Assembly, Elasticity, and Structures of Nanoparticles in Immiscible Polymer Blends

Introducing nanoscale fillers into polymer matrices can serve as a means to compatibilize polymer blends and represents a clever way to manipulate their morphology at the micro-scale. Such a novel “compatibilization” strategy represents a viable route for optimizing the performance of polymer systems, which are ubiquitous in the modern society. The effects of nanoparticles on the micrometer-sized arrangement of the polymer phases, however, are difficult to predict, and most of the recent literature on this topic lack in terms of generality. Many issues remain unclear, and even well-established phenomena are actually far from being fully understood. Is the origin of the uneven distribution of the filler in a multiphase host matrix merely dictated by thermodynamic arguments? Is it possible to drive the systems towards desired non-equilibrium configurations? How the filler affects the blend microstructure? And how the fluids in turn affect the nanoparticle assembly? This dissertation addresses these matters from both a theoretical and a practical point of view, shedding light on the sequence of events which determine the final morphology of nanoparticle-containing polymer blends through a combination of morphological and rheological analyses. In the first experimental part of this study, the physical mechanisms that govern the melt-state microstructural evolutions of polymer blends in the presence of nanoparticles are elucidated through a combination of several analyses and measurements. Using ternary blends of polystyrene (PS), poly(methyl methacrylate) (PMMA), and clay nanoplatelets we prove the generality of the mechanism of morphology stabilization by interfacial crowding of the nanoparticles, which keeps working in spite of the high viscosity of the liquid phases and the plate-like shape of the nanoparticles. The effect of the co-continuous morphology of the host matrix is highlighted through a comparative analysis with systems based on the same polymers and nanoparticles, but in which the matrix is either a single polymer or a drop-in-matrix blend. This allows us to emphasize the role of the multiphase nature of the host medium in driving the nanoparticle assembly. In particular, the elasticity and structure of the three-dimensional filler network which forms above Φc were studied in detail by resorting to the percolation theory. As regards the second part of the study the attention was paid to systems in which the filler gathers inside either of the polymer phases. Nanoclays with different hydrophobicity were selected to evaluate their localizations and consequently their effect on the blend. According to the research findings, it was emerged that the refinement ability of the filler was slightly better in the case of bulk localization, but interfacial nanoplatelets were more effective in stabilizing co-continuous morphologies against phase coarsening in the melt state. Foreground arising from the work carried out, regarding the nanoparticle-induced morphological modifications in multiphase systems, preliminary analyses were exploited for assessing the effect of nanoparticle morphology on the beginning systems

Role of polymer network and gelation kinetics on the mechanical properties and adsorption capacity of chitosan hydrogels for dye removal

Chitosan (CS) hydrogels are receiving growing attention as adsorbents for water purification purposes. The conditions of preparation of this class of materials play a crucial in the determination of their performances; however, this aspect is often neglected in the literature. In this study, we deal with this issue, focusing on the structure-property relationships of CS hydrogels obtained by phase inversion method. We show that the concentration of the starting solution determines the density and strength of intermolecular interactions, and that the gelation kinetics dictates the hydrogel structure at the microscale. Consequently, even subtle changes in the preparation protocol can cause significant differences in the performances of CS hydrogels in terms of mechanical properties and dye adsorption capacity. The observed trends are often neither trivial nor monotonic. Nonetheless, we demonstrate that they can be interpreted looking at the CS network structure, which can be inferred by rheological measurements

Additive electrospraying for scaffold functionalization

In the last decade, micro- and nanostructured platforms with interesting features as bioactive carriers have been fabricated by the deposition of electrospun fibers exhibiting extended surface area and high molecular permeability associated with fully interconnected pore architecture, thus creating the opportunity to incorporate a wide range of actives/drugs for different use. In these systems, molecular release may occur via various molecular transport pathways, namely diffusion, desorption, and scaffold degradation, which may be tuned through a careful control of fiber morphology and composition. Recent studies have demonstrated that several shortcomings involve the possibility to incorporate bioactive species, not exposing molecules to fast and/or uncontrolled denaturation, thus preserving biochemical and biological fiber functionalities. In this context, additive electrospraying, namely the integration of electrosprayed nanoparticles into electrospun fiber network, is emerging as a really interesting route to control “separately” release and functional properties of the scaffolds in order to support cell activities by independent cues, during the tissue formation. Herein, we propose an overview of current progresses in the use of electrospraying and/or electrospinning for tissue engineering and molecular release. Our main objective is oriented to identify the most innovative integrated approaches recently optimized for scaffold functionalization to molecularly encode multicomponent platforms in order to obtain a spatial and time controlled release

Language Development in Preschool Duchenne Muscular Dystrophy Boys

Background: the present study aims to assess language in preschool-aged Duchenne muscular dystrophy (DMD) boys with normal cognitive quotients, and to establish whether language difficulties are related to attentional aspects or to the involvement of brain dystrophin isoforms. Methods: 20 children aged between 48 and 72 months were assessed with language and attention assessments for preschool children. Nine had a mutation upstream of exon 44, five between 44 and 51, four between 51 and 63, and two after exon 63. A control group comprising 20 age-matched boys with a speech language disorder and normal IQ were also used. Results: lexical and syntactic comprehension and denomination were normal in 90% of the boys with Duchenne, while the articulation and repetition of long words, and sentence repetition frequently showed abnormal results (80%). Abnormal results were also found in tests assessing selective and sustained auditory attention. Language difficulties were less frequent in patients with mutations not involving isoforms Dp140 and Dp71. The profile in Duchenne boys was different form the one observed in SLI with no cognitive impairment. Conclusion: The results of our observational cross-sectional study suggest that early language abilities are frequently abnormal in preschool Duchenne boys and should be assessed regardless of their global neurodevelopmental quotient

Chitosan Microgels and Nanoparticles via Electrofluidodynamic Techniques for Biomedical Applications

Electrofluidodynamics techniques (EFDTs) are emerging methodologies based on liquid atomization induced by electrical forces to obtain a fine suspension of particles from hundreds of micrometers down to nanometer size. As a function of the characteristic size, these particles are interesting for a wide variety of applications, due to the high scalability of chemical and physical properties in comparison to the bulk form. Here, we propose the optimization of EFDT techniques to design chitosan systems in the form of microgels or nanoparticles for several biomedical applications. Different microscopy techniques (Optical, SEM, TEM) have been used to investigate the morphology of chitosan systems at multiple size scale. The proposed study confirms the high versatility and feasibility of EFDTs for creating micro and nano-sized carriers for cells and drug species

Interfacial crowding of nanoplatelets in co-continuous polymer blends: Assembly, elasticity and structure of the interfacial nanoparticle network

The sequence of events which leads to the interfacial crowding of plate-like nanoparticles in co-continuous polymer blends is investigated through a combination of morphological and rheological analyses. Very low amounts (∼0.2 vol%) of organo-modified clay are sufficient to suppress phase coarsening in a co-continuous polystyrene/poly(methyl methacrylate) blend, while lower particle loading allows for a tuning of the characteristic size of the polymer phases at the μm-scale. In any case, an interfacial network of nanoparticles eventually forms, which is driven by the preferred polymer-polymer interface. The elastic features and stress-bearing ability of this peculiar nanoparticle assembly are studied in detail by means of a descriptive two-phase viscoelastic model, which allows isolation of the contribution of the filler network. The role of the co-continuous matrix in driving the space arrangement of the nanoparticles is emphasized by means of comparative analysis with systems based on the same polymers and nanoparticles, but in which the matrix is either a pure polymer or a blend with drop-in-matrix morphology. The relaxation dynamics of the interfacial network was found not to depend on the matrix microstructure, which instead substantially affects the assembly of the nanoplatelets. When the host medium is co-continuous, the particles align along the preferred polymer-polymer interface, percolating at a very low amount (∼0.17 vol%) and prevalently interacting edge-to-edge. The stress bearing ability of such a network is much higher than that in the case of matrix based on a homogeneous polymer or a drop-in-matrix blend, but its elasticity shows low sensitivity to the filler content

Degradation properties and metabolic activity of alginate and chitosan polyelectrolytes for drug delivery and tissue engineering applications

Polysaccharides are long monosaccharide units which are emerging as promising materials for tissue engineering and drug delivery applications due to their biocompatibility, mostly good availability and tailorable properties, by to the wide possibility to modify chemical composition, structure—i.e., linear chain or branching—and polymer source (animals, plants, microorganisms). For their peculiar behaviour as polyelectrolites, polysaccharides have been applied in various forms, such as injectable hydrogels or porous and fibrous scaffolds—alone or in combination with other natural or synthetic polymers—to design bioinspired platforms for the regeneration of different tissues (i.e., blood vessels, myocardium, heart valves, bone, articular and tracheal cartilage, intervertebral discs, menisci, skin, liver, skeletal muscle, neural tissue, urinary bladder) as well as for encapsulation and controlled delivery of drugs for pharmaceutical devices. In this paper, we focus on the pH sensitive response and degradation behaviour of negative (i.e., alginate) and positive (i.e., chitosan) charged polysaccharides in order to discuss the differences in terms of metabolic activity of polyelectrolytes with different ionic strength for their use in drug delivery and tissue engineering area

Chitosan-based hydrogel for dye removal from aqueous solutions: Optimization of the preparation procedure

The efficacy of chitosan-based hydrogels in the removal of dyes from aqueous solutions has been investigated as a function of different parameters. Hydrogels were obtained by gelation of chitosan with a non-toxic gelling agent based on an aqueous basic solution. The preparation procedure has been optimized in terms of chitosan concentration in the starting solution, gelling agent concentration and chitosan-to-gelling agent ratio. The goal is to properly select the material- and process-related parameters in order to optimize the performances of the chitosan-based dye adsorbent. First, the influence of such factors on the gelling process has been studied from a kinetic point of view. Then, the effects on the adsorption capacity and kinetics of the chitosan hydrogels obtained in different conditions have been investigated. A common food dye (Indigo Carmine) has been used for this purpose. Noticeably, although the disk-shaped hydrogels are in the bulk form, their adsorption capacity is comparable to that reported in the literature for films and beads. In addition, the bulk samples can be easily separated from the liquid phase after the adsorption process, which is highly attractive from a practical point of view. Compression tests reveal that the samples do not breakup even after relatively large compressive strains. The obtained results suggest that the fine tuning of the process parameters allows the production of mechanical resistant and highly adsorbing chitosan-based hydrogels

Morphology stabilization of co-continuous polymer blends through clay nanoparticles

The influence of plate-like nanoparticles on the morphology evolution of co-continuous polymer blends during quiescent annealing is investigated thorugh viscoelastic analysis. Contextually, the effect of the molten polymer phases on the assembly dynamics and ultimate structure of the filler is also studied. A model co-continuous blend of polystyrene and poly(methyl methacrylate) (45/55 wt/wt) has been selected, and different amount of clay nanoparticles preferentially adsorbing at the polymer-polymer interface are added to this system. The filler inhibits the typical phase coarsening of the co-continuous morphology during thermal treatments even at extremely low filler volume fractions (Φ=0.4 vol.%). In addition, the time evolution of the rheological response of the filled blends resembles that of homopolymer-based nanocomposites, suggesting that the fluid phases do not appreciably alter the nanoparticle dynamics. Exploiting a simple two-phase model, the main elastic features of the filler network that builds up at sufficiently high Φ were found to prescind from the multiphasic nature of the matrix. Nonetheless, the presence of a co-continuous polymer microstructure prevented the elastic and structural features of the network to be discerned through the use of fractal models

Mono- and Bi-Phasic Cellulose Acetate Micro-Vectors for Anti-Inflammatory Drug Delivery

In recent years, different processing technologies have been engineered to fabricate capsules or particles with peculiar properties (e.g., swelling, pH-sensitive response) at the micro and sub-micrometric size scale, to be used as carriers for controlled drug and molecular release. Herein, the development of cellulose acetate (CA) micro-carriers with mono- (MC) or bi-phasic (BC) composition is proposed, fabricated via electrohydrodynamic atomization (EHDA)—an electro-dropping technology able to micro-size polymer solution by the application of high voltage electrostatic forces. Image analysis allows identification of the process parameters to optimize morphology, in terms of size distribution and shape. Meanwhile, an accurate rheological study has enabled investigating the interface between CA solutions with different viscosities to optimize BC systems. Release tests have confirmed that BC carriers can retain the drug more efficiently in acidic conditions, also providing a more gradual and sustained release until six days, with respect to MC carriers. Hence, all these results have proven that biphasic architecture significantly improves the capability of CA microcarriers to release ketoprofen lysinate, thus suggesting a new route to design core/shell systems for the retarded oral administration of anti-inflammatory drugs