Compact laser-assisted tools for high-resolution additive manufacturing

Micro-additive manufacturing has become an enabling technology in biomedical research as it allows for instance creating functional microstructures or studying cellular interactions at the microscale. Among the various manufacturing techniques laser-actuation offers a versatile control means for microprinting applications since it both enables jetting liquids and curing photoresists to form three-dimensional microstructures. In the first part of this thesis, the potential of laser-actuation for embedded three-dimensional printing was studied. In conventional embedded three-dimensional printing, soft microstructures are built by directly depositing ink filaments with a microextruder into a gel-like support material. As microextruders produce continuous ink filaments, they do not allow optimally mimicking the complex three-dimensional micro-architectures of tissues. Thus, to improve the resolution of three-dimensional embedded printing, laser-induced forward transfer, a high-velocity liquid jetting technique, was employed to achieve depth-controlled liquid delivery within a gel-like support substrate. Interestingly, controlling the deposition depth of liquid droplets adds a degree of freedom to laser-induced forward transfer, turning this conventional two-dimensional patterning technique into a direct three-dimensional printing technique. In the second part of this thesis, the potential of laser-actuation to build a compact laser- assisted toolkit for high-resolution manufacturing was further studied. The fabrication of advanced functional parts with multi-material and multi-resolution features stills remains challenging. Existing microfabrication techniques rely on complex and bulky devices, which prevent processing parts with several manufacturing tools on a single platform due to space constraints. Hence, to enable multiprocess additive manufacturing, miniaturized laser-assisted drop-on-demand and direct writing tools were developed in this thesis. In the first component of this compact toolkit, a laser-induced flow focusing phenomenon was studied to generate viscous micro-droplets through a 300-µm glass microcapillary, thus paving the way for a compact drop-on-demand device operating on a wider range of printable liquids than standard inkjet printers. The second component of the miniaturized toolkit is based on oxygen-inhibited single-photon photopolymerization. This non-linear photopolymerization process was investigated and then implemented through a 70-µm multimode fiber to demonstrate three-dimensional microfabrication through an endoscope-like tool. This curing probe provides a compact and affordable alternative to conventional direct laser writing devices, which rely on two-photon absorption, a non-linear absorption phenomenon that entails using femtosecond lasers. Such a miniature additive manufacturing toolkit could also open up possibilities for the fabrication of microstructures in areas otherwise inaccessible, for instance in in vivo applications

Exploring underwater target detection by imaging polarimetry and correlation techniques

International audienceUnderwater target detection is investigated by combining active polarization imaging and optical correlation-based approaches. Experiments were conducted in a glass tank filled with tap water with diluted milk or seawater and containing targets of arbitrary polarimetric responses. We found that target estimation obtained by imaging with two orthogonal polarization states always improves detection performances when correlation is used as detection criterion. This experimentally study illustrates the potential of polarization imaging for underwater target detection and opens interesting perspectives for the development of underwater imaging systems

Endoscopic light delivery for ablation and 3D printing

Laser ablation and 3D printing are complimentary tools in manufacturing. The use of optical fibers to deliver high laser power for material ablation in confined places could open the path for a wide variety of applications (fig 1.). Similarly, the use of optical fibers capable of delivering high peak power focused pulses can be used to make 3D structures via 2 photon polymerization (2PP) in spaces difficult to access (fig 2). However, modal dispersion in multimode fibers scrambles the input wavefront, resulting in a speckle pattern at the output. By using wavefront shaping techniques to shape the light coupled into a multimode fiber, a focus spot can be created at the output. Controlling the wavefront of the input pulse allows scanning of the focus spot around the area of interest. When the peak intensity of the focus spot exceeds the threshold for ablation of the desired material, micro-pattern formation can be achieved. In order to minimize modal dispersion in the fiber, fiber modes of similar propagation constants are selectively excited. We achieved 10 mW of spatial diffraction limited focusing with 120 fs duration through a 5 cm GRIN multimode fiber. This level of peak intensity is suitable for 2PP. Please click Additional Files below to see the full abstract

Inkjet Printing of Viscous Monodisperse Microdroplets by Laser-Induced Flow Focusing

The on-demand generation of viscous microdroplets to print functional or biological materials remains challenging using conventional inkjet-printing methods, mainly due to aggregation and clogging issues. In an effort to overcome these limitations, we implement a jetting method to print viscous microdroplets by laser-induced shockwaves. We experimentally investigate the dependence of the jetting regimes and the droplet size on the laser-pulse energy and on the inks' physical properties. The range of printable liquids with our device is significantly extended compared to conventional inkjet printers's performances. In addition, the laser-induced flow-focusing phenomenon allows us to controllably generate viscous microdroplets up to 210 mPa s with a diameter smaller than the nozzle from which they originated (200 mu m). Inks containing proteins are printed without altering their functional properties, thus demonstrating that this jetting technique is potentially suitable for bioprinting

Transcriptional analysis of late ripening stages of grapevine berry

* Background: The composition of grapevine berry at harvest is a major determinant of wine quality. Optimal oenological maturity of berries is characterized by a high sugar/acidity ratio, high anthocyanin content in the skin, and low astringency. However, harvest time is still mostly determined empirically, based on crude biochemical composition and berry tasting. In this context, it is interesting to identify genes that are expressed/repressed specifically at the late stages of ripening and which may be used as indicators of maturity. * Results: Whole bunches and berries sorted by density were collected in vineyard on Chardonnay (white cultivar) grapevines for two consecutive years at three stages of ripening (7-days before harvest (TH-7), harvest (TH), and 10-days after harvest (TH+10)). Microvinification and sensory analysis indicate that the quality of the wines made from the whole bunches collected at TH-7, TH and TH+10 differed, TH providing the highest quality wines. In parallel, gene expression was studied with Qiagen/Operon microarrays using two types of samples, i.e. whole bunches and berries sorted by density. Only 12 genes were consistently up-or down-regulated in whole bunches and density sorted berries for the two years studied in Chardonnay. 52 genes were differentially expressed between the TH-7 and TH samples. In order to determine whether these genes followed a similar pattern of expression during the late stages of berry ripening in a red cultivar, nine genes were selected for RT-PCR analysis with Cabernet Sauvignon grown under two different temperature regimes affecting the precocity of ripening. The expression profiles and their relationship to ripening were confirmed in Cabernet Sauvignon for seven genes, encoding a carotenoid cleavage dioxygenase, a galactinol synthase, a late embryogenesis abundant protein, a dirigent-like protein, a histidine kinase receptor, a valencene synthase and a putative S-adenosyl-L-methionine: salicylic acid carboxyl methyltransferase. * Conclusions: This set of up-and down-regulated genes characterize the late stages of berry ripening in the two cultivars studied, and are indirectly linked to wine quality. They might be used directly or indirectly to design immunological, biochemical or molecular tools aimed at the determination of optimal ripening in these cultivars

A construção ortodoxa dos números : dos números naturais aos complexos

In this work, we investigated the construction of natural, integer, rational, real, complex, quaternion and Octonion numbers. More precisely, the set of real numbers was achieved by applying two methods: Dedekind Cuts and Equivalence Classes of Cauchy Sequences. Our study is only based on using Peano Axioms, which are directly related to the natural numbers, in order to get the basic properties satis ed by these numbers. In addition, we carefully proved the elementary results involving real numbers. This process in question was developed constructively throughout of the concepts of the integer and rational numbers. Next, we show that it is possible to establish the existence of complex numbers along with their more usual arithmetic properties. Finally, we nish each chapter of our work showing some possible applications in each set worked.No presente trabalhos, investigamos, cuidadosamente, a construção do números Naturais, inteiros, Racionais, Reais e Complexos. Sendo que, o conjunto dos números reais foi obtido através dos conhecidos métodos: Cortes de Dedekind e Classes de Equivalência por sequência de Cauchy. O estudo consistiu em utilizar os famosos Axiomas de Peano, ps quais estão relacionados aos números naturais, em ordem a obter as em conhecidas propriedades elementares, satisfeitas para todos esses números. E, a partir deste conhecimento, encontramos rigorosamente as provas dos resultados básicos envolvendo os números reais. Este processo em questão, foi desenvolvida de maneira construtiva através dos números inteiros e racionais. Em seguida, mostramos que é possível estabelecer a existência de números complexos, juntamente com suas propriedades aritméticas mais usuais. Por fim, terminamos cada capítulo do nosso trabalho, mostrando algumas possíveis aplicações em cada conjunto trabalhado

Development of an optical system for combined imaging and patterned stimulation of the rodentretina

During this Master’s thesis at the Vision Institute (Paris, France), a noncontact optical system for in vivo combined imaging and patterned stimulation of the rodent eye was developed. The objective was to assess the efficiency of the optogenetic therapy, currently tested on rodents, whose aim is to heal blind or low-visual-acuity people. To the best of our knowledge, previous systems did not reach the photometric requirement needed for the stimulation of optogenetic channels and were developed for bigger mammals than rodents. The mounted system allowed us to obtain non-contact mouse and rat eye fundi images with a wide field in both near-infrared and visible illumination. The first tests of the patterned stimulation arm allowed projection of simple patterns on the rat eye and showed that the photometric requirements are almost met for the activation of optogenetic channels. Future developments should include stable alignment of the animal’s eye with the optical axis of the system, which would result in an improved quality of eye fundus images and of the patterned stimulation

System and method of using feedback for correcting three dimensional objects in volumetric tomographic printers

A method for monitoring the generation of a three-dimensional object (5) being formed in a tomographic additive manufacturing system from simulated tomographic two-dimensional back-projections (9) of a desired 3D article comprises the steps of: - illuminating a container (3) comprising a photoresponsive material (103) with a light beam (2a) of two-dimensional light patterns generated from said two-dimensional back-projections (9) at multiple angles, preferably by rotation of the container (3), so as to form the object (5) in the container (3); - capturing images of said object (5) being formed by volumetric printing with an imaging system (6, 7, 8) disposed around the container (3) in which the object (5) is being formed; - determining from said images the shape or extent to which the object has been formed

Compact Drop-on-Demand Apparatus Using Light Actuation Through Optical Fibers

A drop delivery system comprising a light source; an optical waveguide bringing light from the light source; and a liquid supplying means configured to bring a liquid at a tip of the optical waveguide, wherein the light source and the optical waveguide are configured to enable the light to eject a drop of the liquid