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Biomedical subjects

G Ponchel

Publications and source records attributed to G Ponchel.

32 records · Page 2Linked to original sources
PubMed1998

In vitro studies on enhancing effect of sodium glycocholate on transbuccal permeation of morphine hydrochloride.

During the perioperative period, gastric emptying rate and first-pass metabolism limit the use of peroral morphine. Buccal mucosa appears to be a potential site for delivery of morphine as it provides direct entry into the system circulation thereby avoiding the hepatic first-pass effect. However, the low permeability of the buccal epithelium results in a low flux of the drug. The use of a penetration enhancer is required to improve the bioavailability of the drug via buccal route. In this study, the enhancing effect of sodium glycocholate (GC) used at 10 mM and 100 mM concentrations on permeation of morphine hydrochloride (MPH) across the porcine buccal mucosa was studied in vitro. Furthermore, in conjunction with its permeation, accumulation of GC in the tissue with time was also studied in order to elucidate the relationship between GC and enhanced mucosal permeation of the drug. Franz diffusion cells were used in the experiments. Permeation of MPH was increased in the presence of 100 mM GC with an enhancement factor of 9.3 whereas no enhancement was obtained with 10 mM GC. The calculated permeability coefficient for MPH in the presence of 100 mM GC was 2.35 x 10(-5) cm/s. Accumulation of GC at 100 mM in the tissue appears to be more significant at 100 mM concentration which correlated well with the increased permeation of the drug. GC was diffused through the buccal epithelium significantly at 100 mM concentration. Interaction of GC with the tissue appears to be more significant at 100 mM concentration compared to 10 mM concentration, thus resulting in a significant enhancing effect.

Analgesics, Opioid↗
PubMed1998

Combined poly(isobutylcyanoacrylate) and cyclodextrins nanoparticles for enhancing the encapsulation of lipophilic drugs.

PURPOSE: The aim of this study was to prepare and characterize nanoparticulate systems constituted of poly(isobutylcyanoacrylate) and cyclodextrins and intended for increasing the loading of the particles with lipophilic substances. Progesterone was used as a model substance. METHODS: Nanoparticles were prepared by polymerization of isobutylcyanoacrylate in presence of cyclodextrins or progesterone/ hydroxypropyl-beta-cyclodextrin complex. Particle size, zeta potential, cyclodextrin and progesterone loading of the particles were determined. RESULTS: Nanoparticles could be easily prepared in presence of cyclodextrins. An increase in hydroxypropyl-beta-cyclodextrin concentration resulted in small nanoparticles (less than 50 nm). It was found that large amounts of cyclodextrins remained associated to the particles, resulting in a 50 fold increase in progesterone loading compared to nanoparticles prepared in absence of cyclodextrins. CONCLUSIONS: The poly(isobutylcyanoacrylate)cyclodextrin nanoparticles were characterized by the presence of many lipophilic sites belonging to the cyclodextrins which were firmly anchored to the structure of the particles. Therefore, this new type of nanoparticles offers probably an opportunity for increasing the loading of nanoparticles with various lipophilic drugs.

2-Hydroxypropyl-beta-cyclodextrin↗
PubMed1996

Bioadhesion of lectin-latex conjugates to rat intestinal mucosa.

PURPOSE: The specific interactions between three lectin-latex conjugates and different structures of rat intestinal mucosa have been studied ex vivo. METHODS: These systems were prepared by covalent coupling of different ligands, i.e., tomato lectin (TL), asparagus pea lectin (AL), mycoplasma gallisepticum lectin (ML), and bovine serum albumin (BSA) as control, to poly(styrene) latexes. RESULTS: Using mucosa samples without Peyer's patches (PP), the extent of interaction of all three lectin-latex conjugates with the mucosa decreased from duodenum to ileum, probably due to progressive diminution of the mucin concentration along the gastrointestinal tract. The following order of interaction of the conjugates with the mucus gel layer was observed: TL > ML = AL (p < 0.05). For each lectin, these results corresponded well to the concentration of its specific sugar in the mucus. Using intestinal samples with PP, an important increase of interaction of the conjugates with the mucosa was found for ML (about 25%) and AL (about 50%), whereas the interaction of TL decreased about 25%. CONCLUSIONS: Photomicrographs with fluorescent latexes have confirmed the specificity of the ML- and AL-latex conjugates for the PP region and of the TL-latex conjugates for the mucus gel.

Adhesives↗
PubMed1994

Preparation and characterization of lectin-latex conjugates for specific bioadhesion.

This paper reports on the preparation and characterization of certain bioadhesive model drug deliver systems formed by a carrier (e.g. modified nanoparticles of polystyrene) and a ligand (e.g. tomato lectin, asparagus pea lectin, Mycoplasma gallisepticum lectin or albumin). Three different manufacturing methods (carbodiimide and glutaraldehyde coupling and physical adsorption) were studied. The activity of the lectin-latex conjugates and albumin-latex conjugate (control) were tested with gastric pig mucin. The manufacturing method had an insignificant effect on the activity, but all lectin-latex conjugates interacted two or three times more with mucin than with the control.

Adhesives↗
PubMed1994

Mucoadhesion of latexes. II. Adsorption isotherms and desorption studies.

Adsorption isotherms of poly(styrene) latexes on rat intestinal mucosa were studied under static conditions and analyzed according to different isotherm classifications. Isotherms of latexes with a particle size up to 670 nm had the characteristic shape of a disperse adsorbate on a porous adsorbent. Plateaus were reached at latex concentrations of about 2.5 g/L. The results indicated an increase in adsorption with the size and the hydrophilicity of the latexes. Typically, a surfactant-free carboxylate latex of 230 nm had a plateau of 0.66 g/m2, and a latex of 320 nm with added sodium dodecyl sulfate had a plateau of 0.881 g/m2. Surfactant-free carboxylate latex of 2 microns had a Langmuirian isotherm with a plateau level of 2.616 g/m2, which corresponded to a monolayer of adsorbed particles on the surface of mucosa. Desorption studies showed that the adsorption was irreversible. Adhesion to the mucous gel layer would therefore be limited by the mucus turnover.

Adsorption↗
PubMed1994

Mucoadhesion of latexes. I. Analytical methods and kinetic studies.

A Fourier transform infrared spectroscopy/attenuated total reflection technique for direct quantification of adsorbed poly(styrene) latexes on rat intestinal mucosa was developed for deposited latex amounts up to 1.5 g/m2. The method agreed well with another dosage assay of adsorbed particles by turbidimetry after denaturation of the mucus. Adsorption kinetics were made under static conditions at latex concentrations of 4 g/L in physiological saline. Ninety percent of equilibrium was reached after 10 min for a particle size of 230 nm, 20 min for a size of 320 nm, and 30 min for a size of 670 nm. The plateaus were between 0.6 and 0.9 g/m2 (adsorbed mass per apparent surface of mucosa). The first phase of the kinetics was theoretically approached by a diffusion model in the suspension medium. Mucosa from rat jejunum and ileum could be considered as a homogeneous biological model for latex adsorption.

Adsorption↗
PubMed1992

Principle and investigation of the bioadhesion mechanism of solid dosage forms.

The development of bioadhesive tablets requires a good knowledge of their adhesion mechanism and the possibility of using an accurate in vitro evaluation technique. The bioadhesion mechanism is not basically different from the general adhesion mechanism, but it is necessary to take into account the biological nature of at least one of the two substrates involved in the process. The hydrated joint created at the molecular interface, resulting from the inter-penetration of the polymeric chains of the mucin and the bioadhesive product, is especially interesting, because its viscoelastic properties make it a damping device for the stresses transmitted to the bioadhesive surface.

Adhesiveness↗
PubMed1981

[The fate of arterial micrografts stored in Collin's solution (author's transl)].

Use of arterial micrografts stored in Collin's solution is acceptable only for short storage periods and is therefore restricted in common practice. The immunitary reactions on the grafts are considered to be usually minor and were not studied in this series. Preservation alters the media and can result in aneurism and thrombosis. However, considering the lack of a reliable solution in replacing small vessels, research must be pursued to define the optimal storage period and the most adequate preservation liquid for small vessels.

Angiography↗
PubMedDate not supplied

Polymers of malic acid and 3-alkylmalic acid as synthetic PHAs in the design of biocompatible hydrolyzable devices.

Poly(beta-malic acid) and poly(beta-3-alkylmalic acid) derivatives, as synthetic polyhydroxyalkanoates (PHAs), present several advantages as macromolecular materials for temporary biomedical applications. Indeed, such polymers, which can be synthesized through different chemical and biological routes, have cleavable ester bonds in their backbone for hydrolytic degradation, stereogenic centres in the monomers units for controlling the macromolecular structure. bioassimilable or non-toxic repeating units and lateral chemical functions which can be adapted to specific requirements. The strategy for building such complex architectures, with one or several specific pendant groups, is based on the anionic ring-opening polymerization or copolymerization of the large family of malolactonic and 3-alkylmalolactonic acid esters. Because we are able to control the monomer synthesis and the polymerization step, we have been able to prepare different degradable materials for the biomedical field, such as: degradable associating networks made up by the association of random copolyesters containing a small percentage of hydrophobic moieties and beta-cyclodextrin copolymers; degradable macromolecular micelles constituted by degradable amphiphilic block copolymers of poly(beta-malic acid) as hydrophilic segments and poly(beta-alkylmalic acid alkyl esters) as hydrophobic blocks; and degradable nanoparticles made up by hydrophobic poly(beta-malic acid alkyl esters) derivatives. We have also prepared a terpolymer which exhibits growth factor-like properties in vivo. Finally, poly(beta-malic acid) has been used as an additive in the preparation of peritoneal dialysis bags.

Biocompatible Materials↗
PubMedDate not supplied

Formulation of epichlorohydrin cross-linked starch microspheres.

The present work describes a water/oil emulsion technique for the production of microspheres by cross-linking soluble starch with epichlorohyrin, which is a very efficient divalent cross-linking agent for starch. Because they are important features for potential applications, such as pulmonary administration, special attention has been paid to control the mean particle size and size distribution. Microspheres ranging from 0.3-250 microm with narrow size distributions could be obtained. Due to the strongly basic nature of the aqueous phase, no stable emulsions could be obtained in the water/oil emulsion domains. In this context, the stirring rate during the emulsification step was crucial for controlling the particle size. Additionally, a high organic-to-aqueous phase ratio and the presence of a surfactant agent helped to prevent the coalescence of the droplets during the formation of the microspheres. The process was not sensitive to odifications of the chemical conditions, such as the cross-linking ratio, which allows variation of the chemical nature of the polymer forming the core of the microspheres without modifying their morphological characteristics.

Cross-Linking Reagents↗
PubMedDate not supplied

Poly(vinylbenzyl chloride) microsphere synthesis and their chemical modifications.

Vinylbenzyl chloride (VBC) was dispersion polymerized to give monodisperse microspheres in the presence of poly(vinylpyrrolidone) (PVP) as a steric stabilizer. The effect of PVP concentration on the size and on microsphere stability during the polymerization process was investigated. Microsphere size was examined when co-stabilizer molecules were employed with PVP during the polymerization reaction. The built-in reactive chloromethyl groups of the microspheres were the sites of the nucleophilic reaction of two amino-group model molecules, glucosamine (G), a hexosamine implicated in processes of molecular recognition, and also bovine serum albumin (BSA). Elemental analyses and Fourier transform infrared spectroscopy (FTIR) spectra showed that poly(vinylpyrrolidone) was associated with the microsphere network. Elemental analyses, attenuated total reflection infrared spectroscopy (ATR-FTIR), and zeta potential measurements confirmed G and BSA links at the microsphere surface.

Capsules↗
PubMedDate not supplied

Dynamic swelling behaviour of gelatin/poly(acrylic acid) bioadhesive microspheres loaded with oxprenolol.

The dynamic swelling of gelatin/poly(acrylic acid) microspheres loaded with oxprenolol has been evaluated. The movement of two distinct and characteristic swelling boundaries was measured directly using an optical microscope. Swelling rate constants associated with the inner moving front and the outer swelling boundary were determined. A polynomial equation incorporating both Fickian diffusion and case II relaxational models was used to fit the kinetics of liquid uptake. The influence of the concentration of the cross-linking agent, the poly(acrylic acid) load, the pH of the swelling medium and the particle size of the microspheres, on the swelling kinetics, was evaluated and discussed.

Acrylic Resins↗
PubMedDate not supplied

Oxprenolol release from bioadhesive gelatin/poly(acrylic acid) microspheres.

Drug release from gelatin/poly(acrylic acid) oxprenolol-loaded microspheres has been evaluated using an in situ sink immersion method and a wetting method. The kinetics of drug release were analysed by applying the empirical exponential equation and by the calculation of the approximate contribution of the diffusional and relaxational mechanism to the anomalous release process by fitting the data to the coupled Fickian/Case II equation. The influence of glutaraldehyde cross-linking agent concentration, the poly(acrylic acid) content, the pH of the release medium and the particle size of the beads on the drug release kinetics were evaluated and discussed.

Acrylic Resins↗