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Dragan E.S.,Petru Poni Institute of Macromolecular Chemistry
Chemical Engineering Journal | Year: 2014

Interpenetrating polymer networks (IPN) hydrogels have gained great attention in the last decades, mainly due to their biomedical applications. This review aims to give an overview of the recent design concepts of IPN hydrogels and their applications in controlled drug delivery, and separation processes. In the first part, the main strategies for the synthesis of semi-IPN and full-IPN hydrogels, their relevant properties, and biomedical applications are presented based on the nature of the networks, the main categories selected being: IPN hydrogels based on polysaccharides (chitosan, alginate, starch, and other polysaccharides), protein based IPN hydrogels, and IPN hydrogels based only on synthetic polymers. The influence of the second network on the stimuli responsiveness of the "smart" IPN hydrogels is discussed based on the most recent publications in the field. In the second part, an overview of the most specific applications of IPN hydrogels in separation processes is critically presented. Factors which control the separations of dyes and heavy metal ions by semi-IPN and full-IPN as novel sorbents are discussed based on the recently published articles and own results. A special concern is given to the macroporous IPN composite cryogels, which are very attractive materials for separation processes being endowed also with a high reusability. © 2014 Elsevier B.V.

Oprea S.,Petru Poni Institute of Macromolecular Chemistry
JAOCS, Journal of the American Oil Chemists' Society | Year: 2010

Castor oil-polyurethane elastomers were prepared by reacting poly (1,4-butane diol) (Terathane 1400) with aliphatic 1,6-hexamethylene diisocyanate. The pre- polymers were chain-extended with bifunctional precursor chains and/or with castor oil as a trifunctional crosslinker at stoichiometric ratios. These resulted in a series of cross-linked polyurethane elastomers with different structures of the hard segment. The properties of the material were measured by differential scanning calorimetry, thermo- gravimetric analysis, atomic force microscopy, as well as tensile properties measurements. The effect of stoichiom- etric balance (i.e., OH/NCO molar ratio) on the final properties was evaluated. The formation of hydrogen bonds was observed by Fourier transform infrared.spectroscopy The measured properties were found to be strongly influenced by the molar ratio of chain extenders to the diiso-cyanate component. The glass transition temperatures (Tg) for the polyurethanes with OHpolyol/NCO/OHchain extender having molar ratios of 1: 2: 1 and 1: 4: 3 were found to be -70 and -57 °C, respectively. The polyurethanes networks with a OH/NCO molar ratio of 1: 2: 1 had excellent mechanical properties, indicating that this is the optimum ratio to be used in castor oil polyurethane elastomer formulations. The objective of this work was to study the effect of the castor oil crosslinker on the morphology of the resulting crosslinked polyurethanes and to correlate the morphology with the properties of these bio-based crosslinked polyurethanes. © 2009 AOCS.

Manea A.,Petru Poni Institute of Macromolecular Chemistry
Frontiers in bioscience (Scholar edition) | Year: 2012

Oxidative stress is a major contributor to the etiology of all severe vascular pathologies, such as atherosclerosis. NADPH oxidases (Nox) are a class of multicomponent enzymes whose unique function is the generation of reactive oxygen species (ROS) in the vascular cells and in circulating immune cells interacting with blood vessels. Physiological production of Nox-derived ROS contributes to the maintenance of vascular homeostasis. In pathological states, hyperactivity of Nox induces oxidative stress. Nox-derived ROS interact and stimulate other enzymatic sources of oxygen/nitrogen reactive intermediates, and amplify the initial response to insults. In atherosclerosis, Nox-induced lipid peroxidation is highly deleterious and expands the free radical reactions initially produced by activated Nox. Therefore, understanding the molecular mechanisms of Nox regulation, vascular and subcellular compartmentalization of ROS production and its subsequent biological significance, may lead to a focused and effective anti-oxidative stress therapy. We present here, recent advances in Nox regulation in the vasculature and discuss novel potential intrinsic feedback mechanisms and current and pharmacological perspectives to target Nox, which may have an impact in vascular health and disease.

Roman G.,Petru Poni Institute of Macromolecular Chemistry
European Journal of Medicinal Chemistry | Year: 2014

The biological activity of Mannich bases, a structurally heterogeneous class of chemical compounds that are generated from various substrates through the introduction of an aminomethyl function by means of the Mannich reaction, is surveyed, with emphasis on the relationship between structure and biological activity. The review covers extensively the literature reports that have disclosed Mannich bases as anticancer and cytotoxic agents, or compounds with potential antibacterial and antifungal activity in the last decade. The most relevant studies on the activity of Mannich bases as antimycobacterial agents, antimalarials, or antiviral candidates have been included as well. The review contains also a thorough coverage of anticonvulsant, anti-inflammatory, analgesic and antioxidant activities of Mannich bases. In addition, several minor biological activities of Mannich bases, such as their ability to regulate blood pressure or inhibit platelet aggregation, their antiparasitic and anti-ulcer effects, as well as their use as agents for the treatment of mental disorders have been presented. The review gives in the end a brief overview of the potential of Mannich bases as inhibitors of various enzymes or ligands for several receptors. © 2014 Elsevier Masson SAS.

Ghimici L.,Petru Poni Institute of Macromolecular Chemistry | Nichifor M.,Petru Poni Institute of Macromolecular Chemistry
Bioresource Technology | Year: 2010

Flocculation properties of a series of cationic polysaccharides, with N-alkyl-N,N-dimethyl-N-(2-hydroxypropyl)ammonium chloride pendent groups attached to a dextran backbone, were evaluated in clay dispersions with respect to length of the alkyl substituent, molar mass, the charge density, and polycation dose. According to turbidimetric results, the alkyl chain length greatly influenced the optimum polymer dose as well as the width of the flocculation window since both increased from an ethyl to a butyl group and decreased for when octyl or dodecyl group was present. The residual turbidity values also varied with the charge density but no dramatic effect was observed with the molar masses investigated. These findings together with the negative value of the zeta potential at the optimum polymer dose and floc size measurements, point to contributions from both patch and bridging mechanisms for the flocculation process. © 2010 Elsevier Ltd.

Oprea S.,Petru Poni Institute of Macromolecular Chemistry
Composites Part B: Engineering | Year: 2013

Films from multi-crosslinked polyurethane with different contents of guar gum (1-10 wt%) were prepared through a solution-casting method, followed by a thermal treatment or natural light exposure crosslinking procedure. Acrylic terminated prepolymers were prepared by capping the NCO groups of polyurethane prepolymers with pentaerythritol triacrylate. The effect of the guar gum content on the miscibility, morphology and physical properties of the blend films was investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, surface properties and tensile tests. The results reveal that small guar gum content is well embedded in the crosslinked polyurethane network and forms films with good mechanical properties, thermal behavior and hydrophilic properties. These results prove guar gum to be eco-friendly filler for multi-crosslinked polyurethane network. In the case of polyether urethanes, incorporating up to 3 wt% guar gum leads to a slight enhancement of the elongation at break, while for polyester urethanes incorporation up to 3 wt% guar gum slight increases stress at break values. Incorporating guar gum into the polyurethane networks leads to an increase in the hydrophilic nature of the polymer blends and improved surface structure. The properties of guar gum - which can be abundantly found in nature - make it desirable for polymer blends for biomedical applications. © 2012 Published by Elsevier Ltd.

Oprea S.,Petru Poni Institute of Macromolecular Chemistry
Journal of Materials Science | Year: 2011

Polyurethane (PU) elastomers were elaborated from polyethylene glycol of high molecular weight (MW = 4,000), 1,6-hexamethylene diisocyanate and polyethylene glycol (PEG1500) (MW = 1,500) as a long linear chain extender and/or castor oil as a cross-linker and were obtained in the form of transparent films. These poly(ether urethanes) elastomers are obtained by replacing the short-chain diol monomers with high molecular weight polyethylene glycols (PEG1500). High molecular weight polyethylene glycol (MW = 4,000 and 1,500, respectively) have greater chain length thus producing networks with lower cross-linking densities and higher average molecular weight between two consecutive cross-links. The PU properties were investigated using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, mechanical analysis and thermogravimetry. The results showed that the prepared polyurethanes (PUs) had very good tensile properties. The stress-strain data show that the PU elastomers obtained using a 60/40% OHPEG1500/OH castor oil ratio have the best mechanical properties. The thermal degradation of the castor oil cross-linked PU elastomers starts at 280-300 °C, compared to the thermal degradation of linear PUs which begins at 220 °C. During storage at 25 °C, the morphology and mechanical properties of the elastomer films have been observed to change in time. © 2010 Springer Science+Business Media, LLC.

Dragan E.S.,Petru Poni Institute of Macromolecular Chemistry | Apopei D.F.,Petru Poni Institute of Macromolecular Chemistry
Carbohydrate Polymers | Year: 2013

Macroporous semi-interpenetrating polymer networks (semi-IPN) composite hydrogels were synthesized by cross-linking polymerization of acrylamide (AAm) with N,N'-methylenebisacrylamide (BAAm) in the presence of potato starch (PS) or an anionic polyelectrolyte derived from PS (PA), below the freezing point of the reaction solution (-18 °C). The composite cryogels have been further modified by the partial hydrolysis of the amide groups in poly(acrylamide) (PAAm) matrix, under alkaline conditions. The influence of the entrapped polymer on the properties of the composite gels, both before and after the hydrolysis, has been evaluated by the swelling kinetics, FT-IR spectroscopy, scanning electron microscopy, and external stimuli responsiveness. The potential of the anionic composite cryogels as intelligent hydrogels has been evaluated by the investigation of the deswelling/reswelling kinetics as a function of solvent nature, ionic strength, and environment pH. Cryogels with fast responsivity at variation of the external stimuli, which withstood repeated deswelling/ reswelling cycles, have been obtained at a low cross-linker ratio (one mole BAAm for 80 moles of AAm) and a monomer concentration around 3 wt%. © 2012 Elsevier Ltd. All rights reserved.

Oprea S.,Petru Poni Institute of Macromolecular Chemistry
Polymer Degradation and Stability | Year: 2010

In the context of protecting of the environment, this work studies the biodegradation of PEG-based polyurethane elastomer films in the presence of the soft rot fungus Chaetomium globosum, determined via the Petri-dish test. Using PEG with high-molecular weight (MW = 1500) as a chain extender led to polyurethane elastomers with lower physical crosslink density and higher swelling rates. The structural modifications in the hard-segment area (CO and N-H peaks) are considerable and were analyzed by FTIR spectroscopy. Biodegradation lowers the final mechanical properties, but increases yield points, especially in the case of polyurethane elastomers crosslinked with castor oil. Polyurethane elastomer samples showed visible degradation proved by the mechanical weakening of the films. Thus, breaking strains decrease from 670-1180% to 500-680% and tensile strengths decreased from 11.5-27.5 MPa to 4-11.5 MPa after 130 days of fungal biodegradation. The changes in the morphology of the polyurethane films surface were analyzed by SEM and have been found to exhibit increasing porous structure and fungal hyphae. The effects of the hard-segment composition of the polyurethane elastomers on the fungal biodegradation behaviour were investigated.© 2010 Elsevier Ltd. All rights reserved.

Oprea S.,Petru Poni Institute of Macromolecular Chemistry
Journal of Polymer Research | Year: 2012

Polyurethane elastomers incorporating a quinoline moiety along their polymeric backbones and aliphatic, aromatic or heterocyclic crosslinkers have been synthesized and characterized. For this, NCO-terminated urethane oligomers were prepared from poly(butylenes adipate) diol and methylene diphenyl diisocyanate and were subsequently chain extended with 2,4-quinolinediol and different crosslinkers. This study reports the influence of the different crosslinker chemical structures and the hard segment molar ratio on the thermal and dynamic mechanical thermal properties, as well as on the mechanical properties of these elastomers. The fluorescence spectra of polyurethane elastomers were determined at an excitation wavelength of 290 nm. The different chemical structures of the crosslinkers determine the hard segment cohesion and reduce the mobility of the soft phase, having an important effect on thermal stability and on the mechanical properties of the polyurethane films. Thus the incorporation of aromatic crosslinkers results in polyurethanes with lower elongation and stress at break. The highest mechanical properties were obtained for polyurethanes crosslinked with aliphatic crosslinkers. © 2011 Springer Science+Business Media B.V.

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