Surface modification of the polymers present in a polysulfone hollow fiber hemodialyser by covalent binding of heparin or endothelial cell surface heparan sulfate: Flow characteristics and platelet adhesion

The present study addresses the problem of simultaneous surface modification of various polymers, i.e. polysulfone (PSU), polycarbonate (PC), and polyurethane (PU), which constitute the Ultraflux AV 600 S® hollow fibre hemodialyser. An investigation was first made into six different chemical routes aimed at introducing carboxyl groups onto the surface of PSU, PC, and PU model polymers to which heparin (HE) or endothelial cell surface heparan sulfate (ESHS) was covalently bound via the reaction of residual amino groups and a coupling reagent. Carboxyl groups were introduced using three specific reactions based on their nucleophilic or electrophilic introduction into aromatic repeating units of the polymers and three non-specific carboxylation reactions, i.e. UV, heat or redoxactivation via nitrene or radical species. Concentrations of 1-20 nmol COOH groups per cm^-2 led to HE or ESHS surface concentrations corresponding to one or several layers. Two nonspecific carboxylation reactions followed by HE- or ESHS-coupling provided the lowest change in membrane pore structure according to cut off, clearance (urea, phosphate, maltose), ultrafiltration, and diafiltration assessments. In some cases the introduction of excess negatively-charged carboxyl groups and HE improved the flux properties of the modified membranes. The various methods were applied to the dialysis module. Platelet adhesion was not observed in the case of the ESHS-coating of PSU membrane at shear rates of 1050 s^-1, whereas HE and subendothelial matrix showed 56 and 100% coverage, respectively, under similar conditions. The coating of PSU or of other highflux membranes by ESHS appears a promising method for improving membrane properties and to generate biocompatibility characteristics similar to those of natural blood vessels, i.e. inertness to platelet adhesion and no level effects for complement and intrinsic coagulation cascade activation. The ESHS coating may be used without anticoagulants.     

Assembly properties and applications of a new exopolymeric compound excreted by Pseudoalteromonas antarctica NF3

The self assembly properties and applications of an exopolymeric compound (EC) of a glycoprotein character excreted by a new Gram-negative species, Pseudoalteromonas antarctica NF₃, have been reviewed. This compound exhibited surface-active properties in water, with a concentration of 0.20 mg ml^-1 being the key value associated with its physicochemical properties. Unsonicated EC aqueous dispersions showed the coexistence of concentric multilamellar and small unilamellar aggregates by transmission electron microscopy (TEM). Sonication of these dispersions revealed that each lamellae of the initial multilamellar structures were made up of various subunits coiled coils. As for the ability of this exopolymeric biomaterial to coat phosphatidylcholine (PC) liposomes and to protect these vesicles against different surfactants, freeze-fracture TEM micrographs of liposome/EC aggregates revealed that the addition of the EC to liposomes led to the formation of a film (polymer adsorbed onto the bilayers) that coated very well the PC bilayers. The complete coating was already achieved at a PC : EC weight ratio of about 9 :1. An increasing resistance of PC liposomes to surfactants (in particular sodium dodecyl sulfate) occurred as the proportion of EC in the system rose, although this effect was more effective at low EC proportions (PC : EC weight ratios from 9 : 1 to 8 : 2). Although a direct dependence was found between the growth of the enveloping structure and the resistance of the coated liposomes to be affected by the surfactants, the best protection occurred when this structure was a thin film of about 20-25 nm formed by nine to ten layers of about 2-3 nm.     

Changes in morphology of starch-based prothestic thermoplastic material during enzymatic degradation

This work evaluates the structural changes of an interpenetrated starch thermoplastic blend withstanding different enzymatic α-amylase degradation periods (up to 200 days), and establishes the relationships between the kinetics degradation rate and the structure of the material. It characterises the different stages of the enzymatic degradation process on starch/ethylenevinyl-alcohol blends, based on the attack of the connected starch domains that can be accessed by the enzymatic solution. The completely encapsulated starch particles remain practically unchanged. Furthermore, it was also found that the enzymatic degradation process was limited after 100 days of immersion. In order to understand such phenomenon several techniques were used, namely differential scanning calorimetry, contact-angle measurements, high-performance liquid chromatography, Fourier transform infrared spectrometry, scanning electron microscopy and atomic force microscopy. The materials were evaluated with respect to the enzymatic degradation rate, surface morphology and degradation behaviour. The results show that the ethylene-vinylalcohol phase wraps the starch domains, preventing the respective degradation. Consequently, the degraded material in the solution comes only from the starch particles that could be reached by the enzyme.     

Polymerization and surface analysis of electrically-conductive polypyrrole on surface-activated polyester fabrics for biomedical applications

A new synthetic route is reported for the synthesis and covalent bonding of electrically conductive polypyrrole to a poly(ethylene terephthalate) fabric. It involves a three-step process including surface phosphonylation and graft polymerization from the gaseous phase. In the first step, the fibre surfaces are activated using phosphorus trichloride. Then, 1-(3-hydroxypropyl) pyrrole is introduced and grafted to the phosphorus chloride to create an ester bond between the fibres and the pyrrole. Finally, the pyrrole-grafted fibres are dipped in an aqueous FeCl₃ catalyst and exposed to pyrrole monomer vapor for the final polymerization. This last step creates an electrically conductive polypyrrole layer covalently linked to the poly(ethylene terephthalate) fibres. ESCA analysis indicates a high degree of phosphonylation and grafting of the anchor molecules. Scanning electron microscopy reveals an overall smooth and uniform surface coating of polypyrrole on the polyester fibres. The use of ATR-FTIR spectroscopy is not able to distinguish between polypyrrole-coated and non-coated fabrics because of the extremely thin polypyrrole layer. Measurements of dynamic surface wetting indicated that the polypyrrole-coated fabric is more hydrophilic than the untreated control. With values for surface resistivity in the range 10⁴-10⁵ Ω/square, such polypyrrole-coated fabrics are considered attractive candidates for biomedical applications.     

Elevated Lead Contamination in Boat-caulkers' Homes in Southern Thailand

Abstract

Surface-wipe lead loading was measured at various locations in the homes of 31 boat-caulkers and 31 location-matched controls to identify factors associated with household lead contamination. Data were obtained by observation checklist and questionnaire. Lead loading was significantly higher in caulkers' than in control households. Median lead loadings (in μg/ft²) of various locations in caulkers' homes were windowsill, 43.9; exterior entrance, 9.5; interior entrance, 21.1; living room floor, 9.8; and bedroom floors 15.6. Corresponding levels in control homes were all less than 0.2 μg/ft². Regression modeling indicated that lead loading was higher in caulkers' homes that were closer to a boatyard, in which the caulker had a longer duration of boatyard work, and in which there were no children aged under 6 years resident. Exterior and interior entrance and living room floors had lower lead loading than windowsills. However, bedroom floors had significantly higher lead loading, similar to windowsills.     

Protein-Resistant Materials via Surface-Initiated Atom Transfer Radical Polymerization of 2-Methacryloyloxyethyl Phosphorylcholine

Poly(2-methacryloyloxyethyl phosphorylcholine) (poly(MPC)) was grafted from various polymeric substrates to prepare protein-resistant materials. The poly(MPC) chain length was adjusted via the ratio of monomer to sacrificial initiator in solution. The surfaces were characterized by water contact angle and X-ray photoelectron spectroscopy (XPS). The protein-resistant properties of the poly(MPC)-grafted surfaces were evaluated by single adsorption experiments with fibrinogen and lysozyme. It was shown that the simple three-step grafting method could be applied to modify various biomaterial surfaces including polyurethane and silicones. The adsorption of fibrinogen and lysozyme to the modified surfaces was greatly reduced compared to the unmodified surfaces, and adsorption decreased with increasing poly(MPC) chain length. On polyurethane film grafted with poly(MPC) of chain length 100, the reduction in adsorption was approx. 96% for lysozyme and approx. 99% for fibrinogen.     

Hydrogel-microsphere-enhanced surface plasmon resonance for the detection of a K-ras point mutation employing peptide nucleic acid

Highly-sensitive detection of a K-ras point mutation in codon 12, frequently found in pancreatic cancer, based on DNA-carrying hydrogel microspheres as a response enhancer for surface plasmon resonance (SPR), is described. Acrylamide-based microspheres with carboxyl groups were conjugated with DNA probes. Use of the DNA-carrying microsphere in the sandwich method, that is, binding of the microspheres with target DNAs at the sensor surface, enhanced the SPR response as a combined result of increased dielectric constant by the DNA-carrying microspheres. Microspheres lead to response enhancement, as shown by a 100-fold increase in sensitivity compared to that of non-amplified DNA target hybridization. In addition, the advantage of peptide nucleic acid (PNA) in the detection of a K-ras point mutation at the sensor surface by increasing temperature and flow rate is discussed. Results illustrate that the sandwich method through DNA-carrying microspheres for a SPR sensor is a promising approach for ultrasensitive DNA detection.     

Serum protein adsorption and platelet adhesion on aspartic-acid-immobilized polysulfone membranes

Polysulfone (PSf) membranes that covalently conjugated with aspartic acid (ASP-PSf) were prepared and analyzed for hemocompatability. Compared to PSf or other types of surface-modified PSf membranes, the ASP-PSf membranes had a reduced ability to adsorb protein from either a plasma solution or a mixed solution of albumin, globulin and fibrinogen. This appears to be due to the creation of a hydrophilic surface by the aspartic acid zwitterion immobilized on the ASP-PSf membranes. Furthermore, the analyses of membrane protein adsorption showed that a mixed protein solution recapitulates the cooperative adsorption of proteins that occurs in plasma. We also found that the number of adhering platelets was the lowest on the ASP-PSf membranes and, in general, that platelet adhesion decreased in parallel with fibrinogen adsorption. In summary, aspartic acid immobilized on the ASP-PSf membranes, which have zwitterions with a net zero charge, effectively contributes to the hydrophilic and hemocompatible sites on the surface of the hydrophobic PSf membranes.     

Surface properties of PEO–silicone composites: reducing protein adsorption

Silicone-based polymers with reduced protein adsorption were successfully prepared by incorporating mono- or bifunctional poly(ethylene oxide) (PEO) derivatives, respectively, into PDMS during rubber formation using classic room temperature vulcanization chemistry. Characterization of the films by water contact-angle measurements and XPS showed that the PEO was present on the film surface, with greater amounts of PEO at the interface modified with monofunctional PEO. Scanning electron microscopy showed the PEO domains segregated into regular zigzag patterns on the PEO-modified surfaces. Significant reductions in the adsorption of fibrinogen, albumin and lysozyme were observed on both PEO-modified surfaces, although the monofunctional PEO surfaces performed much better in this regard. The reductions in protein adsorption were comparable for all three proteins on both surfaces, suggesting that molecular mass of the protein is not a significant factor in determining the magnitude of protein deposition. Western blot studies showed that the adsorption of proteins from plasma to the monofunctional PEO-modified surfaces was also significantly reduced and surprisingly selective, with very few bands noted relative to the control surfaces and those modified with bifunctional PEO.     

Effects of Chitosan-Coated Fibers as a Scaffold for Three-Dimensional Cultures of Rabbit Fibroblasts for Ligament Tissue Engineering

Material selection in tissue-engineering scaffolds is one of the primary factors defining cellular response and matrix formation. In this study, we fabricated chitosan-coated poly(lactic acid) (PLA) fiber scaffolds to test our hypothesis that PLA fibers coated with chitosan highly promoted cell supporting properties compared to those without chitosan. Both PLA fibers (PLA group) and chitosan-coated PLA fibers (PLA–chitosan group) were fabricated for this study. Anterior cruciate ligament (ACL) fibroblasts were isolated from Japanese white rabbits and cultured on scaffolds consisting of each type of fiber. The effects of cell adhesivity, proliferation, and synthesis of the extracellular matrix (ECM) for each fiber were analyzed by cell counting, hydroxyproline assay, scanning electron microscopy and quantitative RT-PCR. Cell adhesivity, proliferation, hydroxyproline content and the expression of type-I collagen mRNA were significantly higher in the PLA–chitosan group than in the PLA group. Scanning electron microscopic observation showed that fibroblasts proliferated with a high level of ECM synthesis around the cells. Chitosan coating improved ACL fibroblast adhesion and proliferation, and had a positive effect on matrix production. Thus, the advantages of chitosan-coated PLA fibers show them to be a suitable biomaterial for ACL tissue-engineering scaffolds.