Mircea Teodorescu

Biocompatible polyhydroxyalkanoates/bacterial cellulose composites: Preparation, characterization, and in vitro evaluation

Biocompatible composites play a critical role as scaffolds in tissue engineering. Novel biocomposites made from poly(3-hydroxybutyrate) (PHB), polyhydroxyalkanoate (PHA) and bacterial cellulose (BC) in different concentrations were prepared by solution casting and their thermal and mechanical behavior as well as biocompatibility was characterized. BC addition increased the thermal stability of the polymer matrix as evidenced by thermogravimetric analysis. The crystallinity of PHB and the crystallization temperature decreased with the addition of BC and PHA, thus increasing the processing window. BC in small concentration determined an increase in the mechanical properties due to a concerted action of PHA and filler. Good cells attachment and proliferation were observed for all the biocomposites. By the addition of PHA (more hydrophobic than the matrix) and various amounts of BC (highly hydrophilic), surface properties and cell attachment can be controlled. Cytocompatibility studies using L929 cell line revealed that this material is suitable for biomedical applications.

Thermosensitive injectable hydrogels from poly(N-isopropylacrylamide)–dextran aqueous solutions: Thermogelation and drug release properties

ABSTRACT Novel injectable thermosensitive hydrogel formulations with improved both water retention (WR) and drug release profile were prepared by adding dextran (DXT) to poly(N-isopropylacrylamide) (PNIPAM) aqueous solutions as a remedy against the demixing/syneresis phenomenon. The addition of the hydrophilic polysaccharide improved the WR of the hydrogel at 37°C from about 12% in the absence of DXT to about 40–55% out of the initial amount introduced, depending on both PNIPAM and DXT concentrations. Also, the 5-fluorouracil release experiments showed an appreciably reduced “burst effect” for the DXT-containing hydrogels. The shape of the release profiles revealed the presence of two stages, differing each other from the point of view of the drug release rate.

Cellulose-Based Composites for Membranes by “In Situ” Radical Polymerization

Cellulose-containing composites based on copolymers of acrylic acid with styrene, 4-chloro-methyl-styrene and maleic anhydride were prepared for proton conducting membranes. The influence of the substrate on the copolymer composition as well as the copolymer/cellulose ratio on the basic properties of composite materials is discussed using the FT-IR, optical microscopy, SEM, TGA-DSC and conductivity measurements. Moderate water swelling (2–10%) of the synthesized membranes provided volume resistivities down to 1 × 105 Ω · cm, adequate for further processing as proton exchange membrane.

New aspects regarding the synthesis of polyvinyl alcohol

Abstract Quantitative investigations on the evolution of the base-catalyzed alcoholysis of polyvinyl acetate have been carried out by performing the reaction in the mixing chamber of a Brabender-type micromixer or in an all-in-glass reactor fitted with a mechanical stirrer having arms from the bottom to the top of the reactor. The recorded Brabender diagrams displayed two peaks. The first one was ascribed to the gel phase while the second one was ascribed to the aggregation of polyvinyl alcohol particles. The increase of the hydrophobic character of the reaction medium by the addition of an alcohol with a longer hydrocarbon moiety (n-butanol) or of an aromatic hydrocarbon (benzene, toluene, o-xylene) determined the disappearance of the effect of agglomeration of the PVA particles.

Bacterial cellulose-poly(acrylic acid-co-N,N′-methylene-bis-acrylamide) interpenetrated networks for the controlled release of fertilizers

In this study, composite hydrogels with interpenetrated polymer networks (IPNs), based on bacterial cellulose (BC) and poly(acrylic acid-co-N,N′-methylene-bis-acrylamide) (PAA), were synthesized by radical polymerization and characterized herein for the first time. Liquid fertilizer (LF) formulations, containing potassium, phosphorus, ammonium oxides and micronutrients, were encapsulated directly into the IPNs of the composite hydrogels during synthesis. Thermal analyses and scanning electron microscopy of control and composite xerogels highlighted the formation of IPNs between BC and PAA. Swelling determinations confirmed the influence of the crosslinker and of the liquid fertilizer concentration upon the density of the IPNs. Further rheology studies and release profiles indicated how the presence of BC and the increase of the crosslinking density of IPNs improved the mechanical strength and the release profile of LF for the innovative composite BC-PAA hydrogels. Results regarding the fertilizer release indicated that the presence of the BC led to a more controlled liberation of the fertilizer proving that this new formulation is potentially viable for application in agricultural practices.

Synthesis and Characterization of Composites from Layered Silicates and Homo- and Copolymers of 2-Hydroxyethyl Methacrylate and P-Chloromethyl Styrene Obtained by In Situ Radical (Co)polymerization

The hybrids 2-hydroxyethyl methacrylate – chlorometylstyrene – modified montmorillonite were synthesized by means of “in-situ” radical (co)polymerization. The composites were analysed by thermal analysis (DSC-TGA-MS), Fourier-Transform Infrared Spectroscopy (FT-IR), nuclear magnetic resonance (1H-NMR), X-ray diffraction, and scanning electron microscopy (SEM). The influence of the polymerization conditions and compositions on the thermal stability and morphology of the obtained composites is discussed.