Haemocompatibility evaluation of DLC- and SiC-coated surfaces.

Diamond-like carbon (DLC) and silicon carbide (SiC) coatings are attractive because of low friction coefficient, high hardness, chemical inertness and smooth finish, which they provide to biomedical devices. Silicon wafers (Si(waf)) and silicone rubber (Si(rub)) plates were coated using plasma-enhanced chemical vapour deposition (PE-CVD) techniques. This article describes: 1- the characterization of modified surfaces using attenuated total reflection-Fourier transform infrared spectroscopy (ATR/FTIR) and contact angle measurements, 2- the results of three in-vitro haemocompatibility assays. Coated surfaces were compared to uncoated materials and various substrates such as polymethylmethacrylate (PMMA), polyethylene (LDPE), polydimethylsiloxane (PDMS) and medical steel (MS). Thrombin generation, blood platelet adhesion and complement convertase activity tests revealed the following classification, from the most to the least heamocompatible surface: Si(rub)/ DLC-Si(rub)/ DLC-Si(waf)/ LDPE/ PDMS/ SiC-Si(waf)/ Si(waf)/ PMMA/ MS. The DLC coating surfaces delayed the clotting time, tended to inhibit the platelet and complement convertase activation, whereas SiC-coated silicon wafer can be considered as thrombogenic. This study has taken into account three events of the blood activation: coagulation, platelet activation and inflammation. The response to those events is an indicator of the in vitro haemocompatibility of the different surfaces and it allows us to select biomaterials for further in vivo blood contacting investigations.

Maintenance of primary murine hepatocyte functions in multicomponent polymer capsules--in vitro cryopreservation studies.

BACKGROUND/AIMS: The potential of a new encapsulation system has been evaluated as an artificial housing for liver cells. METHODS: Murine hepatocytes were encapsulated in specially designed multicomponent capsules formed by polyelectrolyte complexation of sodium alginate, cellulose sulphate and poly(methylene-co-guanidine) hydrochloride, the permeability of which has previously been characterised. RESULTS: We demonstrate here the absence of cytotoxicity and the excellent biocompatibility of these capsules towards primary culture of murine hepatocytes. Experimental results demonstrated that the encapsulated hepatocytes retained their specific functions--transaminase activity, urea synthesis and protein secretion--over the first 4 days of culture in minimum medium. The cryopreservation of encapsulated hepatocytes, for periods of up to 4 months, did not alter their functional capacities, as no major differences were observed between unfrozen and frozen encapsulated cells for the functions tested. CONCLUSIONS: Because of the absence of cytotoxicity, and the ease of handling and cryopreservation, while maintaining liver specific functions, the described system appears to be valuable for murine liver cell encapsulation. It is also a promising tool for fundamental research into drug metabolism, intercellular regulation, metabolic pathways, and the establishment of banks for the supply and storage of murine hepatocytes.

Development of a coculture model of encapsulated cells.

In the whole animal, metabolic regulations are set by reciprocal interactions between various organs, via the blood circulation. At present, analyses of such interactions require numerous and uneasily controlled in vivo experiments. In a search for an alternative to in vivo experiments, our work aims at developing a coculture system in which different cell types are isolated in polymer capsules and grown in a common environment. The signals exchanged between cells from various origins are, thus, reproducing the in vivo intertissular communications. With this perspective, we evaluated a new encapsulation system as an artificial housing for liver cells on the one hand and adipocytes on the other hand. Murine hepatocytes were encapsulated with specially designed multicomponent capsules formed by polyelectrolyte complexation between sodium alginate, cellulose sulphate and poly(methylene-coguanidine) hydrochloride, of which the permeability has been characterized. We demonstrated the absence of cytotoxicity and the excellent biocompatibility of these capsules towards primary culture of murine hepatocytes. Encapsulated hepatocytes retain their specific functions--transaminase activity, urea synthesis, and protein secretion--during the first four days of culture in minimum medium. Mature adipocytes, isolated from mouse epidydimal fat, were embedded in alginate beads. Measurement of protein secretion shows an identical profile between free and embedded adipocytes. We finally assessed the properties of encapsulated hepatocytes, cryopreserved over a periods of up to four months. The perspective of using encapsulated cells in coculture are discussed, since this system may represent a promising tool for fundamental research, such as analyses of drug metabolism, intercellular regulations, and metabolic pathways, as well as for the establishment of a tissue bank for storage and supply of murine hepatocytes.

New multicomponent capsules for immunoisolation.

A new generation of microcapsules based on the use of oligomers which participate in polyelectrolyte complexation reactions has been developed. These freeze-thaw stable capsules have been applied as a bioartificial pancreas and have resulted in normoglycemia for periods of six months in concordant xenotransplantations. The new chemistry permits the control of permeability and mechanical properties over a wide range and can be adapted both to microcapsule and hollow fiber geometries rendering it a robust tool for encapsulation in general. Methods, and metrics, for the characterization of the mechanical properties and permeability of microcapsules are presented.

Temperature-responsive size-exclusion chromatography using poly(N-isopropylacrylamide) grafted silica.

Silica-based packing materials induce non-specific interactions with proteins in aqueous media because of the nature of their surface, mainly silanol groups. Therefore, the silica surface has to be modified in order to be used as stationary phase for the High Performance Size-Exclusion Chromatography (HPSEC) of proteins. For this purpose, porous silica beads were coated with hydrophilic polymer gels (dextrans of different molecular weights) carrying a calculated amount of diethyl-aminoethyl groups (DEAE). Actually, as shown by HPSEC, these dextran modified supports minimize non-specific adsorption for proteins and pullulans in aqueous solution. Then, in order to change the pore size in response to temperature, temperature responsive polymer of poly(N-isopropylacrylamide) (PIPAAm) was introduced into the surface of dextran-DEAE on porous silica beads. The structure of these supports before and after modification was alternately studied by Scanning Electronic Microscopy (SEM) and Scanning Force Microscopy (SFM). An adsorption of radiolabelled albumin was performed to complete our study. Silica modifications by dextran-DEAE and PIPAAm improve the neutrality of the support and minimize the non-specific interactions between the solid support and proteins in solution. At low temperature, the support having PIPAAm exhibits a high resolution domain in HPSEC and finally permits a better resolution of proteins and pullulans. At higher temperature, hydrophobic properties of PIPAAm produce interactions with some proteins and trigger off a slight delay of their elution time.

Physical and biological effects of a surface coating procedure on polyurethane catheters.

Central venous catheters are widely used in clinical practice; however, complications such as venous thrombosis or infection are frequent. The physical and biological effects of a coating procedure designed to improve the blood-contacting properties of polyurethane central venous catheters (CVCs) were studied. The surface atomic composition of poly(vinyl pyrrolidone) (PVP)-coated or uncoated Pellethane single lumen CVCs was characterized by electron spectroscopy for chemical analysis (ESCA), which confirmed the presence of an oxygen-rich PVP layer on the former material. Topological analysis of both single and triple lumen CVCs by scanning force microscopy (SFM) revealed a very smooth surface in PVP-coated catheters compared to the more frequent surface irregularities found either in uncoated Pellethane or in four additional randomly selected, commercially available triple lumen polyurethane CVCs. The PVP-coated Pellethane showed a strong reduction in either fibrinogen or fibronectin adsorption compared to all other PVP-free polyurethane CVCs. This decreased protein adsorption led to a proportional reduction in protein-mediated adhesion of either Staphylococcus aureus or Staphylococcus epidermidis and in the binding of a monoclonal antibody directed against the cell-binding domain of fibronectin. Increased surface smoothness and hydrophilic properties of polyurethane CVCs might decrease the risk of bacterial colonization and infection.

Effect of toluene extraction on Biomer surface: I. ESCA, ATR/FTIR, contact angle analysis and biological properties.

Biomer is a poly(ether-urethane-urea) block copolymer widely used as biomedical devices. Extraction process of this polymer has purified its surface of low molecular weight polyurethane chains and Santowhite Powder additive. ESCA and ATR/FTIR have suggested a homogenization of the polymer by enrichment of the first layers with poly(aminomethacrylate) additive after extraction. Therefore, the surface of the extracted Biomer exhibits a different wettability and biological response. The treatment causes a significant decrease in fibronectin adsorption and induces a reduction in Staphylococcus aureus adhesion.

Effect of toluene extraction on Biomer surface: II. An atomic force microscopy study.

The surface characterization of Biomer and extracted Biomer has been investigated using atomic force microscopy (AFM) in order to show the influence of extraction process on the morphology and local interactions which monitor surface properties at a molecular scale. The high viscoelasticity of these polymers provided by the soft segments makes AFM imaging in contact mode quite difficult, the scanning of the tip inducing artifacts on the surface. The rate, direction, and number of scans strongly influence this friction effect. The recording of force curves has shown that the extraction and conditions of drying can modify the interaction forces present at the polymer surface. Imaging of the extracted Biomer obtained with AFM in non-contact mode has revealed inclusion nodules embedded in an amorphous phase. This may be attributed to the migration at the surface of the non-eliminated poly(aminomethacrylate) additive.