Simultaneous spray coating of interacting species: general rules governing the poly(styrene sulfonate)/poly(allylamine) system.

Simultaneous spraying of two solutions of interacting species onto a substrate held vertically leads to the formation of nanometer-sized coatings. Here we investigate the simultaneous spraying of poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) solutions leading to the formation of a film composed of PSS/PAH complexes. The thickness of this film increases linearly with the cumulative spraying time. For a given spraying rate of PAH (respectively PSS), the growth rate of the film depends strongly upon the PSS/PAH ratio and passes through a maximum for a PSS/PAH ratio lying between 0.55 and 0.8. For a PSS/PAH ratio that is maintained constant, the growth speed of the film increases linearly with the spraying rate of polyelectrolyte of both solutions. Using X-ray photoelectron spectroscopy, we find that the film composition is almost independent of the PSS/PAH (spayed) ratio, with composition very close to 1:1 in PSS:PAH film. The 1:1 PSS:PAH composition is explained by the fact that the simultaneous spraying experiments are carried out with salt-free solutions; thus, electroneutrality in the film requires exact matching of the charges carried by the polyanions and the polycations. Zeta potential measurements reveal that, depending on whether the PSS/PAH spraying rate ratio lies below or above the optimal spraying rate ratio, the film acquires a positive or a negative excess charge. We also find that the overall film morphology, investigated by AFM, is independent of the spraying rate ratio and appears to be composed of nanometer-sized grains which are typically in the 100 nm range.

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.

Study of the antimicrobial and antifouling properties of different oxide surfaces.

Membrane separation processes find applications in an array of fields as they use far less energy and chemical agents than competing processes. However, a major drawback of membrane technology is that biofilm formation alters membrane performances. Preventing biofilm formation is thus a pivotal challenge for larger-scale development of membrane processes. Here, we studied the comparative antibacterial activities of different inorganic membranes (ceramic and zeolite-coated ceramic with or without copper exchange) using several bacterial strains (Escherichia coli, Staphylococcus aureus, and Bacillus subtilis). In static conditions, alumina plates coated with Cu-exchanged zeolite showed significant bactericidal activity. In dynamic mode (circulation of a contaminated nutrient medium), there was no observable bacterial adhesion at the surface of the Cu-exchanged material. These results confirm the antifouling properties of the Cu-mordenite layer due to both the increased hydrophilicity and antibacterial properties of the active layer.Tests performed with tubular filtration membranes (without copper exchange) showed a significant decline in membrane hydraulic properties during filtration of culture media containing bacteria, whereas copper-exchanged membranes showed no decline in hydraulic permeability. Filtration tests performed with concentrated culture media containing spores of B. subtilis led to a significant decrease in membrane hydraulic permeabilities (but less so with Cu-exchanged membranes). The surfaces showed less effective global antifouling properties during the filtration of a concentrated culture medium due to competition between bacterial growth and the bactericidal effect of copper. Analyses of copper leached in solution show that after a conditioning step, the amount of copper released is negligible.

Effect of several sterilisation techniques on homogeneous self assembled monolayers.

Understanding how cells sense their environment and are able to regulate their metabolism is of great importance for the success of biomaterials implantation. Self assembled monolayers (SAMs) are in use nowadays to model the surface of such materials. They permit the control of different surface parameters (like chemistry, surface energy and topography) enabling to get a greater insight in cells behaviour when interacting with surfaces and thus, in the future, to enhance surface properties of biomaterials. As sterilisation is the compulsory step for in vitro and in vivo assays with living biological materials, it is important to know how SAMs react under sterilisation techniques in use on biomaterials. In this work, the effect of three types of sterilisation techniques: gamma-irradiation, mostly used on biomaterials, dry heat and steam autoclaving, have been investigated on NH2 and CH3 terminated SAMs. Gamma-irradiation destructs drastically the NH2 and partially the CH3 monolayers by producing oxidative compounds (COOH, C=O, C-OH). The main product induced by gamma-irradiation on NH2 monolayers is carboxylic acid, whereas CH3 shows an important increase in the amount of alcoholic groups. This difference in deterioration is assumed to be due to the higher stability of the CH3 monolayer. Steam autoclaving to a lesser extent gives the same results on NH2 monolayers. Dry heat seems to be the most reliable technique, which can be used on such surfaces as it removes physically adsorbed organic contaminants without affecting the integrity of the surface.

Protein covalent immobilization via its scarce thiol versus abundant amine groups: Effect on orientation, cell binding domain exposure and conformational lability.

Quantity, orientation, conformation and covalent linkage of naturally cell adhesive proteins adsorbed or covalently linked to a surface, are known to influence the preservation of their subsequent long term cell adhesion properties and bioactivity. In the present work, we explore two different strategies for the covalent linking of plasma fibronectin (pFN) - used as a cell adhesive model protein, onto a polystyrene (PS) surface. One is aimed at tethering the protein to the surface in a semi-oriented fashion (via one of the 4 free thiol reactive groups on the protein) with a heterofunctional coupling agent (SSMPB method). The other aims to immobilize the protein in a more random fashion by reaction between the abundant pendant primary amine bearing amino acids of the pFN and activated carboxylic surface functions obtained after glutaric anhydride surface treatment (GA method). The overall goal will be to verify the hypothesis of a correlation between covalent immobilization of a model cell adhesive protein to a PS surface in a semi-oriented configuration (versus randomly oriented) with promotion of enhanced exposure of the protein's cell binding domain. This in turn would lead to enhanced cell adhesion. Ideally the goal is to elaborate substrates exhibiting a long term stable protein monolayer with preserved cell adhesive properties and bioactivity for biomaterial and/or cell adhesion commercial plate applications. However, the initial restrictive objective of this paper is to first quantitatively and qualitatively investigate the reversibly (merely adsorbed) versus covalently irreversibly bound protein to the surface after the immobilization procedure. Although immobilized surface amounts were similar (close to the monolayer range) for all immobilization approaches, covalent grafting showed improved retention and stronger "tethering" of the pFN protein to the surface (roughly 40%) after SDS rinsing compared to that for mere adsorption (0%) suggesting an added value to the covalent grafting immobilization methods. However no differences in exposure of the cell binding domains were observed (ELISA results) before SDS rinsing, suggesting that pFN protein grafting to the surface is initially kinetically driven be a stochastic random adsorption phenomenon. Covalent grafting acts in the final stage as a process that simply tethers and stabilizes (or freezes) the initial conformation/orientation of the adsorbed protein on the surface. In addition covalent linkage via the SSMPB approach is likely favored by surface-induce exposure of one of the normally hidden free thiol group pair, thus optimizing covalent linkage to the surface. However after SDS rinsing, this "tethering"/"freezing" effect was significantly more prominent for the GA grafting approach (due to greater number of potential covalent links between the protein and the surface) compared to that for the SSMPB approach. This hypothesis was buttressed by the improved resistance to denaturation (smaller conformational lability) for the GA compared to the SMPB approach and improved exposure of the cell binding domain for the former (>50%) even after SDS rinsing. These results are promising in that they suggest covalent tethering of fibronectin to PS substrate in a monolayer range, with significantly improved irreversible protein surface bonding via both approaches (compared to that for mere adsorption). The latter are likely applicable to a wide range of proteins.

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.

Surface transformation of silicon-doped hydroxyapatite immersed in culture medium under dynamic and static conditions.

A comparative study of in vitro bioactivity of hydroxyapatite (HA) and silicon-doped hydroxyapatite (SiHA) has been carried out by immersion in a cell culture medium with or without fetal bovine serum during 14 days in static and dynamic conditions. A specific bioreactor was developed for the experiments in dynamic conditions. Ceramic surface transformations were characterized by electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy before and after immersion. The monitoring of calcium, phosphate and proteins in immersion medium was also done during the experiment. The two hydroxyapatite surfaces immersed in cell culture medium under dynamic conditions were found to be more probably covered by a new Mg-enriched Ca-deficient apatite layer than surfaces immersed under static conditions. These results suggest that dynamic procedure and medium with serum macromolecules seem to be more adequate to predict the in vivo activity of bioceramics. Moreover, SiHA presented a higher capacity of protein adsorption.

Opposite responses of cells and bacteria to micro/nanopatterned surfaces prepared by pulsed plasma polymerization and UV-irradiation.

Chemically and topographically patterned surfaces have high potential as model surfaces for studying cell and bacteria responses to surface chemistry and surface topography at a nanoscale level. In this work, we demonstrated the possibility to combine pulsed plasma polymerization and UV-irradiation to obtain topographical patterns and chemical patterns perfectly controlled at microlateral resolution and sub-micrometer depth level. Biological experiments were conducted using human osteoprogenitor cells and Escherichia coli K12. Proliferation and orientation of cells and bacteria were analyzed and discussed according to the size and the chemistry of the features. This work showed interesting opposite behavior of bacteria compared to eukaryotic cells, in response to the surface chemistry and to the surface topography. This result may be particularly useful on medical implants. From a methodological point of view, it highlighted the importance of working with versatile and well-characterized surfaces before and after sterilization. It also points out the relevance and the necessity of analyzing eukaryotic cell and bacteria adhesion in parallel way.

Changes in silicon elastomeric surface properties under stretching induced by three surface treatments.

Poly(dimethylsiloxane) (PDMS) substrates are used in many applications where the substrates need to be elongated and various treatments are used to regulate their surface properties. In this article, we compare the effect of three of such treatments, namely, UV irradiation, water plasma, and plasma polymerization, both from a molecular and from a macroscopic point of view. We focus our attention in particular on the behavior of the treated surfaces under mechanical stretching. UV irradiation induces the substitution of methyl groups by hydroxyl and acid groups, water plasma leads to a silicate-like layer, and plasma polymerization causes the formation of an organic thin film with a major content of anhydride and acid groups. Stretching induces cracks on the surface both for silicate-like layers and for plasma polymer thin coatings. This is not the case for the UV irradiated PDMS substrates. We then analyzed the chemical composition of these cracks. In the case of water plasma, the cracks reveal native PDMS. In the case of plasma polymerization, the cracks reveal modified PDMS. The contact angles of plasma polymer and UV treated surfaces vary only very slightly under stretching, whereas large variations are observed for water plasma treatments. The small variation in the contact angle values observed on the plasma polymer thin film under stretching even when cracks appear on the surface are explained by the specific chemistry of the PDMS in the cracks. We find that it is very different from native PDMS and that its structure is somewhere between Si(O2) and Si(O3). This is, to our knowledge, the first study where different surface treatments of PDMS are compared for films under stretching.

[Secondary hyperparathyroidism and articular chondrocalcinosis in the aged]. / Hyperparathyroïdie secondaire et chondrocalcinose articulaire chez le sujet âgé.

The incidence of articular chondrocalcinosis (ACC) in elderly patients hospitalised in geriatric departments is approximately 30%. Routine studies including a 2 hour calcium/phosphorus balance, parathormone assay and radiological investigations enabled the selection of 73 patients with secondary hyperparathyroidism. ACC was present in 38 of these individuals (52%). They were slightly older (87 +/- 5) than cases of secondary hyperparathyroidism without radiological ACC (84 +/- 8). Among patients with secondary hyperparathyroidism with ACC, there were 90% women and 10% men, while the sex ratio in the department was 77% women and 23% men. Results of calcium/phosphorus balance and parathormone levels were similar, in the presence or absence of ACC.