Gradient matters via filament diameter-adjustable 3D printing

Abstract Gradient matters with hierarchical structures endow the natural world with excellent integrity and diversity, such as bone, bamboo, and wood. Currently, direct ink writing (DIW) three-dimensional (3D) printing is attracting tremendous interests, and has been used to explore the fabrication of one-dimensional (1D) and two-dimensional (2D) hierarchical structures by adjusting the diameter, spacing, and angle between filaments. However, it is difficult to generate complex 3D gradient matters owing to the inherent limitations of existing methods in terms of available gradient dimension, gradient resolution, and shape fidelity. Here, we report a filament diameter-adjustable 3D printing (FDA-3DP) strategy that enables conventional DIW 3D printers to produce 1D, 2D, and 3D gradient matters with tunable heterogeneous structures by continuously varying the volume of deposited ink on the printing trajectory. In detail, we developed diameter-programmable filaments by customizing the printing velocity and height. To achieve high shape fidelity, we specially added supporting layers with a constant minimum diameter at needed locations. Next, we showcased the multi-disciplinary applications of our approach in creating horizontal, radial and axial gradient structures, letter-embedded structures, metastructures, tissue-mimicking scaffolds, flexible electronics, and time-driven devices. By showing the enormous potential of this strategy, we anticipate that it could be easily extended to a variety of filament-based additive manufacturing technologies and facilitate the development of functionally graded structures.