PEEK Surfaces Research Articles

Friday, September 28, 2018 10:30 AM–12:00 PM abstracts: innovation, surface technology and biomechanics: 174. Surface topography and chemistry effects on PEEK and titanium osseointegration

BACKGROUND CONTEXT Nearly 500,000 spinal fusion surgeries are performed each year in the U.S. Interbody fusion devices have been used for decades to facilitate fusion across the disc space, yet debate continues over the optimal material and structure used for these devices. Current cages are primarily made from PEEK due to its radiolucency and bone-like stiffness. However, current smooth PEEK cages are often associated with fibrous encapsulation and implant migration. This poor response is often attributed to inherent material properties of PEEK. However, the smooth surface of conventional PEEK surfaces may equally impede osseointegration, particularly when considering that rough and porous surfaces of various non-PEEK materials elicit more favorable osseointegration compared to smooth surfaces. PURPOSE The current study aimed to assess the relative influence of surface topography and chemistry on PEEK osseointegration by investigating the osseous response to smooth, rough, and porous surface topographies possessing a PEEK or titanium surface chemistry. STUDY DESIGN/SETTING Preclinical implant osseointegration model in the proximal tibial metaphysis of the rat. OUTCOME MEASURES Osseointegration was assessed by calculating bone ingrowth percentage, histological tissue evaluation, and biomechanical pullout testing. METHODS Porous PEEK implants were created as described previously. Rough surfaces were created by soda-blasting PEEK surfaces and smooth surfaces maintained an as-machined surface finish. Half of each group was coated with a ∼30nm thick layer of TiO2 using atomic layer deposition (ALD) while the other half maintained their native PEEK chemistry. Sterile implants were implanted into the proximal tibial metaphyses of skeletally mature male Sprague Dawley rats. At 8 weeks, animals were euthanized and bone-implant interfaces were subjected to µCT analysis (n=12), histology (n=4), and biomechanical pullout testing (n=8). All data were reported as mean±SE. Comparisons between groups were calculated using a 2-way ANOVA followed by a Tukey multiple comparisons test. RESULTS Quantitative µCT analysis demonstrated that mineralized tissue ingrowth was 38.9±2.8% for porous PEEK and 30.7±3.3% for porous titanium (p=0.07). µCT tomograms and matching histological sections showed bone ingrowth in porous titanium surfaces primarily consisted of thin bone shells that conformed to the pore walls, leaving the center of pores devoid of bone. In contrast, bone ingrowth within porous PEEK was greater in the center of pores with periodic contact with pore walls. Greater bone-implant contact was observed for titanium compared to PEEK surfaces. Histological and µCT observations were corroborated by biomechanics outcomes. Across all groups both surface chemistry and topography had a significant overall effect on pullout force (p CONCLUSIONS The poor osseointegration of conventional PEEK implants may be linked more to their smooth surface topography rather than their material composition. The effect of surface topography (specifically porosity) dominated the effect of surface chemistry in this study and could lead to further improvements in orthopaedic device design.

Influence of laser structuring of PEEK, PEEK-GF30 and PEEK-CF30 surfaces on the shear bond strength to a resin cement.

The aim of this study was to evaluate the influence of a surface conditioning technique using laser ablation and acid etching on PEEK substrate on its bonding strength to a resin cement. Cylindrical specimens of unfilled PEEK, 30% glass fiber reinforced PEEK and 30% carbon fiber reinforced PEEK were separated in four groups according to the following surface treatments: acid etching with H2SO4, laser ablation with 200 µm holes spaced 400 µm apart (D2E4), laser ablation with 200 µm holes spaced 600 µm apart (D2E6), and laser ablation (D2E4) followed by acid etching. A dual-curing resin cement (Allcem CORE) was then applied to the PEEK surface. Specimens were aged in distilled water at 37 °C for 24 h. Shear bond strength tests were performed to the fracture of the samples. Two-way ANOVA statistical analysis was performed with a significance level of 0.05. Scanning electron microscopy analysis was performed to analyse the conditioned and fracture surfaces. SEM images of the test interfaces showed that the resin cement could not flow in the holes designed by the laser ablation on the PEEK surface. The shear bond strength of PEEK to resin cement was not improved by the surface modification of the PEEK. Also, there was a statistically significant decrease in shear bond strength for unfilled PEEK specimens. On carbon or glass reinforced PEEK, the change was not significant. SEM images of the fracture surfaces revealed that the failure mode was mainly adhesive. Although laser ablation promoted the PEEK surface modification by the formation of retentive holes, the test resin cement could not thoroughly flow on the rough modified surfaces to establish an effective mechanical interlocking. That negatively affected the shear bonding strength of PEEK to the resin cement. Further studies should be carried out to increase the bonding between PEEK and resin cements.

THE EFFECT OF ATMOSPHERIC PLASMA-SPRAYED PEEK IMPLANTS ON OSSEOINTEGRATION

Objectives: The study evaluated the osseointegration of atmospheric plasma treated PEEK implant surfaces versus the untreated PEEK surfaces. Material & Methods: The PEEK implants were milled using carbon reinforced PEEK material with CAD-CAM milling machine. The implants were placed in 6 male mongrel dogs, each dog received 2 groups of PEEK implants. The control group consisted of untreated surface PEEK implants. The study group consisted of atmospheric plasma-sprayed PEEK implants. the implants were placed in the dog femur. After 12 weeks, the animals were sacrificed, and bone-implant sections were obtained for histological evaluations and bone-to-implant contact. Electron microscope scanning was performed to assess the topography of the surface of treated and untreated PEEK implant surface.Results: Qualitative evaluation of the stained histological sections of the PEEK implants demonstrated a well distributed bone in proximity to the atmospheric plasma-sprayed PEEK implant surface after 12 weeks of placements. The bone-to-implant contact showed a significant difference (P < 0.001) between treated and untreated PEEK implant surface.Conclusions: Within the limitation of the present study, it is concluded that the atmospheric plasma-sprayed surface treatment may improve the osseointegration of PEEK implant.Key Words: PEEK, Osseointegration, plasma-spray, titanium, dental implant.

Human Mesenchymal Stem Cell Morphology and Migration on Microtextured Titanium

The implant used in spinal fusion procedures is an essential component to achieving successful arthrodesis. At the cellular level, the implant impacts healing and fusion through a series of steps: first, mesenchymal stem cells (MSCs) need to adhere and proliferate to cover the implant; second, the MSCs must differentiate into osteoblasts; third, the osteoid matrix produced by the osteoblasts needs to generate new bone tissue, thoroughly integrating the implant with the vertebrate above and below. Previous research has demonstrated that microtextured titanium is advantageous over smooth titanium and PEEK implants for both promoting osteogenic differentiation and integrating with host bone tissue; however, no investigation to date has examined the early morphology and migration of MSCs on these surfaces. This study details cell spreading and morphology changes over 24 h, rate and directionality of migration 6–18 h post-seeding, differentiation markers at 10 days, and the long-term morphology of MSCs at 7 days, on microtextured, acid-etched titanium (endoskeleton), smooth titanium, and smooth PEEK surfaces. The results demonstrate that in all metrics, the two titanium surfaces outperformed the PEEK surface. Furthermore, the rough acid-etched titanium surface presented the most favorable overall results, demonstrating the random migration needed to efficiently cover a surface in addition to morphologies consistent with osteoblasts and preosteoblasts.

Augmenting the bioactivity of polyetheretherketone using a novel accelerated neutral atom beam technique.

The surface roughness and contact angle of PEEK and ANAB PEEK was measured. Cell metabolic activity, proliferation and alkaline phosphatase (ALP) was measured and cell attachment was determined by quantifying adhesion plaques with cells. ANAB treatment increased the surface hydrophilicity [91.74 ± 4.80° (PEEK) vs. 74.82 ± 2.70° (ANAB PEEK), p < 0.001] but did not alter the surface roughness. Metabolic activity and proliferation for all cell types significantly increased on ANAB PEEK compared to PEEK (p < 0.05). Significantly increased cell attachment was measured on ANAB PEEK surfaces. MSCs seeded on ANAB PEEK in the presence of osteogenic media, expressed increased levels of ALP compared to untreated PEEK (p < 0.05) CONCLUSION: Our results demonstrated that ANAB treatment increased the cell attachment, metabolic activity, and proliferation on PEEK. ANAB treatment may improve the osteointegration of PEEK implants. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1438-1446, 2017.

Wear rate control of peek surfaces modified by femtosecond laser

This paper presents the effect of laser texturing on the tribological properties of PEEK surfaces under a ball-on-flat contact configuration. Thus, surfaces with circular dimples of various diameters and depth were created. Tests were conducted with a normal load of 5N and a sliding velocity of 0.01ms−1, using bovine calf serum at 37.5°C as a lubricant. The tribological conditions including the sliding frequency and the lubricant viscosity indicate that tests were performed under boundary lubrication regime. Results showed that discs with higher dimple depth exhibited higher friction coefficient and caused more abrasive wear on the ball specimen. Nevertheless, tribosystems (ball and disc) with dimpled disc surfaces showed a higher wear resistance. In the frame of our experiments, wear rates obtained for tribosystems including dimpled surfaces were 10 times lower than tribosystems including limited patterned or untextured surfaces. Applications such as design of spinal implants may be concerned by such a surface treatment to increase wear resistance of components.

Laser surface modification of poly(etheretherketone) to enhance surface free energy, wettability and adhesion

Enhancement of the surface wettability and surface free energy of thermoplastic materials is an effective way of improving their adhesion and consequently the adhesive joint strength. A nanosecond pulsed Nd:YAG laser was selected in this work to provide energetic treatment of PEEK surfaces, in order to investigate its effectiveness in increasing the performance of lap shear adhesive joints. The laser was used to irradiate the PEEK, by rastering a spot of ca. 1mm diameter across a large area. The resulting surfaces were characterised using single lap shear testing, confocal laser scanning microscopy, contact angle analysis, FT-IR, XPS and ToF-SIMS. Single lap shear testing of PEEK joints showed that the strength of adhesively bonded joints is greatly improved by laser treatment, up to 13 times that of untreated PEEK. Confocal laser scanning microscopy showed that the higher laser power intensities (≥107Wmm−2) disrupted the surface of the PEEK more than the lower laser power intensities (<107Wmm−2), but also showed that, as expected, only some of the surface is treated by the laser. Contact angle analysis showed a decrease in water contact angle with increasing laser power intensity, and the derived surface free energy increased accordingly. FT-IR in the specular reflectance mode showed no discernible change but XPS and ToF-SIMS did, suggesting that laser treatment only affects the near surface at the extremity of the 1–2μm sampling depth. XPS showed a decrease in the carbon/oxygen ratio of PEEK on treatment, indicating that oxygen-containing functional groups were being created at the surface. XPS also suggested a cleaning mechanism at a laser intensity of 7.83×106Wmm−2, progressing to surface modification from a laser intensity of 107Wmm−2 and above. ToF-SIMS confirmed that laser treatment cleans the surface of PEEK of extraneous material.

Red selenium nanoparticles and gray selenium nanorods as antibacterial coatings for PEEK medical devices.

Bacterial infections are commonly found on various poly(ether ether ketone) (PEEK) medical devices (such as orthopedic instruments, spinal fusion devices, and segments in dialysis equipment), and thus, there is a significant need for introducing antibacterial properties to such materials. The objective of this in vitro study was to introduce antibacterial properties to PEEK medical devices by coating them with nanosized selenium. In this study, red selenium (an elemental form of selenium) nanoparticles were coated on PEEK medical devices through a quick precipitation method. Furthermore, with heat treatment at 100°C for 6 days, red selenium nanoparticles were transferred into gray selenium nanorods on the PEEK surfaces. Bacteria test results showed that both red and gray selenium-coated PEEK medical devices significantly inhibited the growth of Pseudomonas aeruginosa compared with uncoated PEEK after either 1, 2, or 3 days. Red selenium nanoparticle-coated PEEK showed less bacteria growth on its surface than gray selenium nanorod-coated PEEK after 3 days. This study demonstrated that red, and to a lesser extent gray, nanosized selenium could be used as potential antibacterial coatings to prevent bacteria function on PEEK medical devices. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1352-1358, 2016.

Vinculin focal adhesion of osteoblast‐like cells on PEEK coated with ultra‐thin polymer nano films

ABSTRACTPEEK is the polymer of choice to replace metal encapsulants and other parts in active medical implants fixated into bone. The current challenge is to improve its biocompatibility with bone tissue to ultimately achieve osseointegration. PEEK sheets surfaces coated with plasma deposited nano thin polymer films using CH4, (CH4 + O2) and (CH4 + N2) gases. PEEK samples plasma treated with nonpolymerizing gases (O2) were also used for comparison. The adhesion performance of osteoblast like cells on the plasma‐treated PEEK surfaces and the presence of Vinculin in these cells were evaluated after long culturing period (12 days). X‐ray photoelectron spectroscopy and Auger spectroscopy were used to provide surface molecular information, surface hardness and molecular density. All plasma‐treated surfaces retained functionality after the sterilization process. PEEK surfaces with high number of oxygen functional groups and particularly oxygen rich thin polymer coating (plasma deposition using CH4+O2 gas mixture) resulted in strong cellular adhesion strength and large Vinculin amount. Further, osteoblast‐like cells responded better to surfaces with lower molecular density acting like another signal for cell adhesion. The osteoblast‐like cells response was weaker for surfaces with both thin films with nitrogen functional groups and nonfunctional (nonpolar) films. Furthermore, thin films rich in nitrogen functional groups repelled the cells, showed abnormal cells shape, smaller Vinculin amount and induced thicker cellular clusters with poor spread. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42181.

Covalent attachment of cell-adhesive peptide Gly-Arg-Gly-Asp (GRGD) to poly(etheretherketone) surface by tailored silanization layers technique

Poly(etheretherketone) (PEEK) is a rigid semicrystalline polymer that combines excellent mechanical properties, broad chemical resistance and bone-like stiffness and is widely used in biomedical fields. However, PEEK is naturally bioinert, leading to limited biomedical applications, especially when a direct bone-implant osteointegration is desired. In this study, a three-step reaction procedure was employed to immobilize the cell-adhesive peptide Gly-Arg-Gly-Asp (GRGD) on the surface of PEEK sheet by covalent chemical attachment to favor cell adhesion and proliferation. First, hydroxylation-pretreated PEEK surfaces were silanized with 7-Oct-1-enyltrichlorosilane (OETS) in dry cyclohexane, resulting in a silanization layer with terminal ethenyl. Second, the terminal ethylenic double bonds of the silanization layer on PEEK surface were converted to carboxyl groups through acidic potassium manganate oxidation. Finally, GRGD was covalently attached by carbodiimide mediated condensation between the carboxyl on PEEK surface and amine presents in GRGD. X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, surface profiler and water contact angle measurements were applied to characterize the modified surfaces. The effect of cells attachment and proliferation on each specimen was investigated. Pre-osteoblast cells (MC3T3-E1) attachment, spreading and proliferation were improved effectively on GRGD-modified PEEK surface. PEEK modified with GRGD on its surface has potential use in orthopedic or dental implants.

Fabrication of polyaniline nanofiber arrays on poly(etheretherketone) to induce enhanced biocompatibility and controlled behaviours of mesenchymal stem cells.

As a typical conducting material, polyaniline (PANI) has been processed into various nanostructured materials that have been applied in fields including fuel cells, smart materials and anticorrosive coatings. However, few studies have investigated the properties of PANI nanostructures as biointerfaces. Herein, we developed a controlled and stable PANI nanostructured interface on high-performance poly(etheretherketone) (PEEK) surfaces utilizing the self-initiation of PEEK to graft poly(acrylic acid) (PAAc) interlayers and the in situ diluted polymerization of PANI. The prepared PANI nanofiber array surfaces produced chemical factor and nanocue coeffects enabling PEEK to possess enhanced biocompatibility and controlled cell behaviours with nanosensitivity. Atomic force microscopy (AFM) was adopted to characterize the bioadhesion of a simulated protein particle/single cell to various substrates. The cell behaviours of rat mesenchymal stem cells (rMSCs) on PANI and PEEK surfaces were investigated using scanning electron microscopy (SEM) and immunofluorescence. The PANI-grafted PEEK surfaces have enhanced biocompatibilities and controlled nanocues to mediate the behaviours of MSCs.

Sticky nano-thin films for the adhesion of polymers

Nanometre thick size films (about 2nm thick) that were plasma deposited using a mixture of polymerizing and non-polymerizing gases on a PEEK polymer surface resulted in a remarkable autohesive strength (up to 10 fold when compared with the untreated control). Experimental results on autohesion of semi-crystalline PEEK surfaces treated with plasma immersion ion implantation and deposition (PIIID) showed exceptionally strong autohesive bonds in lap-shear testing. Electron spin resonance (ESR) showed that the radical concentration increased linearly with plasma bias voltage. X-ray photoelectron spectroscopy (XPS) measurements showed no correlation between autohesive bonding strength and the concentration of oxygen and nitrogen elements and or the concentration of CO functional groups on the surface. Contact angle measurements showed that surface energy also showed no correlation. Bond strength values are linked with the percentage of the sp3 components of the C 1s region fitting in XPS spectra. There was strong relationship between the plasma treatment bias voltage and the plasma generated free radical density in the deposited thin film. Bond strength values are also correlated with the percentage of the sp3 components of the C 1s region fitting in XPS spectra. Free radicals induced covalent bonding might be suggested as the major contributor that leads to that the remarkable increase of the adhesion strength.

Cell Adhesion to PEEK Treated by Plasma Immersion Ion Implantation and Deposition for Active Medical Implants

AbstractPolyetheretherketone (PEEK) is an attractive material for the encapsulation of active medical implants. PEEK, however, shows hydrophobic surface properties which are not favorable for protein absorption and cell adhesion. We show that oxygen rich nanofilms “sticky thin film,” deposited on PEEK surfaces from plasma using a plasma immersion ion implantation and deposition technique with a (CH4/O2) gas mixture greatly improved cell adhesion (up to 75%) and spreading (up to 81%). Strong correlations were found between cell adhesion and the water contact angle, the polar component of surface energy, and to a lesser extent oxygen concentration of the PEEK surfaces. Surface polarity of the plasma deposited “sticky thin film” was deemed to be the predominant factor in influencing cell adhesion. magnified image

Scratch deformations of poly(etheretherketone)

Abstract This paper presents the experimental results obtained from the scratching of semicrystalline poly(etheretherketone) (PEEK). Various surface mechanical properties of the PEEK such as the hardness, the friction coefficient, the scratch depth and the prevailing deformation mechanisms are presented in the form of scratching maps, generated as a function of the contact conditions. These scratch maps provide a first order evaluation of the relative scratch resistance of materials for comparison purposes. The penetration depth dependent scratches (in the range 20–200 μm) were produced on the PEEK surfaces using rigid cones of different cone included angles and under different normal loads. The prevailing deformation mechanism and geometry of damage on the scratched polymeric surfaces were assessed using scanning electron microscope (SEM) and an optical profilometer. The deformation modes were seen to be influenced by the imposed experimental parameters; such as the contact geometry, the load, the nominal sliding velocity, the contact temperature and the contact lubrication. In addition to the common deformation mechanisms observed in amorphous polymers; ranging from elastic, ironing, viscoelastic plastic ploughing and brittle deformations, a fibrillation of the semicrystalline PEEK was seen when the polymeric surface was scratched under the severe contact conditions (the higher contact strains and the normal loads).

Effect of different surface pre-treatments and luting materials on shear bond strength to PEEK

Objectives To assess the bonding potential of a universal composite resin cement and an adhesive/composite system to differently pre-treated PEEK surfaces. Methods One hundred and fifty PEEK disks were embedded in epoxy resin, polished (P4000 grit) and treated as follows ( n = 30/group): (A) no treatment, (B) acid etching with sulfuric acid (98%) for 1 min, (C) sandblasting for 10 s with 50 μm alumina, (D) sandblasting for 10 s with 110 μm alumina and (E) silica coating using the Rocatec system (3M ESPE). Polished and sandblasted (50 μm alumina) cp titanium (grade 4) served as a control. Acrylic hollow cylinders were either luted with a universal composite resin cement (RelyX Unicem) or an unfilled resin (Heliobond) and a hybrid composite (Tetric) to the specimens. Bond strength was measured in a shear test and failure modes were assessed. Statistic analysis was performed with one-way ANOVA followed by a post hoc Scheffé test and unpaired t-tests. Results With the universal composite resin cement, no bond could be established on any PEEK surfaces, except specimens etched with sulfuric acid (19.0 ± 3.4 MPa). Shear bond strength to titanium was significantly lower (8.7 ± 2.8 MPa, p < 0.05). Applying the adhesive/composite system, shear bond strength values on pre-treated PEEK ranged from 11.5 ± 3.2 MPa (silica coating) to 18.2 ± 5.4 MPa (acid etched) with no statistically significant differences ( p > 0.05). No bond was obtained on the polished surface. Significance Bonding to PEEK is possible when using a bonding system. No adherence can be achieved with the tested universal composite resin cement except on an etched surface. The results strongly encourage further research in PEEK application in dentistry.

Similarities between Plasma Amino Functionalized PEEK and Titanium Surfaces Concerning Enhancement of Osteoblast Cell Adhesion

The application of gas discharge plasmas for different functionalization and coating strategies is discussed with respect to cell adhesion to polymeric and metallic surfaces. Poly(ether ether ketone) (PEEK) and titanium (Ti) were selected as typical bone cell-contacting biomaterials. The surfaces were equipped with nitrogen-based chemical functionality, mainly amino groups. The behavior of human MG-63 osteoblasts was investigated with respect to cell adhesion and growth on plasma-treated PEEK and Ti surfaces. MG-63 cells adhere faster and occupy a wider cell area on the plasma-treated compared to untreated surfaces, which is not integrin receptor mediated. Although different plasma treatments were applied to functionalize polymeric and metallic surfaces with amino groups, similar cell adhesion properties were achieved.

Tailoring of Poly(ether ether ketone) Surface Properties via Surface-Initiated Atom Transfer Radical Polymerization

The interfacial properties of commercial poly(ether ether ketone) (PEEK) have been tailored by tethering polymeric brushes to the PEEK surface via surface-initiated atom transfer radical polymerization (SI-ATRP). The immobilization of an ATRP initiator on the PEEK surface was achieved by an unprecedented simple two-step wet chemical method. The keto groups at the PEEK surface were first wet chemically reduced to hydroxyl groups, and then 2-bromoisobutyryl groups were covalently anchored at the PEEK surface as ATRP initiator. SI-ATRP was performed at these functionalized PEEK surfaces with the three different monomers: potassium 3-(methacryloyloxy)propane-1-sulfonate (MPS), monomethoxy-terminated oligo(ethylene glycol)methacrylate (MeOEGMA), and N-isopropylacrylamide (NIPAAm). Atomic force microscopy, scanning electron microscopy, attenuated total reflection infrared spectroscopy, water contact angle measurements, and X-ray photoelectron spectroscopy ascertained the successful grafting of these polymer brushes at the PEEK surface. These brush-modified PEEK surfaces exhibited fully the physiochemical properties of the respective polymer brush: the surface with polyMPS brush showed selective staining by electrostatic interaction, while the polyMeOEGMA-modified surface was biorepellent. The surface modified with polyNIPAAm brush demonstrated a thermally responsive polarity change.

Surface Modification of Polymer Films by Pulsed Oxygen Plasma

The surfaces of three kinds of polymer were treated using pulsed oxygen plasma: poly(ether ether ketone) (PEEK), liquid crystalline polymer (LCP), and linear-low-density polyethylene (L-LDPE). Also using pulsed oxygen plasma, oxygen functional groups were introduced on polymer surfaces. The effects of oxygen functional group introduction were investigated to elucidate whether any differences exist in the manner of introduction of oxygen functional groups on the polymer surface, arising from differences in polymer structures. The introduction of oxygen functional groups formed hydrophilic polymer surfaces. Fewer oxygen functional groups were introduced on PEEK and LCP surfaces by pulsed plasma treatment than by continuous oxygen plasma. On the other hand, many oxygen functional groups were introduced on L-LDPE surfaces than by continuous oxygen plasma. Reasons for different attachment of oxygen functional groups by pulsed oxygen plasma processing on polymer surfaces were discussed.

Coating of a thin layer of NaBH4 solution for mercury vapor generation coupled to atomic fluorescence spectrometry

Sodium tetrahydroborate (NaBH4) was, for the first time, coated onto PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene propylene), Excelon (microline) and PEEK (polytetrafluoroethylene) surfaces and used for mercury vapor generation-atomic fluorescence spectrometric determination. A lab-on-valve (LOV) incorporating a miniature membrane phase separation chamber was employed to facilitate the operation. A 600–1200 nm thin film of NaBH4 solution was coated onto the interior surface of tubes by sweeping through 30 μl of NaBH4 solution with an argon stream. Mercury cold vapor was generated as sample solution flowing through the pre-coated tubing carried by argon. The film coating was renewed for each operating run. The vapor was either immediately excited in the outlet of the separator in the LOV and detected by directing the fluorescence to a photomultiplier with optical fibers, or directed to a commercial AFS-920 atomic fluorescence spectrometer. NaBH4 coating not only minimized fluorescence quenching by concomitant hydrogen encountered in conventional AFS, but the coating process also effectively eliminated mercury memory effects. In addition, the coating substantially simplified the operation of vapor generation using a single syringe pump for fluidic delivery. When using PTFE tubing as a coating medium, limits of detection of 0.06 and 0.005 μg l−1 were derived by monitoring with a LOV-AFS system and an AFS-920 spectrometer, respectively, with a sample volume of 500 μl. A sampling frequency of 60 h−1 along with RSDs of 2.9% and 2.0% at 2.0 μg l−1 were achieved. Mercury contents in certified reference materials and a local coastal seawater were measured.

Effect of counterface surface roughness and its evolution on the wear and friction of PEEK and PEEK-bonded carbon fibre composites on stainless steel

The time-dependent variations in the dry sliding wear rate and friction of PEEK (450G and 100P) and carbon fibre-bonded PEEK (APC2) on stainless steel (316S16) have been investigated and the evolution of wear scratches measured with optical profilometry. A three-pin-on-disk tester was used, operating at 0.18 m s −1, with a pressure of 1.0 MPa on 5 mm diameter pin. Specific wear rates were calculated from mass lost by the pins at 15 km intervals and friction force was monitored by a strain-gauged torque beam. Two series of 90-km tests were performed for each pin/disk combination. The stainless steel disks had either a fine-ground or polished surface. The roughness of the ground stainless steel surface was chosen to coincide with the optimum value for low wear rate of the PEEK pins. To maximise pin/disk contact area, the PEEK and APC2 pin surfaces were run-in on 1000-grit silicon carbide paper and ultrasonically cleaned in acetone before the first wear test. There was no significant difference in steady-state wear between these pins and those tested with as-moulded surfaces. The disks were analysed at 15 km intervals with the UBM profilometer, providing 3D surface scans and 2D profiles for roughness parameters without damaging the wear track. All the surface roughness parameters reported in this work were produced from thhe UBM non-contacting optical profilometer. A marked difference in specific wear rate was observed between the two types of PEEK. The 450G had the lowest wear of 6 × 10 −6 mm 3 N −1 m −1 on both the polished and ground counterface, whereas the 100P had wear factors of 1 × 10 −4 mm 3 N −1 m −1 on ground and 2 × 10 −5 mm 3 N −1 m −1 on polished stainless steel. However, the friction forces measured between the 450G PEEK and the polished disk were up to three times higher than those against the ground disk, (0.35±0.01), decreasing to similar values as the polished surface became scratched. The APC2 pins showed very little difference in wear rate between the ground and polished disks. However, a steady decrease from 1 × 10 −6 to 1 × 10 −7 mm 3 N −1 m −1 over a distance of 90 km was measured as more fibres were ground into a graphite transfer film lubricant and the coefficient of friction dropped from 0.35 to 0.18. The specific wear rates and coefficients of friction of the APC2 samples were lower than those for PEEK, however, the APC2 caused more scratch deformation of the polished steel counterface.