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.