Bright Lights - Innovative Micro- and Nano-Patterning for Sensing and Tissue Engineering

QC 20220429

Abstract

Light is the primary source of energy on our planet and has been a significant driver in the evolution of human society and technology. Light finds applications in two-dimensional (2D) photolithography and three-dimensional (3D) printing, where a pattern is transferred to a material of interest by ultraviolet (UV) light exposure, and in laser scribing and cutting, where high power lasers are used to pattern the surface of objects or cut through the bulk of the material of interest. However, conventional light-based processing has three main constraints: a) the wavelength of visible light limits resolution, b) only materials that absorb the wavelength in use can be efficiently processed, and c) intense laser light burns its target, degrading the material surrounding the exposed areas and further limiting material compatibility. Overcoming these limitations is the core of this thesis.

The first part of this thesis describes three different patterning methods enabled by intelligent design and non-linear light-matter interaction. The first work reports the use of light at 365 nm to generate sub-20 nm wide nanowires (NWs) exploiting crack lithography, exceeding the possible resolution given by diffraction limit by 10-fold. The second work describes how the non-linear interaction of femtosecond laser pulses with otherwise transparent glass enables nanostructuring of borosilicate coverslips. Positively charging the nanostructured glass surfaces grants a “attract and destroy” bactericidal functionality and maintains the transparency of the substrate, creating a microscopy compatible platform to study bacteria-surface interactions and providing strategies to fight antibiotic-resistant bacteria. The third and fourth works show how femtosecond lasers can directly pattern carbon nanotube films and 2D materials (graphene, molybdenum disulfide, and platinum diselenide) without damaging the substrate or the material surrounding the exposed area. Non-linear interaction with high-energy laser pulses allows sub-300 nm resolution, circumventing the limit given by light diffraction in the linear regime. The combination of high resolution, femtosecond exposure, and ultrafast scanning speed provides a valid alternative to resist-based photolithography while eliminating the related contamination issues for these sensitive materials.

The second part of this thesis describes two different 3D micromachining approaches enabled by high-intensity laser light. The fifth work presents a collagen patterning method based on laser-induced cavitation, called cavitation molding. This method represents a new biomanufacturing mode that is neither additive nor subtractive. In this study, cavitation molding enables the generation of a micro vascularized cancer-on-chip model, consisting of an in-vivo-like spheroidal mass of cancer cells surrounded by artificial blood vessels. In the sixth and final work, we used two-photon polymerization to generate 3D platforms in a biocompatible resin. This platform enables the study of the physiology of neurons and their interaction with astrocyte cells. The low autofluorescence of the printed resins allows optical readout of the neuronal activity by calcium imaging.

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