Gilbert Legeay

Synthesis and general properties of silated-hydroxypropyl methylcellulose in prospect of biomedical use

Synthesis of grafting silane on a hydro soluble cellulose ether (HPMC) was described. In alkaline medium, this derivate is under gel form. With a decrease of the pH, a self-hardening occurs due to the silanol condensation. For potential biomedical use, we described the silated-HPMC synthesis, the gel behavior after steam sterilization and the parameters of the silanol condensation i.e. pH, silane percentage and temperature. Minimum kinetic of the condensation was observed for pH between 5.5 and 6.5. So temperature catalyzed the reaction and the self-hardening speed was increased by silane percentage.

AF fluoropolymer for optical use: spectroscopic and surface energystudies; comparison with other fluoropolymers

Four fluoropolymers are studied by Infra-Red, Raman and solid state NMR; one of them (Teflon AF) is optically transparent thanks to the presence of large ether cycles which prevent crystallization. Detailed investigations of the different spectra lead to the interpretation of the different lines characteristic of the constitutive fluoro-based sites.

Influence of corona surface treatment on the properties of an artificial membrane used for Langerhans islets encapsulation: permeability and biocompatibility studies

An artificial membrane (AN69 Hospal) suitable for pancreatic islets encapsulation was submitted to a physicochemical treatment (corona discharge) to improve its insulin permeability. This effect depends on the duration of the electrical discharge (expressed as the speed of a conveyor belt) and the distance between the electrodes and the membrane. Among the various treatments tested, the most efficient (distance of 5 cm and a speed of 2 cm s-1) produced a three-fold increase in insulin diffusion. This improvement persisted after a protein-coating test which mimics in vivo conditions. At 1 y after the peritoneal implantation, the corona-treated membrane remained biocompatible. Thus, corona discharge treatment may serve to optimize the properties of artificial membranes used for pancreatic islets encapsulation.

Plasma-induced polymerization

Low vapor tension polymerized acrylates as thin films when they are subjected to a cold plasma. The plasma-induced polymerization is described in terms of direct or indirect energy transfer from the plasma to the monomer. The indirect transfer is related to the absorption of UV-visible radiations by the monomer. The radiations are emitted from excited species of the plasma. Direct transfers correspond to the reactive species collision (radicals, ions metastable species) with a molecule of monomer. The polymerization is a result of these two kinds of transfers. Direct transfers lead to competitive reactions (addition, terminations and degradation, etc.) and acrylate polymerization is mostly induced by the UV-visible radiations.

Surface treatment of polycarbonate films aimed at biomedical application

Aiming to encapsulate pancreatic islets, a biocompatible polycarbonate membrane (What-man) was treated with plasma argon in order to improve its surface properties. The argon plasma treatment decreased the hydrophobicity of the membrane by fixing polyvinylpyrrolidone (PVP) at the surface. The water angle contact decreased from 47° to 20° after this treatment, while the structure and pore diameter were preserved. The treatment also increased significantly the water permeability from 62 ± 8 ml/min to 200 ± 29 ml/min (P < 0.001). ToF-SIMS analyses revealed that the argon plasma treatment of the membrane allowed the installation of an uniform PVP layer at the surface. The concentration equilibrum in glucose was reached after 8 h diffusion for the treated membrane, while it was only 32.4 ± 8.6% (P < 0.01) for the untreated membrane. The biocompatibility of the polycarbonate membrane was assessed after one month of implantation in rats and proved to be unaffected by the surface treatment. In conclusion, the present study provided sufficient information to establish a relationship between the physicochemical modifications of the PVP-plasma-treated polycarbonate membrane and the improvement in its permeability.

Physicochemical and biological studies of corona-treated artificial membranes used for pancreatic islets encapsulation: Mechanism of diffusion and interface modification

The artificial AN69 membrane (Hospal), a synthetic copolymer composed of acrylonitrile and sodium methallyl sulphonate suitable for pancreatic islet encapsulation, was submitted to physicochemical treatment (Corona discharge) to improve its insulin permeability. X-ray photoelectron spectroscopy (XPS) analysis of the AN69 membrane indicated the presence of up to two molecular layers of glycerol at its surface while the surface energies revealed the presence of hydrophilic sites (-SO3Na/glycerol) located at the membrane surface and acrylonitrile hydrophobic groups inside the material. The Corona discharges decreased the number of glycerol molecules at the membrane surface and from a biological point of view, produced a threefold increase in insulin diffusion. Furthermore, the biocompatibility of the treated membrane was preserved after 1 year of intraperitoneal implantation. The increase in insulin permeability should result from a decrease of the membrane polarity and of a steric hindrance in pores. Thus, Corona discharge treatment may serve to optimize the properties of artificial membranes used for pancreatic islets encapsulation.

Elaboration of nano-structured grafted polymeric surface

The surface grafting of multi-polymeric materials can be achieved by grafting as components such as polymers poly(N-isopropylacrylamide) and/or surfactant molecules (hexatrimethylammonium bromide, polyoxyethylene sorbitan monolaurate). The chosen grafting techniques, i.e. plasma activation followed by coating, allow a large spectrum of functional groups that can be inserted on the surface controlling the surface properties like adhesion, wettability and biocompatibility. The grafted polypropylene surfaces were characterized by contact angle analyses, XPS and AFM analyses. The influence of He plasma activation, of the coating parameters such as concentrations of the various reactive agents are discussed in terms of hydrophilic character, chemical composition and morphologic surface heterogeneity. The plasma pre-activation was shown inevitable for a permanent polymeric grafting. PNIPAM was grafted alone or with a mixture of the surfactant molecules. Depending on the individual proportion of each component, the grafted surfaces are shown homogeneous or composed of small domains of one component leading to a nano-structuration of the grafted surface.

Interaction between hydroxypropyl methylcellulose and biphasic calcium phosphate after steam sterilisation: capillary gas chromatography studies.

The purpose of this study was to check the chemical stability of an injectable bone substitute (IBS) composed of a 50/50 w/w mixture of 2.92% hydroxypropyl methylcellulose (HPMC) solution in deionized water containing biphasic calcium phosphate (BCP) granules (60% hydroxyapatite/40% β-tricalcium phosphate w/w). After separation of the organic and mineral phases, capillary gas chromatography (GC) was used to study the possible modification of HPMC due to the contact with BCP granules following steam sterilisation and 32 days storage at room temperature. HPMC was extracted from IBS in aqueous medium, and a dialytic method was then used to extract calcium phosphate salts from the HPMC. The percentage of HPMC extracted from BCP was 98.5% ± 0.5%, as measured by UV. GC showed no chemical modifications after steam sterilisation and storage.

Surface Engineering and Cell Adhesion

Cell adhesion is a multi-process phenomenon involving physical, physico-chemical and biological mechanisms. The complexity of interfaces is the reason why progress in the theory of cell adhesion has been slow. Greater understanding of interaction mechanisms has been enhanced by complete knowledge of supports and of biological components, in particular the extracellular matrix, membrane walls, cell multiplication processes and apoptosis. The construction of novel surfaces with strongly hydrophilic or ultrahydrophobic properties has allowed new theoretical advances, while at the same time offering numerous and varied technological applications. These include: • Bioadhesion with mechanical anchoring using ubiquitous surface roughness and deformability of certain micro-organisms. • Physico-chemical bioadhesion or repellence resulting mainly from the energy characteristics of support surfaces. • Processes of sorting and guidance by biomolecules present at the support–biofilm interface, generating biochemical responses that can induce cell multiplication or degeneration (as in cancer), or cell death.

Are the Interactions between Recombinant Prion Proteins and Polymeric Surfaces Related to the Hydrophilic/Hydrophobic Balance?

New non-fouling tubes are developed and their influence on the adhesion of neuroproteins is studied. Recombinant prion proteins are considered as a single component representative of hydrophobic proteins. Samples are stored for 24 h at 4 °C in tubes coated with two different coatings: poly(N-isopropylacrylamide) as a hydrophilic surface and a plasma-fluorinated coating as a hydrophobic one. The protein adhesion is monitored by ELISA tests, XPS and confocal microscopy. It appears that the highest recovery of recombinant prion protein in the liquid phase is obtained with the hydrophilic surface while the hydrophobic character of the storage tube induces an important amount of biological loss. However, the recovery is not complete even for tubes coated with poly(N-isopropylacrylamide).