Ch. Baquey

PLASMA TREATMENT OF EXPANDED PTFE OFFERS A WAY TO A BIOFUNCTIONALIZATION OF ITS SURFACE

Abstract Biointegration is the ideal outcome which is expected for an artificial implant. That means that the phenomena which seats at the interface between the implant and the host tissues does not induce neither any deleterious effect, such as chronic inflammatory response, nor the formation of unusual tissues. Thus it is of paramount importance to design biomaterials, used for the fabrication of implants, with the best appropriate surface properties. At the same time these biomaterials must feature bulk properties which meet other requirements, especially mechanical properties, deriving from the intended function of the implant in which they are involved. As it is quite impossible to design biomaterials which fulfil at the same time both types of requirements, it is commonly agreed that the solution to this issue goes through the selection or the design of biomaterials with adequate bulk properties, and a further treatment of the surface which would improve the properties of the latter. In this respect ionizing radiations and plasma based treatments, offer a wide panel of possibilities; as an example we describe here how the surface of expanded poly(tetrafluoroethylene) samples can be activated using cold plasma, in order to open a way to chemical modifications of such a surface. Subsequently, Radio Frequency Glow Discharge (RFGD) containing oligopeptides, known for their role in mediating the adhesion of cells to the extracellular matrix, were bound to the modified surface, and the affinity of endothelial cells for the latter was investigated.

New artificial connective matrix-like structure: thrombogenicity and use as endothelial cell culture support

The recently described artificial connective matrix made of elastin solubilized peptides, type I+III collagens and connective proteins is shown to have structural and biological properties very close to the natural arterial subendothelium: the capacity to promote endothelial cell cultures maintaining their phenotype expression and its non-thrombogenicity. This new bioactive composite material could be used to replace arteries.

Mechanical properties of cellulose in orthopaedic devices and related environments

The authors have undertaken a series of mechanical tests in order to assess the performance of regenerated cellulose under either static or dynamic conditions, and to evaluate its long-term behaviour under mechanical stress. In this respect, bending stiffness, resistance to compression, creep under compressive stress, in vitro and in vivo ageing and fatigue resistance were studied. It appears that this material demonstrates mechanical properties which depend upon its density, which is itself related to its water content. Moreover, this material is very stable under dynamic stress. This could be an interesting property for use in orthopaedic devices.

In vitro study of the hemocompatibility of superparamagnetic contrast agent for magnetic resonance imaging

Five different nanoparticles, potentially useful in magnetic resonance imaging (MRI) after venous administration, were studied for their hemocompatibility. The in vitro methodology evaluated these materials by several parameters: cytotoxicity towards cells cultured in vitro, aggregation ability of platelets, hemolysis inducibility, intrinsic and extrinsic coagulation pathway activation, and complement activation. With the proposed clinical dose, regardless of the cell type used (murine cell line or human endothelial cells) no toxicity was observed. The presence of the particles in blood did not produce any considerable damage: either hemolysis or platelet aggregation or blood coagulation were recorded. However, a slight decrease in aggregation ability of platelets was noticed as well as an increase in partial thromboplastin time. Because of the quick removal of the particles from the bloodstream, these phenomena must be short-lived, thus avoiding significant adverse clinical effects.

Biocompatibility of polyacrylamide microcapsules implanted in peritoneal cavity or spleen of the rat effect on various inflammatory reactions in vitro

The biocompatibility of polyacrylamide microcapsules was investigated by implanting microcapsules in the peritoneal cavity or the spleen of rats. The capsules were retrieved every four weeks for twenty weeks. They remained isolated and free in the peritoneal cavity, but led to a slight inflammatory reaction in the spleen. These results were confirmed, in vitro, by determinations of chemiluminescence and interleukin I levels, and by evaluation of attachment and growth of human fibroblasts. The microcapsules did not enhance these inflammatory reactions, and they were a poor support for cellular proliferation.

Radiosterilization of albuminated polyester prostheses

The study reported here is concerned with the radio-sterilization of Dacron vascular prostheses coated with crosslinked albumin. gamma-Radiations have no effect on the mechanical properties of the polyester fibres or on their crystallinity, whether irradiated in a dry state or immersed in saline. Special attention has been paid to the release of the albumin, or protein fragments from the reticulum using 125I-labelled albumin as a radiotracer. The albumin leakage depends upon the type of Dacron fabrics considered but the values derived from radioactivity measurements are always greater than those directly measured, which indicates a radio-induced break of the bond between iodine and albumin; this has nothing to do with the break of the association between albumin and Dacron. Moreover no cytotoxicity of the irradiated immersion medium has been observed using a test based on organotypic culture in liquid medium. Thus radio-sterilization of an albuminated polyester vascular prosthesis immersed in saline appears to be a suitable procedure.

Polymorphonuclear cell apoptosis in exudates generated by polymers

Flow cytometry was used to quantify apoptotic and necrotic polymorphonuclear (PMN) cells in an exudate generated by biomaterials, and the results were compared with determinations of spontaneous apoptosis and necrosis in PMN cells from the bloodstream. The exudate formed inside cylindrical tubes subcutaneously implanted in the dorsal region of rats was collected over a 1-week period. A rapid and simple staining procedure based on the spectral properties of the bisbenzemide Hoechst 33342 was used to identify apoptotic PMN cells. Quantification of permeabilized PMN cells stained by propidium iodide was possible in the same unfixed specimens. The percentages of apoptotic and permeabilized PMN cells in peripheral rat blood were low (1.8 +/-0 0.5% and 1.7 +/- 0.7%, respectively), similar to results found in humans. In exudates generated by polyvinyl chloride (PVC), the percentages of apoptotic and permeabilized PMN cells were higher than in the blood. The percentage of PMN cells undergoing apoptosis progressively increased with time and reached a maximum at day 2 (27% +/- 6%). The percentage of permeabilized cells progressively increased with time and was much higher than the percentage of apoptotic cells on days 4 and 8. Apoptosis and necrosis of PMN cells at day 2 were inhibited when tubes were filled with 10% serum. Selective inhibition of apoptosis with a caspase inhibitor in vivo indicated that apoptosis and necrosis are two separate pathways leading to the death of PMN cells in the exudate. At day 2, polyurethane (PU) was associated with a lower rate of apoptosis than PVC or a random copolymer of trimethylene carbonate (TMC) and epsiloncaprolactone (ECL). Apoptosis was interpreted as an organized cell removal process that limits inflammation. Apoptosis was the natural route of PMN cell death at the early stage of inflammation.

First use of cultured human urothelial cells for biocompatibility assessment: Application to urinary catheters

For several years, studies performed to estimate in vitro biocompatibility of urinary catheters have been carried out using permanent cell lines. But for a rational design of the testing procedure, the cell culture model should relate to the material application. This work presents the results of a probe study designed to obtain an in vitro model of normal human urothelial cells (HUC) and to test the relevance of this system in cytocompatibility experiments of urinary catheters currently used.A comparison is made with continuous cell lines, the use of which is recommended by normalization bodies. We exposed monolayers of HUC (well characterized for their proliferation, qualitative evaluation, and quantitative measurement of cytokeratins) and two continuous human cell lines to liquid extracts (either pure or diluted in the culture medium) of nine available catheters, including positive (latex) and negative controls, for a 24 h incubation. Then colorimetric assays (Neutral Red and MTT) were performed. The extracts of two polyurethanes provoked a significant toxic effect on HUC only, suggesting differences in sensitivity between the models used. This effect could be due to the presence of a great amount of barium (used as a radioopacifier) in extracts, as highlighted by results of absorption emission spectroscopy. A culture model of HUC may be of relevance for the screening of materials intended for urological practice.

Cytocompatibility study of NHLBI primary reference materials using human endothelial cells

Four different materials, low density polyethylene (LDPE), polydimethylsiloxane (PDMS), polyvinylcholoride (PVC) and cellulose, were selected by the Devices and Technology Branch of the National Heart Lung and Blood Institute (NHLBI) as primary reference materials for blood contacting. Among the wide variety of tests proposed to assess hemocompatibility of short-term blood contacting catheters, it was desirable to rule out whether these materials could release toxics for vascular cells of the physiological environment. Thus, the cytocompatibility of these materials have been checked towards human umbilical vein endothelial cells: the method used avoids direct contact between cells and materials but evaluates the effect of possible toxic substances leached from materials. These substances were obtained under defined conditions according to a standard. The results show that the extracts of cellulose and LDPE provoke an important cytotoxic effect on the endothelial cell cultures, while the extracts of PDMS and PVC allow the obtention of endothelial cell lining of the reference surface, with a correct global metabolic activity and the intracellular presence of von Willebrand factor.

Physico-chemistry and cytotoxicity of ceramics: Part I – Characterization of ceramic powders

The morphology of Al2O3, ZrO2/Y2O3, AIN, B4C, BN, SiC, Si3N4, TiB2, TiC, TiN ceramic, graphite and diamond powders has been studied by scanning electron microscopy (SEM) and the specific area of each powder was determined with the BET method. X-ray diffraction (XRD) investigations have been carried out in order to evaluate the crystallinity and determine the constitutive phases. The chemical composition was assessed by classical chemical analyses and by X-ray microprobe; some powders were studied by the laser micro-Raman technique. Correlations have been established between all these results.