Stéphane Benayoun

Functionalization of Titanium with Chitosan via Silanation: Evaluation of Biological and Mechanical Performances

Complications in dentistry and orthopaedic surgery are mainly induced by peri-implant bacterial infections and current implant devices do not prevent such infections. The coating of antibacterial molecules such as chitosan on its surface would give the implant bioactive properties. The major challenge of this type of coating is the attachment of chitosan to a metal substrate. In this study, we propose to investigate the functionalization of titanium with chitosan via a silanation. Firstly, the surface chemistry and mechanical properties of such coating were evaluated. We also verified if the coated chitosan retained its biocompatibility with the peri-implant cells, as well as its antibacterial properties. FTIR and Tof-SIMS analyses confirmed the presence of chitosan on the titanium surface. This coating showed great scratch resistance and was strongly adhesive to the substrate. These mechanical properties were consistent with an implantology application. The Chitosan-coated surfaces showed strong inhibition of Actinomyces naeslundii growth; they nonetheless showed a non significant inhibition against Porphyromonas gingivalis after 32 hours in liquid media. The chitosan-coating also demonstrated good biocompatibility to NIH3T3 fibroblasts. Thus this method of covalent coating provides a biocompatible material with improved bioactive properties. These results proved that covalent coating of chitosan has significant potential in biomedical device implantation.

Preparation of boron nitride-based coatings on metallic substrates via infrared irradiation of dip-coated polyborazylene

BN-based coatings on metallic (titanium, aluminium and copper) substrates are prepared by infrared irradiation of a dip-coated polyborazylene. This innovative strategy creates an access towards the molecular design of hexagonal-boron nitride coatings as protective materials for low melting point metals.

The effects of femtosecond laser-textured Ti-6Al-4V on wettability and cell response

To study the biological activity effects of femtosecond laser-induced structures on cell behavior, TA6V samples were micro-textured with focused femtosecond laser pulses generating grooves of various dimensions on the micrometer scale (width: 25-75μm; depth: 1-10μm). LIPSS (Laser Induced Periodic Surface Structures) were also generated during the laser irradiation, providing a supplementary structure (sinusoidal form) of hundreds of nanometers at the bottom of the grooves oriented perpendicular (⊥ LIPPS) or parallel (// LIPPS) to the direction of these grooves. C3H10 T1/2 murine mesenchymal stem cells were cultivated on the textured biomaterials. To have a preliminary idea of the spreading of biological media on the substrate, prior to cell culture, contact angle measurement were performed. This showed that the post-irradiation hydrophilicity of the samples can decrease with time according to its storage environment. The multiscale structuration either induced a collaborative or a competitive influence of the LIPSS and grooves on the cells. It has been shown that cells individually and collectively were most sensitive to microscale grooves which were narrower than 25μm and deeper than 5μm with ⊥ LIPPS. In some cases, cells were individually sensitive to the LIPSS but the cell layer organization did not exhibit significant differences in comparison to a non-textured surface. These results showed that cells are more sensitive to the nanoscale structures (LIPSS), unless the microstructuress size is close to the cell size and deeper than 5μm. There, the cells are sensitive to the microscale structures and go on spreading following these structures.

Hybrid silica coatings on polycarbonate: enhanced properties

Hybrid silica coatings based on 3- glycidoxypropyltriethoxysilane (GPTES), tetraethylorthosilicate (TEOS) and colloidal silica were deposited on polycarbonate (PC) by the sol–gel method, in order to obtain a material with enhanced properties with respect to raw PC (mainly scratch resistance, hydrophobicity and density), and consequently reach increased durability. The necessity of performing a N2-plasma treatment on PC (before coating deposition) was highlighted in order to obtain a good adherence between the coating and the substrate: XPS measurements showed that after treatment, nitrogenous radicals had formed on the PC surface and were able to link covalently with the sol during its deposition. Adherence was also higher when young sols (<8-day-old) were used. Different alkoxysilanes/colloidal silica ratios were tested to optimize the coating resistance: crack resistance of the coatings was found to be greater when the ratio was high. Scratch resistance of raw PC was enhanced as soon as PC was coated, irrespective of the alkoxysilanes/colloidal silica ratio or the sol ageing time. The density of the coatings was assessed by environmental ellipsometric porosimetry and found to be very high. Water contact angle measurements showed that the hydrophobicity of the coatings was inferior to raw PC. The addition in the sol of a small wt% of octyltriethoxysilane (OTES), 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FTES) and silicone surface additive (BYK-306) allowed a significant increase in hydrophobicity of the samples.

Mechanical properties of sol-gel coatings on polycarbonate: a review

Abstract Organic/inorganic hybrid coatings prepared via the sol–gel process have received lot of interests during the early twenty-first century. Devices obtained thanks to this low-temperature route display a large panel of bulk and surface properties that can be modulated according to the target. Moreover, this versatility enables to offer solutions in various domains and industrial applications such as microelectronics, optic, aeronautic, automotive, health. When the aimed application required polymer as substrate, the use of sol–gel process takes its full interest as soft chemistry. This review is dedicated to mechanical properties improvement of a common polymer substrate, e.g., polycarbonate, when a transparent sol–gel coating recovered it.Graphical Abstract

Wear Protection without Surface Modification Using a Synergistic Mixture of Molecular Brushes and Linear Polymers

We describe the design of lubricating and wear protecting fluids based on mixtures of bottle-brushes (BB) and linear polymer solutions. To illustrate this concept, we used hyaluronic acid (HA), a naturally occurring linear polyelectrolyte, and a water-soluble synthetic BB polymer. Individually, these two polymers exhibit poor wear protecting capabilities compared to that of saline solutions. Mixture of the two polymers in pure water or in saline allows the wear protection of surfaces over a wide range of shearing conditions to drastically increase. We demonstrate that this synergy between the BB and HA polymers emerges from a strong cohesion between the two components forming the boundary film due to entanglements between both polymers. We show that this concept can be applied to other types of linear polymers and surfaces and is independent of the chemical and mechanical properties of the surfaces.

Structural study of a titanium–titanium boride cermet coating formed upon laser fusion of boron on a titanium foil

The laser melting conditions of boron and titanium on the surface of a titanium foil have been determined. Both fusions induce a chemical reaction resulting in the formation of a cermet (ceramic–metal composite) coating on the surface of the titanium sample. This coating, the hardness of which lies between 300 and 500 Hv (whereas its thickness lies between 100 and 160 µm) is made of an intimate mixture of α-Ti, TiB2 and TiB, the metallic phase being the major one. Underlying, α-Ti is only heat affected with, just beneath the cermet layer, acicular looking grains. Crystallographic analyses of TiB2 indicate that the phase presents rather large crystallites with sizes of about 0.07 µm and 1 µm along the [00l] and [h00] directions, respectively. This phase presents no preferred orientation and almost no network strains.

Scratch-resistant sol–gel coatings on pristine polycarbonate

The deposition of protective transparent coatings on polycarbonate (PC) with higher scratch resistance than that of the polymeric substrate is performed using an original sol–gel system. Our strategy relies on the preparation of hybrid organic–inorganic (HOI) films using sol–gel based on 3-glycidoxypropyltrimethoxysilane (GPTMS), tetraethoxysilane (TEOS) and zirconium(IV) propoxide (ZTP). We demonstrate that despite a low coating-to-PC adhesion (<2 J m−2), it is possible to maintain the coating integrity under high applied scratch forces when the organic domains of the film are highly connected. In this case, the increase in organic network connectivity was achieved through the reaction of epoxide rings in the presence of ZTP, as evidenced by FTIR. The subsequent additional plasticity of the coating led to an increase in scratch-test delamination force by more than twofold: from 1.7 N for the hybrid film without ZTP to 3.8 N with the highest degree of ZTP content. In regard to the inorganic network, an increasing number of Si–O–Zr and Zr–O–Zr bonds with increasing ZTP content were evidenced by FTIR and 17O MAS NMR, allowing improved hydrolysis resistance, and therefore more durable coatings. Altogether, these results demonstrate the key role played by ZTP in tuning the mechanical properties and durability of HOI coating without requiring adhesion-promoting treatments.

Influence of the polypropylene structure on the replication of nanostructures by injection molding

In this paper, an experimental study of replication by injection molding of sub-micrometer features is presented. Two polypropylenes with different melt flow rates (MFR) were used throughout this study. The used removable mold insert was textured with a femtosecond laser. Replication of these periodic structures, called ripples, is thus investigated. Despite different MFR, we show that the viscosities of the two polymers at the investigated temperatures and injection shear rates are similar. The reproducibility of the injected molded samples and the texture of the mold were analyzed. We propose a specific methodology to quantify the reproducibility quality replicas. The latter introduces morphological parameters such as anisotropy rate, power density, etc. A difference between the two replicas was noticeable. Based on rheological analysis, the viscosity was ruled out as the origin of this difference. Other properties were identified as the source such as the chain length and the stress relaxation time. Their impact on the replication quality was investigated and found interesting.

Ultrafast laser spatial beam shaping based on Zernike polynomials for surface processing.

In femtosecond laser machining, spatial beam shaping can be achieved with wavefront modulators. The wavefront modulator displays a pre-calculated phase mask that modulates the laser wavefront to generate a target intensity distribution in the processing plane. Due to the non-perfect optical response of wavefront modulators, the experimental distribution may significantly differ from the target, especially for continuous shapes. We propose an alternative phase mask calculation method that can be adapted to the phase modulator optical performance. From an adjustable number of Zernike polynomials according to this performance, a least square fitting algorithm numerically determines their coefficients to obtain the desired wavefront modulation. We illustrate the technique with an optically addressed liquid-crystal light valve to produce continuous intensity distributions matching a desired ablation profile, without the need of a wavefront sensor. The projection of the experimental laser distribution shows a 5% RMS error compared to the calculated one. Ablation of steel is achieved following user-defined micro-dimples and micro-grooves targets on mold surfaces. The profiles of the microgrooves and the injected polycarbonate closely match the target (RMS below 4%).