Polished Disks Research Articles

Improvement of arthroscopic cartilage stiffness probe using amorphous diamond coating

During arthroscopic evaluation of articular cartilage unstable contact and even slipping of the measurement instrument on the tissue surface may degrade the reproducibility of the measurement. The main aim of the present study was to achieve more stable contact by controlling the friction between articular cartilage surface and the arthroscopic cartilage stiffness probe (Artscan 200, Artscan Oy, Helsinki, Finland) using amorphous diamond (AD) coating. In order to obtain surfaces with different average roughnesses (R(a)), polished stainless steel disks were coated with AD by using the filtered pulsed arc-discharge (FPAD) method. Dynamic coefficient of friction (mu) between the articular cartilage (n = 8) and the coated plates along one non-coated plate was then determined. The friction between AD and cartilage could be controlled over a wide range (mu = 0.027-0.728, p < 0.05, Wilcoxon test) by altering the roughness. Possible deterioration of cartilage was investigated by measuring surface roughness after friction tests and comparing it with the roughness of the adjacent, untested samples (n = 8). Importantly, even testing with the roughest AD (R(a) = 1250 nm) did not damage articular surface. On the basis of the friction measurements, a proper AD coating was selected for the stiffness probe. The performance of coated and non-coated probe was compared by measuring bovine osteochondral samples (n = 22) with both instruments. The reproducibility of the stiffness measurements was significantly better with the AD-coated probe (CV% = 4.7) than with the uncoated probe (CV% = 8.2). To conclude, AD coating can be used to safely control dynamic friction with articular surface. Sufficient friction between articular surface and reference plate of the arthroscopic probe improves significantly reproducibility of the stiffness measurements.

Einfluss einer TiO2-Beschichtung auf Biokompatibilität, Korrosionsund Auslaugverhalten verschiedener Implantatlegierungen / Corrosion behaviour, metal release and biocompatibility of implant materials coated by TiO2-sol gel chemistry

Alloys based on titanium or cobalt have been used as implant materials for decades with good success. Because of their natural oxide layer these alloys reveal good corrosion behaviour. In contact with physiological solution metal release takes place, which can cause inflammation. Coatings can improve the corrosion behaviour. In this study Ti6Al4V and Co28Cr6Mo alloys, which are frequently used as implant materials, were tested. Polished discs of these alloys and polished discs, which were coated with TiO2-layers by sol-gel chemistry, were compared regarding their corrosion behaviour and metal ion releasing. The releasing of Al, V, Ti, Co, Cr and Mo was quantified by ICP-MS analysis. The TiO2-coating reduced the release of all ions except of the Al-ion. Both alloys showed a deviating kinetic of ion releasing. In addition, cell response (cell vitality, cell proliferation, endothelial marker CD31 and actin allocation) of osteoblasts and endothelial cells were investigated.

Reactive ion etching of TiN, TiAlN, CrN and TiCN Films in CF4/O2 and CHF3/O2 Plasmas

AbstractThe reactive ion etching of a range of hard coatings (TiN, TiCN, CrN and TiAlN) has been examined as a function of rf power, flow rate and pressure. The films were deposited by filtered arc deposition (TiN, TiAlN and CrN) or low energy electron beam (TiCN) on polished disc substrates of M2 tool steel. The flat surfaces were lithographically patterned with a grating structure (∼1 μm pitch). The TiN and TiCN layers have shown significantly higher etch rates (100-250 nm/min) than the CrN and TiAlN (∼5 nm/min) coatings. These regimes of higher and low etch rate were identified as ion-enhanced chemical etching and physical sputtering, respectively. In CF4/O2 plasma, the etch rate of the TiN and TiCN layers increased with rf power, flow rate and pressure which were parameters known to enhance the density of active fluorine species. The etch rates of TiN and TiCN layers were higher in CF4/O2 plasma than in CHF3/O2 gases in which polymer deposition was produced at pressure ≥ 35 mTorr.

Bone cell adhesion on ion implanted titanium alloys

The authors have previously reported than ion implantation can have a significant effect on osseointegration of an implant, specially when the latter is introduced in areas of poorer bone density. These results indicate that this process is particularly suited for implant devices introduced in elderly patients or in those regions that have a poor quality of bone. The aim of this work is directed to study osteoblast adhesion on Ti alloy surfaces with different ion implantation treatments, so osseoconductive properties of several surfaces can be assessed. Polished discs of Ti–6Al–4V and Ti CP GR1 titanium alloy have been prepared and ion implanted with different species and parameters (dose and energy). Afterwards, the samples have been sterilized by UV light, inoculated with 1.5×10 5 human bone cells and incubated during 4 h at 37 C and 5% CO 2 atmosphere. Then, once fixed and rinsed, image analysis has been used to quantify the number of cells attached to the Ti discs. On a second round of tests, cell proliferation tests have been conducted during 24, 48, 144 and 192 h, respectively. Furthermore, surface analysis techniques (e.g. AFM) have been applied to learn about the qualitative behavior, i.e. morphology, of the attached cells. Cell attachment has shown to be highly sensitive to ion implantation parameters. Although some quantitative differences have been observed, the more significant differences were qualitative. AFM analysis has shown that the star-shaped bone cells attached spread more and occupied larger surfaces like in osseointegration prone surfaces, most probably due to extracellular matrix synthesized around them, while other surfaces showed mainly large and narrow shaped or round shaped bone cells often with great cellular nucleus in the middle of the cells and little extracellular matrix around. So, ion implanted surfaces that facilitate osseointegration have been identified, in terms of initial bone cell attachment quality, where although the number of attached cells were not necessarily always larger, they tended to occupy wider areas with healthier cells.

Growth rings, growth ring formation and age determination in the mangrove Rhizophora mucronata.

The mangrove Rhizophora mucronata has previously been reported to lack annual growth rings, thus barring it from dendrochronological studies. In this study the reported absence of the growth rings was reconsidered and the periodic nature of light and dark brown layers visible on polished stem discs investigated. In addition, the formation of these layers in relation to prevailing environmental conditions, as well as their potential for age determination of the trees, was studied. Trees of known age were collected and a 2.5-year cambial marking experiment was conducted to determine the periodic nature of the visible growth layers. Annual indistinct growth rings were detected in R. mucronata and are defined by a low vessel density earlywood and a high vessel density latewood. The formation of these growth rings and their periodic nature was independent from site-specific environmental conditions in two forests along the Kenyan coast. However, the periodic nature of the rings was seriously affected by slow growth rates, allowing accurate age determination only in trees with radial growth rates above 0.5 mm year(-1). The onset of the formation of the low vessel density wood coincided with the onset of the long rainy season (April-May) and continues until the end of the short rainy season (November). The high vessel density wood is formed during the dry season (December-March). Age determination of the largest trees collected in the two studied forests revealed the relatively young age of these trees (+/-100 years). This study reports, for the first time, the presence of annual growth rings in the mangrove R. mucronata, which offers further potential for dendrochronological and silvicultural applications.

Packed Powder Electrodes for Characterizing the Reactivity of Granular Iron in Borate Solutions

Electrochemical aspects of the corrosion of iron metal have been studied using polished disk, wire, and iron coupon electrodes, but these model systems do not represent many characteristics of the granular iron used in environmental remediation applications. To address this issue, we have modified a rotating disk electrode with a cavity that accommodates a wide range of iron powders. By comparison with conventional and disk electrodes, we found that our powder disk electrodes (PDEs) packed with unpretreated, <147 μm granular iron give anodic polarization curves that are unaffected by the underlying disk material and are consistent with a large electroactive surface area of iron that is initially coated with an air-formed passive film. Thus, we believe this electrode design will allow us to begin electrochemical studies of the reduction of aqueous environmental contaminants by relevant iron powders. In preparation for this, we report here on some of the experimental factors that effect response of an iron PDE in pH 8.4 borate buffer. Cavity size and rotation rate have synergistic effects that suggest that most of the iron powder is electroactive, hydrogen evolution in the active region is kinetically limited, and iron dissolution in the active region is affected by mass transport of solutes out of the cavity pore space and by the formation of a passivating film. © 2004 The Electrochemical Society. All rights reserved.

Human alveolar bone cell adhesion and growth on ion-implanted titanium.

Surface characteristics play a vital role in determining the biocompatibility of materials used as bone implants. Calcium ion implantation of titanium was previously reported to enhance osseointegration and bone formation in vivo, although the lack of consistent and reproducible effects highlight the need to understand the basic mechanisms involved in the response of target cells to such surfaces. The aim of this study was therefore to measure the precise effects of ion implantation of titanium on bone cells in vitro. Alveolar bone cells were seeded on the surface of polished titanium disks implanted with calcium, potassium, and argon ions. Using radioisotopically tagged bone cells, the results showed that although the calcium ion implanted surface reduced cell adhesion, it nevertheless significantly enhanced cell spreading and subsequent cell growth. In contrast, few differences in bone cell behavior were observed between the potassium- and argon-implanted titanium and the control nonimplanted titanium disks. These findings suggest the possibility that the calcium-implanted surface may significantly affect the biocompatibility of titanium implants by enhancing bone cell growth. Surface modification by ion implantation could thus prove to be a valuable tool for improving the clinical efficacy of titanium for bone repair and regeneration in vivo.

Effect of slide track shape on the wear of ultra-high molecular weight polyethylene in a pin-on-disk wear simulation of total hip prosthesis.

Prosthetic joints appear to show a strong relationship between the type of relative motion and wear, requiring careful consideration in the design of wear simulators. This relationship was studied with a 12-station pin-on-disk device, specifically adapted for the wear simulation of prosthetic hip joints. Each station had a unique motion, characterized by the so-called slide track, the track of the pin on the disk. The slide track shapes included 10 ellipses, their aspect ratio (AR) varying from 1.1 to 11.0, and a circle and a straight line as extreme cases. Hence for the first time in hip wear simulation, the motion was systematically varied over a wide range. Conventional UHMWPE pins were tested against polished CoCr disks in diluted calf serum three times for 3 million cycles. Below the AR value of 5.5, the polyethylene wear factor and wear mechanisms agreed with clinical observations. Above this value, the wear factor decreased to unrealistically low values, and the wear surface topography differed from that of retrieved acetabular cups. The wear particles, however, were similar to those isolated from periprosthetic tissues, irrespective of the AR value. In conclusion, it is recommended that the AR value be kept well below the critical point of 5.5.

Near Surface Vacancy Defects in Sintered Polished UO2 Disks

Near Surface Vacancy Defects in Sintered Polished UO2 Disks

The proliferation and phenotypic expression of human osteoblasts on tantalum metal

Tantalum (Ta) is increasingly used in orthopaedics, although there is a paucity of information on the interaction of human osteoblasts with this material. We investigated the ability of Ta to support the growth and function of normal human osteoblast-like cells (NHBC). Cell responses to polished and textured Ta discs were compared with responses to other common orthopaedic metals, titanium and cobalt–chromium alloy, and tissue culture plastic. No consistent differences, that could be attributed to the different metal substrates or to the surface texture, were found in several measured parameters. Attachment of NHBC to each substrate was similar, as was cell morphology, as determined by confocal microscopy. Cell proliferation was slightly faster on plastic than on Ta at 3 days, but by 7 days neither the absolute cell numbers, nor the number of cell divisions, was different between Ta and the other substrates. No consistent, substrate-dependent differences were seen in the expression of a number of mRNA species corresponding to the pro-osteoclastic or the osteogenic activity of osteoblasts. No substrate-dependent differences were seen in the extent of in vitro mineralisation by NHBC. These results indicate that Ta is a good substrate for the attachment, growth and differentiated function of human osteoblasts.

Anodisation of a Nb–Zr alloy

Anodisation of a Nb–Zr alloy was studied in ammonium sulphate and hydrochloric acid electrolytes using electrochemical and surface analysis methods. Using electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry, a value of ε r=27 was estimated for the relative permittivity and of 0.4 V nm −1 for the electrical field in the oxide film. Annealing of a mechanically polished disc sample to 600 °C for 14 h in UHV resulted in a fourfold surface enrichment of zirconium. This enrichment remained after anodisation in the sulphate solution, but could be removed with an anodisation in hydrochloric acid. Auger electron spectroscopy was used to estimate the thickness and composition of the anodic oxides. The film thickness measurements suggested a logarithmic growth law. The surface concentration of zirconium at the outer film surface of heat-treated samples decreased logarithmically when anodisation was performed in 1 M hydrochloric acid. No corresponding decrease in zirconium concentration was observed during immersion at open circuit.

The influence of the dentin smear layer on adhesion: a self-etching primer vs. a total-etch system

Objective. To determine the effect of dentin smear layers created by various abrasives on the adhesion of a self-etching primer (SE) and total-etch (SB) bonding systems. Methods. Polished human dentin disks were further abraded with 0.05 μm alumina slurry, 240-, 320- or 600-grit abrasive papers, # 245 carbide, # 250.9 F diamond or # 250.9 C diamond burs. Shear bond strength (SBS) was evaluated by single-plane lap shear, after bonding with SE or SB and with a restorative composite. Smear layers were characterized by thickness, using SEM; surface roughness using AFM; and reaction to the conditioners, based on the percentage of open tubules, using SEM. Results. Overall, SBS was lower when SB was used than when SE was used. SBS decreased with increasing coarseness of the abrasive in the SE group. Among burs, the carbide group had the highest SBS, and 320- and 240-grit papers had SBS close to the carbide group. Surface roughness and smear layer thickness varied strongly with coarseness. After conditioning with SE primer, the tubule openness of specimens abraded by carbide bur did not differ from 240- or 320-grit paper, but did differ from the 600-grit. Significance. Even though affected by different surface preparation methods, SE yielded higher SBS than SB. The higher SBS and thin smear layer of the carbide bur group, suggests its use when self-etching materials are used in vivo. Overall, the 320-grit abrasive paper surface finish yielded results closer to that of the carbide bur and its use is recommended in vitro as a clinical simulator when using the SE material.

Tribological characterization of diamond-like carbon (DLC) coatings sliding against DLC coatings

Two different qualities (single-layer and multi-layer) of thick diamond-like carbon (DLC) coatings were prepared on both extremely polished ( R a ∼0.01 μm) stainless steel disks and 6 mm diameter stainless steel balls. Morphological and micro-structural evaluations reveal that multi-layer DLC coatings are superior in nature compared to the single-layer coatings. Tribological characterisations using a pin (ball)-on-disk tribometer shows that, even though the multi-layer DLC coating exhibits superior qualities, when it slides against the same displays relatively higher friction and wear compared to that of single-layer DLC sliding against the same. Multi-layer DLC coated steel ball sliding against the single-layer DLC coated disk displays the best tribological performance. However, stress cracking was observed very rarely at the sliding edge of the multi-layer film prepared on the ball and is believed to be due to the relatively higher compressive stress in the film combined with the applied stress. The tribological performance of the single-layer DLC sliding against the same is also found to be excellent, and is comparable to that of the multi-layer DLC coated ball against the single-layer DLC coated disk. No cracks were observed on the low stress single-layer DLC coated ball after the friction test. The study reveals that the single-layer DLC sliding against the same would provide the best tribological DLC pair for relatively higher load applications such as in orthopaedic implants.

Atomic force microscopy characterization of ultrathin polystyrene films formed by admicellar polymerization on silica disks

AbstractAtomic force microscopy was used to study the characteristics of polymer films formed via admicellar polymerization (the polymerization of monomers solubilized in adsorbed surfactant aggregates). The investigated system included cetyltrimethylammonium bromide (C16TAB) as a cationic surfactant, styrene, 2,2′‐azobisisobutyrilnitrile as an initiator, and polished silica disk substrates. Our goal was to examine changes in the properties and morphology of the formed polymer films due to changes in the surfactant and monomer feed levels. Normal tapping and phase‐contrast modes in air were used to image the nanoscopic and microscopic morphologies of the polystyrene‐modified silica. The root‐mean‐square roughness of the surface before and after modification was statistically analyzed and compared. The images were captured with loading‐force set‐point ratios of 0.2–0.9, and this allowed us to examine the stability of the polystyrene films. In the first series, for which the feed ratio of C16TAB to styrene was kept constant and the total feed concentration was varied, a uniform layer of a polystyrene film was observed along with some nanometer‐size aggregates at high feed concentrations of both C16TAB and styrene. These droplets eventually agglomerated with the film beneath and formed larger macrodroplets in a ring arrangement. At lower concentrations, droplets and holes were observed that eventually agglomerated to form a bicontinuous thin film. In the second experimental series, the concentration of C16TAB was kept constant, and the feed ratio of C16TAB to styrene was varied. A smooth thin film was observed at high concentrations of styrene. This film could be deformed and/or removed to expose the silica surface beneath. At lower styrene loadings, the polystyrene film became unstable and formed dropletlike aggregates, possibly because of either the uneven adsolubilization of the styrene monomer within the admicelle or the dewetting effect during washing and drying. The structure of the polystyrene film formed on a smooth silica disk was very dependent on the amount of the surfactant fed to the system; this contrasted with the results on precipitated silica. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 36–46, 2003

In Situ Characterization of Adsorbates in Solid−Liquid Interfaces by Reflection−Absorption Infrared Spectroscopy

A cell has been designed for the in situ characterization of catalytic intermediates adsorbed at liquid−solid interfaces by single-reflection infrared spectroscopy. The design of our cell is based on previous setups used for the study of electrochemical systems, and consists of a cylindrical Teflon body terminated by a calcium fluoride prism cut in a trapezoidal shape with two faces beveled to 60° to let the infrared beam in and out of the cell on one end and by a polished platinum disk (the solid sample) mounted on a retractable rod on the other. The solid sample is cleaned by repeated electrochemical oxidation−reduction cycles using KClO4, HClO4, or H2SO4 electrolytes, and a thin liquid film is then trapped between the two surfaces for the liquid−solid adsorption studies. The performance of this cell was first tested by studies on the adsorption of carbon monoxide from 1.0 M H2SO4 solutions. Significant signals were detected for the adsorbed CO, comparable to those seen under vacuum or under high pressures of CO gas, and also to data reported previously. A more detailed characterization of our experimental setup was carried out with cinchona alkaloids. Discrimination between adsorbed and dissolved species was accomplished by dividing spectra obtained with p- and s-polarized light, and was corroborated by a number of tests, including a variation in the liquid film thickness and the nature of the adsorbing surface. The importance of the in situ characterization was assessed by comparing spectra for quinoline deposited under vacuum versus adsorbed from a carbon tetrachloride solution.

Adhesion of bone cells to ion-implanted titanium.

The use of ion-implantation to encourage osseointegration has been investigated using an in vitro model cell culture system and surface analysis. Polished titanium discs were implanted with calcium, potassium and argon ions. The adhesion of bone-derived cells was measured using radioactively labeled cells and the morphology examined using scanning electron microscopy. Similar numbers of cells were found to adhere to the potassium and argon-implanted titanium as to control (non-implanted) titanium. However, adhesion to the calcium-implanted titanium discs was significantly reduced. Moreover, although the cells were found to be well spread on the calcium and potassium-implanted titanium, a much greater proportion of cells appeared to remain rounded and poorly attached on the argon-implanted surface. These differences are discussed in relation to the observed surface roughness and chemistry, which were assessed using interferometry and X-ray photoelectron spectroscopy, respectively.

Osteoblast culture on polished titanium disks modified with phosphonic acids.

Titanium is widely used in dental implants due to its suitable physical properties and its good biocompatibility. However, it is integrated into bone only passively, and the resulting fixation in the bone, which is necessary for the function, is mainly mechanical in nature. With the objective of increasing the chemical interaction between the implant and the bone tissue, several phosphonic acids were synthesized and grafted onto titanium disks. Here we report on the proliferation, differentiation, and protein production of rat osteoblastic cells (CRP10/30) on phosphonic-acid-modified titanium surfaces studied in vitro. No statistical differences were found in osteoblast proliferation among the phosphonic-acid-modified titanium, unmodified titanium, and tissue culture plastic (used as a positive control), indicating that the phosphonic acids used were not cytotoxic to the osteoblasts used. For all surfaces (modified or not), the alkaline phosphatase activity was at least as good as it was on tissue culture plastic. However, the total amount of protein, and especially the collagen type I synthesis, was sensitive to surface modification. On titanium modified with ethane-1,1,2-triphosphonic acid, the total amount of synthesized protein was significantly higher than it was on unmodified titanium surfaces. A significant increase (up to 16%) of collagen type I production was observed on titanium surfaces modified with this acid or with methylenediphosphonic acid compared to unmodified titanium surfaces.

In situ atomic force microscopy of partially demineralized human dentin collagen fibrils

Dentin collagen fibrils were studied in situ by atomic force microscopy (AFM). New data on size distribution and the axial repeat distance of hydrated and dehydrated collagen type I fibrils are presented. Polished dentin disks from third molars were partially demineralized with citric acid, leaving proteins and the collagen matrix. At this stage collagen fibrils were not resolved by AFM, but after exposure to NaOCl aq for 100–240 s, and presumably due to the removal of noncollagenous proteins, individual collagen fibrils and the fibril network of dentin connected to the mineralized substrate were revealed. High-aspect-ratio silicon tips in tapping mode were used to image the soft fibril network. Hydrated fibrils showed three distinct groups of diameters: 100, 91, and 83 nm and a narrow distribution of the axial repeat distance at 67 nm. Dehydration resulted in a broad distribution of the fibril diameters between 75 and 105 nm and a division of the axial repeat distance into three groups at 67, 62, and 57 nm. Subfibrillar features (4 nm) were observed on hydrated and dehydrated fibrils. The gap depth between the thick and thin repeating segments of the fibrils varied from 3 to 7 nm. Phase mode revealed mineral particles on the transition from the gap to the overlap zone of the fibrils. This method appears to be a powerful tool for the analysis of fibrillar collagen structures in calcified tissues and may aid in understanding the differences in collagen affected by chemical treatments or by diseases.

Influence of the substrate reflectance on the quantum efficiency of thin CsI photocathodes

Performance of thin CsI films operated, at the same time, as reflective and semitransparent photocathodes is presented. Photoemission properties have been analysed on CsI films deposited on aluminium substrates made out of either polished disks or thin films evaporated onto fused silica disks. A comparison between measured values of quantum efficiency (QE) of such photocathodes and the QE of traditional reflective photocathodes is presented.

Optimizing filler content in an adhesive system containing pre-reacted glass-ionomer fillers

Objectives. (1) To evaluate the optimal concentration of the calcium type pre-reacted glass-ionomer (PRG-Ca) fillers in experimental light-activated adhesives for bonding to tooth substrates and fluoride release; (2) to evaluate the polymerization reactivity of these experimental filled adhesives; and (3) to examine the ultrastructure of the resin–dentin interface bonded with the commercial version of this self-etching adhesive (Imperva Fluoro Bond, Shofu Inc., Kyoto, Japan). Materials and methods. PRG-Ca fillers were prepared from the acid–base reaction of calcium type fluoroaluminosilicate glass with poly(acrylic acid) in water. Different experimental light-cured adhesives were prepared, with 0–57 wt% PRG-Ca fillers and 3 wt% aerosil silica incorporated in a resin matrix. Twenty-four hours shear bond strengths to bovine enamel and dentin were assessed using the adhesive with/or without accelerated aging. The cumulative amount of fluoride released from the cured adhesives and differential scanning calorimetry (DSC) measurements were also conducted. 180-grit SiC paper polished human dentin disks were treated with Imperva Fluoro Bond that contains 17 wt% PRG-Ca fillers and prepared for TEM examination. Results. Increase in PRG-Ca filler content of experimental adhesives was highly correlated with the decrease in bond strengths to dentin ( r=−0.96 to −0.99), the increase in cumulative fluoride release, ( r=0.97) and the decrease in polymerization energy (cal/g) of the adhesives ( r=−0.99) ( p<0.001). A PRG-Ca content of 17 wt% provided optimal bond strength to enamel and dentin after accelerated aging and fluoride release. TEM showed that salt-like matrices were present around the hydrogels and remnant glass cores of the PRG-Ca fillers. The commercial self-etching primer completely dissolved the smear layer and formed 2 μm thick hybrid layers in intact dentin. Significance. The use of silanized PRG-Ca fillers provides good adhesion and a source of fluoride release in a commercially available self-etching adhesive system.