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The rapid development of additive manufacturing, also known as three-dimensional (3D) printing, is driving innovations in both industry and academia. Direct ink writing (DIW), an extrusion-based 3D printing technology, can build 3D structures through the deposition of custom-made inks and produce devices with complex architectures, excellent mechanical properties, and enhanced functionalities. A paste-like ink is the key to successful printing. However, as new ink compositions have emerged, the rheological requirements of inks have not been well connected to printability, or the ability of a printed object to maintain its shape and support the weight of subsequent layers. In this review, we provide an overview of the rheological properties of successful DIW inks and propose a classification system based on ink composition. Factors influencing the rheology of different types of ink are discussed, and we propose a framework for describing ink printability using measures of rheology and print resolution. Furthermore, evolving techniques, including computational studies, high-throughput rheological measurements, machine learning, and materiomics, are discussed to illustrate the future directions of feedstock development for DIW. The goals of this review are to assess our current understanding of the relationship between rheological properties and printability, to point out specific challenges and opportunities for development, to provide guidelines to those interested in multi-material DIW, and to pave the way for more efficient, intelligent approaches for DIW ink development.
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A New 3D Printing Strategy by Harnessing Deformation, Instability, and Fracture of Viscoelastic Inks
Abstract Direct ink writing (DIW) has demonstrated great potential as a multimaterial multifunctional fabrication method in areas as diverse as electronics, structural materials, tissue engineering, and soft robotics. During DIW, viscoelastic inks are extruded out of a 3D printer's nozzle as printed fibers, which are deposited into patterns when the nozzle moves. Hence, the resolution of printed fibers is commonly limited by the nozzle's diameter, and the printed pattern is limited by the motion paths. These limits have severely hampered innovations and applications of DIW 3D printing. Here, a new strategy to exceed the limits of DIW 3D printing by harnessing deformation, instability, and fracture of viscoelastic inks is reported. It is shown that a single nozzle can print fibers with resolution much finer than the nozzle diameter by stretching the extruded ink, and print various thickened or curved patterns with straight nozzle motions by accumulating the ink. A quantitative phase diagram is constructed to rationally select parameters for the new strategy. Further, applications including structures with tunable stiffening, 3D structures with gradient and programmable swelling properties, all printed with a single nozzle are demonstrated. The current work demonstrates that the mechanics of inks plays a critical role in developing 3D printing technology.
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- Award ID(s):
- 1661627
- PAR ID:
- 10048281
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 30
- Issue:
- 6
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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