D. Le Cerf

Residual solvent effect on the permeation properties of fluorinated polyimide films

The main aim of this study was to determine how the residual solvent remaining after fabrication affected the gas permeation properties of 6FDA–mPDA polyimide films. For this purpose, films were made by spreading solutions of polyimide from different solvents on glass plates, then treated at 200°C for different periods of time. The films obtained were characterized by differential scanning calorimetry, thermogravimetry and permeametry. Permeation parameters (D, P, S) of the films towards N2 and CO2 were determined at 35°C. They were found to be dependent on the residual solvent in the films. Whatever the solvent, the difference in behaviour was found to decrease as the amount of solvent became smaller and to increase with the molar volume of the solvent. Solvents with high molar volumes left an imprint in the material during thermal treatment.

Solution properties of gum exudates from Sterculia urens (Karaya gum)

Abstract Dilute solution properties of Karaya gum from Sterculia urens were studied using size-exclusion chromatography, static and dynamic light scattering and viscosity experiments in 0·1 m aq. NaCl. Solubility in water was found to be strongly dependent on the degree of acetylation. The native acetylated Karaya gum assumes a rather compact and branched conformation in aqueous solution, as evidenced by the low values of power-law exponents. In contrast, the fully deacetylated Karaya gum assumes a more expanded conformation and behaves as a random coil.

New amphiphilic and pH-sensitive hydrogel for controlled release of a model poorly water-soluble drug.

This paper presents the development of new pH-sensitive, amphiphilic and biocompatible hydrogels based on alginate-g-PCL, cross-linked with calcium ions to form beads, prepared for controlled delivery of poorly water-soluble drug. We have focused our study on the effect of the length of PCL chains (530 and 1250 g mol(-1)). Swelling profiles obtained clearly indicated that these hydrogels swell slightly (10-14%) in a simulated gastric fluid (pH 1.2), and strongly (700-1300% before disintegration) in a simulated intestinal fluid (pH 6.8). In both media, rates of swelling were lower for beads based on amphiphilic derivatives than for alginate/Ca2+ ones due to the hydrophobic PCL grafts, and decreased when hydrophobic character increased. A model drug, theophylline, was entrapped into these hydrogels and release studies were carried out. The drug was protected in acidic fluid (only 14-20% of release for alginate-g-PCL hydrogel against 35% of release for alginate hydrogel during 350 min). The drug is released completely in neutral fluid due to ion exchanges and disintegration of the hydrogel. PCL leads to decrease in the release kinetics in SIF (2h for alginate-g-PCL/Ca2+ beads against 1h for alginate/Ca2+ beads). It was demonstrated that the establishment of clusters inside beads by intramolecular interactions between PCL grafts of 530 g mol(-1) in salt media allowed to retain the drug and to slow down its release considerably.

Aggregation of amphiphilic pullulan derivatives evidenced by on-line flow field flow fractionation/multi-angle laser light scattering.

Size-exclusion chromatography (SEC) is a useful steric separation technique for the analysis of water-soluble polysaccharides in aqueous solution. However, in the case of amphiphilic derivatives, the usefulness is limited because of interactions between hydrophobic segments and the stationary phase. Alkyl-bearing pullulans differing from the extent and the length of alkyl groups were characterized using flow-field flow fractionation with on-line coupling multi-angle laser light scattering (F4/MALLS). Comparison of SEC and F4 is presented and the interest of F4 in the field of amphiphilic derivatives is demonstrated.

Effect of chitosan coating on the swelling and controlled release of a poorly water-soluble drug from an amphiphilic and pH-sensitive hydrogel.

In the present work, a new particulate controlled release system was prepared, by coating alginate-g-PCL/Ca(2+) beads with chitosan. The swelling behaviour and controlled release of a poorly water-soluble drug (theophylline) model were studied in media of varying pH, by simulating human fluids at 37 degrees C. In a simulated gastric fluid (SGF, pH 1.2), coated beads presented weak swelling (8-22%) and weak release rates (24-32% within 120min), and were able to protect the drug from this harsh environment. In a simulated intestinal fluid (SIF, pH 6.8), the swelling rates of amphiphilic beads (before disintegration) were strongly reduced (300-1100%) comparatively with those of uncoated beads (700-1700%). This can be explained by the strong electrostatic interactions between the amino groups of chitosan and the carboxylate groups of alginate-g-PCL, leading to the formation of a protective membrane of strong polyelectrolyte complex around the beads. This outermost layer effectively promoted the stability of beads under gastro-intestinal tract conditions, while the hydrophobic interactions between theophylline and PCL grafts allowed a considerable slowing down of the drug release. It was found out that combination of the protective effect of the polyelectrolyte membrane in SIF associated with the hydrophobicity of PCL grafts allowed to release a poorly water-soluble drug, in a controlled manner, for 7h, along a simulated gastro-intestinal tract.

Influence of solvent and non-solvent on polyimide asymmetric membranes formation in relation to gas permeation

Abstract Asymmetric 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA)-2-methyl-1, 3-phenylenediamine (mPDA) polyimide membranes were prepared by phase inversion process. Using different non-solvents and solvents, the correlation between membrane elaboration conditions and final morphology and properties has been investigated. Equilibrium thermodynamics and diffusion coefficients data were determined as a preliminary analysis in order to underline competitivity between thermodynamic and kinetic parameters. Scanning electron microscopy and gas permeation experiments (CO 2 , N 2 ) were used for the determination of structure-permeability relationships. Sponge-like structure membranes and highest selectivity were obtained when using non-solvent/solvent/6FDA-mPDA systems having important coagulation time.

Solvent effect on the conformation in solution of two polyimides

The dilute solution properties of two polyimides have been studied using size exclusion chromatography, light scattering and viscometry in various solvents. Molecular parameters (conformation and aggregation) are found to be solvent dependent. Addition of a non-solvent (H2O) to 6FDA-mPDA, a fluorine-containing polyimide, or Ultem a polyetherimide, in the good solvent N-methyl-2-pyrrolidone is responsible for an increase in molecular weight. This is attributed to aggregation of polyimides in these conditions. ©1997 SCI

Collagens, stromal cell-derived factor-1α and basic fibroblast growth factor increase cancer cell invasiveness in a hyaluronan hydrogel

Abstract.  Objective: Beyond to control of cell migration, differentiation and proliferation, the extracellular matrix (ECM) also contributes to invasiveness of human cancers. As the roles of hyaluronan (HA) and collagens in this process are still controversial, we have investigated their involvement in cancer pathogenesis. Materials and methods: With this aim in view, we developed a three‐dimensional matrix, as reticulate HA hydrogel alone or coated with different collagens, in which cells could invade and grow. Results: We show that cancer cells, which were non‐invasive in a single HA hydrogel, acquired this capacity in the concomitant presence of type I or III collagens. Both types of ECM compound, HA and collagens, possess the capacity to stimulate production of metalloprotease‐2, recognized otherwise as a factor for poor cancer prognosis. HA‐provoked cellular invasiveness resulted from CD44‐mediated increase in cytosolic [Ca2+] and its subsequent hydrolysis due to ADAM (a disintegrin and metalloprotease) proteolytic activity. Interestingly, this mechanism seemed to be absent in non‐invasive cancer cell lines. Conclusion: Furthermore, using basic fibroblast growth factor and stromal cell‐derived factor‐1α, we also show that this three‐dimensional reticulate matrix may be considered as a valuable model to study chemokinetic and chemotactic potentials of factors present in tumour stroma.

Mechanical spectroscopy of karaya gum—alginate mixed dispersions

Abstract The rheological properties of blends obtained by mixing alginate and karaya gum dispersions were described from oscillation, shear and creep experiments using a controlled stress rheometer. The mechanical spectra shown by such mixtures were strongly modified when compared with those of each of the blend components. It was found that the viscoelastic behaviour of mixtures was strongly affected by the age of the karaya gum. Contrary to that which is observed with fresh karaya gum, maximum synergy was observed with a mixture containing 75% aged karaya gum. It is suggested that mutual incompatibility between the two polysaccharides could explain the formation of a mixed network.