Publications by authors named "Olivier Stephan"

14 Publications

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3D two-photon polymerization of smart cell gelatin - collagen matrixes with incorporated ruthenium complexes for the monitoring of local oxygen tensions.

Acta Biomater 2021 08 12;130:172-182. Epub 2021 Jun 12.

MoVe, Laboratoire interdisciplinaire de physique, CNRS UMR 5588, Université Grenoble Alpes, St-Martin d'Hères, France. Electronic address:

The extra cellular matrix plays a major role in the biomechanical properties of tissues that impact cell behavior and fate. It is therefore crucial to mimic these complex cell-matrix interactions in 3D cell cultures. Here, two-photon polymerization is applied to produce gelatin methacryloyl (GelMA) - collagen matrixes that further enable local pO measurement, when ruthenium complexes are used as photo-activators. The fluorescence intensity of these complexes has a direct and inverse relationship with the local pO. The 3D structures reached their maximum size in cell culture conditions after 3H with a swelling factor of ~1.5. Their shape and the ruthenium fluorescence intensity of the alveoli walls stayed constant for at least 2 weeks in the absence of cells. They were used in time series to monitor the local pO adjacent to cancer cells during their division, migration and the formation of a tumor tissue mass. At the presence of these cell activities that consume O, a significant ~3-fold increase of the ruthenium fluorescence intensity in the alveoli walls was observed. This study demonstrates that online monitoring of the local pO is possible. The ruthenium complexes provide the bio-optical sensors that are useful for further analysis of cancer and healthy cell energy metabolism in a 3D matrix that better mimics in vivo conditions and migration paths. Unraveling the cancer cell metabolic adaptations in a changing micro-environment will help the development of new therapeutic opportunities. STATEMENT OF SIGNIFICANCE: In 3D cell cultures, monitoring pericellular pO is as critical as controlling pH. This facility is currently missing. Here, we take advantage of the direct and inverse relationship between pO and the fluorescence intensity of ruthenium complexes to generate stable gelatin-collagen matrixes able to continuously monitoring the pO at the pericellular level. The ruthenium complexes, which are photo-activators in the two-photon polymerization of these matrixes, became covalently bind to the collagen fibers. Indeed, local O consumption by cancer cells during migration, mitosis and tumor mass formation caused a 3-fold increase of the ruthenium fluorescence. In the future, incorporating ruthenium complexes with other bio-optical sensors will create new drug screening platforms that monitor cell culture parameters at the pericellular level.
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http://dx.doi.org/10.1016/j.actbio.2021.06.021DOI Listing
August 2021

Polyhedral Bubble Vibrations.

Phys Rev Lett 2021 Feb;126(5):054502

University Grenoble Alpes, CNRS, LIPhy, F-38000 Grenoble, France.

Underwater bubbles are extremely good acoustic resonators, but are freely evolving and dissolving. Recently it was found that bubbles can be stabilized in frames, but the influence of the frame shape is still undocumented. Here we first explore the vibration of polyhedral bubbles with a low number of faces, shaped as the five Platonic solids. Their resonance frequency is well approximated by the formula for spherical bubbles with the same volume. Then we extend these results to shapes with a larger number of faces using fullerenes, paving the way to obtain arbitrary large resonant bubbles.
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http://dx.doi.org/10.1103/PhysRevLett.126.054502DOI Listing
February 2021

Acoustic interaction between 3D-fabricated cubic bubbles.

Soft Matter 2020 Mar 27;16(11):2829-2835. Epub 2020 Feb 27.

CNRS/Université Grenoble-Alpes, LIPhy UMR 5588, Grenoble, F-38401, France.

Spherical bubbles are notoriously difficult to hold in specific arrangements in water and tend to dissolve over time. Here, using stereolithographic printing, we built an assembly of millimetric cubic frames overcoming these limitations. Indeed, each of these open frames holds an air bubble when immersed into water, resulting in bubbles that are stable for a long time and are still able to oscillate acoustically. Several bubbles can be placed in any wanted spatial arrangement, thanks to the fabrication process. We show that bubbles are coupled acoustically when disposed along lines, planes or in 3D arrangements, and that their collective resonance frequency is shifted to much lower values, especially for 3D arrangements where bubbles have a higher number of close neighbours. Considering that these cubic bubbles behave acoustically as spherical bubbles of the same volume, we develop a theory allowing one to predict the acoustical emission of any arbitrary group of bubbles, in agreement with experimental results.
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http://dx.doi.org/10.1039/c9sm02423aDOI Listing
March 2020

Multi-directional bubble generated streaming flows.

Ultrasonics 2020 Mar 2;102:106054. Epub 2019 Dec 2.

Univ. Grenoble Alpes and CNRS, UMR 5588 LIPhy, F-38402 Grenoble, France.

In previous work, we have demonstrated the use of single-holed Armoured Microbubbles (AMBs) for microfluidic mixing and self-propulsion. AMBs are hollow partial spheres, inside which we capture a bubble. Under ultrasound, the bubble oscillates, generating a streaming flow with velocities of 1-100 mm/s in water. In this paper, inspired by our successful fabrication of a C60 geometry (buckyball), we study AMBs with multiple surface holes. We show more holes generate additional pairs of fast circulations around the AMB. However, as the number of holes increases further, the circulations become small and the in-plane flow is dominated by a source or sink flow. For an AMB with two different sized holes, we demonstrate each hole can be independently activated, potentially useful for multi-directional swimming.
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http://dx.doi.org/10.1016/j.ultras.2019.106054DOI Listing
March 2020

Acoustics of Cubic Bubbles: Six Coupled Oscillators.

Phys Rev Lett 2019 Dec;123(25):254501

Univ. Grenoble Alpes, CNRS, LIPhy, F-38000 Grenoble, France.

We introduce cubic bubbles that are pinned to 3D printed millimetric frames immersed in water. Cubic bubbles are more stable over time and space than standard spherical bubbles, while still allowing large oscillations of their faces. We find that each face can be described as a harmonic oscillator coupled to the other ones. These resonators are coupled by the gas inside the cube but also by acoustic interactions in the liquid. We provide an analytical model and 3D numerical simulations predicting the resonance with very good agreement. Acoustically, cubic bubbles prove to be good monopole subwavelength emitters, with nonemissive secondary surface modes.
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http://dx.doi.org/10.1103/PhysRevLett.123.254501DOI Listing
December 2019

Bubble-based acoustic micropropulsors: active surfaces and mixers.

Lab Chip 2017 04;17(8):1515-1528

Univ. Grenoble Alpes and CNRS, UMR 5588 LIPhy, F-38402 Grenoble, France.

Acoustic micropropulsors present great potential for microfluidic applications. The propulsion is based on encapsulated 20 μm bubbles excited by a contacless ultrasonic transducer. The vibrating bubbles then generate a powerful streaming flow, with speeds 1-100 mm s in water, through the action of viscous stresses. In this paper we introduce a full toolbox of micropropulsors using a versatile three-dimensional (3D) microfabrication setup. Doublets and triplets of propulsors are introduced, and the flows they generate are predicted by a theoretical hydrodynamic model. We then introduce whole surfaces covered with propulsors, which we term active surfaces. These surfaces are excited by a single ultrasonic wave, can generate collective flows and may be harnessed for mixing purposes. Several patterns of propulsors are tested, and the flows produced by the two most efficient mixers are predicted by a simple theoretical model based on flow singularities. In particular, the vortices generated by the most efficient pattern, an L-shaped mixer, are analysed in detail.
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http://dx.doi.org/10.1039/c7lc00240hDOI Listing
April 2017

Obstructive micro diffracting structures as an alternative to plasmonics nano slits for making efficient microlenses.

Opt Express 2012 Nov;20(24):26542-7

IMEP-LAHC, Minatec, Grenoble-INP, CNRS- UMR 5130, Grenoble, France.

Miniature optical components at the wavelength scale remain today a theoretically opened challenging problem of great technological interest. Appart from refractive micro-optics, plasmonics have been proposed to realize micro lenses with properly designed planar metallic nano-patterns. We show in this paper that efficient light focusing at the diffraction limit with higher transmission can be obtained with micro-structures much easier to fabricate than nano ones, such as a simple micro-slit studied here as an example. Optical properties are attributed to diffraction and a quantitative excellent agreement between experiment and theory is obtained.
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http://dx.doi.org/10.1364/OE.20.026542DOI Listing
November 2012

Metallic nanowires can lead to wavelength-scale microlenses and microlens arrays.

Opt Express 2012 Jul;20(14):15516-21

Univ. Grenoble 1 / CNRS, LIPhy UMR 5588, Grenoble, F-38041, France.

We theoretically and experimentally demonstrate that the diffraction of microstructures based on silver nanowires leads to very efficient microfocusing effects. Pairs of parallel nanowires act as ultrasmall cylindrical microlenses with diffraction-limited resolution in the Fresnel region. This is a new diffraction scheme to make micron-sized optical lenses with higher transmittance than plasmonic microlens based on nano-aperture arrays. Calculations based on the scalar Rayleigh-Sommerfeld integral highlights the pure scalar diffractive contribution. Thus, the plasmon contribution is negligible in such micron-sized metallic geometry. We demonstrate that two-dimensional grids of nanowires can be used to fabricate dense arrays of microlenses, i.e. 10000x10000 DPI (dots per inch).
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http://dx.doi.org/10.1364/OE.20.015516DOI Listing
July 2012

Tetranuclear manganese(II) complexes of sulfonylcalix[4]arene macrocycles: synthesis, structure, spectroscopic and magnetic properties.

Dalton Trans 2012 Mar 23;41(9):2707-13. Epub 2012 Jan 23.

Laboratoire des Multimatériaux et Interfaces (UMR 5615) Université Claude Bernard Lyon1, Villeurbanne, France.

Two tetranuclear manganese(II) complexes {K(+)[Mn(4)(ThiaSO(2))(2)(OH)](-)} (1) and {K(+)[Mn(4)(ThiaSO(2))(2)(F)](-)} (2) have been synthesized under solvothermal conditions in methanol with p-tert-butylsulfonylcalix[4]arene (ThiaSO(2)). For both complexes, the structure has been established from single-crystal X-ray diffraction. The two complexes are best described as manganese squares sandwiched between two thiacalixarene macrocycles. In both complexes, in the center of the square formed by the four manganese(II) atoms, the unexpected presence of μ(4)-OH(-) or μ(4)-F(-) gives a negative charge to the cluster. The two tetranuclear complexes exhibit strong orange luminescence behavior resulting from the symbiosis between the ThiaSO(2) and the Mn(2+). Despite similar chemical formulation, (1) and (2) present difference in emission intensity and lifetime τ.
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http://dx.doi.org/10.1039/c2dt11786jDOI Listing
March 2012

Photodynamic therapy and two-photon bio-imaging applications of hydrophobic chromophores through amphiphilic polymer delivery.

Photochem Photobiol Sci 2011 Jul 18;10(7):1216-25. Epub 2011 Apr 18.

Université de Lyon, CNRS UMR 5182, Institut de Chimie de Lyon, Université Lyon 1, Ecole Normale Supérieure de Lyon, Site Monod, 46 allée d'Italie, 69364, Lyon Cedex 07, France.

The synthesis and photophysical properties of two lipophilic quadrupolar chromophores featuring anthracenyl (1) or dibromobenzene (2) were described. These two chromophores combined significant two-photon absorption cross-sections with high fluorescence quantum yield for 1 and improved singlet oxygen generation efficiency for 2, in organic solvents. The use of Pluronic nanoparticles allowed a simple and straightforward introduction of these lipophilic chromophores into biological cell media. Their internal distribution in various cell lines was studied using fluorescence microscopy and flow-cytometry following a successful staining that was achieved upon 2 h of incubation. Finally, multiphoton excitation microscopy and photodynamic therapy capability of the chromophores were demonstrated by cell exposure to a 820 nm fs laser and cell death upon one photon resonant irradiation at 436 ± 10 nm, respectively.
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http://dx.doi.org/10.1039/c0pp00381fDOI Listing
July 2011

Deep in vivo two-photon imaging of blood vessels with a new dye encapsulated in pluronic nanomicelles.

J Biomed Opt 2011 Mar;16(3):036001

Laboratoire de Spectrométrie Physique, CNRS UMR 5588, Saint Martin d'Hères, France.

Our purpose is to test if Pluronic® fluorescent nanomicelles can be used for in vivo two-photon imaging of both the normal and the tumor vasculature. The nanomicelles were obtained after encapsulating a hydrophobic two-photon dye: di-stryl benzene derivative, in Pluronic block copolymers. Their performance with respect to imaging depth, blood plasma staining, and diffusion across the tumor vascular endothelium is compared to a classic blood pool dye Rhodamin B dextran (70 kDa) using two-photon microscopy. Pluronic nanomicelles show, like Rhodamin B dextran, a homogeneous blood plasma staining for at least 1 h after intravenous injection. Their two-photon imaging depth is similar in normal mouse brain, using 10 times less injected mass. In contrast with Rhodamin B dextran, no extravasation is observed in leaky tumor vessels due to their large size: 20-100 nm. In conclusion, Pluronic nanomicelles can be used as a blood pool dye, even in leaky tumor vessels. The use of Pluronic block copolymers is a valuable approach for encapsulating two-photon fluorescent dyes that are hydrophobic and not suitable for intravenous injection.
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http://dx.doi.org/10.1117/1.3548879DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4020796PMC
March 2011

Electroless growth of silver nanoparticles into mesostructured silica block copolymer films.

Langmuir 2010 Jun;26(11):8729-36

Laboratoire des Multimatériaux et Interfaces, UMR CNRS 5615, Université Claude Bernard Lyon 1, 43 Bd 11 novembre 1918, 69622 Villeurbanne, France.

Silver nanoparticles and silver nanowires have been grown inside mesostructured silica films obtained from block copolymers using two successive reduction steps: the first one involves a sodium borohydride reduction or a photoreduction of silver nitrate contained in the film, and the second one consists of a silver deposit on the primary nanoparticles, carried out by silver ion solution reduction with hydroxylamine chloride. We have demonstrated that the F127 block copolymer ((PEO)(106)(PPO)(70)(PEO)(106)), "F type", mesostructured silica film is a suitable "soft" template for the fabrication of spherical silver nanoparticles arrays. Silver spheres grow from 7 to 11 nm upon the second reduction step. As a consequence, a red shift of the surface plasmon resonance associated with metallic silver has been observed and attributed to plasmonic coupling between particles. Using a P123 block copolymer ((PEO)(20)(PPO)(70)(PEO)(20)), "P type", mesostructured silica film, we have obtained silver nanowires with typical dimension of 10 nm x 100 nm. The corresponding surface plasmon resonance is blue-shifted. The hydroxylamine chloride treatment appears to be efficient only when a previous chemical reduction is performed, assuming that the first sodium borohydride reduction induces a high concentration of silver nuclei in the first layer of the porous silica (film/air interface), which explains their reactivity for further growth.
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http://dx.doi.org/10.1021/la904491vDOI Listing
June 2010

Fluorescent Pluronic nanodots for in vivo two-photon imaging.

Nanotechnology 2009 Jun 18;20(23):235102. Epub 2009 May 18.

Laboratoire de Spectrométrie Physique, UMR 5588, Saint Martin d'Hères, France.

We report the synthesis of new nanosized fluorescent probes based on bio-compatible polyethylene-polypropylene glycol (Pluronic) materials. In aqueous solution, mini-emulsification of Pluronic with a high fluorescent di-stryl benzene-modified derivative, exhibiting a two-photon absorption cross section as high as 2500 Goeppert-Mayer units at 800 nm, leads to nanoparticles exhibiting a hydrodynamic radius below 100 nm. We have demonstrated that these new probes with luminescence located in the spectral region of interest for bio-imaging (the yellow part of the visible spectrum) allow deep (500 microm) bio-imaging of the mice brain vasculature. The dose injected during our experiments is ten times lower when compared to the classical commercial rhodamine-B isothicyanate-Dextran system but gives similar results to homogeneous blood plasma staining. The mean fluorescent signal intensity stayed constant during more than 1 h.
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http://dx.doi.org/10.1088/0957-4484/20/23/235102DOI Listing
June 2009

Monodisperse fluorene oligomers exhibiting strong dipolar coupling interactions.

Chem Commun (Camb) 2002 Aug(15):1608-9

Laboratoire de Stéréochimie et Interactions Moléculaires, ENS-Lyon and CNRS, 46 Allée d'Italie, 69364 Lyon, France.

Well-defined fluorene oligomers (n = 1 to 6) were prepared step by step using Suzuki and Yamamoto couplings, while absorption and photoluminescence properties evidenced very large dipolar coupling interactions between fluorene moieties.
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http://dx.doi.org/10.1039/b201414aDOI Listing
August 2002
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