Preview

PDF, English Download (10MB) | Terms of use

Abstract

3D printing has experienced a tremendous development in recent decades on the technological as well as material side. However, most 3D printable materials are restricted in one aspect: They produce static 3D geometries, unable to respond or adapt to their environment – limiting in this way their applicability for smart technologies where a dynamic behavior is needed. To overcome this issue, the concept of “4D printing” emerged, where the incorporation of time as fourth dimension in 3D geometries enables new features such as responsiveness or adaptivity towards external stimuli. The simplest strategy to access such 4D structures is the utilization of smart polymeric materials for ink design, which can respond to external stimuli on-demand. In particular, the use of shape memory polymers (SMP) – one of the promising materials investigated in this thesis – is suitable for this purpose. Although the concept (and use) of SMP has already been investigated at the macroscale, the microscale is only scarcely explored. Taking one step further, this work presents – in the first part - a novel SMP ink system offering printability of thermoresponsive structures at macro- and microscale using light-based techniques namely digital light processing (DLP) and two-photon laser printing (2PLP). In particular, formulations based on designed SMP ink system are designed and adapted to fulfill requirements of each technique. At both size regimes (macro and micro) excellent printability as well as shape memory properties are demonstrated. Especially the microformulation is considered as promising system for applications in future fields such as microrobotics, biomedical therapies or smart microsensors. In a further work, push-pull azo dye species are incorporated into the SMP formulation giving access to light responsive 4D architectures fabricated at high resolution using DLP. By exploitation of the dyes’ photothermal effects, new features are achieved. Translation towards light as stimulus allows excellent spatial control during shape recovery and access to a multiplicity of intermediate shapes. Last, investigating another aspect of 4D printing, “living” radical polymerization features are incorporated in 3D microstructures permitting the generation of 3D geometries, enabling precise setting of their properties for customized applications. In particular, dormant alkoxyamine bonds were integrated during 2PLP fabrication, allowing postmodification by network decrosslinking via nitroxide exchange reaction (NER) and by chain extension with styrene via nitroxide-mediated polymerization (NMP). Remarkable changes in mechanical properties and size are achieved, giving in this way access to precisely manufacturable and adjustable microscopic geometries –relevant for areas and fields where customized precise architectures are of highest necessity.