Guy Schlatter

Synthesis and characterization of high molecular weight polyrotaxanes: towards the control over a wide range of threaded α-cyclodextrins

This work focuses on the synthesis of polyrotaxanes with high molecular weight template poly(ethylene glycol) PEG (20 kg mol) having various and well-defined amounts of α-cyclodextrins (α-CD) per chain from 3 up to 125. is the complexation degree of the polyrotaxane defined to be the average number of cyclodextrin molecules per template chain. The usual route has been used for high values of , while sparsely complexed polyrotaxanes have been synthesized with an original one pot synthesis in water. Furthermore, a systematic study was carried out to understand and control the complexation degree of the polyrotaxane as a function of the complexation time, the temperature and the initial ratio of α-CD to template polymer. It has been shown that a high temperature thermal plateau leads to the formation of very sparsely complexed (low ) pseudo-polyrotaxanes for which, the threaded α-CD act like nuclei and generate a favourable driving force for the final complexation at lower temperature.

Osteogenetic Properties of Electrospun Nanofibrous PCL Scaffolds Equipped With Chitosan-Based Nanoreservoirs of Growth Factors

Bioactive implants intended for rapid, robust, and durable bone tissue regeneration are presented. The implants are based on nanofibrous 3D-scaffolds of bioresorbable poly-ϵ-caprolactone mimicking the fibrillar architecture of bone matrix. Layer-by-layer nanoimmobilization of the growth factor BMP-2 in association with chitosan (CHI) or poly-L-lysine over the nanofibers is described. The osteogenetic potential of the scaffolds coated with layers of CHI and BMP-2 is demonstrated in vitro, and in vivo in mouse calvaria, through enhanced osteopontin gene expression and calcium phosphate biomineralization. The therapeutic strategy described here contributes to the field of regenerative medicine, as it proposes a route toward efficient repair of bone defects at reduced risk and cost level.

Formation and Self-Organization Kinetics of α-CD/PEO-Based Pseudo-Polyrotaxanes in Water. A Specific Behavior at 30 °C†

alpha-Cyclodextrins (alpha-CDs) have the ability to form inclusion complexes with poly(ethylene oxide) (PEO) polymer chains. These pseudo-polyrotaxanes (PPRs) can be obtained by quenching an alpha-CD/PEO mixture in water from 70 degrees C down to a lower temperature (typically in the range from 5 to 30 degrees C) thanks to favorable interactions between alpha-CD cavities and PEO chains. Moreover, starting from a liquid alpha-CD/PEO mixture at a total mass fraction of 15% w/w at 70 degrees C, the formation of PPRs with time at a lower temperature induces a white physical gel with time, and phase separation is observed. We established that PPR molecules are exclusively found in the precipitated phase although unthreaded alpha-CD molecules and unthreaded PEO chains are in the liquid phase. At 30 degrees C, the physical gel formation is much slower than at 5 degrees C. At 30 degrees C, we established that, in a first step, alpha-CDs thread onto PEO chains, forming PPR molecules which are not in good solvent conditions in water. At a higher length scale, rapid aggregation of the PPR molecules occurs, and threaded alpha-CD-based nanocylinders form (cylinder length L = 5.7 nm and cylinder radius R = 4.7 nm). At a higher length scale, alpha-CD-based nanocylinders associate in a Gaussian way, engendering the formation of precipitated domains which are responsible for the high turbidity of the studied system. At the end of this first step (i.e., after 20 min), the system still remains liquid and the PPRs are totally formed. Then, in a second step (i.e., after 150 min), the system undergoes its reorganization characterized by a compacity increase of the precipitated domains and forms a physical gel. We found that PPRs are totally formed after 20 min at 30 degrees C and that the system stays in a nongel state up to 150 min. This opens new perspectives regarding the PPR chemical modification: between these two characteristic times, we can easily envisage an efficient chemical modification of the PPR molecules in water, as for instance an end-capping reaction leading to the synthesis of polyrotaxanes.

Numerical simulation of polymerization in interdigital multilamination micromixers

Free radical polymerization in microfluidic devices modeled with the help of numerical simulations is discussed. The simulation method used allows the simultaneous solvation of partial differential equations resulting from the hydrodynamics, thermal and mass transfer (convection, diffusion and chemical reaction). Three microfluidic devices are modeled, two interdigital multilamination micromixers respectively with a large and short focusing section, and a simple T-junction followed by a microtube reactor together considered as a bilamination micromixer with a large focusing section. The simulations show that in spite of the heat released by the polymerization reaction, the thermal transfer in such microfluidic devices is high enough to ensure isothermal conditions. Moreover, for low radial Peclet number, microfluidic devices with a large focusing section can achieve better control over the polymerization than a laboratory scale reactor as the polydispersity index obtained is very close to the theoretical limiting value. As the characteristic dimension of the microfluidic device increases, i.e. for high radial Peclet number, the reactive medium cannot be fully homogenized by the diffusion transport before leaving the system resulting in a high polydispersity index and a loss in the control of the polymerization.

From self-assembly of electrospun nanofibers to 3D cm thick hierarchical foams

Electrospinning usually results in the formation of scaffolds that are a few hundred microns in thickness with pore sizes in the micron range. However some applications, such as tissue engineering, necessitate the fabrication of cm-thick nanofibrous scaffolds with large pore sizes that allow for cell infiltration. Here, we demonstrate for the first time the production of bioresorbable poly(e-caprolactone) nanofibrous cm-thick foams using the electrospinning technique. These scaffolds were obtained through the dynamic self-assembly of electrospun nanofibers into honeycomb patterns, which resulted in a unique columnar hierarchical structure with both micropores and mesopores of up to several hundreds of microns in size. This specific morphology leads to mechanical properties of thick scaffolds, suitable for handling and implanting in vivo.

Simultaneous Electrospinning and Electrospraying: A Straightforward Approach for Fabricating Hierarchically Structured Composite Membranes

We present here for the first time a simple method for micropatterning nonwoven composite membranes. The approach is based on the simultaneous electrospraying of microparticles and electrospinning of nanofibers from different polymer solution feeds (polyethylene glycol and poly(D,L-lactide)) on a common support. The mechanism of self-organization between fibers and particles into hierarchical honeycomb-like structures, as well as the evolution of the later as a function of the thickness of the composite, is investigated. We demonstrate that aggregates of particles, leading to a nonuniform distribution of the electrostatic field near the collector, are necessary to form the self-organized composite. Furthermore, it is shown that the specific dimensions of the generated patterns can be controlled by tuning the flow rate of electrospraying. The obtained composite mat exhibits a multilevel porous structure, with pore sizes ranging from few up to several hundreds of micrometers. Finally, it is shown that the microparticles can be selectively leached, allowing the production of a monocomponent membrane and retaining the hierarchical organization of the nanofibers suitable for biomedical and filtration applications.

Multiblock copolymer behaviour of α-CD/PEO-based polyrotaxanes: towards nano-cylinder self-organization of α-CDs

The present work demonstrates that α-cyclodextrin/poly(ethylene oxide) (α-CD/PEO)-based polyrotaxanes (PRs) behave as multiblock copolymers. One block type consists of a rod-like tube made of 6 to 7 weakly stacked α-CDs threaded along the PEO chain. The other one is made of a naked PEO segment, i.e. the PR part that is not covered by α-CDs. This multiblock behaviour induces the self-organization of PRs in concentrated solution in dimethyl sulfoxide (DMSO) at room temperature leading to the formation of nano-cylinders. These nano-cylinders consist of assemblies of roughly 60 α-CD rod-like tubes through hydrogen bonding. Moreover, crystallites of naked PEO segments are formed since PEO is in poor solvent conditions (DMSO) at room temperature. Furthermore, the formation of α-CD nano-cylinders as well as of naked PEO segment crystallites leads to physical gelation of PRs in DMSO.

Large amplitude oscillatory shear and uniaxial extensional rheology of blends from linear and long-chain branched polyethylene and polypropylene

In this article, normal stresses and shear stresses in oscillatory shear flow are measured at small and large deformation amplitudes. New material parameters are then introduced based on Fourier transform rheology and stress decomposition analysis of normal and shear stress measurements. Furthermore, uniaxial extensional measurements are performed and compared to simulation results using the molecular stress function model. Different behaviors were observed for the polyethylene and polypropylene type blends, which are believed to arise from the different types of long-chain branching (LCB) topology present in each of the systems. The use of the new material parameters proposed and described within this article has the potential to allow for a better understanding of structure-property relationships in industrial LCB materials.

Differentiation of human adipose-derived stem cells seeded on mineralized electrospun co-axial poly(ε-caprolactone) (PCL)/gelatin nanofibers

Abstract Mineralized poly(ε-caprolactone)/gelatin core–shell nanofibers were prepared via co-axial electrospinning and subsequent incubation in biomimetic simulated body fluid containing ten times the calcium and phosphate ion concentrations found in human blood plasma. The deposition of calcium phosphate on the nanofiber surfaces was investigated through scanning electronic microscopy and X-ray diffraction. Energy dispersive spectroscopy results indicated that calcium-deficient hydroxyapatite had grown on the fibers. Fourier transform infrared spectroscopy analysis suggested the presence of hydroxyl-carbonate-apatite. The results of a viability assay (MTT) and alkaline phosphatase activity analysis suggested that these mineralized matrices promote osteogenic differentiation of human adipose-derived stem cells (hASCs) when cultured in an osteogenic medium and have the potential to be used as a scaffold in bone tissue engineering. hASCs cultured in the presence of nanofibers in endothelial differentiation medium showed lower rates of proliferation than cells cultured without the nanofibers. However, endothelial cell markers were detected in cells cultured in the presence of nanofibers in endothelial differentiation medium.

One‐Pot Synthesis of a Nitrogen‐Doped Carbon Composite by Electrospinning as a Metal‐Free Catalyst for Oxidation of H2S to Sulfur

A macroscopic composite consisting of nitrogen‐doped carbon fibers (N@CFs) was synthesized by electrospinning. The as‐prepared N@CF material was further applied as a metal‐free catalyst in the catalytic oxidation of H2S to sulfur, which is one of the most important purification processes for raw chemical resources (that is, biogas, natural gas, and petrochemical compounds). The catalyst, after a carbonization step at T=800 °C, exhibits a high and stable desulfurization activity for more than 100 h of testing with 57 % H2S conversion and 95 % sulfur selectivity at T=230 °C, which is two times higher than that of the most active metal‐based catalyst (Fe2O3/SiC). The desulfurization performance could also be improved by changing the reactant velocity. Moreover, the macroscopic shaping with an inner hierarchical structure network allows the avoidance of problems linked with the transport and handling of nanoscopic carbon‐based materials and also enhances the mass diffusion during the oxidation reaction.