Bulletin of the American Physical Society, Mar 21, 2005
Thin films of block-copolymers have received great attention as they can self-assemble in ordered... more Thin films of block-copolymers have received great attention as they can self-assemble in ordered periodic structures at the molecular scale [1]. There are different ways by which ordering can be obtain over large areas [2-4]. One such way consists of the local tailoring of the substrate by placing chemical moieties at regularly repeated locations [5]. Here we present another versatile way to control the ordering of block-copolymers over micrometer-scale areas. Fabrication process and examples of chemically nanopatterned substrates will be first shown. The substrates are created by combining the ability of the e-beam lithography to create nanometer-scale regions with self-assembly of alkanethiols. In a second part, the study of self-assembly of symmetric and asymmetric block-copolymers on such nanopatterns will be presented. References [1]
Photochemical and Photobiological Sciences, Feb 4, 2008
We report on the grafting of coumarin chromophores on flat silicon surfaces and in regions of nan... more We report on the grafting of coumarin chromophores on flat silicon surfaces and in regions of nanometric dimensions drawn on silicon surfaces. The coumarin derivative was grafted by using the quaternization of a tertiary amine group of the chromophore with a ((chloromethyl)phenylethyl)-dimethylchlorosilane (CMPDCS) grafted on silicon. Complete characterization of the grafted layer was performed as a function of reaction time by X-ray photoelectron spectroscopy, X-ray reflectometry, atomic force microscopy, fluorescence spectroscopy and laser-scanning confocal microscopy. The results indicate that about one chromophore molecule is grafted every second CMPDCS molecule, resulting in a surface density of coumarin of slightly more than one coumarin per nm 2. A broadening of the distribution of the fluorescence lifetimes was observed, suggesting that the grafted molecules experience a larger distribution of environments in the grafted layer than in solution. Since this reaction is fully compatible with silicon processing technology, the grafting could also be performed in nano-regions of size as small as 250 nm defined by combining electron-beam lithography with silanization. In such nano-sized regions the distribution of fluorescence lifetimes was narrower, suggesting a possible influence of the confinement on the organization of the molecules.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
... Reddy et al. [4] showed that titanium containing molecular sieves may lead to a certain chemo... more ... Reddy et al. [4] showed that titanium containing molecular sieves may lead to a certain chemo-and stereoselectivity. ... Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (61). 4. RS Reddy, JS Reddy, R. Kumar, P. Kumar, J. Chem. Soc., Chem. Commun. ...
Bulletin of the American Physical Society, Mar 16, 2006
The ability to control the position and local orientation of organic crystals at the nanometer sc... more The ability to control the position and local orientation of organic crystals at the nanometer scale paves the way to the fabrication of hybrid nano-devices displaying better properties. Here, we present two ways to control the assembly of organic chain compounds into nanometric crystals of defined location or orientation. We first show how the location of crystals of model oligomers can be directed by chemical nano-templates [1]. The templates are obtained by combining electron-beam lithography with the deposition of self-assembled monolayers [2]. These surfaces can then be used to control a variety of assembly processes [3], such as the crystallization of model alkane-1-ol oligomers in solution. By using directing maps with the appropriate chemical inks, nano-squares, nano-corrals and nano-lines of organic crystals are rapidly and massively grown at pre-defined locations, at least down to 60 nm. At this scale, confinement effects mediated by van der Waals forces become prominent, providing a unique handle to design crystal growth. Then, we show how the nucleation and orientation of polymer crystals can be controlled by nano-imprint lithography [4]. The combination of confinement, and of preferential nucleation at the vertical walls of the nano-molds probably arising from partial chain orientation due to the polymer flow during embossing, results in local control over the 3D orientation of the crystals. We demonstrate that crystals may be guided through complex geometries, and investigate the case of systems where conflicting instructions are delivered to the crystallizing chains.
Synthetic precision oligomers with complementary sticky ends and functional catalytic groups form... more Synthetic precision oligomers with complementary sticky ends and functional catalytic groups form dynamic constitutional libraries comprising cyclic di(oligomer)s which prove much more efficient for catalysis than other components of the library.
Cell culture on microcarriers emerges as an alternative of two-dimensional culture to produce lar... more Cell culture on microcarriers emerges as an alternative of two-dimensional culture to produce large cell doses, which are required for cell-based therapies. Herein, we report a versatile and easy solvent-free greener fabrication process to prepare microcarriers based on a biosourced and compostable polymer. The preparation of the microcarrier core, which is based on poly(L-lactide) crystallization from a polymer blend, allows us to easily tune the density, porosity, and size of the microparticles. A bioadhesive coating based on biopolymers, devoid of animal protein and optimized to improve cell adhesion, is then successfully deposited on the surface of the microcarriers. The ability of these new microcarriers to expand human adipose-derived stromal cells with good yield, in semistatic and dynamic conditions, is demonstrated. Finally, bead-to-bead cell transfer is shown to increase the yield of cell production without having to stop the culture. These microcarriers are therefore a promising and efficient green alternative to currently existing systems.
The synthesis of discrete catalytic oligomers and their potential in supported cooperative cataly... more The synthesis of discrete catalytic oligomers and their potential in supported cooperative catalysis are presented.
The development of a functional in vitro model for microcirculation is an unresolved challenge, w... more The development of a functional in vitro model for microcirculation is an unresolved challenge, with major impact for the creation and regeneration of organs in the tissue engineering. The absence of prevascularized engineered tissues limits enormously their efficacy and integration. Therefore, in this study, the in vitro formation of tubular-like structures with human umbilical vein endothelial cells (HUVECs) is investigated thanks to three-dimensional polycarbonate (PC) microchannel (ÎŒCh) scaffolds, surface biofunctionalized with hyaluronic acid/chitosan (HA/CHI) layer-by-layer (LbL) films grafted with adhesive (RGD) and angiogenic (SVV and QK) peptides, alone and in combination. The importance of this work lies in the formation of capillaries in the order of tens of ÎŒm, developing spontaneous microvessels, without the complexity of microfluidic approaches, and in a short timescale. Ellipsometry, confocal laser scanning microscopy, and fluorospectrometry are used to characterize the biofunctionalized microchannels. PC-ÎŒCh scaffolds functionalized with (HA/CHI) 12.5 film (PC-LbL) and further grafted with RGD and QK peptides (PC-RGD+QK) or with RGD and SVV peptides (PC-RGD+SVV) are then tested for in vitro blood vessel formation. These assays evidence a rapid formation of tubular-like structures after 2 h of incubation. Moreover, a coculture system involving HUVECs and human pericytes derived from placenta (hPCs-PL) stabilizes the tubes for a longer time.
We report on a simple and versatile method for the preparation in one-step of omniphobic textiles... more We report on a simple and versatile method for the preparation in one-step of omniphobic textiles, using only aqueous suspensions of silica particles and polyurethane devoid of long perfluoroalkyl chains (C8) that are now legally-banned because of severe environmental concerns. The omniphobic coatings can be applied on different substrates including fabrics, can resist acidic and basic conditions and a moderate number of washing cycles, and repel liquids such as n-octane, dodecane, hexadecane, ethylene glycol, glycerol, olive oil, and water. Analysis of the wetting properties of coated fabrics indicates that the liquid repellence results from the trapping of air in the re-entrant roughness created by aggregates of silica particles, together with the low surface tension of the polyurethane which bears legally accepted short perfluoroalkyl chains (C4). Our study is a significant step forward toward achieving more environmentally-friendly and robust omniphobic textiles.
Background: Human adipose-derived stromal cells (hASCs) have been gaining increasing popularity i... more Background: Human adipose-derived stromal cells (hASCs) have been gaining increasing popularity in regenerative medicine thanks to their multipotency, ease of collection, and efficient culture. Similarly to other stromal cells, their function is particularly sensitive to the culture conditions, including the composition of the culture medium. Given the large number of parameters that can play a role in their specification, the rapid assessment would be beneficial to allow the optimization of their culture parameters. Method: Herein we used the design of experiments (DOE) method to rapidly screen the influence and relevance of several culture parameters on the osteogenic differentiation of hASCs. Specifically, seven cell culture parameters were selected for this study based on a literature review. These parameters included the source of hASCs (the different providers having different methods for processing the cells prior to their external use), the source of serum (fetal bovine serum vs. human platelet lysate), and several soluble osteoinductive factors, including dexamethasone and a potent growth factor, the bone morphogenetic protein-9 (BMP-9). The expression of alkaline phosphatase was quantified as a readout for the osteogenic differentiation of hASCs. Results: The DOE analysis enabled to classify the seven studied parameters according to their relative influence on the osteogenic differentiation of hASCs. Notably, the source of serum was found to have a major effect on the osteogenic differentiation of hASCs as well as their origin (different providers) and the presence of L-ascorbate-2phosphate and BMP-9. Conclusion: The DOE-based screening is a valuable approach for the classification of the impact of several cell culture parameters on the osteogenic differentiation of hASCs.
Ferroelectric materials are important components of sensors, actuators and non-volatile memories.... more Ferroelectric materials are important components of sensors, actuators and non-volatile memories. However, possible device configurations are limited due to the need to provide screening charges to ferroelectric interfaces to avoid depolarization. Here we show that, by alternating ferroelectric and semiconducting nanowires over an insulating substrate, the ferroelectric dipole moment can be stabilized by injected free charge carriers accumulating laterally in the neighboring semiconducting nanowires. This lateral electrostatic coupling between ferroelectric and semiconducting nanowires offers new opportunities to design new device architectures. As an example, we demonstrate the fabrication of an elementary non-volatile memory device in a transistor-like configuration, of which the source-drain current exhibits a typical hysteretic behavior with respect to the poling voltage. The potential for size reduction intrinsic to the nanostructured hybrid layer offers opportunities for the d...
Biomaterials aim to mimic in vivo extracellular matrices where cell interactions occur on the nan... more Biomaterials aim to mimic in vivo extracellular matrices where cell interactions occur on the nanoscale. Thus, incorporation of nanosized components is interesting in the preparation of bioactive surfaces. We present a technique using nanoimprint lithography to create chemical nanopatterns on silicon surfaces functionalized with bioactive motifs. Due to high throughput and versatility, a wide range of geometries and dimensions can be efficiently patterned. In our study, we prepared and characterized two types of bioactive nanodots (150 nm diameter with 350 nm spacing, and 80 nm diameter with 110 nm spacing) functionalized with cell adhesion-promoting RGD peptides. We examined mesenchymal stem cell adhesion and commitment on these modified material surfaces with respect to homogeneous RGD and non-functionalized surfaces. We report that bioactive nanostructures induce fibrillar adhesions on human mesenchymal stem cells with an impact on their behavior and dynamics specifically in terms of cell spreading, cell-material contact, and cell differentiation.
Magnetoelectric layers with a strong coupling between ferroelectricity and ferromagnetism offer a... more Magnetoelectric layers with a strong coupling between ferroelectricity and ferromagnetism offer attractive opportunities for the design of new device architectures such as dual-channel memory and multiresponsive sensors and actuators. However, materials in which a magnetic field can switch an electric polarization are extremely rare, work most often only at very low temperatures, and/or comprise complex materials difficult to integrate. Here, we show that magnetostriction and flexoelectricity can be harnessed to strongly couple electric polarization and magnetism in a regularly nanopatterned magnetic metal/ferroelectric polymer layer, to the point that full reversal of the electric polarization can occur at room temperature by the sole application of a magnetic field. Experiments supported by finite element simulations demonstrate that magnetostriction produces large strain gradients at the base of the ferroelectric nanopillars in the magnetoelectric hybrid layer, translating by fle...
Bulletin of the American Physical Society, Mar 21, 2005
Thin films of block-copolymers have received great attention as they can self-assemble in ordered... more Thin films of block-copolymers have received great attention as they can self-assemble in ordered periodic structures at the molecular scale [1]. There are different ways by which ordering can be obtain over large areas [2-4]. One such way consists of the local tailoring of the substrate by placing chemical moieties at regularly repeated locations [5]. Here we present another versatile way to control the ordering of block-copolymers over micrometer-scale areas. Fabrication process and examples of chemically nanopatterned substrates will be first shown. The substrates are created by combining the ability of the e-beam lithography to create nanometer-scale regions with self-assembly of alkanethiols. In a second part, the study of self-assembly of symmetric and asymmetric block-copolymers on such nanopatterns will be presented. References [1]
Photochemical and Photobiological Sciences, Feb 4, 2008
We report on the grafting of coumarin chromophores on flat silicon surfaces and in regions of nan... more We report on the grafting of coumarin chromophores on flat silicon surfaces and in regions of nanometric dimensions drawn on silicon surfaces. The coumarin derivative was grafted by using the quaternization of a tertiary amine group of the chromophore with a ((chloromethyl)phenylethyl)-dimethylchlorosilane (CMPDCS) grafted on silicon. Complete characterization of the grafted layer was performed as a function of reaction time by X-ray photoelectron spectroscopy, X-ray reflectometry, atomic force microscopy, fluorescence spectroscopy and laser-scanning confocal microscopy. The results indicate that about one chromophore molecule is grafted every second CMPDCS molecule, resulting in a surface density of coumarin of slightly more than one coumarin per nm 2. A broadening of the distribution of the fluorescence lifetimes was observed, suggesting that the grafted molecules experience a larger distribution of environments in the grafted layer than in solution. Since this reaction is fully compatible with silicon processing technology, the grafting could also be performed in nano-regions of size as small as 250 nm defined by combining electron-beam lithography with silanization. In such nano-sized regions the distribution of fluorescence lifetimes was narrower, suggesting a possible influence of the confinement on the organization of the molecules.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
... Reddy et al. [4] showed that titanium containing molecular sieves may lead to a certain chemo... more ... Reddy et al. [4] showed that titanium containing molecular sieves may lead to a certain chemo-and stereoselectivity. ... Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (61). 4. RS Reddy, JS Reddy, R. Kumar, P. Kumar, J. Chem. Soc., Chem. Commun. ...
Bulletin of the American Physical Society, Mar 16, 2006
The ability to control the position and local orientation of organic crystals at the nanometer sc... more The ability to control the position and local orientation of organic crystals at the nanometer scale paves the way to the fabrication of hybrid nano-devices displaying better properties. Here, we present two ways to control the assembly of organic chain compounds into nanometric crystals of defined location or orientation. We first show how the location of crystals of model oligomers can be directed by chemical nano-templates [1]. The templates are obtained by combining electron-beam lithography with the deposition of self-assembled monolayers [2]. These surfaces can then be used to control a variety of assembly processes [3], such as the crystallization of model alkane-1-ol oligomers in solution. By using directing maps with the appropriate chemical inks, nano-squares, nano-corrals and nano-lines of organic crystals are rapidly and massively grown at pre-defined locations, at least down to 60 nm. At this scale, confinement effects mediated by van der Waals forces become prominent, providing a unique handle to design crystal growth. Then, we show how the nucleation and orientation of polymer crystals can be controlled by nano-imprint lithography [4]. The combination of confinement, and of preferential nucleation at the vertical walls of the nano-molds probably arising from partial chain orientation due to the polymer flow during embossing, results in local control over the 3D orientation of the crystals. We demonstrate that crystals may be guided through complex geometries, and investigate the case of systems where conflicting instructions are delivered to the crystallizing chains.
Synthetic precision oligomers with complementary sticky ends and functional catalytic groups form... more Synthetic precision oligomers with complementary sticky ends and functional catalytic groups form dynamic constitutional libraries comprising cyclic di(oligomer)s which prove much more efficient for catalysis than other components of the library.
Cell culture on microcarriers emerges as an alternative of two-dimensional culture to produce lar... more Cell culture on microcarriers emerges as an alternative of two-dimensional culture to produce large cell doses, which are required for cell-based therapies. Herein, we report a versatile and easy solvent-free greener fabrication process to prepare microcarriers based on a biosourced and compostable polymer. The preparation of the microcarrier core, which is based on poly(L-lactide) crystallization from a polymer blend, allows us to easily tune the density, porosity, and size of the microparticles. A bioadhesive coating based on biopolymers, devoid of animal protein and optimized to improve cell adhesion, is then successfully deposited on the surface of the microcarriers. The ability of these new microcarriers to expand human adipose-derived stromal cells with good yield, in semistatic and dynamic conditions, is demonstrated. Finally, bead-to-bead cell transfer is shown to increase the yield of cell production without having to stop the culture. These microcarriers are therefore a promising and efficient green alternative to currently existing systems.
The synthesis of discrete catalytic oligomers and their potential in supported cooperative cataly... more The synthesis of discrete catalytic oligomers and their potential in supported cooperative catalysis are presented.
The development of a functional in vitro model for microcirculation is an unresolved challenge, w... more The development of a functional in vitro model for microcirculation is an unresolved challenge, with major impact for the creation and regeneration of organs in the tissue engineering. The absence of prevascularized engineered tissues limits enormously their efficacy and integration. Therefore, in this study, the in vitro formation of tubular-like structures with human umbilical vein endothelial cells (HUVECs) is investigated thanks to three-dimensional polycarbonate (PC) microchannel (ÎŒCh) scaffolds, surface biofunctionalized with hyaluronic acid/chitosan (HA/CHI) layer-by-layer (LbL) films grafted with adhesive (RGD) and angiogenic (SVV and QK) peptides, alone and in combination. The importance of this work lies in the formation of capillaries in the order of tens of ÎŒm, developing spontaneous microvessels, without the complexity of microfluidic approaches, and in a short timescale. Ellipsometry, confocal laser scanning microscopy, and fluorospectrometry are used to characterize the biofunctionalized microchannels. PC-ÎŒCh scaffolds functionalized with (HA/CHI) 12.5 film (PC-LbL) and further grafted with RGD and QK peptides (PC-RGD+QK) or with RGD and SVV peptides (PC-RGD+SVV) are then tested for in vitro blood vessel formation. These assays evidence a rapid formation of tubular-like structures after 2 h of incubation. Moreover, a coculture system involving HUVECs and human pericytes derived from placenta (hPCs-PL) stabilizes the tubes for a longer time.
We report on a simple and versatile method for the preparation in one-step of omniphobic textiles... more We report on a simple and versatile method for the preparation in one-step of omniphobic textiles, using only aqueous suspensions of silica particles and polyurethane devoid of long perfluoroalkyl chains (C8) that are now legally-banned because of severe environmental concerns. The omniphobic coatings can be applied on different substrates including fabrics, can resist acidic and basic conditions and a moderate number of washing cycles, and repel liquids such as n-octane, dodecane, hexadecane, ethylene glycol, glycerol, olive oil, and water. Analysis of the wetting properties of coated fabrics indicates that the liquid repellence results from the trapping of air in the re-entrant roughness created by aggregates of silica particles, together with the low surface tension of the polyurethane which bears legally accepted short perfluoroalkyl chains (C4). Our study is a significant step forward toward achieving more environmentally-friendly and robust omniphobic textiles.
Background: Human adipose-derived stromal cells (hASCs) have been gaining increasing popularity i... more Background: Human adipose-derived stromal cells (hASCs) have been gaining increasing popularity in regenerative medicine thanks to their multipotency, ease of collection, and efficient culture. Similarly to other stromal cells, their function is particularly sensitive to the culture conditions, including the composition of the culture medium. Given the large number of parameters that can play a role in their specification, the rapid assessment would be beneficial to allow the optimization of their culture parameters. Method: Herein we used the design of experiments (DOE) method to rapidly screen the influence and relevance of several culture parameters on the osteogenic differentiation of hASCs. Specifically, seven cell culture parameters were selected for this study based on a literature review. These parameters included the source of hASCs (the different providers having different methods for processing the cells prior to their external use), the source of serum (fetal bovine serum vs. human platelet lysate), and several soluble osteoinductive factors, including dexamethasone and a potent growth factor, the bone morphogenetic protein-9 (BMP-9). The expression of alkaline phosphatase was quantified as a readout for the osteogenic differentiation of hASCs. Results: The DOE analysis enabled to classify the seven studied parameters according to their relative influence on the osteogenic differentiation of hASCs. Notably, the source of serum was found to have a major effect on the osteogenic differentiation of hASCs as well as their origin (different providers) and the presence of L-ascorbate-2phosphate and BMP-9. Conclusion: The DOE-based screening is a valuable approach for the classification of the impact of several cell culture parameters on the osteogenic differentiation of hASCs.
Ferroelectric materials are important components of sensors, actuators and non-volatile memories.... more Ferroelectric materials are important components of sensors, actuators and non-volatile memories. However, possible device configurations are limited due to the need to provide screening charges to ferroelectric interfaces to avoid depolarization. Here we show that, by alternating ferroelectric and semiconducting nanowires over an insulating substrate, the ferroelectric dipole moment can be stabilized by injected free charge carriers accumulating laterally in the neighboring semiconducting nanowires. This lateral electrostatic coupling between ferroelectric and semiconducting nanowires offers new opportunities to design new device architectures. As an example, we demonstrate the fabrication of an elementary non-volatile memory device in a transistor-like configuration, of which the source-drain current exhibits a typical hysteretic behavior with respect to the poling voltage. The potential for size reduction intrinsic to the nanostructured hybrid layer offers opportunities for the d...
Biomaterials aim to mimic in vivo extracellular matrices where cell interactions occur on the nan... more Biomaterials aim to mimic in vivo extracellular matrices where cell interactions occur on the nanoscale. Thus, incorporation of nanosized components is interesting in the preparation of bioactive surfaces. We present a technique using nanoimprint lithography to create chemical nanopatterns on silicon surfaces functionalized with bioactive motifs. Due to high throughput and versatility, a wide range of geometries and dimensions can be efficiently patterned. In our study, we prepared and characterized two types of bioactive nanodots (150 nm diameter with 350 nm spacing, and 80 nm diameter with 110 nm spacing) functionalized with cell adhesion-promoting RGD peptides. We examined mesenchymal stem cell adhesion and commitment on these modified material surfaces with respect to homogeneous RGD and non-functionalized surfaces. We report that bioactive nanostructures induce fibrillar adhesions on human mesenchymal stem cells with an impact on their behavior and dynamics specifically in terms of cell spreading, cell-material contact, and cell differentiation.
Magnetoelectric layers with a strong coupling between ferroelectricity and ferromagnetism offer a... more Magnetoelectric layers with a strong coupling between ferroelectricity and ferromagnetism offer attractive opportunities for the design of new device architectures such as dual-channel memory and multiresponsive sensors and actuators. However, materials in which a magnetic field can switch an electric polarization are extremely rare, work most often only at very low temperatures, and/or comprise complex materials difficult to integrate. Here, we show that magnetostriction and flexoelectricity can be harnessed to strongly couple electric polarization and magnetism in a regularly nanopatterned magnetic metal/ferroelectric polymer layer, to the point that full reversal of the electric polarization can occur at room temperature by the sole application of a magnetic field. Experiments supported by finite element simulations demonstrate that magnetostriction produces large strain gradients at the base of the ferroelectric nanopillars in the magnetoelectric hybrid layer, translating by fle...
Uploads
Papers by Alain Jonas