Magnetic Field-assisted Stereolithography for Production of Multimaterial Objects with Surface Structures

Multi-material, multi-scale hierarchical structures have a range of applications in sensors, imaging and bio-medical industry. From a fabrication standpoint, there is an increasing demand for multi-material fabrication techniques capable of manufacturing complex structures with multi-scale features. Additive manufacturing (AM) or 3D printing provides an advanced technology platform that can be utilized for fabricating such multi-material multi-scale objects. Despite recent advances, current multi-material multi-scale AM technologies have been restricted by several challenges. None of the current approaches are readily able to model customized combinations of different materials and their distributions in multiple scales ranging from nano- to meso-scale. In this thesis, the research goal is to develop an advanced AM technique for productions of multi-material objects with multi-scale hierarchical surface structures with locally engineered mechanical properties. A novel multi-scale multi-material 3D printing method, magnetic field-assisted stereolithography (M-SL), for fabricating complex hierarchical particle-polymer structures are presented and validated. M-SL technique can spatially control the multi-material composition, magnetic particle filler orientation and ratio to achieve locally programmed material intelligence with engineered mechanical, magnetic, and surface properties. The research plan and this dissertation have been developed in accordance with the overarching goal in a step by step manner, with four specific objectives and corresponding tasks. First task is to achieve the goal of multi-material distribution control in M-SL process. The developed M-SL fabrication technique is first presented in chapter 2, which includes detailed descriptions of the hardware experimental setup, software, feedstock material and preparation process and the M-SL printing process. Chapters 3 and 4 further investigate the magnetic field control and magnetic ink writing process innovation to fulfil the task 1 objective. Chapter 3 discusses the magnetically induced particle alignments and the integration of magnetic field alignments and M-SL process to manipulate the material distribution during the printing process. Chapter 4 further integrates magnetic writing to the M-SL process with graded material distribution and investigates the printed properties. The M-SL process is used to control the particle dispersion and alignment to create magnetic particle traces (i.e., magnetic writing) in the base polymer. With the process innovation of M-SL in chapter 3 and 4, task 1 is completed and the M-SL is capable of multi-scale material distribution control in M-SL. The second task is to integrate surface structuring in M-SL. Chapter 5 focuses on this investigation and describes the development of multi-scale magnetic particle-gel structuring process within the M-SL technology. It also demonstrates the feasibility of fabricating multi-scale (nano-meso) hierarchical structures with spatially varied material compositions such as cone structures with wrinkled surface and pores. Task 3 (chapter 6) investigates the printing performances such as accuracy, printing resolution, and analyzes magnetic and curing properties of samples with different material distributions and correlates these properties with material distributions and surface structure dimensions. After process development and the material-process-property correlation study (tasks 1-3), validation studies are conducted in task 4 by comparing modeling, simulation and experimental results. Applications of the M-SL manufacturing technology developed in this dissertation were demonstrated through three studies: i) fabrication of hierarchical surfaces with super-hydrophobicity (chapter 5), ii) fabrication of a functional gripper with graded material distribution (chapter 4, 7) and iii) fabrication of multi-material untethered soft robots with multi-scale surface features and multi-functionality (chapter 7). Finally, chapter 8 concludes the results and discusses future work that can be done to extend this Ph.D. thesis research. The contribution of this research include: (1) Development of a novel magnetic field-assisted stereolithography (M-SL) 3D printing technology for fabricating multi-material objects with multi-scale hierarchical surface structures. The integration of magnetic fields into the printing process enables localized control of 0D-3D distribution of magnetic particles for enhanced mechanical properties and multi-functionality such as super-hydrophobicity. (2) Fundamental understanding of the physics underlying the particle flow, patterning and curing process, and the correlation between particle distribution and composite properties. (3) Design and development of an inchworm-inspired soft-robot using the developed M-SL printing process. The multi-scale untethered soft robot is capable of multi-degrees of freedom bending (z axis and x-y plane) and crawling locomotion using the external magnetic actuation. The robot deflection profile is designed and optimized using an image-processing guided digital design framework and voxelized material representation. The robot design also includes multi-scale biocompatible footpads with hierarchical surface structures, a functional gripper with graded material distribution, and a magnetically controllable reservoir for drug-delivery applications.