Autografts remain the gold standard for orthopedic transplantations. However, to overcome its limitations, bone tissue engineering proposes new strategies. This includes the development of new biomaterials such as synthetic polymers, to serve as scaffold for tissue production. The objective of this present study was to produce poly(lactic) acid (PLA) scaffolds of different pore size using fused deposition modeling (FDM) technique and to evaluate their physicochemical and biological properties. Structural, chemical, mechanical, and biological characterizations were performed. We successfully fabricated scaffolds of three different pore sizes. However, the pore dimensions were slightly smaller than expected. We found that the 3D printing process induced decreases in both, PLA molecular weight and degradation temperatures, but did not change the semicrystalline structure of the polymer. We did not observe any effect of pore size on the mechanical properties of produced scaffolds. After the sterilization by γ irradiation, scaffolds did not exhibit any cytotoxicity towards human bone marrow stromal cells (HBMSC). Finally, after three and seven days of culture, HBMSC showed high viability and homogenous distribution irrespective of pore size. Thus, these results suggest that FDM technology is a fast and reproducible technique that can be used to fabricate tridimensional custom-made scaffolds for tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 887-894, 2018.

In this study the possibilities offered by “living” ring-opening metathesis polymerization (ROMP) are exploited to engineer novel macromolecular architectures. It is indeed shown that amphiphilic branched structures of hitherto unreported topologies can be prepared by ROMP of miscellaneous macromonomers, provided the latter polymers carry an end-standing norbornene unsaturation. Janus-type architectures are, for instance, accessible by sequential ROMP of polystyrene (PS) and poly(ethylene oxide) (PEO) macromonomers; other original branched structures, whose topology makes them particularly attractive for applications such as unimolecular micelles or associative thickeners, can be obtained through homopolymerization of macromonomers based on PS-b-PEO diblock copolymers.

We study oil-in-water emulsions stabilised by pH-sensitive colloidal silica or latex particles. Depending on the composition of the continuous phase, the same type of particles and the same emulsification process lead to emulsions characterised either by large drops densely covered by the particles, or to small droplets which are weakly covered. The two kinetically stable states can be tuned reversibly by using pH or salinity as compositional stimuli. We examine the emulsions' behaviour in these two limiting cases and we discuss the possible mechanisms allowing stabilisation, especially in the case of low surface coverage.

This work focuses on the synthesis and the ring-opening metathesis polymerization of α-norbornenylpoly(ethylene oxide) macromonomers. Although obtained in 100% yield and with a narrow distribution of molar masses, the polymacromonomers exhibit degrees of polymerization that are systematically higher than expected. The reasons for this feature are thoroughly discussed.

We synthesized surface-active lipophilic core-hydrophilic shell latex particles, and we probed their efficiency as emulsion stabilizers. The relative weight percentage of the shell, RS/P, was varied to trigger the balance between lipophilicity and hydrophilicity of the particles. Particle wettability could concomitantly be tuned by the pH of the aqueous phase determining the surface charge. Emulsions covering a wide range of RS/P and pH values were fabricated, and their type, oil-in-water (O/W) or water-in-oil (W/O), and kinetic stability were systematically assessed. By adapting the particle gel trapping technique to pH-variable systems and by exploiting the limited coalescence process, we were able to determine the proportion of oil/water interfacial area, C, covered by the particles as well as their contact angle, θ. All of these data were gathered into a single generic diagram showing good correlation between the emulsion type and the particle contact angle (O/W for θ < 90° and W/O for θ > 90°) in agreement with the empirical Finkle rule. Interestingly, no stable emulsion could be obtained when the wettability was nearly balanced and a "bipolar"-like behavior was observed, with the particles adopting two different contact angles whose average value was close to 90°. For particles such that θ < 90°, O/W emulsions were obtained, and, depending on the pH of the continuous phase, the same type of particles and the same emulsification process led to emulsions characterized either by large drops densely covered by the particles or by small droplets that were weakly covered. The two metastable states were also accessible to emulsions stabilized by particles of variable origins and morphologies, thus proving the generality of our findings.

The frictional forces between grafted layers on silica and a nanotip have been investigated as a function of the tip velocity. A comparative study has been performed between the friction behavior of the triethoxysilane molecules and polymer grafted on the silica. The polymer, a substituted polyacetylene, has been grafted following a two-step process. The silica surface is first pretreated with the triethoxysilane molecules, then the polymer is grafted on the silane molecules acting as a coupling agent. This two-step process allows the polymer to be firmly fixed. The good reproducibility of the data is accompanied by a robustness in the friction behavior. Both the silane molecules and the polymer grafted on the coupling agent show a linear increase of the force of friction with the logarithm of the sliding velocity. For the polymer, the force of friction is doubled that measured for the silane molecules and the forces of friction are found to be linearly dependent of the effective applied load. These two results are also supported by the measurement of the dynamic friction coefficient of the two grafted layers. The trends in these friction data have been found to be amenable to an analysis based upon a simple stress-modified thermally-activated Eyring model. A good consistency of the evolution of the different parameters, shear strengths, and barrier heights, computed with the model is obtained. From these results and their interpretation one gets a step forward for more quantitative information to be extracted with an atomic force microscope. Also, with the help of the Eyring model we provide a qualitative interpretation of what process is taking place to explain the increase of dissipation when the sliding experiment is performed on the grafted polymer.

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Surfactant-free micro- and nanolatexes from Pickering emulsions stabilized by acetylated cellulose nanocrystals (CNCs).