Miriam C. Strumia

Functional dendritic polymer architectures as stimuli-responsive nanocarriers

Stimuli-responsive polymer architectures are molecular systems which evolve with an external signal. The observed changes are mainly decomposition, isomerization, polymerization, activation, supramolecular aggregation, and structural modifications of these molecules. The external stimuli, which can be combined in order to provoke these molecular changes, are numerous. In this review, we have chosen to present an overview on different mechanisms to impart responsiveness to dendritic polymers, with the particular aim of delivery and release of bioactive molecules.

Thermosensitive nanogels based on dendritic polyglycerol and N-isopropylacrylamide for biomedical applications

In this paper we describe a methodology for the synthesis of thermoresponsive polyglycerol-based nanogels through precipitation polymerization. A systematic analysis of the preparative conditions and composition regarding the nanogel size is presented. The thermoresponsive properties of the synthesized nanogels, as well as the cytotoxicity and uptake in three different cell lines were investigated. The thermoresponsive behavior, the enhanced biocompatible profile, and the cell penetrating properties of the nanogels highlight the potential of such constructs for application as smart, environmentally-responsive materials.

pH-induced changes in the fabrication of multilayers of poly(acrylic acid) and chitosan: fabrication, properties, and tests as a drug storage and delivery system.

Multilayers of poly(acrylic acid), PAA, and chitosan, CHI, have been built by the layer-by-layer (LbL) method from aqueous solutions at different pH values and analyzed by the dissipative quartz crystal microbalance (D-QCM) and ellipsometry. The results showed that under all of the assembly conditions considered the growth of the films is nonlinear. The thickness of the PAA layers increases as the pH of the assembling solutions decreases, whereas the adsorption of CHI is almost unaffected by the pH conditions. The comparison of the thickness obtained by D-QCM and by ellipsometry has allowed us to calculate the water content of the films, showing that the multilayers are highly hydrated, with an average water content higher than 20%. The analysis of D-QCM data has provided high-frequency values of the complex shear modulus that are in the megapascal range and shows a transition from mainly viscous to mainly elastic behavior for the added PAA layers, depending on the pH. The monomer surface density in each layer (obtained from the combination of ellipsometry and differential refractive index measurements) indicated that the monomer density depends on the assembly conditions. It was found that the adsorption kinetics is a bimodal process, with characteristic times that depend on the number and nature of the layers. Finally, the possibility of using of these multilayers as a drug storage and delivery system has been evaluated.

Immobilization of Caffeic Acid on a Polypropylene Film: Synthesis and Antioxidant Properties

The immobilization of caffeic acid (CA) on a polypropylene (PP) film was successfully performed through the covalent binding of the caffeoyl chloride on a modified polymeric surface of PP films grafted with hydroxyethyl methacrylate as monomer (PP-g-HEMA). The different reaction steps were monitored by FT-IR spectroscopy. The synthesized films were characterized by Folin-Ciocalteu method by measuring the available phenolic groups as caffeic acid equivalents linked to the surface. The antioxidant efficiency of the modified polymers was evaluated by typical spectrophometric methods, such as the bleaching of radicals DPPH(•) and ABTS(•+), and the inhibition of the enzymatically induced coupled oxidation of linoleic acid and betacarotene. The available phenolic groups on the modified film presented a good correlation with the antiradical activity toward DPPH(•). Moreover, the polymer synthesized in this work showed a good protective activity against ascorbic acid oxidation in real samples of orange juice.

Macroporous Monolithic Polymers: Preparation and Applications

In the last years, macroporous monolithic materials have been introduced as a new and useful generation of polymers used in different fields. These polymers may be prepared in a simple way from a homogenous mixture into a mold and contain large interconnected pores or channels allowing for high flow rates at moderate pressures. Due to their porous characteristics, they could be used in different processes, such as stationary phases for different types of chromatography, high-throughput bioreactors and in microfluidic chip applications. This review reports the contributions of several groups working in the preparation of different macroporous monoliths and their modification by immobilization of specific ligands on the products for specific purposes.

Electrochemical Study of a Dendritic Family at the Water/ 1,2-Dichloroethane Interface

The transfer of six dendritric molecules, DMs, across the water/1,2-dichloroethane interface was investigated using cyclic voltammetry. From the variation of peak potential with pH, two different mechanisms of transfer were postulated depending on the nature of the molecules. Voltammetric parameters were employed to evaluate the hydrophilic/hydrophobic character and calculate the acid dissociation constant of these molecules. The results were explained taking into account the nature and multiplicity of functional surface groups.

Preparation of adsorbents applicable to pseudobiospecific ligand affinity chromatography using different spacers and ligands

Abstract In this paper, a series of different adsorbents for pseudobiospecific ligand affinity chromatography is presented. They were obtained using ligands as histidine, Cu 2+ - or Zn 2+4 -chelating iminodiacetic acid and Cibacron Bhue F3GA dye, attached to poly(butadiene-hydroxyethylmethacrylate) (PB-HEMA) matrix. The histidine and metal-iota-chelating iminodiacetic acid were attached on matrix through epichlorohydrin (ECH) or 1,4-butanediol diglycidyl ether (BDGE) as spacers and activators, while dye was directly bound onto the matrix.

Chitosan films modified selectively on one side with dendritic molecules

Novel chitosan films dendronized on one side were prepared by reaction between a cross-linked biopolymer and weisocyanate dendron. According to ATR-FTIR analysis, it can be concluded that the dendronization took place on only one of the faces of the films. The highlight of this work is that the modification grants different hydrophilic and hydrophobic properties on both sides of the system. Interactions between the dendron-polymer network and the hydrophobic characteristics of the dendron modify the physical properties of the films. As the thermal stability of the films increases, the degree of swelling and WVP values decrease, and the elastic modulus increases, turning the network more rigid. The dendronized films were swollen at pH 3.4 and 6.8 which are the pHs of the different wound healing stages. The films remained stable for an extended period. The films obtained can be potentially applied as wound dressings able to maintain a moist environment at the wound interface and act as a barrier to microorganisms, removing excess exudates. The product is made from a readily available biomaterial that requires minimal processing, possesses antimicrobial properties and could promote wound healing.

Effects of experimental variables on the synthesis of porous matrices

Macroporous beads, poly(ethylene glycol dimethacrylate-co-acrylic acid) [poly(EGDMA-co-AAc)], and poly(ethylene glycol dimethacrylate-co-hydroxyethyl methacrylate) [poly(EGDMA-co-HEMA)] were prepared by the suspension polymerization technique in the presence of a porogen agent. Different experimental conditions such as amount of initiator, porogen type, and temperature were studied to optimize the polymerization systems. These hydrophilic copolymers were characterized by IR spectroscopy, scanning electron microscopy, specific surface area, and swelling in water. A new parameter, H, defined as the ratio between the equilibrium weight swelling ratio (q w ) and equilibrium volume swelling ratio (q v ), allowed to select the reaction conditions from which matrices with high capacity of water sorption and low stretching degree were reached.

New dendronized polymers from acrylate Behera amine and their ability to produce visco-elastic structured fluids when mixed with CTAT worm-like micelles.

Two new water soluble dendronized polymers (PLn) from acrylate Behera amine monomer of different molecular weights were successfully synthesized. The polymers were characterized by FTIR, NMR, GPC and DLS. Both GPC and DLS results indicated that these PLn have a remarkable tendency to form aggregates in solution that lead to apparent molecular weights that are much higher than their theoretical values, as well as large diameters in solution. However, the addition of any PLn to water did not cause any increase in viscosity up to concentrations of 1000 ppm. The possible interactions of PLn with the cationic surfactant CTAT were explored by solution rheometry. A synergistic viscosity enhancement was found by adding small amounts of dendronized PLn polymers to a CTAT solution composed of entangled worm-like micelles. The highest association tendency with CTAT was found for PL1 at the maximum polymer concentration before phase separation (i.e., 100 ppm). The solution viscosity at low-shear rates could be increased by an order of magnitude upon addition of 100 ppm of PL1 to a 20mM CTAT solution. For this mixture, the fluid obtained was highly structured and exhibited only shear thinning behavior from the smallest shear rates employed. These PL1/CTAT mixtures exhibited an improved elastic character (as determined by dynamic rheometry) that translated in a much longer value of the cross-over relaxation time and a pronounced thixotropic behavior which are indicative of a strong intermolecular interaction. In the case of the polymer with a higher theoretical molecular weight, PL2, its association with CTAT leads to an extraordinary doubling of solution viscosity with just 0.25 ppm polymer addition to a 20mM CTAT solution. However, such synergistic viscosity enhancement saturated at rather low concentrations (25 ppm) indicating an apparent lower solubility as compared to PL1, a fact that may be related to its higher molecular weight.