Vincent Armbruster

Contractile forces generated by striae distensae fibroblasts embedded in collagen lattices

Striae distensae are characterized by linear, smooth bands of atrophic-appearing skin that are reddish at first and finally white. They are due to stretching of the skin, as in rapid weight gain, or mechanical stress, as in weight lifting. The pathogenesis of striae distensae is unknown but probably relates to changes in the fibroblast phenotype. In order to characterize striae distensae fibroblasts, alpha-smooth muscle actin expression and contractile forces were studied. Five healthy women with early erythematous striae and five healthy women with older striae were selected. Paired biopsies were taken from the center of lesional striae and adjacent normal skin. Fibroblasts were obtained by an explant technique and expanded in vitro in Dulbecco’s modified Eagle‘s medium. Contractile forces generated by fibroblasts in collagen lattices were measured with the Glasbox device developed in our laboratory. Alpha-smooth muscle actin expression was studied by immunofluorescence labeling of cells and by flow cytometry. Fibroblasts from early striae distensae were the richest cells in alpha-smooth muscle actin filaments and generated the highest contractile forces. Their peak contractile force was 26% greater than normal fibroblasts. There was a 150% higher level of alpha-smooth muscle actin content in fibroblasts from early striae distensae compared with fibroblasts from normal skin. In contrast, there was no significant difference in force generation between old striae fibroblasts and normal fibroblasts with cells expressing no alpha-smooth muscle actin. The contractile properties of fibroblasts from striae distensae varies depending on the stage of the disease. In early striae distensae, fibroblasts acquire a more contractile phenotype, corresponding to that of myofibroblasts.

Production and Validation of CR-39-Based Dishes for α-Particle Radiobiological Experiments

Abstract Gaillard, S., Armbruster, V., Hill, M. A., Gharbi, T. and Fromm, M. Production and Validation of CR-39-Based Dishes for α-Particle Radiobiological Experiments. Radiat. Res. 163, 343–350 (2005). The study of radiobiological effects induced in vitro by low fluences of α particles would be significantly enhanced if the precise localization of each particle track in the cell monolayer was known. From this perspective, we developed a new method based on tailor-made UV-radiation-cured CR-39, the production of which is described. Its validation both as a petri dish and as solid-state nuclear track detectors is demonstrated. With respect to the demands on solid-state nuclear track detectors in such experiments, these biologically compatible detectors have a controlled micrometric thickness that allows them to be crossed by the α particles. In this study, we present a method for obtaining 10-μm-thick CR-39, its chemical characterization, and its properties as a solid-state nuclear track detector under the environmental conditions of radiobiological experiments. The experimental studies performed with 3.5 MeV α particles show that their transmitted energy is sufficient enough to cross the entire cellular volume. Under optimal conditions, etched tracks are clearly defined 2 h after etching. Moreover, the UV-radiation-cured CR-39 represents an essentially zero background that is due to the short time between the production and use of the polymer. Under a confocal microscope, this thin solid-state nuclear track detector allows the precise localization of the impact parameter at the subcellular level.

A micromachined connector for the coupling of optical waveguides and ribbon optical fibers

This paper describes in details the fabrication and tests of a micromechanical connector, which is used for the precise optical self-alignment of multi-waveguide optical integrated circuits (OIC) to ribbon optical fibers, without injecting light in the fiber. Nickel alignment pins are electrodeposited on the OIC using a photolithographic process, and these pins are inserted into suitable openings made on a silicon micromachined platform, on which optical fibers are accurately positioned using V-grooves. A simultaneous fabrication of several microstructures which are used as an assistance for the assembly of the fibers and the waveguides is presented for the first time. Design and fabrication issues are reported, as well as preliminary experimental results which show that excess optical losses on the order of 3 dB per coupling facet can be obtained.

Towards objective evaluation of the skin aspect: principles and instrumentation.

Background/aims: The aim of this paper is to propose an objective procedure for the evaluation of the skin aspect. This work is based on light scattering phenomena and in‐vivo measurements of the skin profile and of the skin Bi‐directional Reflection Distribution Function (BRDF).

Microconnectors for the passive alignment of optical waveguides and ribbon optical fibers

This paper describes the fabrication of a new mechanical microconnector, which is used for the precise optical self-alignment of multi-waveguide Optical Integrated Circuits (OIC) to ribbon optical fibers, without injecting light in the fiber. Nickel alignment pins are electrodeposited on the OIC using a photolithographic process, and the pins are inserted into suitable openings made on a silicon micromachined platform, on which optical fibers are accurately positioned using V-grooves. Design and fabrication issues are reported, as well as preliminary experimental results which show that excess optical losses on the order of 3 dB can be obtained.

Adjustment of the coupling ratio by laser ablation of Ti:LiNbO3 directional couplers

Abstract The coupling ratio of directional couplers in Z-cut Y-propagation and X-cut Z-propagation LiNbO 3 crystals was adjusted by laser ablation. The coupling ratio change is more efficient for the TM-mode of Z-cut couplers. The method can be used to correct the uncertainty of the coupling ratio for directional couplers that occurs during fabrication process.

Effective refractive index change of X-cut Z-propagation Ti:LiNbO3 waveguides by laser ablation

Laser ablation was applied to X -cut Z-propagation Ti:LiNbO 3 waveguides. The effective refractive index change of the waveguides after the ablation was measured for both TE and TM modes. The change is more sensitive to the ablation for the TE than for the TM mode. This phenomenon was confirmed by measuring the modal effective refractive indices of a nonablated and an ablated planar Ti:LiNbO 3 waveguide with the m -line method. A photoelastic effect that may cause the different effective index changes of the waveguide modes after ablation is discussed.

Mechanical clip-on and flip-chip assembly on silicon submount for self aligned fiber to waveguide coupling

Flip chip bonding by use of solder bumps has been widely developed to hybridize active devices such as lasers, detectors, and amplifiers, onto silicon microbenches. We report here a new method allowing hybridization of any kind of substrate onto a silicon submount with a passive and high precision self alignment process, the substrate being held in three dimensions, allowing coupling of waveguides to multiple fibers. Moreover the system allows a detachable configuration and avoids any additional micromachining of the waveguide substrate. Alignment of the waveguide axis with the V-grooves axis was obtained with an accuracy better than 2 /spl mu/m. Preliminary results indicate that the excess loss during the self-alignment and coupling of a fiber by insertion in a V-groove compared to an active alignment was typically of -3 dB.