Vat 3D printable materials and post-3D printing procedures for the development of engineered devices for the biomedical field

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3D Scanning of transparent objects

Many practical tasks in industry, such as automatic inspection or robot vision, often require scanning of three-dimensional shapes with non-contact techniques. However, transparent objects, such as those made of glass, still pose difficulties for classical scanning techniques. The reconstruction of surface geometry for transparent objects is complicated by the fact that light is transmitted through, refracted and in some cases reflected by the surface. Current approaches can only deal relatively well with sub-classes of objects. The algorithms are still very specific and not generally applicable. Furthermore, many techniques require considerable acquisition effort and careful calibration. This thesis proposes a new method of determining the surface shape of transparent objects. The method is based on local surface heating and thermal imaging. First, the surface of the object is heated with a laser source. A thermal image is acquired, and pixel coordinates of the heated point are calculated. Then, the 3D coordinates of the surface are computed using triangulation and the initial calibration of the system. The process is repeated by moving the transparent object to recover its surface shape. This method is called Scanning From Heating. Considering the laser beam as a point heating source and the surface of the object locally at at the impact zone, the Scanning From Heating method is extended to obtain the surface normals of the object, in addition to the 3D world coordinates. A scanner prototype based on Scanning From Heating method has been developed during the thesis

Beyond solid-state lighting: Miniaturization, hybrid integration, and applications og GaN nano- and micro-LEDs

Gallium Nitride (GaN) light-emitting-diode (LED) technology has been the revolution in modern lighting. In the last decade, a huge global market of efficient, long-lasting and ubiquitous white light sources has developed around the inception of the Nobel-price-winning blue GaN LEDs. Today GaN optoelectronics is developing beyond lighting, leading to new and innovative devices, e.g. for micro-displays, being the core technology for future augmented reality and visualization, as well as point light sources for optical excitation in communications, imaging, and sensing. This explosion of applications is driven by two main directions: the ability to produce very small GaN LEDs (microLEDs and nanoLEDs) with high efficiency and across large areas, in combination with the possibility to merge optoelectronic-grade GaN microLEDs with silicon microelectronics in a fully hybrid approach. GaN LED technology today is even spreading into the realm of display technology, which has been occupied by organic LED (OLED) and liquid crystal display (LCD) for decades. In this review, the technological transition towards GaN micro- and nanodevices beyond lighting is discussed including an up-to-date overview on the state of the art

Printed soft optical waveguides for delivering light into deep tissue

To implement light-based diagnosis and therapies in the clinic, implantable patient-friendly devices that can deliver light inside the body while being compatible with soft tissues are needed. This Thesis presents the development of optical waveguides for guiding light into tissue, obtained by printing technologies from three different polymer combinations. Firstly, D,L-dithiothreitol (DTT) bridged PEG diacrylate were synthesized and printed into waveguides, which exhibited tunable mechanical properties and degradability, and low optical losses (as low as 0.1 dB cm-1 in visible range). Secondly, degradable waveguides from amorphous poly(D,L-lactide) and derived copolymers were developed by printing, which showed elasticity at body temperature and could guide VIS to NIR light in tissue for tens of centimeters. At last, soft and stretchable optical waveguides consisting of polydimethylsiloxane (PDMS) core and acrylated Pluronic F127 cladding were fabricated by coaxial extrusion printing, which could be stretched to 4 times of their length and showed optical loss values in tissue as low as 0.13 -0.34 dB cm-1 in the range of 405-520 nm. For proof-of-concept, above printed optical waveguides were used to deliver light across 5-8 cm tissue to remotely activate photochemical processes in in vitro cell cultures. The presented work exemplifies how rational study of medically approved biomaterials can lead to useful and cost-effective optical components for light applications.Neue optische Technologien verändern die Zukunft der Medizin und fördern die Entwicklung von Implantaten, die im Körper Licht abgeben. Diese Arbeit beschreibt drei gewebekompatible, optische Wellen¬leiter für medizinische Zwecke, die mit 3D-Extrusionsdruck gefertigt werden. Zum einem wurden Wellen¬leiter mit einstellbaren mechanischen Eigenschaften und kontrollierter Abbaubarkeit im Körper als Funktion des Dithio¬threitol (DTT)-Anteils in DTT-modifizierten Poly¬ethylen¬glykol¬diacrylat-Hydro¬gelen entwickelt. Die bei der Extrusion in-situ-photopolymerisierten Wellen¬leiter haben nur 0,1 dB/cm optischen Verlust im VIS-Bereich und wurden verwendet, um photo¬chemische Prozesse in In-vitro-Zellkulturen zu aktivieren. Zum anderen wurden im Körper abbaubare Wellenleiter aus amorphem Poly(D,L-Lactid) und dessen Copolymeren gedruckt. Diese Wellenleiter sind bei Körpertemperatur elastisch und leiten in mehreren zehn Zentimetern Gewebe Licht vom VIS- bis NIR-Bereich. Schließlich wurden mit koaxialem Extrusions¬druck weiche und dehnbare Wellenleiter hergestellt, die aus einem PDMS-Kern und einer acrylierten Pluronic F127 Hülle bestehen. Diese Wellenleiter sind aufs Vierfache dehnbar und haben in Gewebe nur 0,13 bis 0,34 dB/cm optische Verluste bei 405-520 nm. Die vorgestellte Arbeit zeigt, wie Materialauswahl mit Drucktechnologien kombiniert werden können, um optische Wellenleiter für medizinische Anwendungen mit bemerkenswerter Leistung bei angemessenem Aufwand zu entwickeln

Highly Nonlinear Dynamics of In Vivo Deep-Tissue Interaction with Femtosecond Laser Pulses at 1030 nm

We report on the highly nonlinear behavior observed in the central nervous system tissue of zebrafish (Danio rerio) when exposed to femtosecond pulses at 1030 nm. At this irradiation wavelength, photo damage becomes detectable only after exceeding a specific peak intensity threshold, which is independent of the photon flux and irradiation time, distinguishing it from irradiation at shorter wavelengths. Furthermore, we investigate and quantify the role of excessive heat in reducing the damage threshold, particularly during high-repetition-rate operations, which are desirable for label-free and multi-dimensional microscopy techniques. To verify our findings, we examined cellular responses to tissue damage, including apoptosis and the recruitment of macrophages and fibroblasts at different time points post-irradiation. These findings substantially contribute to advancing the emerging nonlinear optical microscopy techniques and provide a strategy for inducing deep-tissue, precise and localized injuries using near-infrared femtosecond laser pulses

3D Cell Printed Tissue Analogues: A New Platform for Theranostics

Stem cell theranostics has received much attention for noninvasively monitoring and tracing transplanted therapeutic stem cells through imaging agents and imaging modalities. Despite the excellent regenerative capability of stem cells, their efficacy has been limited due to low cellular retention, low survival rate, and low engraftment after implantation. Three-dimensional (3D) cell printing provides stem cells with the similar architecture and microenvironment of the native tissue and facilitates the generation of a 3D tissue-like construct that exhibits remarkable regenerative capacity and functionality as well as enhanced cell viability. Thus, 3D cell printing can overcome the current concerns of stem cell therapy by delivering the 3D construct to the damaged site. Despite the advantages of 3D cell printing, the in vivo and in vitro tracking and monitoring of the performance of 3D cell printed tissue in a noninvasive and real-time manner have not been thoroughly studied. In this review, we explore the recent progress in 3D cell technology and its applications. Finally, we investigate their potential limitations and suggest future perspectives on 3D cell printing and stem cell theranostics.116Nsciescopu