Effect of Recombinant Human Perlecan Domain V Tethering Method on Protein Orientation and Blood Contacting Activity on Polyvinyl Chloride

Surface modification of biomaterials is a promising approach to control biofunctionality while retaining the bulk biomaterial properties. Perlecan is the major proteoglycan in the vascular basement membrane that supports low levels of platelet adhesion but not activation. Thus, perlecan is a promising bioactive for blood-contacting applications. This study furthers the mechanistic understanding of platelet interactions with perlecan by establishing that platelets utilize domains III and V of the core protein for adhesion. Polyvinyl chloride (PVC) is functionalized with recombinant human perlecan domain V (rDV) to explore the effect of the tethering method on proteoglycan orientation and bioactivity. Tethering of rDV to PVC is achieved via either physisorption or covalent attachment via plasma immersion ion implantation (PIII) treatment. Both methods of rDV tethering reduce platelet adhesion and activation compared to the pristine PVC, however, the mechanisms are unique for each tethering method. Physisorption of rDV on PVC orientates the molecule to hinder access to the integrin-binding region, which inhibits platelet adhesion. In contrast, PIII treatment orientates rDV to allow access to the integrin-binding region, which is rendered antiadhesive to platelets via the glycosaminoglycan (GAG) chain. These effects demonstrate the potential of rDV biofunctionalization to modulate platelet interactions for blood contacting applications.

Factor XII activation markers do not reflect FXII dependence of thrombin generation induced by polyvinylchloride

The role of factor XII (FXII) as the main trigger of the coagulation cascade during haemodialysis has been recently challenged. Polyvinylchloride (PVC) is the standard polymer for haemodialysis circuit tubings, but its interaction with FXII has not been extensively characterized. In a modified Chandler tubing loop model using heparinized fresh human whole blood we selectively inhibited coagulation factors VII, X or XII with monospecific antibodies. Contact of whole blood with PVC induced a strong thrombin generation [thrombin-antithrombin complexes (TAT) 64 ± 24 μg/l, before <1 μg/l]. Despite this, levels of FXII coagulation activity, free FXIIa or FXIIa-C1 inhibitor complexes remained unchanged. The anti-FXII antibody abolished thrombin generation (TAT 8 ± 5 μg/l, P < 0.05) and made the free FXIIa undetectable. Inhibition of FVII did not affect coagulation activation (TAT 68 ± 26 μg/l). Our data provide definitive evidence that PVC triggers the coagulation system via FXII. However, all FXII activation markers in plasma failed to detect contact activation.

Surface modification of poly (L-lactide) by atmospheric pressure plasma treatment and cell response

This study investigated the influence of atmospheric pressure plasma treatment on the surface properties and cell response of poly(L-lactide) (PLLA) samples. The samples were analyzed by means of X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), micro- and nanosurface roughness, water contact angle, and zeta potential. Furthermore, cell adhesion assay and cell proliferation assay on the samples were carried out using MC3T3-E1 cells. Plasma treatment significantly increased the oxygen content of the samples and decreased the contact angle and zeta potential of the samples, resulting in hydrophilic surfaces. Further, plasma treatment of the samples also enhanced the number and growth of adhering MC3T3-E1 cells. These results therefore indicate that plasma treatment is effective for surface modification and cell responses.

Plasma protein adsorption and thrombus formation on surface functionalized polypyrrole with and without electrical stimulation

A surface modification technique was developed in which heparin was covalently immobilized onto electrically conductive polypyrrole (PPY) film through poly(ethylene glycol) methacrylate (PEGMA) graft copolymerization and subsequent cyanuric chloride activation. In vitro plasma protein adsorption and thrombus formation experiments were carried out on the various films. The PEGMA-graft-copolymerized PPY surfaces with immobilized heparin have good bioactivity indicated by low level of protein adsorption, high ratio of albumin to fibrinogen adsorption, and low thrombus formation, making them potentially good candidates for biomedical applications. Since the PPY film retained significant electrical conductivity after surface modification, the effect of electrical stimulation on protein adsorption and thrombus formation was also evaluated. The covalently immobilized heparin on the PPY film was able to retain its bioactivity after 4 days of immersion in PBS. The film after long-term immersion in PBS also retained sufficient electrical conductivity for electrical stimulation still to be effective for reducing protein adsorption.

Effect of complement inhibition and heparin coating on artificial surface-induced leukocyte and platelet activation

BACKGROUND

Exposure of blood to artificial surfaces, as in cardiopulmonary bypass, induces an inflammatory response involving complement, leukocyte and platelet activation. To elucidate the specific role of complement in this process, studies were performed on blood circulated in polyvinyl chloride tubing in the absence and presence of complement inhibitors. Parallel experiments were performed with heparin-coated polyvinyl chloride tubing, which is known to prevent complement and cell activation.

METHODS

A novel experimental model was used, based on human whole blood anticoagulated with lepirudin. Complement activation products, myeloperoxidase, lactoferrin, and thrombospondin were quantified in enzyme immunoassays. Leukocyte CD11b expression and leukocyte-platelet conjugates were detected by flow cytometry.

RESULTS

Increased levels of C3 activation products, alternative pathway convertase, and the terminal SC5b-9 complex, combined with unchanged levels of C1rs-C1-inhibitor complexes and marginal changes in C4 activation demonstrated that complement was activated through the alternative pathway. Granulocyte and monocyte CD11b expression and granulocyte-platelet conjugate formation were efficiently attenuated by blocking either factor D, C3, C5, or C5a receptor. In contrast, monocyte-platelet conjugate formation and release of myeloperoxidase, lactoferrin, and thrombospondin were not reduced by complement inhibition. Heparin-coated polyvinyl chloride tubing efficiently reduced all inflammatory markers studied, except for C1rs-C1-inhibitor complexes, which increased, consistent with the enhancing effect of heparin on C1-inhibitor function. This effect did not, however, reduce fluid-phase classic pathway activation induced by heat-aggregated immunoglobulin G.

CONCLUSIONS

Leukocyte and platelet activation in response to artificial materials occur by mechanisms that vary in their dependence on complement. Heparin coating precludes both the complement-dependent and complement-independent reactions.

APPROACHES TO QUOTIDIAN DIALYSIS: Bellco Formula Domus Home Care System

There are certain characteristics in a dialysis machine that would be desirable for use in home and limited care environments. These features relate to safety, ease of use, consideration of physical space, and reliability. The Bellco Formula Domus Home Care System was designed to meet all these requirements. Bellco's philosophy of patient treatment centers on global biocompatibility. This is evident in the design of the Formula Domus Home Care System. It has the smallest hydraulic fluid pathway of any dialysis machine on the market. Formula is capable of preparing ultrapure dialysate. The ultrafiltration measurement mechanism, the patented Coriolis flow meter, measures the mass of the dialysate, not the volume. For this reason it is the only dialysis machine that detects actual backfiltration, not just the theoretical possibility of it based on transmembrane pressure. The Coriolis flow meter also ensures that dialysate flow is a true single pass. The operator interface is a single window operating control. It is possible to select up to 14 different languages. There is an online help key to assist patients with troubleshooting. Programmable start-up and shutdown times save time for the patient. Formula is the only dialysis machine to offer a backup battery feature. Formula is capable of communicating with any software available. The focus on global biocompatibility ensures the best quality dialysis treatments for a population of patients who will likely remain on dialysis for a longer period of time than conventional dialysis patients.

Immobilization of a nonsteroidal antiinflammatory drug onto commercial segmented polyurethane surface to improve haemocompatibility properties

A method has been developed in which a layer of p-aminosalicylic acid (4-amino-2-hydroxybenzoic acid) (PAS), a water soluble pharmaceutical compound of the nonsteroidal anti-inflammatory drug (NSAID) class with antiaggregant platelet activity, is covalently immobilized onto a segmented polyurethane, Biospan (SPU) surface. Thus, SPU surfaces were modified by grafting of hexamethylenediisocyanate. and the free isocyanate remaining on the SPU surface were then coupled through a condensation reaction to amine groups of p-aminosalicylic acid. The bonding of PAS from aqueous solution onto SPU surface was studied by ATR-FTIR. UV and fluorescence spectroscopy. Plateau levels of coupled PAS were reached within 1.2 microg/cm2 using PAS solution concentrations of 1mg/ ml. The surface wettability of the polymeric films measured by contact angle indicate that the introduction of the PAS turns the surface more hydrophilic (theta(water) = 43.1 +/- 2.1) relatively to the original SPU films (theta(water) = 70.3 +/- 1.9). The in vitro albumin (BSA) adsorption shows that the PAS-SPU films adsorb more BSA (250/microgmm2) than the original SPU (112 microg mm2). Thrombogenicity was assessed by measuring the thrombus formation and platelet adhesion of the SPU containing PAS relatively to nonmodified SPU surfaces. The polymeric surfaces with immobilized PAS had better nonthrombogenic characteristics as indicated by the low platelet adhesion, high adsorption of albumin relatively to fibrinogen and low thrombus formation, making them potentially good candidates for biomedical applications.

Evaluation of a system for the perfusion of isolated, rodent organs

Perfusion of isolated organs is a common experimental approach. However, the surfaces of the perfusion system might alter the components of the blood and thereby negatively affect organ function. The aim of this study was to minimize the influence of the perfusion system on the blood components and to evaluate the system. Pressure and flow in the perfusion system consisting of a roller-pump, reservoir, oxygenator, hemo-filter and bubble-trap with a total tubing length of 4.5 m are controlled by a computer software (DASYLAB, Datalog, Moenchengladbach, Germany) via a transducer connected to the system. The organ to be perfused is positioned under a microscope (Orthoplan, Leica, Bensheim, Germany), allowing the investigation of microcirculatory parameters. The images raised are recorded on video tapes. To evaluate the system it was perfused with human blood (Hct 28 to 30%) for 90 min. Heparin (n = 6) or citrate (n = 6) served as anti-coagulants. The disappearance of cells from the blood was determined at time points 0, 1, 5, 10, 15, 20, 30, 45, 60, 75 and 90 min by means of a cell counter (AC T8, Coulter Beckmann, Krefeld, Germany). Cell activation was assessed by analysis of the expression of L- and P-selectin and CD11b. The activation of the complement system was examined by measuring the serum levels of the complement factors C3c and C4. There was no significant loss or activation of the blood cells at any of the above given time points. The serum levels of the complement factors remained within the physiological range and showed no changes throughout the whole experiments. Thus, the perfusion system does not have a negative influence on the blood and its individual components, and is therefore a reliable tool for perfusion experiments.

Blood tubing and cytokine production: effect of sterilization

Blood tubings commonly represent an integral component of hemodialysis circuits. Different factors may influence their biocompatibility, such as the type of material, the sterilization mode and the geometry. In vivo the final biocompatibility may be further complicated by the individual host response, the flow parameters, and the impact of mechanical trauma on blood's cellular components (i.e. erythrocytes). In this in vitro study we evaluated some commercially available blood tubings sterilized by different methods as to their interaction with normal leukocyte population and tested the response of these cells in terms of cytokines (IL-1beta, IL-1Ra, TNF-alpha). As a positive control, leukocytes were incubated with 0.5 ng/mL of bacterial lipopolysaccharide (LPS) or with Cuprophan of comparable surface. The results showed that cytokine production was markedly reduced, particularly in the case of gamma-ray-sterilized tubings. Of interest, it was not always related to the adherence. However in some cases, particularly of gamma-ray sterilization, adherence was none, despite the cytokine production.

Release of microparticles in LDL apheresis

Particle contamination of blood always takes place in extracorporeal systems and few studies have been conducted to evaluate potential risks. Particle concentration was measured in the efferent blood line on original equipment for two established LDL elimination procedures (DALI) (Fresenius) and Liposorber (Kaneka). Acquired data were compared with standards for infusion solutions from European (EP) and American (USP) Pharmacopoeia. All values were well below the given limits. Even in extreme situations (>20 pump stops) particle concentration did not exceed the standards. Considering an average treated blood volume of 7.31 for the DALI-System and 17.01 for Liposorber (long term clinical studies) the absolute amount of particles infused per treatment was 167,000 (DALI) and 465,000 (Liposorber) particles > or = 2 microm.

Particle release in extracorporeal low-density lipoprotein lowering therapies

Release of microparticles into the blood during extracorporeal circulation must be kept low because of possibly serious acute and chronic adverse effects. Concentration and size distribution of microparticles were measured during simulated treatments (n = 7) on original equipment for 2 standard low-density lipoprotein (LDL) elimination procedures (DALI 750, Fresenius AG, St. Wendel, Germany and Liposorber, Kaneka Corporation, Osaka, Japan) and compared to hemofiltration solutions. For both systems as well as in hemofiltration solutions, the mean particle concentrations in 500 ml portions gathered from the efferent blood line stayed below 10% of pharmacopoeia standards for infusion solutions (United States Pharmacopoeia, European Pharmacopoeia) in all measured size classes. Although particle concentrations were comparable in all systems, the mean total number of particles > or =2 microm released per session was lowest in the DALI (167,000) compared to the Liposorber (465,000) and hemofiltration solutions (2,240,000). This was mainly due to different total processed blood volumes necessary to achieve the required LDL reduction.

In vitro investigation of the blood response to medical grade PVC and the effect of heparin on the blood response

This paper reports the results of an investigation into the blood response of polymers in vitro, using non-anticoagulated and heparinised blood and plasma. The materials studied were regenerated cellulose, (Cuprophan), an acrylonitrile-allyl sulphonate copolymer (AN69S), and medical grade polyvinyl chloride plasticised with di-2-ethyl-hexyl-phthalate (PVC/DEHP). Blood-material or plasma-material contact was achieved using a parallel plate flow cell, and C3a generation and FXII-like activity measured. The results of the study with non-anticoagulated human blood show that PVC/DEHP is a high complement activator. C3a concentration in the blood was higher after contact with PVC/DEHP than after contact with regenerated cellulose. The introduction of heparin in the blood induced complex alterations in the blood response. C3a generation could be elevated, decreased, or remain the same, depending on the material. The FXII-like activity on the surface of the PVC/DEHP after contact with plasma was also higher than the other two polymers. The introduction of heparin could increase or decrease FXII-like activity, depending on material. The patterns of response obtained with non-anticoagulated blood in vitro for AN69S and Cuprophan bore a strong resemblance with patterns of response obtained in the clinic, whereas those obtained with heparinised blood in vitro did not.

Identification of plasticizers in medical products by a combined direct thermodesorption--cooled injection system and gas chromatography--mass spectrometry

The combination of a new thermodesorption module with a cooled injection system now provides a powerful system for direct analysis of volatile trace compounds in gaseous, liquid and solid samples by gas chromatography-mass spectrometry (GC-MS). As a cooled injection system is used for the cryofocusing of the desorbed volatiles the GC-MC system still can be used for the regular analysis of liquid samples. Although plasticizers usually are analyzed by GC-MS after solvent extraction, contaminated solvents and glassware are very well known problems. Analysis of plasticizers in plastic materials by direct thermodesorption instead saves time and avoids cross contaminations. Many medical products are made of plasticized polyvinyl chloride. Extraction of the common plasticizer di(2-ethylhexyl) phthalate (DEHP) into blood will occur, and harmful effects of DEHP in the human body have been suggested. We therefore analyzed 21 different plastic devices which are used for various invasive techniques in medicine by direct thermodesorption GC-MS. In some of the plastics up to 30 different components were identified. By far the most common plasticizer found was DEHP, followed by diethyl and dibutyl phthalates.

Considerations on developmental aspects of biocompatible dialysis membranes

Modern strategies in developing new polymers for dialysis membranes aim to improve their blood compatibility. To achieve such a goal, two approaches have been successfully applied: existing cellulosic polymers were modified, either by introducing functional groups through ester or ether bonds, by mixing synthetic polymers with bulk additives, or by using copolymerization techniques. As a detailed example, the first synthetically modified cellulose membrane, Hemophan, was prepared by substituting some hydrogen atoms in the cellulosic glucose unit by diethyl-amino-ethyl groups with the modification having a considerable impact on the membrane's hemocompatibility. It is further known that the hemocompatibility of hydrophobic synthetic membranes is improved by rendering these materials partially hydrophilic. We tested the hypothesis, whether the hemocompatibility of a material, which is hydrophilic per se, such as unmodified cellulose, is changed after the introduction of hydrophobic substituents. For this purpose, the number and nature of substituents have been systematically varied in order to alter surface properties, and these variations have been subsequently related to blood compatibility parameters. As expected, thrombin generation as well as complement- and cell-activation depend on the number and nature of the substituents whereby some of the substituents show a very narrow optimum if their hemocompatibility is related to the degree of substitution. Changes in hemocompatibility can be followed by physical methods, such as surface angle analyses and zeta potential determinations. Data show that alterations in the lipophilic/hydrophilic balance on the polymer surface may explain substituent-related changes in polymer hemocompatibility.(ABSTRACT TRUNCATED AT 250 WORDS)