Gérard Hélary

A new approach to graft bioactive polymer on titanium implants: Improvement of MG 63 cell differentiation onto this coating.

Integration of titanium implants into bone is only passive and the resulting fixation is mainly mechanical in nature, with anchorage failure. Our objective, to increase the biointegration of the implant and the bone tissue, could be obtained by grafting a bioactive ionic polymer to the surface of the titanium by a covalent bond. In this paper, we report the grafting of an ionic polymer model poly(sodium styrene sulfonate) (polyNaSS), in a two-step reaction procedure. Treatment of the titanium surface by a mixture of sulfuric acid and hydrogen peroxide allows the formation of titanium hydroxide and titanium peroxide. In the second reaction step, heating of a metal implant, placed in a concentrated solution of sodium styrene sulfonate monomer (NaSS), induces the decomposition of titanium peroxides with the formation of radicals capable of initiating the polymerization of NaSS. Various parameters, such as temperature of polymerization and time of polymerization, were studied in order to optimize the yield of polyNaSS grafting. Colorimetry, Fourier-transformed infrared spectra recorded in an attenuated total reflection, X-ray photoelectron spectroscopy techniques and contact angle measurements were applied to characterize the surfaces. MG63 osteoblastic cell response was studied on polished, oxidized and grafted titanium samples. Cell adhesion, alkaline phosphatase activity and calcium nodules formation were significantly enhanced on grafted titanium samples compared to unmodified surfaces.

A bioactive polymer grafted on titanium oxide layer obtained by electrochemical oxidation. Improvement of cell response

The anchorage failure of titanium implants in human body is mainly due to biointegration problem. The proposed solution is to graft a bioactive polymer at the surface of the implant in order to improve and control the interactions with the living system. In this paper, we describe the grafting of poly sodium styrene sulfonate on titanium surface by using a silanization reaction. The key point is to increase the TiOH content at the surface of the implant which can react with methoxy silane groups of 3-methacryloxypropyltrimethoxysilane (MPS). Two procedures were used: chemical oxidation and electrochemical oxidation. The last oxidation procedure was carried out in two different electrolytes: oxalic acid and methanol. These different oxidation methods allow controlling the roughness and the depth of the oxide layer. The methacryloyl group of MPS grafted at the titanium surface by silanization reaction is copolymerized with sodium styrene sulfonate using a thermal initiator able to produce radicals by heating. Colorimetric method, ATR-FTIR, XPS techniques and contact angle measurements were applied to characterize the surfaces. MG63 osteoblastic cell response was studied on polished, oxidized and grafted titanium samples. Cell adhesion, Alkaline Phosphatase activity and calcium nodules formation were significantly enhanced on grafted titanium surfaces compared to un-modified surfaces.

Functional polysiloxanes. I. Microstructure of poly(hydrogenmethylsiloxane-co-dimethylsiloxane)s obtained by cationic copolymerization

Poly(hydrogenmethylsiloxane-co-dimethylsiloxane)s of various compositions have been prepared by cationic ring-opening polymerization of octamethylcyclotetrasiloxane (D4) and 1,3,5,7-tetramethylcyclotetrasiloxane (D) in the presence of hexamethyldisiloxane as end-blocker or by rearrangement of poly(hydrogenmethylsiloxane) in the presence of D4. These copolymers were examined by high resolution 1H NMR (500.13 MHz) and 29Si NMR (99.37 MHz) spectroscopies. Triad effects were observed by 1H and up to heptad effects by 29Si NMR. The chemical shifts were assigned for these stereosequences. The intensities of the triad signals were used to calculate the quantitative parameters describing the microstructure of the copolymer chains: number-average block length (L) and persistence ratio (η). The values of these parameters for copolymers prepared in various experimental conditions show that the time necessary for redistribution reactions (backbiting) is much larger than the time required to establish the equilibrium between linear polymer and cyclic oligomers. However, redistribution is fast enough to prevent the formation of block copolymers even in the case of the rearrangement of poly(hydrogenmethylsiloxane) in the presence of D4.

Functional polysiloxanes. II. Neighboring effect in the hydrosilylation of poly(hydrogenmethylsiloxane-co-dimethylsiloxane)s by allylglycidylether

Polysiloxanes bearing epoxy groups as lateral substituents were prepared by the hydrosilylation of 1-allyloxy-2,3-epoxypropane (allylglycidylether) with poly(hydrogenmethylsiloxane-co-dimethylsiloxane)s (DH-D copolymers) of various compositions. To determine the optimal conditions of the hydrosilylation catalyzed by hexachloroplatinic acid, the kinetics of the reaction were investigated for the poly(hydrogenmethylsiloxane) homopolymer. The reaction was first order in platinum, first order in double bonds, and 0.5 in SiH. This kinetic law was consistent with the hypothesis that hydrogenmethylsiloxane dyads are much more reactive than isolated units, which may be explained by the simultaneous insertion of two vicinal SiHs in a binuclear complex of platinum. This peculiar type of neighboring effect was investigated further by comparison of the kinetics of the hydrosilylation of D-DH copolymers of various compositions and DH block lengths and was confirmed by the microstructure of a D-DH copolymer (50/50) before and after partial hydrosilylation. Triad analysis by 29Si NMR showed that the resulting copolymer was not statistical but contained a high proportion of isolated SiH. This explains why hydrosilylation proceeded in two steps: a fast reaction of DH-DH dyads and a slow reaction of the remaining isolated DH units.

Terpolymerization of methyl methacrylate, poly(ethylene glycol) methyl ether methacrylate or poly(ethylene glycol) ethyl ether methacrylate with methacrylic acid and sodium styrene sulfonate: determination of the reactivity ratios

Abstract Materials bearing ionic monomers were obtained through free radical terpolymerization of methyl methacrylate (MMA), poly(ethylene glycol) methyl ether methacrylate (PMEM) or poly(ethylene glycol) ethyl ether methacrylate (PEEM) with methacrylic acid (MA) and sodium styrene sulfonate (NaSS). The reactions were carried out in dimethyl sulfoxide using azobis(isobutyronitrile) as initiator. The reactivity ratios of the different couple of monomers were calculated according to the general copolymerization equation using the Finnemann–Ross, Kelen–Tudos and Tidwell–Mortimer methods. The values of the reactivity ratios indicate that the different monomer units can be considered as randomly distributed along the chains for terpolymerizations of MMA, PMEM or PEEM with MA and NaSS. The average composition of the comonomers in the different terpolymers were calculated, showing a good agreement between the experimental and theoretical compositions. The instantaneous compositions are constant until about 70% of conversion. For higher conversions, the insertion of ionic monomers increases or decreases according to the system studied.

Electroactive poly(3,6-carbazolediyl) with lateral aminoalkyldisiloxane groups

SummaryPoly[N-(9-dimethylamino 4,4,6,6-tetramethyl 5-oxa 4,6-disila nonyl) 3,6-carbazolediyl] was prepared by electrochemical synthesis. The solubility of this polymer in many organic solvents allows its characterization by GPC and 13C NMR.

Terpolymerization of 3-methacryloxypropyl tris(trimethylsiloxy)silane, methacrylic acid and dimethyl octyl ammonium styrene sulfonate: determination of the reactivity ratios

\overline {Dp} _n s

Stereocomplex formation in polybutadiene-syndiotactic poly (methyl methacrylate) block copolymers blended with isotactic poly (methyl methacrylate)

are relatively low (≃6), probably due to a reaction of debromination which occurs during the synthesis of the monomer and leads to monofunctional reactants limiting the polymer growth. Electro-oxidation of solution-cast films gives rise to two reversible color changes : yellowish to green and green to blue. Films display a relatively good electrochemical stability in the blue state (up to 1.4 V vs SCE).