosity data and verified using molecular weight determination of the degraded samples. The experimental results show that the molecular weight and the viscosity of Nodax decrease with time over the range of temperatures that were studied (155–175°C). The degradation kinetics, which exhibited first‐order behavior, were determined as a function of the flow history and thermal history. An apparent activation energy of 189 ± 5 kJ/mol for thermal degradation was found by modeling variations in the rate with temperature using an Arrhenius law model. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 66–74, 2005     

Inkjet Printing of Self‐Assembled 2D Titanium Carbide and Protein Electrodes for Stimuli‐Responsive Electromagnetic Shielding

2D titanium carbides (MXene) possess significant characteristics including high conductivity and electromagnetic interference shielding efficiency (EMI SE) that are important for applications in printed and flexible electronics. However, MXene‐based ink formulations are yet to be demonstrated for proper inkjet printing of MXene patterns. Here, tandem repeat synthetic proteins based on squid ring teeth (SRT) are employed as templates of molecular self‐assembly to engineer MXene inks that can be printed as stimuli‐responsive electrodes on various substrates including cellulose paper, glass, and flexible polyethylene terephthalate (PET). MXene electrodes printed on PET substrates are able to display electrical conductivity values as high as 1080 ± 175 S cm^?1, which significantly exceeds electrical conductivity values of state‐of‐the‐art inkjet‐printed electrodes composed of other 2D materials including graphene (250 S cm^?1) and reduced graphene oxide (340 S cm^?1). Furthermore, this high electrical conductivity is sustained under excessive bending deformation. These flexible electrodes also exhibit effective EMI SE values reaching 50 dB at films with thicknesses of 1.35 µm, which mainly originate from their high electrical conductivity and layered structure.     

Increase in the length of poly(ethylene oxide) blocks in amphiphilic copolymers facilitates their cellular uptake

Amphiphilic nonionic block copolymers induce different biological effects on living cells. In particular, the hydrophobic members of the Pluronics family suppress drug efflux systems in multidrug‐resistant cells, whereas hydrophilic Pluronics support cell viability. However, the relationship between the copolymer structure and its binding to cells is still unclear. Using a tritium‐labeling approach, we analyzed interactions of nine Pluronics and three diblock copolymers with human and murine cells in vitro and revealed that the binding efficiency of the copolymers increased in line with the length of their poly(ethylene oxide) (PEO) blocks. In contrast, partitioning of the same polymers into artificial lipid bilayers determined by Isothermal Titration Calorimetry (ITC) decreased with increasing length of the PEO block. The opposite influence of hydrophilic blocks on the copolymer affinity to living cells and artificial lipid bilayers implied the binding of long PEO blocks to the hydrophilic moieties of cellular membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45492.     

Amino‐terminated polylactide micelles with an external poly(ethylene oxide) corona as carriers of drug‐loaded anionic liposomes

Micelles were prepared from a mixture of NH₂‐terminated poly(l ‐lactide) and poly(d ,l ‐lactide)‐block‐poly(ethylene oxide) (molar ratio of 3:7). The micelles were complexed with bilayer lipid vesicles (liposomes) composed of anionic palmitoyloleoylphosphatidylserine and zwitterionic dioleoylphosphatidylcholine in a molar ratio of 3:7. The micelles and micelle–liposome complexes were characterized using dynamic light scattering, laser electrophoresis, fluorimetry, transmission electron microscopy, enzymatic hydrolysis and cell viability with the following main findings. (i) Average diameter of micelle cores was found to be 70 ± 10 nm. (ii) Each micelle carried ca 20 000 amino groups. (iii) In a pH 7 solution the impact of the protonated NH₂ groups in the total surface of micelles was negligible owing to their screening by bulky poly(ethylene oxide) blocks. (iv) The micelles were stable in slightly acidic and neutral aqueous solutions, but aggregated in slightly alkaline solutions. (v) The micelles showed no cytotoxicity up to 0.04 mg mL^?1 concentration (the maximum concentration in the experiment). (vi) Each micelle adsorbed ca 30 anionic liposomes loaded with the antitumor antibiotic doxorubicin; the liposomes retained their integrity upon binding with micelles. (vii) The initial micelles and the micelle–liposome complexes showed two‐week stability to enzymatic hydrolysis. © 2018 Society of Chemical Industry     

Bioinspired Directional Surfaces for Adhesion,Wetting, and Transport

In Nature, directional surfaces on insect cuticle, animal fur, bird feathers, and plant leaves are composed of dual micro‐nanoscale features that tune roughness and surface energy. Here, experimental and theoretical approaches for the design, synthesis, and characterization of new bioinspired surfaces demonstrating unidirectional surface properties are summarized. The experimental approaches focus on bottom‐up and top‐down synthesis methods of unidirectional micro‐ and nanoscale films to explore and characterize their anomalous features. The theoretical component focuses on computational tools to predict the physicochemical properties of unidirectional surfaces.     

Template-based and template-free preparation of nanostructured parylene via oblique angle polymerization

Parylene is an important class of polymer thin film that has wide-ranging applications due to its well-recognized properties, such as low-dielectric constant, biocompatibility, and exceptional barrier properties. Here, we studied the deposition of parylene nanofibers by template-based and template-free methods, which combine both vapor deposition polymerization and oblique angle deposition. A comparative study of two approaches based on surface characterization techniques is presented. These nanofibers, deposited by both approaches, have potential applications in catalysis, biodetection, and biomedical coatings.     

Materials Fabrication from Native and Recombinant Thermoplastic Squid Proteins

Natural elastomers made from protein extracts have received significant interest as eco‐friendly functional materials due to their unique mechanical and optical properties emanating from secondary structures. The next generation sequencing approach is used to identify protein sequences in a squid ring teeth complex extracted from Loligo vulgaris and the use of recombinant expression is demonstrated in the fabrication of a new generation of thermoplastic materials. Native and recombinant thermoplastic squid proteins exhibit reversible solid to melt phase transition, enabling them to be thermally shaped into 3D geometries such as fibers, colloids, and thin films. Direct extraction or recombinant expression of protein based thermoplastics opens up new avenues for materials fabrication and synthesis, which will eventually be competitive with the high‐end synthetic oil based plastics.     

Multi-objective feasibility enhanced particle swarm optimization

This article introduces a new method entitled multi-objective feasibility enhanced partical swarm optimization (MOFEPSO), to handle highly-constrained multi-objective optimization problems. MOFEPSO, which is based on the particle swarm optimization technique, employs repositories of non-dominated and feasible positions (or solutions) to guide feasible particle flight. Unlike its counterparts, MOFEPSO does not require any feasible solutions in the initialized swarm. Additionally, objective functions are not assessed for infeasible particles. Such particles can only fly along sensitive directions, and particles are not allowed to move to a position where any previously satisfied constraints become violated. These unique features help MOFEPSO gradually increase the overall feasibility of the swarm and to finally attain the optimal solution. In this study, multi-objective versions of a classical gear-train optimization problem are also described. For the given problems, the article comparatively evaluates the performance of MOFEPSO against several popular optimization algorithms found in the literature.