Macromolecular Symposia最新文献

Natural or synthetic polycations are used in nucleic acid-based therapies as complexing agents which interact electrostatically with nucleic acids, condense them into nanoparticles, protect them and control their entry into cells. However, although the literature on the formation of nanoparticles known as complexes is well documented, fewer studies have focused on the physical chemistry behind their disassembly, especially under physicochemical conditions found in an intracellular environment. There are several theories of the disassembly of these complexes, one of them consisting in the exchange between the polycations of these particles with biological polyanions. This project is focused on the study of the complexation mechanism of chitosan and calf-thymus DNA, as well as the stability of the obtained complexes in presence of biological polyanions, i.e., glycosaminoglycans (GAGs). In the presence of polyelectrolyte complexes, GAGs that are present in cells are expected to compete with nucleic acids and dissociate the complex if polycation–GAG association is thermodynamically favored. It is found that chitosan/DNA complexes colloidal stability depends on its [N⁺]/[P⁻] charge ratio (R). Furthermore, it is determined that the aggregation onset of the complexes, generated by the addition of different GAGs, depends on the structure and the charge density of the GAGs.

Nanogels are nanostructures with dimensions within the nanoscale, composed of crosslinked polymers through their functional groups. Nanogels can display sensitiveness to stimuli, such as pH or temperature. This characteristic has been used in the design of new platforms for the transport and release of active ingredients. Biopolymer-based nanogels are of great interest due to their biodegradability, biocompatibility, nontoxicity, and among others. In this project, pH-responsive nanogels are synthesized through a novel methodology, using two polysaccharides classified as safe, biocompatible, and easily accessible materials, i.e., chitosan (CS) and maltodextrin (MD). A reductive amination reaction between CS and partially oxidized MDs allows to synthesized MD/CS nanogels with sizes ranging from 90 ± 5 to 194 ± 40 nm and with a colloidal stability up to 7 weeks. It is found that the variation of nanogels size and charge depends on CS concentration, molecular weight, and pH, as well as on the % oxidation of the MD. As evidence of nanogels pH-responsiveness, an increase of size and ζ-potential is observed by decreasing the pH. This size increase is attributed to the swelling of the nanogels upon a change in pH. Finally, doxorubicin is encapsulated in MD/CS nanogels, with a loading capacity up to 57%.

Commercial low acyl gellan (LAG) is purified by the fractional dissolution method. An aqueous solution of purified commercial LAG exhibits polyelectrolyte character due to its high molar mass and carboxylic groups in glucuronic acid fragments. The empirical Fuoss equation determines the intrinsic viscosity of purified LAG in salt-less water. Fractionation of commercial LAG is carried out by ultrasound treatment. LAG fractions are characterized by ¹H NMR and FTIR spectroscopy. The intrinsic viscosities of ultrasonically treated LAG samples are measured in 0.025 m of tetramethylammonium chloride (TMACl). The molecular weights of LAG fractions are determined by the Mark–Kuhn–Houwink equation.

Stimuli-responsive hydrogels are of great interest in many biomedical applications, from drug delivery to tissue engineering. In this work, thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) hydrogels are prepared by adding different amounts of crosslinking agent (N,N′-methylenebisacrylamide, BIS) in a two-step-freezing polymerization method, which is simple and potentially able to reduce fabrication times and costs. The hydrogel swelling behavior and the temporal evolution of the volume variation in response to temperature changes are investigated. Results demonstrate how the thermo-responsive behavior of these materials is related to the content of the BIS crosslinking agent, which is helpful to guide the synthesis of dynamic hydrogels with tunable functional properties.

Screen printing is an interesting technique for the high-volume production of printed conductive electronic devices on flexible substrates. In this study, silver conductive lines have been produced by screen-printing technique on flexible PEN substrates and optimized in order to provide maximum electrical conduction. The geometry of the obtained conductive samples has been modified by performing thermoforming tests in a mold with complex geometry, replicating a significant section of dashboard coating. The functionality of the shape-deformed substrates has been assessed.

The present paper introduces a preliminary analysis and the recent development of three-dimensional (3D) printed thermoplastic polyurethane (TPE-U) as a replacement of polyurethane (PU) foams that has led to a recyclable product. Among the various 3D printing techniques available, the team focuses on Fused Deposition Modeling (FDM) because of its simplicity, affordability, and versatility in printing geometries and recyclability of materials. Four thermoplastic polyurethane (TPU) elastomers with different stiffness (in the range of Shore A) are used. Therefore, through the combination of different printing geometries, modulation of the main printing parameters, and different materials, an attempt is made to simulate the mechanical behavior of PU foams, which are commonly used for the production of paddings. The mechanical evaluation, by means of dynamic mechanical analysis (DMA), of the of 3D printed specimens has highlighted a qualitatively different and potentially superior behavior with respect to that of PU foam.

The study develops an oxidative kinetic model of acrylic-urethane network during photo-aging. The kinetic model can track chemical reaction dynamics well and also enables to estimate the network lifetime by counting scission/crosslinking events. Estimated network lifetime is semiquantitively coincided with the one derived from different statistical approach.

This study aims to develop a new class of versatile silica-based materials for medical applications, synthesized via the sol–gel method. Different molecules are incorporated into the silica matrix to improve its biological properties and to use these materials as better-performing implants. Polyethylene glycol (PEG) is added to silica-based materials to improve biocompatibility, increase hydrophilicity, and enhance cellular adhesion and growth. The effect of loading the silica/PEG matrix with chlorogenic acid (CGA), a natural compound present in different types of plants, is investigated to understand how the material is affected. The interactions among different components in the hybrid materials are studied by Fourier-transform infrared (FTIR) spectroscopy. Furthermore, the materials are encapsulated in 2% w/v of alginate to evaluate the different releases of CGA, using UV-Vis Spectrophotometer. Finally, antimicrobial assessment against Escherichia coli and Pseudomonas aeruginosa of the several hybrids is observed by measuring the diameter of the zone of inhibition.

Screen printing technology is employed to prepare poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/double-walled carbon nanotubes (DWCNT) films as active p-type material for flexible thermoelectric generators (TEGs). Performance of the PEDOT:PSS/CNT composites have been optimized by changing the formulation inks to make them suitable for screen printing, by varying the CNT concentrations and by treating the printed polymeric films in ethylene glycol (EG). The purpose of this work is finding the processing conditions that optimize conductivity, Seebeck coefficient, and the power factor of the fully printed material. From experimental data, the composite with 10% by weight of DWCNT chemically treated in EG maximizes conductivity, Seebeck coefficient, and power factor of the material.

Carbon fiber reinforced polymers are widely used to manufacture aerospace deployable structures. These structures are folded in launch configuration and then deployed in space for operational activities. Since the stowage of deployable structures in folded configuration occurs for long time, the understanding of the viscoelastic properties of the material is essential to predict the structural behavior during both the deployment phase and the operational life. In this work, numerical relaxation analysis is performed on the representative volume element (RVE) of a carbon fiber reinforced polymer using a homogenization approach at the microscale. This aims to predict the effects of matrix viscoelasticity on the structural performance of a deployable structure.