Embedded 3D Printing of Newtonian Fluids in Elasto-viscoplastic Matrix

Area of Science:

• Materials Science and Engineering
• Fluid Dynamics
• Additive Manufacturing

Background:

• Embedded 3D printing (EM3D) allows freeform patterning of soft materials within a supporting matrix.
• Printing Newtonian fluids, unlike shear-thinning or viscoplastic inks, is challenging due to matrix yielding and Rayleigh-Plateau instability.

Purpose of the Study:

• To investigate the challenges of printing Newtonian fluids (silicone oil, liquid metal) using EM3D.
• To develop strategies to overcome matrix yielding and Rayleigh-Plateau instability for reliable EM3D of Newtonian inks.

Main Methods:

• Utilized an elasto-viscoplastic Laponite matrix for EM3D experiments.
• Employed particle image velocimetry for flow visualization and rheology for yield threshold determination.
• Investigated straight and bent needle geometries and derived a theoretical stability criterion for interfacial tension and yield stress.

Main Results:

• Matrix yielding around the needle scales with the ratio of characteristic shear rate to yield threshold.
• A bent-needle geometry significantly reduces matrix yielding and improves print fidelity compared to a straight needle.
• The derived stability criterion (τ_Y ∝ Γ/d) accurately predicts printability for inks with varying surface tensions.

Conclusions:

• A unified design framework combining rheological and geometric strategies enables reliable EM3D of Newtonian inks.
• Findings provide fundamental insights into fluid-matrix interactions for EM3D.
• This work expands the material scope for EM3D, offering practical guidelines for soft electronics and bioprinting.