Isabelle Pezron

Conformation of gelatin chains in aqueous solutions: 1. A light and small-angle neutron scattering study

Abstract Gelatin solutions in dilute and semi-dilute regimes were characterized by using light and small-angle neutron scattering techniques. Absolute intensity measurements allowed us to evaluate the molecular parameters of these protein chains (radius of gyration, persistence length, cross-section, mass per unit length) and to determine the quality of the solvent (0.1 M NaCl solutions in H2O or D2O at pH = 7). The classical model of worm-like chains was adopted for the theoretical interpretation of chain conformation in the sol state (T = 50°C) with a persistence length of about 20 A. In semi-dilute solutions the correlation length was measured for different concentrations. Agreement was found with the scaling laws, although the description is not totally satisfactory: non-trivial scattering effects are detected in both static and dynamic light scattering experiments, which can be attributed to the presence of inhomogeneities having a different local density. Their apparent radius of gyration is of the order of several hundred angstroms. The nature and extension of these inhomogeneities are discussed.

Lipid emulsions as vehicles for enhanced nasal delivery of insulin

The objective of this work is to explore lipid emulsion based formulations of insulin as an enhancer of nasal absorption. Insulin was incorporated into the aqueous phases of water-in-oil (w/o) and oil-in-water (o/w) emulsions. The formulations were perfused through the nasal cavity of rats in situ. Enhancement of insulin absorption was observed when insulin was incorporated into the continuous aqueous phase of an o/w emulsion. The presence of a small fraction of oil droplets along with insulin in the aqueous phase appeared to favor insulin absorption. When the oil phase constitutes the external phase, as in w/o emulsion, no insulin absorption was noted. Inhibition of insulin absorption might arise from a rate limiting barrier effect of the membrane completely covered by a stagnant oil layer. The in situ model was validated by in vivo experiments, which also revealed an increase in insulin absorption with o/w emulsions. However at lower insulin doses there was no statistically significant enhancing effect. In situ perfusion experiments across rat nasal pathway appear to be an appropriate model to study the enhancement effect of nasal formulations.

Enhanced pulmonary delivery of insulin by lung lavage fluid and phospholipids.

Pulmonary delivery appears to be the most promising non-parenteral route of insulin administration. In this work, we investigated the enhancement of insulin absorption in the presence of phospholipids and lung lavage fluid in vivo and in vitro. In-vitro experiments of insulin uptake by type II cells showed a significantly enhanced absorption in presence of lavage fluid, compared to various buffer preparations. The same trend was obtained with in-vivo studies of tracheal instillation of insulin. The incorporation of phospholipids as absorption enhancers in 1,2-dipalmitoyl phosphatidylcholine (DPPC) dispersion was compared to blank liposomes. A significantly higher blood glucose decrease was observed with a DPPC-insulin physical mixture compared to liposome, suggesting a possible effect of the phospholipid chain physical state on the insulin in-vivo absorption.

Characterization of biomaterials polar interactions in physiological conditions using liquid–liquid contact angle measurements: Relation to fibronectin adsorption

Wettability of biomaterials surfaces and protein-coated substrates is generally characterized with the sessile drop technique using polar and apolar liquids. This procedure is often performed in air, which does not reflect the physiological conditions. In this study, liquid/liquid contact angle measurements were carried out to be closer to cell culture conditions. This technique allowed us to evaluate the polar contribution to the work of adhesion between an aqueous medium and four selected biomaterials widely used in tissue culture applications: bacteriological grade polystyrene (PS), tissue culture polystyrene (tPS), poly(2-hydroxyethyl methacrylate) film (PolyHEMA), and hydroxypropylmethylcellulose-carboxymethylcellulose bi-layered Petri dish (CEL). The contributions of polar interactions were also estimated on the same biomaterials after fibronectin (Fn) adsorption. The quantity of Fn adsorbed on PS, tPS, PolyHEMA and CEL surfaces was evaluated by using the fluorescein-labeled protein. PolyHEMA and CEL were found to be hydrophilic, tPS was moderately hydrophilic and PS was highly hydrophobic. After Fn adsorption on PS and tPS, a significant increase of the surface polar interaction was observed. On PolyHEMA and CEL, no significant adsorption of Fn was detected and the polar interactions remained unchanged. Finally, an inverse correlation between the polarity of the surfaces and the quantity of adsorbed Fn was established.

Contact Angle Assessment of Hydrophobic Silica Nanoparticles Related to the Mechanisms of Dry Water Formation

Dry water is a very convenient way of encapsulating a high amount of aqueous solutions in a powder form made of hydrophobic silica nanoparticles. It was demonstrated in previous studies that both solid and liquid interfacial properties influence the quality of the final product resulting occasionally in mousse formation. To explain this behavior, contact angles of silica nanoparticles have been measured for water and water/ethanol solution by means of liquid intrusion experiments. It was found that the quality of the final product correlates with the contact angle, i.e., contact angle close to 105 degrees leads to mousse formation whereas a slightly higher value of approximately 118 degrees allows dry water formation. The proposed explanation was based on the energy of immersion and adhesion defined as the energy needed for a spherical particle to respectively penetrate into the liquid or attach at the liquid/air interface. Significantly lower energy of immersion calculated for lower contact angle might account for particle penetration into the liquid phase during processing, leading to continuous network aggregation, air entrapment, and finally mousse formation.

Stability of W/O and W/O/W emulsions as a result of partial solidification

Abstract This communication reviews the drastic modifications that may occur within emulsions when they are submitted to temperature variations during manufacturing, storage, transport and use. Emphasis will be given to the modifications resulting from changes after solidification. Pathways of solidification of W/O and W/O/W emulsions will be presented. Due to the specific structure of the emulsions under study (simple or multiple) only partial solidification may be obtained. This situation, out of thermodynamic equilibrium, may lead to a water transfer across the oil phase. Resulting emulsion transformation and destabilization are examined.

Monoglyceride surface films: Stability and interlayer interactions

Abstract Interactions between surfaces coated with monolayers of monoglycerides immersed in water have been studied using the surface force apparatus. The monolayers were deposited onto hydrophobized mica surfaces by means of the Langmuir-Blodgett technique. The measured forces between monopalmitin monolayers in the gel state show the existence of an adhesive minimum at a separation of about 10A; this attraction decreases when the temperature increases. At even shorter separations a strong repulsion dominates the interaction. The forces between monoolein monolayers deposited in the liquid expanded state are repulsive at all separations and the range of the hydration/steric force is 10–15A. Deposited monolayers of monopalmitin in the gel state exhibit a good stability and remarkable rehealing properties. In contrast, deposited monolayers of monoolein are unstable and readily transform into different structures.

Water transfer in mixed water-in-oil emulsions studied by differential scanning calorimetry

Abstract Water transfers are observed within complex systems containing aqueous phases separated by a membrane or an oil phase, such as biological cells or multiple emulsions. In order to better understand water transfer mechanism, a system made of a mixed water-in-oil (W/O) emulsion containing two kinds of aqueous droplets — pure water and a 30 % urea solution — was developed. Water transfer from pure water droplets to urea solution droplets was evidenced by Differential Scanning Calorimetry (DSC). Finally the mixed emulsion contains one kind of droplets made of a diluted urea solution which composition is in agreement with formulation and data obtained from experiments performed on single W/O emusions which dispersed phase is a diluted urea solution of the same composition. These mixed emulsions have been pictured as a three-fluid phases system containing two aqueous phases separated by a plane oil membrane. From a homogeneous solubility-diffusion model applied to a quasi-stationnary regime, the water intra-diffusion coefficient has been obtained and compared to the value calculated from the Stokes-Einstein equation. A factor ten makes the discrepancy between the two values, the value deduced from the model being the highest. A possible influence of the emulsifier molecules has been evoked.

Soft tissue adhesion of polished versus glazed lithium disilicate ceramic for dental applications.

OBJECTIVE Ceramics are widely used materials for prosthesis, especially in dental fields. Despite multiple biomedical applications, little is known about ceramic surface modifications and the resulting cell behavior at its contact. The aim of this study is to evaluate the biological response of polished versus glazed surface treatments on lithium disilicate dental ceramic. METHODS We studied a lithium disilicate ceramic (IPS e.max(®) Press, Ivoclar Vivadent) with 3 different surface treatments: raw surface treatment, hand polished surface treatment, and glazed surface treatment (control samples are Thermanox(®), Nunc). In order to evaluate the possible modulation of cell response at the surface of ceramic, we compared polished versus glazed ceramics using an organotypic culture model of chicken epithelium. RESULTS Our results show that the surface roughness is not modified as demonstrated by equivalent Ra measurements. On the contrary, the contact angle θ in water is very different between polished (84°) and glazed (33°) samples. The culture of epithelial tissues allowed a very precise assessment of histocompatibility of these interfaces and showed that polished samples increased cell adhesion and proliferation as compared to glazed samples. SIGNIFICANCE Lithium disilicate polished ceramic provided better adhesion and proliferation than lithium disilicate glazed ceramic. Taken together, our results demonstrate for the first time, how it is possible to use simple surface modifications to finely modulate the adhesion of tissues. Our results will help dental surgeons to choose the most appropriate surface treatment for a specific clinical application, in particular for the ceramic implant collar.

Probing Fibronectin−Surface Interactions: A Multitechnique Approach

The development of adhesive as well as antiadhesive surfaces is essential in various biomaterial applications. In this study, we have used a multidisciplinary approach that combines biological and physicochemical methods to progress in our understanding of cell-surface interactions. Four model surfaces have been used to investigate fibronectin (Fn) adsorption and the subsequent morphology and adhesion of preosteoblasts. Such experimental conditions lead us to distinguish between anti- and proadhesive substrata. Our results indicate that Fn is not able to induce cell adhesion on antiadhesive materials. On adhesive substrata, Fn did not increase the number of adherent cells but favored their spreading. This work also examined Fn-surface interactions using ELISA immunoassays, fluorescent labeling of Fn, and force spectroscopy with Fn-modified tips. The results provided clear evidence of the advantages and limitations of each technique. All of the techniques confirmed the important adsorption of Fn on proadhesive surfaces for cells. By contrast, antiadhesive substrata for cells avoided Fn adsorption. Furthermore, ELISA experiments enabled us to verify the accessibility of cell binding sites to adsorbed Fn molecules.