Papers by Author: Cornelia Vasile

Abstract: Different types of stimuli responsive polymers that respond with a property change to a variation in the environmental conditions are an attractive class of materials for advanced applications in biomedical or pharmaceutical fields. Three types of responsive biocompatible and biodegradable polymer matrices are presented as potential biomaterials for medical application as carriers for various drugs and tissue engineering substitutes. Hybrid hydrogels based on collagen/ N-isopropyl acrylamide containing montmorillonite nanoparticles are promising materials for tissue engineering and also as carriers for norfloxacin, a chemotherapeutic antibacterial agent. Semi-interpenetrated hydrogels based either on substituted anhydride modified collagen and 2-hydroxyethyl methacrylate or on alginate and poly (N-isopropylacrylamide) were tested as matrices for the controlled delivery of bisoprolol fumarate, an antihypertensive drug and respectively of ketoprofen, a non-steroidal anti-inflammatory drug.

Abstract: The article emphasizes the improvement of compatibility in a polymer blend composed of two normally incompatible constituents as LDPE and PA6. The effect of amount and type of compatibilizing agents is evaluated using electronic microscopy and dielectric spectroscopy, to obtain the optimum materials structure.

Abstract: Stimuli responsive hydrogels are very attractive for applications in sustained and/or targeted drug delivery systems. As the release of drugs is related to the swelling behavior of hydrogels, the swelling kinetic studies become of great importance to appreciate the release kinetics from hydrogel matrices. Hydrogels with high performance properties have been prepared from N-isopropylacryl amide (NIPAAm) and sodium alginate, crosslinked with N,N`-methylene-bis-(acrylamide) (MBAAm). This study is focused on the investigation of swelling and drug release kinetics, coupled by morphological studies. The kinetic parameters of the swelling at different temperatures for hydrogels samples have been evaluated and confirmed their temperature-responsive behavior. The swelling rate constant (ksw) decreases of with increasing temperature and slight increases with the alginate content in the samples. The drug release kinetic study from the prepared hydrogel matrices was performed in twice-distilled water and ethanol for bioactive agents as vanillin and ketoprofen, respectively. An increase of alginate content results in a slower rate and smaller percentage of vanillin and ketoprofen released. It has been established that the ketoprofen occurs according with case II of transport and vanillin release behavior occurs by an anomalous transport mechanism. The values of the release rate constant (kr) decreased by increasing swelling degree in case of 75/25 NIPAAm/alginate hydrogels and decreased also by increasing content of alginate in hydrogels with various compositions. Morphological studies performed by environmental scanning electron microscopy (ESEM) evidenced a relaxed network at high relative humidity, which explain both swelling and release profiles.

Abstract: Nanocomposites based on layered silicate organically modified montmorillonite (Cloisite 20A) and acrylic comonomers (butyl acrylate and methyl methacrylate) were prepared by simple “in situ” batch emulsion polymerization method. The particle size and zeta potential of the emulsions were analyzed. The structural characterizations of the nanocomposites were performed by FTIR, thermal behaviors of the films were investigated by DSC, mechanical properties of the films were tested by DMA and intercalation success was viewed by XRD. The mechanical properties of the nanocomposites were improved significantly especially at the temperatures above Tg. The ultrasonication process was found to be useful for increasing the homogeneity of the emulsions and intercalation success. The obtained nanocomposite emulsions were applied on garment leathers in a finishing formulation as aqueous binders sharing good film forming ability and elasticity.

Abstract: Characterization of chitosan / layered silicate nanocomposites obtained by solution-mixing technique, having different compositions including treated and untreated montmorilonite (MMT) has been performed. The optimum amount of MMT and also the effect of nanoparticles type on nanocomposite properties by DSC, X-ray diffraction and TG measurements have been established. The chitosan chains were inserted into silicate layers to form the intercalated nanocomposites. The interlayer distance of the silicates in the nanocomposites enlarged as their amount increased. The stiffness and thermal stability enhanced.