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Towards Programmable 3D Structures at the Microscale

Subject Area Synthesis and Properties of Functional Materials
Polymer Materials
Term from 2019 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 419400349
 
Final Report Year 2023

Final Report Abstract

In recent decades 3D printing has undergone tremendous progress on the technological and the material side. However, most materials for 3D printing are limited in one aspect: They produce static 3D geometries unable to respond or adapt to environment – confining in this way their applicability for future smart technologies that require dynamic behavior. Overcoming these limitations – the concept of “4D printing” emerged, implementing the fourth dimension “time” into 3D printed structures, equipping them features such as adaptivity and responsiveness towards external stimuli like temperature or light. One strategy for fabrication of such 4D structures is the exploitation of smart polymeric materials such as shape memory polymers (SMPs) for 4D ink design. Although the concept of SMPs has already been investigated at the macroscale, the microscale is only scarcely explored. In the framework of this project the concept was further extended: a novel SMP ink was designed offering excellent printability of thermoresponsive 4D structures at the macro- and microscale using light-based printing methods (digital light processing (DLP) and two-photon laser printing (2PLP)). To achieve this, a SMP ink system was designed and optimized for each method resulting in an ink formulation for each scale. Excellent printability and shape memory properties were demonstrated at macro- and microscale. Especially the 2PLP-printable microformulation appears to be a promising system for future applications in microrobotics, biomedical therapies or smart microsensors. Extending the applicablity of the macroformulation, push-pull azo dyes were incorporated into the SMP formulation, enabling DLP-based generation of light responsive 4D geometries. The stimulus light offers here additional spatial control and access to a multiplicity of programmed intermediate shapes during the shape memory cycle. Furthermore, another aspect of 4D printing was investigated, implementing functionalities into 3D printed microgeometries prone to postmodification via alkoxyamine chemistry, permitting tunability and thus programmability of mechanical properties and size. This was achieved by integration of dormant alkoxyamine bonds during the 2PLP fabrication process, giving access to postprinting modification by network decrosslinking via nitroxide exchange reaction (NER) and by chain extension via nitroxide mediated polymerization (NMP). Employing this approach remarkable tunability of mechanical properties and size was achieved – open pathways towards precisely fabricable and customizable “living” microstructures, highly relevant for areas were precisely manufactured tunable microstructures are needed.

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