Effets spéciaux

Les effets spéciaux (souvent notés SFX, pour special effects, en anglais) sont des techniques utilisées au cinéma pour créer l’illusion d’actions et simuler des objets, des environnements, des personnages ou des phénomènes qui n’existent pas dans la réalité ou qui ne pourraient pas être filmés au moment du tournage mais qui ne sont pas obtenus par des moyens numériques. Ces derniers, totalement créés ou modifiant des images déjà obtenues en tournage normal, sont appelés des effets visuels. On parle aussi de trucages, ou truquages. Principes Les effets spéciaux font appel à différents procédés liés à l’image et au son : synthèse d'image 3D, traitement numérique, maquettes, animation , pixilation, ralenti et accéléré, maquillage, bruitage, capture de mouvement, etc. Ils peuvent être réalisés pendant le tournage ou après (en postproduction), ou par la combinaison des deux. Les cinéastes utilisent les effets spéciaux pour des besoins divers :

pour reproduire une atmosphère

On chip cellular dielectric spectroscopy

Ludovica Colella

In the recent years, the development of automated systems for cellular monitoring has been highly promoted in basic biological research as well as in industries and medical diagnostic. Several methods for transduction of cellular signals have been investigated and it has been demonstrated that impedance-based techniques have great potential for real-time, non invasive cell-based assays for both high throughput screening and research laboratory environments. This thesis presents the fabrication and design of a microelectrodes-based dielectric sensor for cellular analysis, and its application to monitor in-vitro physiological functions of different cell types. A dual array of planar interdigitated microelectrodes has been patterned on the bottom of two microchambers used for cells culture. The system allows real-time dynamic cellular monitoring with high temporal resolution and high sensitivity. The device enables multifrequency characterization (frequency between 100Hz and 30MHz), so that the integral cellular response is obtained and several independent effects can be monitored in parallel at different frequencies. Analytical models are used to evaluate the evolution of various cell parameters, such as cell membrane capacitance and cytoplasm conductivity, and to obtain information about cell morphology and adhesion. To interface the microelectrode array to the external instrumentation, a printed circuit board has been developed, which includes the circuitry controlling the switch between reference/sensing chamber and calibration/measurement mode. In addition, the device is controlled by a computer interface, to automatize the acquisition of the impedance spectra and select long or short term response monitoring. Two innovative biological applications are proposed for the presented device. The effect of D-glucose on biconcave erythrocytes has been investigated. The variation of glucose concentration in plasma is an important biological process and it has been extensively studied because of its implication in diseases like diabetes. Measurements have been performed on erythrocyte suspensions exposed to several D-glucose concentrations. The results have shown that glucose induces variations in the dielectric properties of erythrocytes and affects mainly the plasma membrane capacitance. A better understanding of this mechanism is fundamental for a future development of impedance glucose sensors based on the evaluation of the dielectric properties of the red blood cells. Furthermore, a functional assay of the anthrax toxin receptor on endothelial cells has been performed using the developed device. This transmembrane protein is encoded by the Capillary Morphogenesis Gene 2 (CMG2), which was identified as a gene overexpressed in endothelial cells during capillary morphogenesis. This protein is known as an anthrax toxin receptor and it has been discovered that its mutations lead to a rare human disease (Hyaline Fibromatosis Symdrome). On the contrary, its physiological function has still to be revealed. To investigate a potential physiological ligand of CMG2, vascular endothelial cells (HUVEC) have been cultured on the microelectrodes array coated with different extracellular matrix protein. The adhesion kinetic of wild-type HUVEC has been recorded for several hours and compared with the adhesion of vascular cells in which the receptor CMG2 is inhibited. The results obtained in this work provide new knowledge about the physiological role of this receptor associated with different ECM proteins.

EPFL2012

Subsurface ablation of tissue by ultrafast laser

Thomas Jean Victor Marie Lanvin

Laser-induced optical breakdown (LIOB) is a multiphoton process which can be used for selective removal of material. It revolves around the creation of a plasma in the focal volume of a beam, and requires very high peak intensities in the order of the GW.cm-2. For this reason, ultrafast lasers sending high energy pulses with very short durations below 1 ps are favorite tools for triggering LIOB. The local creation of the plasma can induce a sharp rise in temperature and pressure over a few micrometers, which produce a cavitation bubble. The combined mechanical effects from the bubble creation and chemical effects from the free electrons in the plasma can induce dramatic changes in and around the focal volume. This is particularly true in sensitive samples such as biological tissues, where cells can be selectively destroyed by LIOB. The axial and lateral confinement of the plasma creation due to the multiphoton nature of LIOB opens interesting perspectives in the field of microsurgery. In this regard, the work presented in this thesis concerns the analysis of the effects of LIOB in soft biological tissues. More specifically, we investigate the case of arterial tissues and the opportunities this technique could offer in the treatment of atherosclerosis. First, we present the current knowledge on the mechanism and impact of LIOB on the surrounding medium, and particularly in biological samples. We discuss their modeling, both via simulation and replication in organic and inorganic phantoms. We consider the theory of the linear and non-linear mechanisms driving the evolution of the plasma density in the focal volume, the minimum requirements for the creation of a cavitation bubble, and optical effects which can modify the shape of a plasma. We then observe the behavior described by this theory in transparent and scattering phantoms mimicking biological tissues, and investigate scanning approaches to remove volumes of material. The following section of this thesis is devoted to investigating the effect of LIOB at the cellular level. We discuss an approach according to which LIOB may be of interest in the treatment of atherosclerosis or other pathologies which could benefit from the control of the population of cells undergoing controlled cell death (apoptosis). We then investigate the effect of LIOB on populations of epithelial cells in 2D and 3D cultures. We monitor the increase in the number of necrotic and apoptotic cells, in different regimes of ablation. We then present the methods and results of subsurface ablation in arterial tissue, both healthy and atherosclerotic. On ex-vivo experiments, we focus on the observation of a bubble produced by LIOB, and the structural damage generated. On in-vivo experiments, we investigate the effect on necrosis and apoptosis of cells around the target area, and compare our findings with the results obtained in cell cultures and phantoms. Finally, delivering the high intensities pulses to the target area in a minimally invasive way is essential in biomedical applications of LIOB, and we investigate this question in the final part of this thesis. We present two different approaches to answer this challenge: first by the use of transmission of pulses via a hollow-core photonic crystal fiber, and secondly by wavefront shaping of a pulse through a multicore fiber. Through both methods, we demonstrate subsurface ablation of biological tissue.

EPFL2017

Subsurface ablation of tissue by ultrafast laser

Thomas Jean Victor Marie Lanvin

EPFL2017

On chip cellular dielectric spectroscopy

Ludovica Colella

EPFL2012

On chip cellular dielectric spectroscopy

A 3D Meso-scale Model to describe the Mechanical Effects of the Alkali-silica Reaction in Concrete

Subsurface ablation of tissue by ultrafast laser

A 3D Meso-scale Model to describe the Mechanical Effects of the Alkali-silica Reaction in Concrete

Subsurface ablation of tissue by ultrafast laser

On chip cellular dielectric spectroscopy