3D parameter to quantify the anisotropy measurement of periodic structures on rough surfaces.

In this paper, a new 3D roughness parameter, Sreg, is proposed to quantify the regularity of a surface, independent of the amplitude and the scanning length units of the surface. The efficiency of this parameter is tested on noisy periodical surfaces with degrees of anisotropy. This parameter lies between zero (perfect noise) and 100% (a perfect periodic surface). This parameter enables the identification of the anisotropy directions of regularity for a given surface. For a periodical surface, the greater the noise, the lower the anisotropy. A direction function is proposed to analyse the direction of regularity of a rough surface, which then permits characterization of the directional regularity of the topography. The regularity parameter can be used for several purposes: to identify the direction of periodical structures formed by laser-pulsed radiations on the surface of solid workpieces; to examine the reproducibility of surface machining methods such as finishing process; and to identify the surface regularity produced by abrasive machining, such as precision surface grain, abrasive slotting, and lapping.

Reflection on the measurement and use of the topography of the indentation imprint.

The goal of this paper is to study the main uses of the residual imprint of the indentation test. It also discusses the different technologies and methods employed in this context. The difficulties encountered when trying to exploit the full potentials of the imprint are thoroughly examined. A survey of the literature on the quantification of the pile-up clearly shows that there is a lack of consensus on the measurement of the residual imprint as well as on treatment methods. Therefore, in order to widen the application fields of the indentation residual imprint, relevant and standardized indicators should be established.

On the relation between surface roughness of metallic substrates and adhesion of human primary bone cells.

Surface characteristics of materials, whether their topography, chemistry, or surface energy, play an essential part in osteoblast adhesion on biomaterials. Thus, the quality of cell adhesion will influence the cell's capacity to proliferate and differentiate in contact with a biomaterial. We have developed for more than ten years numerous studies on the influence of topography and chemistry of metallic substrates on the response of primary human bone cells. The originality of our approach is that contrary to most of other authors, we quantified the adhesion of primary human bone cells on metallic substrates with perfectly characterized surface topography after some hours but also over 21 days. Moreover, we have developed original statistical approaches for characterizing the relation between surface roughness and cell-adhesion parameters. In this article, we will illustrate different studies we did these last ten years concerning the development of a new adhesion parameter, the adhesion power; the correlation between short-term adhesion, long-term adhesion, and proliferation; the influence of roughness organization on cell adhesion and the development of the order parameter; our modeling approach of cell adhesion on surface topography; the relative influence of surface chemistry and topography on cell adhesion and contact angle; the relation between surface features dimensions and cell adhesion. Further, some considerations will be given on the methods for scanning surface topography for cell-adhesion studies. Finally, perspectives will be given to elucidate these intracellular mechanotransduction mechanisms induced by the deformation of cells on model sinusoidal peaks-or-valleys surfaces.

Dynamic evolution of interface roughness during friction and wear processes.

Dynamic evolution of surface roughness and influence of initial roughness (S(a) = 0.282-6.73 µm) during friction and wear processes has been analyzed experimentally. The mirror polished and rough surfaces (28 samples in total) have been prepared by surface polishing on Ti-6Al-4V and AISI 1045 samples. Friction and wear have been tested in classical sphere/plane configuration using linear reciprocating tribometer with very small displacement from 130 to 200 µm. After an initial period of rapid degradation, dynamic evolution of surface roughness converges to certain level specific to a given tribosystem. However, roughness at such dynamic interface is still increasing and analysis of initial roughness influence revealed that to certain extent, a rheology effect of interface can be observed and dynamic evolution of roughness will depend on initial condition and history of interface roughness evolution. Multiscale analysis shows that morphology created in wear process is composed from nano, micro, and macro scale roughness. Therefore, mechanical parts working under very severe contact conditions, like rotor/blade contact, screws, clutch, etc. with poor initial surface finishing are susceptible to have much shorter lifetime than a quality finished parts.

Optimization of the straightness measurements on rough surfaces by Monte Carlo simulation.

The straightness error of a coordinate measuring machine (CMM) is determined by measuring a rule standard. Thanks to a reversal technique, the straightness uncertainty of the CMM is theoretically dissociated from the straightness uncertainty of the rule. However, stochastic variations of the whole measurement system involve uncertainties of the CMM straightness error. To quantify these uncertainties, different sources of stochastic variations are listed with their associated probability density functions. Then Monte Carlo methods are performed first to quantify error and secondly to optimize measurement protocol. It is shown that a 5-measurement distance from 0.1 mm to each measurement coordinate allows a double reduction of uncertainties, principally due to the rule roughness amplitude (R(a) = 0.35 µm) and because this optimal distance of 0.1 mm is equal to the autocorrelation length of the rule roughness. With this optimal configuration, the final uncertainly on the straightness error of the CMM studied is less than 1 µm on the whole evaluated length of the rule (1 m). An algorithm, including Probe Tip Radius of the CMM and surface roughness of the piece, is finally proposed to increase CMM reliability by minimizing error measurements due to surface roughness of the measured piece.

How to select the most relevant 3D roughness parameters of a surface.

In order to conduct a comprehensive roughness analysis, around sixty 3D roughness parameters are created to describe most of the surface morphology with regard to specific functions, properties or applications. In this paper, a multiscale surface topography decomposition method is proposed with application to stainless steel (AISI 304), which is processed by rolling at different fabrication stages and by electrical discharge tool machining. Fifty-six 3D-roughness parameters defined in ISO, EUR, and ASME standards are calculated for the measured surfaces. Then, expert software "MesRug" is employed to perform statistical analysis on acquired data in order to find the most relevant parameters characterizing the effect of both processes (rolling and machining), and to determine the most appropriate scale of analysis. For the rolling process: The parameter Vmc (the Core Material Volume--defined as volume of material comprising the texture between heights corresponding to the material ratio values of p = 10% and q = 80%) computed at the scale of 3 µm is the most relevant parameter to characterize the cold rolling process. For the EDM Process, the best roughness parameter is SPD that represents the number of peaks per unit area after segmentation of a surface into motifs computed at the scale of 8 µm.

Existence of a typical threshold in the response of human mesenchymal stem cells to a peak and valley topography.

Our objective in this study was to determine whether a threshold in sensitivity of human mesenchymal stem cells (hMSC) to isotropic roughness exists. Using electrical discharge machining a very wide range of roughnesses (1.2µm

Statistical approach of chemistry and topography effect on human osteoblast adhesion.

Our objective in this work was to determine statistically the relative influence of surface topography and surface chemistry of metallic substrates on long-term adhesion of human bone cell quantified by the adhesion power (AP). Pure titanium, titanium alloy, and stainless steel substrates were processed with electro-erosion, sandblasting, or polishing giving various morphologies and amplitudes. The surface chemistry was characterized by X-ray photoelectron spectroscopy (XPS) associated with an extensive analysis of surface topography. The statistical analysis demonstrated that the effect on AP of the material composition was not significant. More, no correlation was found between AP and the surface element concentrations determined by XPS demonstrating that the surface chemistry was not an influencing parameter for long-term adhesion. In the same way, the roughness amplitude, independently of the process, had no influence on AP, meaning that roughness amplitude is not an intrinsic parameter of long-term adhesion. On the contrary, the elaboration process alone had a significant effect on AP. For a same surface elaboration process, the number of inflexion points, or G parameter, was the most pertinent roughness parameter for describing the topography influence on long-term adhesion. Thus, more the inflexion points, more the discontinuities, higher the long-term adhesion.

Definition of a simple statistical parameter for the quantification of orientation in two dimensions: application to cells on grooves of nanometric depths.

Contact guidance is generally evaluated by measuring the orientation angle of cells. However, statistical analyses are rarely performed on these parameters. Here we propose a statistical analysis based on a new parameter sigma, the orientation parameter, defined as the dispersion of the distribution of orientation angles. This parameter can be used to obtain a truncated Gaussian distribution that models the distribution of the data between -90 degrees and +90 degrees. We established a threshold value of the orientation parameter below which the data can be considered to be aligned within a 95% confidence interval. Applying our orientation parameter to cells on grooves and using a modelling approach, we established the relationship sigma=alpha(meas)+(52 degrees -alpha(meas))/(1+C(GDE)R) where the parameter C(GDE) represents the sensitivity of cells to groove depth, and R the groove depth. The values of C(GDE) obtained allowed us to compare the contact guidance of human osteoprogenitor (HOP) cells across experiments involving different groove depths, times in culture and inoculation densities. We demonstrate that HOP cells are able to identify and respond to the presence of grooves 30, 100, 200 and 500 nm deep and that the deeper the grooves, the higher the cell orientation. The evolution of the sensitivity (C(GDE)) with culture time is roughly sigmoidal with an asymptote, which is a function of inoculation density. The sigma parameter defined here is a universal parameter that can be applied to all orientation measurements and does not require a mathematical background or knowledge of directional statistics.

Relative influence of surface topography and surface chemistry on cell response to bone implant materials. Part 1: physico-chemical effects.

Knowledge of the complexity of cell-material interactions is essential for the future of biomaterials and tissue engineering, but we are still far from achieving a clear understanding, as illustrated in this review. Many factors of the cellular or the material aspect influence these interactions and must be controlled systematically during experiments. On the material side, it is essential to illustrate surface topography by parameters describing the roughness amplitude as well as the roughness organization, and at the scales pertinent for the cell response, i.e., from the nano-scale to the micro-scale. Authors interested in this field must be careful to develop surfaces or methods systematically, allowing perfect control of the relative influences of surface topography and surface chemistry.

Relative influence of surface topography and surface chemistry on cell response to bone implant materials. Part 2: biological aspects.

A current medical challenge is the replacement of tissue which can be thought of in terms of bone tissue engineering approaches. The key problem in bone tissue engineering lies in associating bone stem cells with material supports or scaffolds that can be implanted in a patient. Beside bone tissue engineering approaches, these types of materials are used daily in orthopaedics and dental practice as permanent or transitory implants such as ceramic bone filling materials or metallic prostheses. Consequently, it is essential to better understand how bone cells interact with materials. For several years, the current authors and others have developed in vitro studies in order to elucidate the mechanisms underlying the response of human bone cells to implant surfaces. This paper reviews the current state of knowledge and proposes future directions for research in this domain.

Statistical demonstration of the relative effect of surface chemistry and roughness on human osteoblast short-term adhesion.

The effects of material composition, surface chemistry or surface topography on cell attachment (short-term adhesion) have been largely studied on bone-derived cells. However, no statistical demonstration of these effects has been performed until now. With this objective, we quantified the attachment after 24 hours of human osteoblasts on pure titanium, titanium alloy and stainless steel substrates presenting 6 different surface morphologies and 2 different roughness amplitude obtained by sand-blasting, electro-erosion, acid etching, polishing and machine-tooling. The coating by a gold-palladium layer of these surfaces allowed determining the relative effect of the surface roughness and of the surface chemistry. By multiple analysis of variance, we demonstrated that neither material composition nor surface roughness amplitude influenced cell attachment except on sandblasted pure titanium substrates. On the contrary, a high significant influence of the process used to produce the surface was observed meaning that the main influent factor on cell attachment could be either the surface morphology or the surface chemistry induced by the process. As the coating of surfaces by a gold-palladium layer decreased significantly the attachment of cells on the majority of substrates, we concluded that attachment is rather influenced by surface chemistry than by surface topography.

A kinetic approach to osteoblast adhesion on biomaterial surface.

An incompletely understood question in the field of biomaterials is how eucaryotic cells adhere on material surfaces. The adhesion of cells on materials is generally studied after some hours. Because this evaluation after some hours cannot let us presume about the future of the cells on the material, we have developed a culture model that does allow study in the long term of an elaborate cell/material interface closer to the in vivo situation. For that, we used a progressive trypsin-based detachment method. Here we report on the mathematical modeling of long-term human primary osteoblastic cell adhesion on metallic substrates, which allows us to quantify the real adhesion simultaneously by taking into account the effect of cell proliferation. A time-dependent adhesion index t(d) is proposed, which varies with culture time t according to the power law: t(d)(t) = at(b), a being independent of b. The exponent b is equal to 0.5 +/- 0.03 and is independent of the substrate's characteristics, meaning that the long-term adhesion increases proportionally to the square root of culture time. On the contrary, the parameter a significantly depends on the material's nature, the surface's topography, and the surface chemistry of the substrate and is sufficient to characterize cell adhesion. From this relationship, we suggest that a diffusion-based process related to the kinetic of formation of extracellular matrix should be involved in long-term adhesion on materials.

Topography effects of pure titanium substrates on human osteoblast long-term adhesion.

Classically various treatments are applied to increase the roughness of titanium implants and improve their integration in the tissues. Many in vitro studies have been performed to better understand the mechanisms underlying the adhesion of cells on materials. Frequently, the adhesion is related to the attachment of cells during the first hours of contact with the substrate. For several years, our objective has been to develop experimental methods to evaluate the long-term adhesion of human osteoblasts from some hours to several weeks in order to model in vitro a tissue-like interface. This culture model allows for the formation over 21 days of a complex osteoblast/extracellular matrix/material interface. We recently developed a new parameter called adhesion power (AP) to evaluate this long-term adhesion. In this study, our objective is to check its efficiency in discriminating the long-term adhesion of human osteoblasts on pure titanium substrates with seven different surface morphologies obtained by electro-erosion, sandblasting, polishing, acid-etching and machine-tooling. By scanning electron microscopy, we observed that the human osteoblasts did spread more intimately on surface with low roughness amplitude than on rough ones. However, the AP was higher on rough isotropic surfaces obtained by electro-erosion, sandblasting or acid-etching and lower on smoother surfaces obtained by polishing and machine-tooling. We demonstrated that the AP was pertinent for evaluating human osteoblast's long-term adhesion on pure titanium surfaces with various roughness parameters. Its correlation with the order parameter, which describes the organization of the roughness, confirmed once more that human osteoblasts are more sensitive to the organization and morphology of the roughness than to its amplitude.

Bootstrap analysis of the relation between initial adhesive events and long-term cellular functions of human osteoblasts cultured on biocompatible metallic substrates.

Classically, the evaluation of cellular adhesion of cells on substrates is limited to the evaluation of cell attachment after some hours. We have claimed for several years that this evaluation is incomplete concerning the evaluation of cell adhesion and more precisely of the quality of the in vitro cell/biomaterial interface. With a view to demonstrating this assertion, we develop in this paper statistical correlations between short-term adhesion (STA) evaluating the attachment after 24 h (IA: initial attachment) and long-term adhesion (LTA) evaluating the strength of the cell/matrix substrate interface over 21 days of culture (AP: adhesion power). Additionally, as the adhesion phase is known to influence further growth of cells we proceed to the correlation of STA with the number of cells after 21 days. We demonstrate statistically the expected positive relation existing between STA and cell growth and we show that this relation is totally independent of the substrate's surface topography or chemistry. More surprisingly, we demonstrate the absence of correlation between IA and AP. This illustrates the fact that different mechanisms underlie STA and LTA. Moreover, this study demonstrates that the evaluation of the number of attached cells after some hours cannot let us presume either that cells will survive or that they will adhere at later times by forming a complex cell/substrate interface by synthesis of extracellular matrix proteins. Finally, the originality of this work lies in the extensive statistical correlation analysis performed between biological parameters describing the cell behaviour on a substrate.

Statistical correlation between cell adhesion and proliferation on biocompatible metallic materials.

Our ambition for several years is to appreciate and quantify the long-term adhesion of cells on materials at times where the interface between cells and substrate becomes more complex, more closed to the cell/matrix/substrate interface existing in vivo. With this objective, we quantified the long-term adhesion and proliferation of human osteoblasts cultured from 24 h to 21 days on pure titanium, titanium alloy, and stainless-steel substrates presenting six different surface morphologies and two different roughness amplitude. Hence, we did proceed to the statistical correlation of cell adhesion and cell proliferation on 30 different substrates. Additionally, we described surface topography not only by the roughness amplitude but also by the roughness morphology using new specific parameters. By multiple analysis of variance, we demonstrated that nor material composition nor surface roughness amplitude did influence cell proliferation, whereas a very significant influence of the process used to produce the surface was observed meaning that the main influent factor on cell proliferation was the surface morphology. The long-term adhesion and proliferation capacity of cells were positively correlated on 23 types of substrates on 30, this positive correlation being statistically asserted on 13 types of substrates on 23. This study is the first demonstration of the existence of a statistical correlation between long-term adhesion and proliferation capacity of human bone cells on substrates with various chemical composition, surface chemistry, and surface topography.

Kinetic study of the expression of beta-catenin, actin and vinculin during osteoblastic adhesion on grooved titanium substrates.

Intercellular adhesions are known to play an important role in differentiation of osteoblasts and in the development of bone tissue architecture. However, to our knowledge, they have never been studied during the formation of bone tissue in contact with a biomaterial surface. In an in vitro kinetic study, we followed the expression of proteins involved in cell-cell interactions (beta-catenin), in cell-material interactions (vinculin) and in cytoskeleton (actin) of human osteoblastic cells cultured on grooved titanium-based substrates during 1, 2, 4, 6, 24, 48, and 72 hours. The human osteoblasts aligned themselves in the 150 microm wide grooves only after 24 hours. The distribution of vinculin-positive focal contacts, actin cytoskeleton and beta-catenin positive-adherens junctions was not significantly influenced by the cell alignment. beta-catenin-positive adherens junctions were expressed by human osteoblasts as soon as 1 hour after inoculation. At this time, they showed a patch-like aspect along cytoplasmic processes in contact with an underlying or an adjacent cell. After 2 hours, the patches were more and more numerous underlining the connections between cells. After 4 hours and more, the patches were organised in a parallel arrangement perpendicular to the two connected cells forming a "zip-like" aspect. Additionally, using double immuno-staining, we demonstrated that sometimes beta-catenin and vinculin appeared co-localised and sometimes not. The linkage of catenin/cadherin complex and vinculin-positive focal contacts with actin filaments may explain this apparent co-localisation.

[Mechanisms of damage to metal-on-polyethylene articulating surfaces of total hip prostheses: influence of intra-articulate migration of metallic debris]. / Mécanismes d'endommagement des pièces de frottement des arthroplasties de hanche à couple métal-polyéthylène. Influence de la migration intra-articulaire de débris métalliques.

PURPOSE OF THE STUDY: The objective of this work was to identify the mechanisms leading to deterioration of the polyethylene acetabular surface in total hip prostheses. MATERIAL AND METHODS: We conducted an in vivo analysis of damage caused to articulating surfaces of metal-on-polyethylene total hip prostheses. This analysis was performed on three of the 45 explants of Harris-Galante prostheses available to use from our series of 1480 implantations performed between 1985 and 1996. These three pieces were selected because large-sized fibers of metallic debris were identified on the polyethylene surface and because the explants had been performed for reasons other than loosening in aseptic patients. Macroscopic examination was combined with scan electron microscopy to analyze morphological changes. RESULTS: We found that identical damage could be observed on the polyethylene explants despite the different sizes of the metallic heads and different metal-on-polyethylene combinations. Our analysis confirmed the deleterious effect of metallic foreign bodies trapped in contact with the articulate surfaces. These foreign bodies resulted in one case from rupture of a multifilament wire used for the trochanteric fixation and in two cases from the surfacing of the non-cemented Harris-Galante cups. The microscopic analysis demonstrated several successive localizations of the foreign bodies on the polyethylene surface before becoming deeply encrusted in the polyethylene where they deteriorated the femoral head surface (rough) and wore the polyethylene surface (abrasion). When the fibers came from the surfacing of the Harris-Galante cups, the metallic debris remained unrecognized during the revision procedure and were only identified later during the systematic examination of prosthetic explants. DISCUSSION AND CONCLUSION: These findings emphasize the importance of quality surface treatments for non-cemented prostheses and argue in favor of particular precautions during operative manipulation of these components. A systematic analysis of the prosthetic explants is advisable, particularly for components explanted because of wear or unexplained osteolysis. Use of multifilament trochanteric wires should be avoided because rupture raises the risk of intra-articulate migration of metallic debris. If the prosthesis involves a polyethylene acetabular surface, ceramic heads should be preferred to improve resistance to abrasion, particularly to limit the deleterious effect of a third body.

An unscaled parameter to measure the order of surfaces: a new surface elaboration to increase cells adhesion.

We present a new parameter to quantify the order of a surface. This parameter is scale-independent and can be used to compare the organization of a surface at different scales of range and amplitude. To test the accuracy of this roughness parameter versus a hundred existing ones, we created an original statistical bootstrap method. In order to assess the physical relevance of this new parameter, we elaborated a great number of surfaces with various roughness amplitudes on titanium and titanium-based alloys using different physical processes. Then we studied the influence of the roughness amplitude on in vitro adhesion and proliferation of human osteoblasts. It was then shown that our new parameter best discriminates among the cell adhesion phenomena than others' parameters (Average roughness (Ra em leader )): cells adhere better on isotropic surfaces with a low order, provided this order is quantified on a scale that is more important than that of the cells. Additionally, on these low ordered metallic surfaces, the shape of the cells presents the same morphological aspect as that we can see on the human bone trabeculae. The method used to prepare these isotropic surfaces (electroerosion) could be undoubtedly and easily applied to prepare most biomaterials with complex geometries and to improve bone implant integration. Moreover, the new order parameter we developed may be particularly useful for the fundamental understanding of the mechanism of bone cell installation on a relief and of the formation of bone cell-material interface.

In vitro MC3T3 osteoblast adhesion with respect to surface roughness of Ti6Al4V substrates.

This work investigates the role of the surface roughness of Ti6Al4V on the cell morphology, proliferation and adhesion, and in particular on the variation of the expression of cell adhesion proteins. Standardised test samples with five different surface preparations are used: sandblasted, 80, 1200, and 4000 grade polished, mirror polished. Surface roughness is analysed by Scanning Electron Microscopy and LASER Confocal Microscopy. Cell culture experiments are performed with MC3T3-E1 mouse osteoblasts after 3 days culture: proliferation rate, morphology and adhesion are assessed. The variations of expression of cell adhesion proteins are evidenced by indirect immune fluorescence method: actin from the cytoskeleton, vinculin from the focal adhesion complex, fibronectin and collagen I from the extracellular matrix. The results reveal a clear influence of surface roughness of Ti6Al4V on cell proliferation, morphology and adhesion. A significant correlation is established between surface roughness and cell growth. More the surface is smooth more the osteoblasts proliferate and appear spread out on the test samples. In addition, the expression of adhesion proteins varies with respect to the surface roughness. These results indicate a direct relationship between the decrease of cell adhesion and the increase of cell proliferation on mirror polished materials.