Trypsinated (immobilized) nylon surfaces: antithrombogenicity

An attempt is made to immobilize low molecular weight trypsin on nylon surface and to evaluate how such surfaces affect blood compatibility by investigating variations in surface energy parameters, plasma recalcification time and platelet adhesion using calf’s blood.     

Surface treatment of polycarbonate and polyethersulphone for SiNx thin film deposition

Silicon nitride thin films were deposited with good adhesion on plasma treated polyethersulphone (PES) and polycarbonate (PC) substrates by in-situ rf magnetron sputtering. The surfaces of the PES and PC substrates were performed by plasma treatment at various rf powers and processing time in Ar, O₂ atmosphere. From the X-ray Photoelectron Spectroscopy (XPS) examination of the surface of the treated substrates, it was found that the ratio of oxide containing bonds increased with increasing rf power. The surface roughness of the PES and PC substrates increased with increasing rf power. The plasma treated surface of the substrates became hydrophilic as measured by the water contact angle. The water contact angle for the PES and PC substrates decreased with increasing rf power and processing time, significantly. The lowest value of the contact angle of 14.09° was observed at rf power of 200 W. It was observed that the adhesion properties between the SiN_x films and substrates were enhanced by the plasma treatment.     

Fig tree sap: antithrombogenicity on nylon surfaces

An effort is made to study the anti-thrombogenic property of the latex of fig tree by immobilizing its components on nylon surface. It is also evaluated, how such surfaces may effect the blood compatibility by investigating variations in surface energy parameters, plasma recalcification time and platelet adhesion using calf’s blood.     

Surface and bioproperties of nanocrystalline diamond/amorphous carbon nanocomposite films

Nanocrystalline diamond/amorphous carbon (NCD/a-C) nanocomposite films have been deposited by microwave plasma chemical vapour deposition from CH₄/N₂ mixtures. In order to investigate their suitability as templates for the immobilization of biomolecules, e.g. for applications in biosensors, four differently prepared surfaces, namely as-grown, hydrogen plasma treated, oxygen plasma treated, and chemically treated with aqua regia, have been thoroughly characterized by methods such as XPS, TOF-SIMS, AFM, and contact angle measurements. In addition, in order to investigate the affinity of these surface to non-specific bonding of biomolecules, they have been exposed to bovine serum albumin (BSA). It turned out that already the as-grown surface is hydrogen terminated; the degree of the termination is even slightly improved by the hydrogen plasma treatment. Reaction with aqua regia, on the other hand, led to a partial destruction of the H-termination. The oxygen plasma treatment, finally, causes a termination by O and OH, rather than by carboxylic acid groups. In addition, an increase of sp² bonded carbon is observed. All surfaces were found to be susceptible to attachment of BSA proteins, but the coverage of the hydrogen terminated was lower than that of the O-terminated film. The highest BSA concentrations were found for the aqua regia sample where the H-termination has been removed partially. Finally, our results show that even minor surface contaminations have a great influence on the BSA coverage.     

Glutaraldehyde proteinated surfaces: blood compatibility

This paper reports our attempts to crosslink low molecular weight proteins namely trypsin and insulin using glutaraldehyde on polycarbonate surface and to evaluate how such surfaces may affect the blood compatibility of the polymer, by studying the interfacial energies of the modified polymer surface using advancing contact angle technique. The plasma recalcification time and platelet adhesion studies were also carried out. It has been observed that such low molecular weight proteins retard clotting.     

Characterization and tribological evaluation of duplex treatment by depositing carbon nitride films on plasma nitrided Ti-6Al-4V

Carbon nitride (CN_X) films (with N/C ratio of 0.5) were deposited on both untreated and plasma nitrided Ti-6Al-4V substrates by D.C. magnetron sputtering using a graphite target in nitrogen plasma. TEM and XPS analysis revealed the formation of both amorphous CN_X structure and crystalline -C₃N₄ phases in the deposited coatings. Nano-indentation tests showed that the film hardness was about 18.36 GPa. Both the scratch tests and indentation tests showed that compared with CN_X film deposited directly on Ti-6Al-4V, the load bearing capacity of CN_X film deposited on plasma nitrided Ti-6Al-4V was improved dramatically. Ball-on-disk wear tests under both dry sliding and lubricated conditions (with simulated body fluids) were performed to evaluate the friction and wear characteristics of the deposited coatings. Results showed that under both dry and lubricated conditions, the duplex treated system (i.e., with CN_X film deposited on plasma nitrided Ti-6Al-4V substrate) was more effective in maintaining a favorable low and stable coefficient of friction and improving wear resistance than both individual plasma nitriding and CN_X films on Ti-6Al-4V substrate. Under dry sliding conditions, the generated wear debris of spalled films were accumulated on the wear track, mechanically alloyed and graphitized, thus significantly reducing the coefficient of friction and preventing wear of the substrate. However, under lubricated conditions, due to the flowing of the fluids, the lubricating wear debris was taken away by the fluids, and therefore, the direct contact of two original surfaces resulted in high coefficient of friction and extensive abrasive wear of the substrate for CN_X films deposited on Ti-6Al-4V substrate. Also when there was some small-area spallation of CN_X films, the fluids could seep into the interface between the film and substrate, thus degrading the interfacial adhesion and resulting in a large area spallation.     

Glow discharge plasma-induced immobilization of heparin and insulin on polyethylene terephthalate film surfaces enhances anti-thrombogenic properties

Polyethylene terephthalate (PET) films were treated with DC glow discharge plasma followed by graft copolymerization with acrylic acid (AA) and polyethylene glycol (PEG). The obtained PET–PEG was coupled to heparin or insulin molecules. The surfaces were then characterized by contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The surface energies of the modified PET films were estimated using contact angle measurements, and the changes in crystallinity of the plasma-modified PET film surfaces were investigated by X-ray diffraction (XRD) analysis. The blood compatibilities of the surface-modified PETs were examined by in vitro thrombus formation, whole blood clotting time, platelet contact and protein adsorption experiments. The results revealed that the contact angle value decreased and that the interfacial tension between the modified PET films and blood protein was drastically diminished compared to unmodified PET film. The XPS results showed that the PET–AA surface containing carboxylic acid and the immobilized PET surface containing both carboxylic acid and amino groups exhibited a hydrophilic character, and AFM results showed marked morphological changes after grafting of AA, PEG and biomolecule immobilization. Heparin and insulin-coupled PET surfaces exhibited much less platelet adhesion and protein adsorption than the other surface-modified PET film surfaces.     

Blood compatibility of gas plasma-treated diamond-like carbon surface—Effect of physicochemical properties of DLC surface on blood compatibility

From the knowledge that zwitterion-type polymers show good blood compatibility, the introduction of both cationic and anionic functional groups onto diamond-like carbon (DLC) surface is expected to improve blood compatibility. Thus, DLC films were treated with oxygen and ammonia gas plasmas. The surfaces were characterized in terms of chemical composition by XPS, contact angle, and zeta potential. XPS analysis showed the introductions of a carboxyl group by oxygen plasma treatment and nitrogen atoms by ammonia plasma treatment. The evaluation of blood compatibility for the DLC surfaces was carried out in terms of platelets and the coagulation system. Excellent improvement of platelet compatibility was observed by the treatment with the gas plasmas, regardless of the plasma species. As for the compatibility with the coagulation system, DLC surfaces with a high concentration of carboxyl groups (COOH) markedly activated the system via the intrinsic pathway. However, the surfaces treated with ammonia plasma did not activate the system even though they had high COOH concentration. Measurement of the zeta potential revealed that the ammonia plasma treatment raised the potential from a negative value to a positive one. Though the introduction of amino groups to the surface was not detected directly, the treatment of ammonia plasma changed the electrical state of the DLC surface having COOH group, causing a difference in blood compatibility among the DLCs obtained by various plasma conditions.     

TiN/TiC multilayer films deposited by pulse biased arc ion plating

TiN/TiC multilayer films were deposited on high-speed-steel (HSS) substrates using pulse biased arc ion plating. For comparison, TiN and TiC films were also deposited. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Auger electron spectroscopy (AES) were applied to investigate the modulation period thickness, microstructure and content depth distribution of the films, respectively. And microhardness and film/substrate adhesion were also analyzed using knoop tester and scratching method. The results showed that the multilayer films with different modulation period of 40-240 nm exhibit a modulation structure and the interface width is about 20∼30 nm. Microhardness of the multilayer films were not obviously improved compared to that of TiN and TiC film, and the reason was analyzed. In comparison to TiN film, film/substrate adhesion values of the multilayer films were deteriorated with the increasing of modulation period due to the brittle characteristics of TiC film.     

Effect of oxygen plasma treatment on bonding states for columnar structured a-CNx thin films prepared by reactive sputtering

Amorphous carbon nitride (a-CN) thin films were deposited on silicon single crystal substrates by rf-reactive sputtering method using a graphite target and nitrogen gas. The substrate temperature was varied from room temperature (RT) to 853 K. After deposition, the effect of oxygen plasma treatment on bonding structures of the film surface has been studied by using an oxygen discharge at 16 Pa and rf power of 85 W. The chemical bonding states and film composition were analyzed by X-ray photoelectron spectroscopy (XPS), while film thickness was obtained from scanning electron microscopy (SEM) and ellipsometer. XPS study revealed that the films have NO₂ and NO₃ bonding structures when the films are deposited at temperatures higher than 673 K. After exposure to oxygen plasma, carbon in the film surface was etched selectively and this phenomenon was observed in all films. In contrast, the surface concentration of nitrogen was ket at constant values before and after oxygen plasma treatment. The NO₃ bonding state had dramatically increased after oxygen plasma treatment for films deposited at higher deposition temperatures. The film surfaces have been observed to change the function from hydrophobic to hydrophilic after oxygen plasma treatment.     

A neural cell culture study on thin film electrode materials

Functional neural stimulation requires good interface between the neural cells and the electrode surfaces. In order to study the effect of electrode materials and surface structure on cell adhesion and biocompatibility, we cultured cortical neurons on thin films of platinum and iridium oxide. We used both flat, as-deposited and laser micro-structured films. The laser micro-structuring consisted of creating regular arrays of micro-bumps or holes with diameters of 4–5 μm and height of about 1.5 μm. The micro-bumps were fabricated onto platinum and iridium film surfaces deposited on borosilicate glass substrates, using mask-projection irradiation with single nano-second pulses from a KrF excimer laser (λ = 248 nm). Amorphous and crystalline (deposited at 250 °C) IrO₂ films were deposited onto the laser micro-structured iridium films by pulsed-DC reactive sputtering to obtain micro-structured IrO₂ films. Cortical neurons isolated from rat embryo brain were cultured onto these film surfaces. Our results indicate that flat and micro-structured film surfaces are biocompatible and non-toxic for neural cell growth. The use of poly-d-lysine as a mediator for cell adhesion onto the thin film surfaces is also discussed.     

Improved electrochemical performance of nitrocarburised stainless steel by hydrogenated amorphous carbon thin films for bone tissue engineering

In this study, hydrogenated amorphous carbon thin films, structurally similar to diamond‐like carbon (DLC), were deposited on the surface of untreated and plasma nitrocarburised (Nitrocarburizing‐treated) stainless steel medical implants using a plasma‐enhanced chemical vapour deposition method. The deposited DLC thin films on the nitrocarburising‐treated implants (CN+DLC) exhibited an appropriate adhesion to the substrates. The results clearly indicated that the applied DLC thin films showed excellent pitting and corrosion resistance with no considerable damage on the surface in comparison with the other samples. The CN+DLC thin films could be considered as an efficient approach for improving the biocompatibility and chemical inertness of metallic implants.Inspec keywords: tissue engineering, bone, biomedical materials, electrochemistry, amorphous state, carbon, hydrogen, thin films, plasma CVD, adhesion, corrosion resistance, surface hardeningOther keywords: electrochemical performance, plasma nitrocarburised stainless steel medical implants, hydrogenated amorphous carbon thin films, bone tissue engineering, plasma‐enhanced chemical vapour deposition method, adhesion, corrosion resistance, biocompatibility, chemical inertness, metallic implants, C:H     

Effect of RF-plasma deposition parameters on the composition and properties of organic layers deposited on glass fibers

Thin films were deposited from vinyltriethoxysilane (VTES) and tetravinylsilane (TVS) by radio frequency (RF) cold plasma operated in a pulsed mode on the surface of E-glass fibers. Film thickness and molecular structure was controlled by the length of plasma cycle expressed as ratio of time on/time off (t_on/t_off). It was found that t_on as short as 1 ms was long enough for vinylsilane precursor gas fragmentation. Time t_off was the main parameter controlling structural variables of the deposited films. Short t_off led to apparently disordered and cross-linked structure. Increased t_off led to more uniform films with enhanced properties compared to the short t_off deposited films. Only films prepared under long t_off improved adhesion between the glass fiber and polyester resin as measured employing the micro-droplet test. Strong effect of the molecular structure of the vinylsilane precursor has also been observed under the conditions used. VTES film deposited under t_on/t_off = 1:999 increased interfacial adhesion only by 20%, TVS film deposited at 1:99 improved adhesion by 48%, compared to the solution deposited coating of the VTES used commercially.     

Effect of micro-characterization on thrombus formation ability of TiO2 film

The thrombus formation ability of a biomedical microcoil for hemangioma treatment is one of the basic requirements in clinical intervention application. Surface modification of a biomedical microcoil can improve its thrombus formation ability. In this work, TiO₂ films were deposited using the unbalanced magnetron sputtering method. The structures, components and micro-morphologies of the films were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), and scanning electron microscope (SEM). The thrombus formation ability of the films was studied by in vitro platelet adhesion test. The results indicated that a certain characteristic TiO₂ film has the ability to increase thrombus formation. Furthermore, the biological behavior of cultured human umbilical vein endothelial cells (HUVECs) onto different films was investigated by an in vitro HUVECs cultured experiment. The results showed that endothelial cells on certain TiO₂ film surfaces have good adherence, growth and proliferation. Additionally, the relationship between the micro-characterization and biological properties of TiO₂ films is discussed.     

Factors affecting the adhesion of microwave plasma deposited siloxane films on polycarbonate

The effects of a radiofrequency oxygen plasma pretreatment and residual water content in the substrate on the adhesion of microwave plasma deposited tetramethyldisiloxane thin films on Bisphenol-A polycarbonate (BPA-PC) were investigated. Samples were characterised using a crosshatch adhesion test, optical and electron microscopy, and X-ray photoelectron spectroscopy. It was found that the use of a low power (5 W) and low treatment time (0.1 s) oxygen plasma can improve adhesion while greater treatment times (1–30 s) and higher oxygen plasma powers (40 W) resulted in a decreased level of adhesion. In addition, it was shown that a BPA-PC water content greater than 90 ppm resulted in rapid adhesion failure of deposited films at the substrate–plasma polymer interface during outdoor weathering. All films degraded substantially when exposed to environmental weathering, indicating ageing reactions within the plasma polymer films themselves, and at the bulk polymer–coating interface.     

Surface modification of poly(ethylene terephthalate) by plasma polymerization of poly(ethylene glycol)

Poly(ethylene glycol) (PEG) was ‘polymerized’ onto poly(ethylene terephthalate) (PET) surface by radio frequency (RF) plasma polymerization of PEG (average molecular weight 200 Da) at a monomer vapour partial pressure of 10 Pa. Thin films strongly adherent onto PET could be produced by this method. The modified surface was characterized by infra red (IR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), cross-cut test, contact angle measurements and static platelet adhesion studies. The modified surface, believed to be extensively cross-linked, however showed all the chemical characteristics of PEG. The surface was found to be highly hydrophilic as evidenced by an interfacial free energy of about 0.7 dynes/cm. AFM studies showed that the surface of the modified PET became smooth by the plasma polymerized deposition. Static platelet adhesion studies using platelet rich plasma (PRP) showed considerably reduced adhesion of platelets onto the modified surface by SEM. Plasma ‘polymerization’ of a polymer such as PEG onto substrates may be a novel and interesting strategy to prepare PEG-like surfaces on a variety of substrates since the technique allows the formation of thin, pin-hole free, strongly adherent films on a variety of substrates.     

Plasma deposited thin films suitable as moisture sensors

Plasma polymerized thin films from a mixture of hexamethyldisiloxane (HMDSO) and ammonia (NH₃) deposited directly onto a microdielectrometer chip have been evaluated as moisture sensors. Microdielectrometry was chosen as the measuring technique because of its fast response and real time detection capability. The sheet resistance of the plasma polymerized film was found to decrease by eight orders of magnitude with an increase in relative humidity from 0 to 92%. The moisture effect on the sheet resistance was also found to be reversible. The composition and structure of the films deposited from various mixtures of HMDSO/NH₃ have been elucidated by Electron Spectroscopy for Chemical Analysis (ESCA) and infrared spectroscopy.     

Influence of bilayer period on the characteristics of nanometre-scale ZrN/TiAIN multilayers

In the last decade, considerable research effort was directed to the deposition of multilayer films with layer thicknesses in the nanometer range (superlattice coatings), in order to increase the performance of various cutting tools and machine parts. The goal of the present work was to investigate the main microstructural, mechanical and wear resistance characteristics of a superlattice coating, consisting of alternate multilayer ZrN/TiAIN films, with various bilayer periods (5 / 20 nm). The coatings were deposited by the cathodic arc method on Si, plain carbon steel and high speed steel substrates to be used as wear resistance surfaces. The multilayer structures were prepared by using shutters placed in front of each cathode (Zr and Ti+Al). The characteristics of multilayer structures (elemental and phase composition, texture, Vickers microhardness, thickness, adhesion, and wear resistance) were determined by using various techniques (AES, XPS, XRD, microhardness measurements, scratch, and tribological tests). A comparison with the properties of ZrN and TiAIN single-layer coatings was carried out.     

Heparin-containing block copolymers

Newly synthesized heparin-containing block copolymers, consisting of a hydrophobic block of polystyrene (PS), a hydrophilic spacer-block of poly (ethylene oxide) (PEO) and covalently bonded heparin (Hep) as bioactive block, were coated either onto glass, poly (dimethylsiloxane), polyurethane or PS substrates. Coated surfaces were characterized by determination of the surface-bound heparin activity, adsorption of AT III, plasma recalcification time assays, adhesion of platelets and by an ex vivo rabbit A-A shunt model.It was demonstrated that heparin was available at the surface of all heparin-bound surfaces to interact with AT III and thrombin and to prevent the formation of clots. The maximum immobilized heparin activity was found to be 5.5×10^-3 U cm^-2. Coated surfaces showed a significant prolongation of the plasma reclacification times as compared to control surfaces, due to surface-immobilized heparin. The platelet adhesion demonstrated that platelets reacted only minimally with the heparin-containing block copolymers in the test system and that the heparin-containing block copolymers seemed to passify the surface as compared to control surfaces. In the ex vivo A-A shunt experiments, which were carried out under low flow and low shear conditions, the heparin-containing block copolymers exhibited prolonged occlusion times, indicating the ability of the heparin-containing block copolymers to reduce thrombus formation at the surface.     

Structure of polycrystalline silicon films deposited at low temperature by plasma CVD on substrates exposed to different plasma

Polycrystalline silicon (poly-Si) films were deposited on glass substrates (corning 7059) at 300°C by a plasma enhanced chemical vapor deposition (PECVD) from a SiH₄/SiF₄ mixture. All poly-Si films were prepared under the same deposition conditions on the substrates subjected to nitrogen, hydrogen and/or CF₄ plasma with different gas pressures, just before deposition of the poly-Si films. Effects of such pretreatments for substrates on the structural properties of the resultant poly-Si films have been investigated. The Si film deposited on the substrates without any pretreatments was amorphous. However, formation of a strong 〈110〉 preferentially oriented poly-Si with improved crystallinity was obtained for the films deposited on the glass substrate after plasma pretreatments, which exhibit smoother surfaces. This result was interpreted in terms of a removal of weak Si–Si bonds during nucleation and the subsequent grain growth.