Plasma gas discharge deposited fluorocarbon polymers exhibit reduced elutability of adsorbed albumin and fibrinogen

MyD88-dependent Toll-like receptor 2 signaling modulates macrophage activation on lysate-adsorbed Teflon™ AF surfaces in an in vitro biomaterial host response model

The adsorbed protein layer on an implanted biomaterial surface is known to mediate downstream cell-material interactions that drive the host response. While the adsorption of plasma-derived proteins has been studied extensively, the adsorption of damage-associated molecular patterns (DAMPs) derived from damaged cells and matrix surrounding the implant remains poorly understood. Previously, our group developed a DAMP-adsorption model in which 3T3 fibroblast lysates were used as a complex source of cell-derived DAMPs and we demonstrated that biomaterials with adsorbed lysate potently activated RAW-Blue macrophages via Toll-like receptor 2 (TLR2). In the present study, we characterized the response of mouse bone marrow derived macrophages (BMDM) from wildtype (WT), TLR2-/- and MyD88-/- mice on Teflon™ AF surfaces pre-adsorbed with 10% plasma or lysate-spiked plasma (10% w/w total protein from 3T3 fibroblast lysate) for 24 hours. WT BMDM cultured on adsorbates derived from 10% lysate in plasma had significantly higher gene and protein expression of IL-1β, IL-6, TNF-α, IL-10, RANTES/CCL5 and CXCL1/KC, compared to 10% plasma-adsorbed surfaces. Furthermore, the upregulation of pro-inflammatory cytokine and chemokine expression in the 10% lysate in plasma condition was attenuated in TLR2-/- and MyD88-/- BMDM. Proteomic analysis of the adsorbed protein layers showed that even this relatively small addition of lysate-derived proteins within plasma (10% w/w) caused a significant change to the adsorbed protein profile. The 10% plasma condition had fibrinogen, albumin, apolipoproteins, complement, and fibronectin among the top 25 most abundant proteins. While proteins layers generated from 10% lysate in plasma retained fibrinogen and fibronectin among the top 25 proteins, there was a disproportionate increase in intracellular proteins, including histones, tubulins, actins, and vimentin. Furthermore, we identified 7 DAMPs or DAMP-related proteins enriched in the 10% plasma condition (fibrinogen, apolipoproteins), compared to 39 DAMPs enriched in the 10% lysate in plasma condition, including high mobility group box 1 and histones. Together, these findings indicate that DAMPs and other intracellular proteins readily adsorb to biomaterial surfaces in competition with plasma proteins, and that adsorbed DAMPs induce an inflammatory response in adherent macrophages that is mediated by the MyD88-dependent TLR2 signaling pathway.

Trifluoromethyl-functionalized poly(lactic acid): a fluoropolyester designed for blood contact applications

Fluorinated polymers are strong candidates for development of new cardiovascular medical devices, due to their lower thrombogenicity as compared to other polymers used for cardiovascular implants.

Surface fluorination of polylactide as a path to improve platelet associated hemocompatibility

Surface-induced thrombosis is still a significant clinical concern for many types of blood-contacting medical devices. In particular, protein adsorption and platelet adhesion are important events due to their ability to trigger the coagulation cascade and initiate thrombosis. Poly(lactic acid) (PLA) has been the predominant polymer used for making bioresorbable stents. Despite long-term advantages, these stents are associated with higher rates of early thrombosis compared with permanent metallic stents. To address this issue, we modified the surface of PLA with a perfluoro compound facilitated by surface activation using radio frequency (RF) plasma. Fluoropolymers have been extensively used in blood contacting materials, such as blood vessel replacements due to their reduced thrombogenicity and reduced platelet reactivity. The compositions of plasma-treated surfaces were determined by electron spectroscopy for chemical analysis (ESCA). Also, contact angle measurements, cell cytotoxicity and the degradation profile of the treated polymers are presented. Finally, relevant blood compatibility parameters, including plasma protein adsorption, platelet adhesion and morphology, were evaluated. We hypothesized that tight binding of adsorbed albumin by fluoropolymers enhances its potential for blood-contacting applications.

STATEMENT OF SIGNIFICANCE

Although bioresorbable stents made from poly(lactic acid) (PLA) may have long-term clinical advantages, they have shown higher rates of early thrombosis as compared with permanent metallic stents. To improve the thromboresistance of PLA, we developed a novel method for surface fluorination of this polymer with a perfluoro compound. Fluoropolymers (e.g., expanded polytetrafluoroethylene) have long been used in blood-contacting applications due to their satisfactory clinical performance. This is the first report of PLA surface fluorination which might be applied to the fabrication of a new generation of fluorinated PLA stents with improved platelet interaction, tunable degradability and drug release capabilities. Also, we describe a general strategy for improving the platelet interactions with biomaterials based on albumin retention.

Blood compatibility assessment of polymers used in drug eluting stent coatings

Differences in thrombosis rates have been observed clinically between different drug eluting stents. Such differences have been attributed to numerous factors, including stent design, injury created by the catheter delivery system, coating application technologies, and the degree of thrombogenicity of the polymer. The relative contributions of these factors are generally unknown. This work focuses on understanding the thrombogenicity of the polymer by examining mechanistic interactions with proteins, human platelets, and human monocytes of a number of polymers used in drug eluting stent coatings, in vitro. The importance for blood interactions of adsorbed albumin and the retention of albumin was suggested by the data. Microscopic imaging and immunostaining enhanced the interpretation of results from the lactate dehydrogenase cell counting assay and provided insight into platelet interactions, total quantification, and morphometry. In particular, highly spread platelets may be surface-passivating, possibly inhibiting ongoing thrombotic events. In many of the assays used here, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) showed a differentiated protein deposition pattern that may contribute to the explanation of the consistently thromboresistant blood-materials interaction for fluororpolymers cited in literature. These results are supportive of one of several possible factors contributing to the good thromboresistant clinical safety performance of PVDF-HFP coated drug eluting stents.

Platelet adhesion to radiofrequency glow-discharge-deposited fluorocarbon polymers preadsorbed with selectively depleted plasmas show the primary role of fibrinogen

Fluorocarbon radio-frequency glow-discharge (RFGD) treatment has previously been shown to cause decreased platelet adhesion despite the presence of adsorbed fibrinogen on the surfaces. In this study platelet adhesion to fluorocarbon RFGD-treated surfaces preadsorbed with human plasma was further examined. A series of plasma deposited fluorocarbon thin films were made by varying the C3F6/CH4 ratio in the monomer feed. The surfaces were preadsorbed with plasma, serum, or plasma selectively depleted of fibronectin, vitronectin, or Von Willebrand factor, and platelet adhesion was measured. We also measured fibrinogen adsorption to the surfaces from plasma, monoclonal antibody binding to adsorbed fibrinogen and SDS elutability of the adsorbed fibrinogen. The antibodies used bind to the three putative platelet binding sites on fibrinogen, namely, M1 antibody binds to the dodecapeptide at the C-terminus of the gamma chain, gamma (402-411), R1 antibody binds to a sequence in the Aalpha chain (87-100) which includes RGDF at Aalpha (95-98) and R2 antibody binds a sequence in the Aalpha chain (566-580) which includes RGDS at Aalpha (572-575). Fibrinogen was found to play a decisive role in mediating platelet adhesion to the fluorocarbon surfaces contacting plasma. Few platelets adhered to the fluorocarbon surfaces preadsorbed with serum, while preadsorption with plasma selectively-depleted of either fibronectin, vitronectin, or von Willebrand factor did not decrease platelet adhesion significantly. Replenishment of exogenous fibrinogen to serum restored platelet adhesion, while replenishment of the other proteins had no effect. Platelet adhesion to the fluorocarbon surfaces was lower than to PET or the methane glow-discharge-treated PET. However, there was no apparent correlation between platelet adhesion and the amount of fibrinogen adsorption or monoclonal antibody binding to surface-bound fibrinogen.

Plasma modified surfaces for covalent immobilization of functional biomolecules in the absence of chemical linkers: towards better biosensors and a new generation of medical implants

Plasma modification and plasma polymer deposition are valuable technologies for the preparation of surfaces for the covalent binding of biomolecules for applications such as biosensors, medical prostheses, and diagnostic devices as well as surfaces for enzyme-mediated reactions. Covalency is conveniently tested by the ability of the surface to retain the attached molecules after vigorous washing with sodium dodecyl sulphate (SDS). Covalency is indicated if the fraction of protein retained lies above the curve characteristic of physisorption. Confidence in covalency is strengthened when the washing protocol is aggressive enough to remove all adsorbed protein from a control significantly more hydrophobic than the test surface. The use of linker chemistry to space the molecules from the surface is in some cases beneficial. However, the use of linker chemistry is not necessary to retain molecular function for long periods when the polymer surface is modified by energetic bombardment. The energetic bombardment retains hydrophilicity of the surface by crosslinking the subsurface, and this appears to facilitate retention of protein function. Energetic bombardment also increases the functional life of molecules immobilized and then freeze dried on plasma-modified surfaces. Analysis of the surfaces shows that the covalent binding mechanism is related to the presence of free radicals on the surface and in the subsurface regions. The unpaired electrons associated with the radicals appear to be mobile within the modified region and can diffuse to the surface to take part in binding interactions. Proactive implantable devices can make use of these principles of covalent attachment by seeding the surface of an implant with a biomolecule that elicits the desired interaction with cells and prevents undesirable responses.

Linker-free covalent attachment of the extracellular matrix protein tropoelastin to a polymer surface for directed cell spreading

Polymers are used for the fabrication of many prosthetic implants. It is desirable for these polymers to promote biological function by promoting the adhesion, differentiation and viability of cells. Here we have used plasma immersion ion implantation (PIII) treatment of polystyrene to modify the polymer surface, and so modulate the binding of the extracellular matrix protein tropoelastin. PIII treated, but not untreated polystyrene, bound tropoelastin in a sodium dodecyl sulfate (SDS)-resistant manner, consistent with previous enzyme-binding data that demonstrated the capability of these surfaces to covalently attach proteins without employing chemical linking molecules. Furthermore sulfo-NHS acetate (SNA) blocking of tropoelastin lysine side chains eliminated the SDS-resistant binding of tropoelastin to PIII-treated polystyrene. This implies tropoelastin is covalently attached to the PIII-treated surface via its lysine side chains. Cell spreading was only observed on tropoelastin coated, PIII-treated polystyrene surfaces, indicating that tropoelastin was more biologically active on the PIII-treated surface compared to the untreated surface. A contact mask was used to pattern the PIII treatment. Following tropoelastin attachment, cells spread preferentially on the PIII-treated sections of the polystyrene surface. This demonstrates that PIII treatment of polystyrene improves the polymer's tropoelastin binding properties, with advantages for tissue engineering and prosthetic design.

Adsorbed serum albumin is permissive to macrophage attachment to perfluorocarbon polymer surfaces in culture

Monocyte/macrophage adhesion to biomaterials, correlated with foreign body response, occurs through protein-mediated surface interactions. Albumin-selective perfluorocarbon (FC) biomaterials are generally poorly cell-conducive because of insufficient receptor-mediated surface interactions, but macrophages bind to albumin-coated substrates and also preferentially to highly hydrophobic fluorinated surfaces. Bone marrow macrophages (BMMO) and IC-21, RAW 264.7, and J774A.1 monocyte/macrophage cells were cultured on FC surfaces. Protein deposition onto two distinct FC surfaces from complex and single-component solutions was tracked using fluorescence and time-of-flight secondary ion mass spectrometry (ToF-SIMS) methods. Cell adhesion and growth on protein pretreated substrates were compared by light microscopy. Flow cytometry and integrin-directed antibody receptor blocking were used to assess integrins critical for monocyte/macrophage adhesion in vitro. Albumin predominantly adsorbs onto both FC surfaces from 10% serum. In cultures preadsorbed with albumin or serum-dilutions, BMMO responded similar to IC-21 at early time points. Compared with Teflon AF, plasma-polymerized FC was less permissive to extended cell proliferation. The beta(2) integrins play major roles in macrophage adhesion to FC surfaces: antibody blocking significantly disrupted cell adhesion. Albumin-mediated cell adhesion mechanisms to FC surfaces could not be clarified. Primary BMMO and secondary IC-21 macrophages behave similarly on FC surfaces, regardless of preadsorbed protein biasing, with respect to adhesion, cell morphology, motility, and proliferation.

Modulation of gene expression in neonatal rat cardiomyocytes by surface modification of polylactide-co-glycolide substrates

Myocardial tissue engineering presents a potential treatment option for heart disease. Cardiomyocytes isolated at various stages of development retain the ability to form contractile networks in vitro, which suggests that it should be possible to reconstitute viable myocardium given the appropriate architecture, stimuli, and cardiomyogenic cell source. This study investigates the effects of modifying substrate surface energy (by plasma etching) and protein coating (by fibronectin adsorption) on neonatal rat ventricular myocyte (NRVM) function. Primary NRVMs were cultured for 96 h on modified and control films of a common degradable polymer, polylactide-co-glycolide. Cultures were analyzed for cell spreading, protein content, and mRNA expression of atrial natriuretic factor and beta-myosin heavy chain. The results demonstrate that NRVMs cultured on etched films significantly increased in spreading, myofibril development, protein content, and gene expression of atrial natriuretic factor and beta-myosin heavy chain compared with unetched films, and that this surface energy effect is overwhelmed by the addition of fibronectin. Conclusions from this study are that surface energy and protein adsorption influence the gene expression of adherent NRVMs, and may be important for modulating the function of engineered myocardium.

Tissue-culture surfaces with mixtures of aminated and fluorinated functional groups. Part 2. Growth and function of transgenic rat insulinoma cells (betaG I/17)

Interactions of transplantable cells with synthetic polymers can influence the function of biohybrid artificial organs. This study explored growth and secretion of human insulin by betaG I/17 cells cultured on surfaces bearing diamine groups (N2), trifluoropropyl groups (F3) and mixtures of the two. Cells cultured on high-F3 and high-N2 surfaces spread well, grew rapidly and produced >1.8 mol lactate per mol glucose consumed, closely resembling cells grown on the permissive control, glass. On one mixed surface, with a molar ratio of 33 N2 groups:67 F3 groups, cells had a lower lactate/glucose ratio, adopted a rounded form, grew slowly and were quick to form emergent aggregates, similar to cultures on the inhibitory control, untreated polystyrene. Cultures on surfaces with higher F3 content secreted the most insulin and, in the case of the highest-F3 surface, showed improved responsiveness to secretagogues. Hormone secretion was roughly 50% greater when cells were grown on F3 surfaces conditioned by earlier cultures of betaG I/17. Incubation of conditioned surfaces with high concentrations of a polyclonal anti-laminin serum prior to re-plating partially abolished this improvement in secretory function. Polymers bearing trifluoropropyl groups appear to be attractive candidates for use in the artificial endocrine pancreas. Surface coatings that include laminin might promote function of transgenic insulinoma cells in vitro and in vivo.

Endothelialization of small-diameter vascular prostheses

In the field of arterial vascular reconstructions there is an increasing need for functional small-diameter artificial grafts (inner diameter < 6mm). When autologous replacement vessels are not available, for example because of the bad condition of the vascular system in the patient, the surgeon has no other alternative than to implant a synthetic polymer-based vessel. After implantation the initial major problem concerning these vessels is the almost immediate occlusion, due to blood coagulation and platelet deposition, under the relatively low flow conditions. As the search for the perfect bio-inert polymer has not revealed a material with suitable properties for this application, improved performance of small-diameter artificial blood vessels is now being sought in the biological field. The poor blood-compatibility of an artificial vascular graft is not simply because of its coagulation-stimulating or platelet-activating properties, but more due to its inability to actively participate in the prevention of blood coagulation and platelet deposition. As these functions are naturally performed by endothelial cells, the utilization of these cells seems inevitable for the construction of a functional small-diameter artificial blood vessels. This review describes the current status of the use of endothelial cells to improve the performance of artificial vascular prostheses.

Surface characterization and platelet adhesion studies on fluorocarbons prepared by plasma-induced graft polymerization

It is believed that the interactions between the biological environment and biomaterial surface are the key factors influencing its biocompatibility. Therefore, plasma processing, which can vary the surface properties without altering the bulk properties, has been considered as one of the important techniques for improving a materials' biocompatibility. In this investigation, plasma-induced grafting polymerization of vinylidene fluoride (VDF) and chlorotrifluoroethylene (CTFE), instead of direct plasma polymerization, was attempted with an aim to improve the substrate blood compatibility. Contact angle measurement indicated both fluorocarbon-grafted Pdyethylenes (PEs) are hydrophobic. Due to the additional fluorine and chlorine atoms on the CTFE chain, the PCTFE-grafted PE exhibited a higher hydrophobicity than the PVDF-grafted one. ESCA analysis has revealed that these two plasma-induced fluorocarbon deposits contain almost no CFx (x > 2) binding on the surface layer, indicating the grafting polymerization mainly follows the free radical mechanism instead of the molecule-highly-fragmented reaction steps commonly seen in the direct plasma polymerization treatment. In addition, ATR-FTIR has shown the surface chemical configuration of these PVDF- and PCTFE-grafted PEs to be very similar to those of the bulk samples of PVDF and PCTFE. The surface roughness decreased after oxygen plasma treatment and was further reduced by VDF and CTFE grafting polymerization. In vitro platelet adhesion testing indicated these two fluorocarbon grafted PEs are less platelet-activating than the nontreated PE control and oxygen plasma activated one.

Fibrinogen adsorption and host tissue responses to plasma functionalized surfaces

The physical and chemical characteristics of material surfaces are thought to play important roles in biomaterial-mediated tissue responses. To understand the importance of discrete biomaterial chemical characteristics in modifying host tissue responses, we constructed surfaces bearing different functional groups using radio frequency glow discharge plasma polymerization. Surfaces evaluated included those having high concentrations of -OH, -NH2, -CF3, and siloxyl groups. These surfaces and polyethylene terephthalate controls were used to assess the importance of particular physicochemical characteristics in surface:protein:cell interactions both in vitro and in vivo. The results obtained show that surface functionalities do significantly affect both the adsorption and "denaturation" of adsorbed fibrinogen (which is an important mediator of inflammatory responses to biomaterial implants). In addition, these surfaces provoke different degrees of acute inflammatory responses. Interestingly, the amounts of "denatured" fibrinogen that spontaneously accumulate on the individual surfaces correlate closely with the extent of biomaterial-mediated inflammation. These results suggest that surfaces that tend to "irreversibly" bind fibrinogen prompt greater acute inflammatory responses. Unexpectedly, all test surfaces except those bearing a siloxyl group engender relatively similar biomaterial-mediated fibrotic responses. Thus surface functionalities alone may not be sufficient to affect subsequent fibrotic responses.

Small-diameter vascular graft prostheses: current status

In contrast to large-diameter vascular grafts (i.e. larger than 5 mm) which remain excellent for more than 10 years after implantation, small-diameter vascular grafts of both Dacron and Teflon occlude rapidly upon implantation. In this overview article, the strategies used to improve the patency of these small-diameter grafts, the current status in clinical trials, and further perspectives in the field of artificial vascular graft development are reviewed. It is concluded that, in view of recent developments in tissue engineering approaches, the future of small-diameter vascular prostheses looks promising.

Covalent attachment and non-specific binding of reactive probe molecules onto surfaces

Optimization of strategies for the covalent attachment of proteins onto polymer surfaces requires the development of analytical methods which can differentiate between proteins that are covalently attached and those that are non-covalently bound (physisorbed). We probed for the surface density of reactive amine, carbonyl, and hydrazide groups using solution phase derivatization reactions to mimic and explore protein immobilization reaction strategies. Labeling compounds investigated were fluorescein derivatives, which were quantified by adsorption spectroscopy, and fluorinated phenyl compounds which were quantified by XPS. Control experiments consisted of performing the same labeling reactions using surfaces without reactive groups, or immersing the polymer surface into the labeling solution after blocking the reactive group of the labeling compound by a covalent reaction in solution. We always found non-negligible contributions arising from physisorption of the derivatization labels. Multiple control surfaces and a novel 'crossover derivatization-XPS' method were studied with the aim of improving compensation for physisorption. Our documentation of surprisingly large physisorption components even for small molecule labels, together with the known propensity of proteins to adsorb onto polymers, suggests caution in quantitative analysis of surface groups by derivatization, and in interpreting covalent protein immobilizations onto polymeric surfaces.

Platelet and monoclonal antibody binding to fibrinogen adsorbed on glow-discharge-deposited polymers

The state of fibrinogen adsorbed on untreated and glow-discharge-treated surfaces was examined by measuring platelet adhesion, monoclonal antibody (mAb) binding, the amount of fibrinogen adsorbed, and the amount of adsorbed fibrinogen which could be eluted with sodium dodecyl sulfate (SDS). Tetrafluoroethylene (TFE) glow-discharge-treated polymers have a lower surface free energy (in air) and retain a larger fraction of adsorbed fibrinogen than untreated surfaces after SDS elution. Platelet adhesion was lowest on the TFE-treated surfaces which retain the highest amounts of fibrinogen after SDS elution. Fibrinogen may undergo unfolding or spreading on the TFE-treated surfaces to minimize interfacial free energy (in water) and maximize protein-surface interactions. When it is adsorbed on the TFE-treated surfaces, fibrinogen evidently assumes a state which somehow prevents its recognition and binding by platelet receptors. Monoclonal antibodies that bind to the three regions in fibrinogen thought to be involved in platelet adhesion were therefore used to detect changes in adsorbed fibrinogen. These regions and the antibodies which bind to them are: the COOH-terminal of the gamma-chain, mAb M1; the RGD peptide sequence at A alpha 95-98, mAb R1; the RGD sequence at A alpha 572-575, mAb R2. For fibrinogen adsorbed on the untreated or TFE-treated surfaces, M1 and R2 binding was relatively high compared to background, while R1 binding was low. However, the amount of binding of each mAb to fibrinogen adsorbed on the TFE-treated surfaces was equal to or greater than fibrinogen adsorbed to the untreated surfaces. Therefore, antibody-detectable changes in the platelet binding regions of adsorbed fibrinogen that might have been caused by conformational or orientational rearrangements were not observed for the TFE-treated surfaces. The data suggest that the tight binding of fibrinogen on a surface may directly affect the ability of the fibrinogen to interact with the platelet receptors--i.e., that fibrinogen must be loosely held to facilitate maximal interaction with platelet receptors.

Surface and blood-contacting properties of alkylsiloxane monolayers supported on silicone rubber

Self-assembled monolayers of alkylsiloxanes supported on polydimethyl siloxane (PDMS) rubber were used as model systems to study the relation between blood compatibility and surface chemistry. The inner lumen of PDMS tubes was first treated with an oxygen plasma. The resultant oxidized surfaces were postderivatized by reacting them with alkyltrichlorosilanes to form the monolayer films. The chemical properties of the monolayers were controlled by varying the head-group chemical compositions. Surface derivatization was verified using variable-angle X-ray photoelectron spectroscopy (XPS or ESCA). Blood compatibility was evaluated using a canine ex vivo arteriovenous series shunt model. Surfaces grafted with hydrophobic head-groups as -CH3 and -CF3 had significantly lower platelet and fibrinogen deposition than the surfaces composed of hydrophilic groups such as -CO2CH3, -(CH2CH2O)3COCH3, and -(OCH2CH2)3OH.

Molecular surface tailoring of biomaterials via pulsed RF plasma discharges

A pulsed RF plasma glow discharge is employed to demonstrate molecular level controllability of surface film deposits. Molecular composition of plasma deposited films is shown to vary in a significant manner with the RF duty cycle. Three fluorocarbon monomers are used to illustrate the process. All three exhibit a trend towards increased surface CF2 content with decreasing pulsed RF duty cycle, including exclusion of oxygen. Significant variations in carbon-fluorine surface functionalities are obtained over a controllable range of film thickness. Film growth rate measurements reveal the occurrence of surface reactions during significant portions of the off portion of the duty cycle. Albumin adsorption on fluorocarbon-treated PET films is unchanged from PET controls for a 100-fold range of bulk concentrations and 60-fold range of adsorption times. However, increased retention of albumin is observed following incubation with protein-denaturing sodium dodecyl sulfate solution, the retention decreasing with increasing bulk concentration of albumin. The increased retention of albumin suggests the treated surfaces may have promise as biocompatible materials.

Synthesis and nonthrombogenicity of fluoroalkyl polyetherurethanes

New polyetherurethanes carrying fluoroalkyl substituents in the side chains were synthesized from N,N-di(hydroxyethyl)heptadecafluorooctyl-sulfonamide (a chain extender), 4,4'-disocyanatodiphenylmethane, and poly(tetramethylene glycol). Various kinds of polyetherurethanes having different tensile properties were prepared by changing the content of fluoroalkyl chain extender or the molecular weight of poly(tetramethylene glycol). The surface of a film made from the fluoroalkyl polyetherurethane was strongly water-repulsive. The in vitro thrombus formation on the fluoroalkyl polyetherurethanes was reduced by increasing the content of chain extender for the same molecular weight of poly(tetramethylene glycol). Protein adsorption, platelet adhesion, and platelet activation on the fluoroalkyl polyetherurethanes were also investigated.

Activity of horseradish peroxide adsorbed on radio frequency glow discharge-treated polymers

Horseradish peroxidase (HRP) has been used as a model enzyme in this study of its physical adsorption and residual enzyme activity on radio frequency glow discharge (RFGD)-treated polymers. The specific enzymatic activity of HRP adsorbed on different surfaces was assumed to be an indication of the extent of its conformational alterations on the surfaces. The surfaces studied were poly (ethylene terephthalate) (PET), polytetrafluoroethylene (PTFE), and tetrachloroethylene and tetrafluoroethylene glow discharge-treated PET, abbreviated as TCE/PET and TFE/PET. All surfaces were characterized by electron spectroscopy for chemical analysis (ESCA) and liquid contact angles in air. HRP adsorbs more strongly onto the two discharge-treated surfaces than onto the untreated polymers, as evidenced by the lower amount of HRP eluted by sodium dodecyl sulfate (SDS) from the treated polymers. For example, seventy percent of the HRP adsorbed on TCE/PET or TFE/PET remains on the surface after overnight elution with a 1% solution of SDS. In contrast, untreated PET and PTFE each retains only c. 20% of the absorbed enzyme. The enzymatic activity of HRP adsorbed on the different surfaces was studied using hydrogen peroxide (H2O2) as the substrate. HRP adsorbed on the higher energy surfaces, PET and TCE/PET, retains significantly more activity than the HRP adsorbed on the lower energy surfaces, PTFE and TFE/PET which appear to destroy rapidly almost all of the activity of HRP after it adsorbs. HRP adsorbed on TCE/PET is relatively more stable over time than HRP adsorbed on PET or free HRP in solution. (For example, only 45% of the specific enzymatic activity of HRP adsorbed on TCE/PET was lost after 3 h of storage in phosphate buffer at 37 degrees C, while 70% of that adsorbed on PET was lost.) In summary, when HRP is adsorbed on TCE/PET, it is very tightly bound, and yet it maintains a significant fraction of its initial specific activity and also retains this activity for 3 h in phosphate buffer at 37 degrees C. Thus, tenacious physical adsorption of proteins such as enzymes on TCE glow discharge-treated surfaces may have potential as a new method of immobilization of such molecules, for uses in biosensors, diagnostics, bioseparations, cell culture and bioreactors.

Growth of human cells on plasma polymers: putative role of amine and amide groups

The attachment and growth of human endothelial cells and fibroblasts was studied on polymer surfaces fabricated by the polymerization of volatile amine and amide compounds in a low pressure gas plasma, and by the treatment of various surfaces in ammonia plasmas, which served to increase the nitrogen content of the surface layers. Infrared spectra showed the presence of amide groups, including those cases where the volatile compound ('monomer') did not contain oxygen. The performance of the surfaces in cell attachment correlated with the surface hydrophilicity and the nitrogen content, although for the latter a fair degree of scatter indicated that a more complex relationship applies. All these surfaces supported the attachment and growth of human cells. Generally, amide plasma polymers were best but the individual monomer and the plasma parameters also played a role. From comparisons of the various surfaces, it is suggested that the amide group is the main promoter of cell attachment in nitrogen-containing plasma surfaces.