Structuring Hydrogel Cross-Link Density Using Hierarchical Filament 3D Printing

Abstract

Polymer hydrogels, water-laden 3D cross-linked networks, find broad application as advanced biomaterials and functional materials because of their biocompatibility, stimuli responsiveness, and affordability. The cross-linking density reports material properties such as elasticity, permeability, and swelling propensity. However, this critical design parameter can be challenging to template locally. Here, we report a continuous processing scheme that uses laminar flow to direct the organization of cross-linking density across a single sample. Dilute and concentrated poly­(ethylene glycol) diacrylate solutions are fed into custom serpentine millifluidic devices. These feature a modular sequence of splitting, rotation, and recombination elements, which create patterned streamlines that serve as a template for hierarchical concentration distributions. Poly­(acrylic acid) microgels impart viscoplasticity, which stabilizes layered flow during multiplication and ensures reliable advection. The devices produce structured, seamless filaments, which are then arranged into objects using 3D printing, and photopolymerized to secure the heterogeneous distribution. The flow-encoded, multiscale architecture provides mechanical contrast, which is demonstratively exploited to program robust and reversible shape transformations, potentially useful in soft actuator and sensor applications. The unique structures achieved, and the geometrically dictated, chemistry-agnostic operating principles used to achieve them, provides a new means to engineer hydrogels to suit a variety of applications.

An energy-optimization method to study gel-swelling in confinement

“…While we investigated homogeneous hydrogels, our framework can be easily used to impose a position-dependent swelling ratio, elasticity, etc. which can also be used in applications such as hydrogel bilayers [32][33][34][35] or other functional hydrogels. Furthermore, it can be readily extended to include ionic contributions.…”

Nozzle Innovations That Improve Capacity and Capabilities of Multimaterial Additive Manufacturing

“…94,128 Here the term "advective assembly" is preferred since the same junctions can be combined to produce arbitrary patterns that do not necessarily qualify mathematically as fractals. 57,127 The "advective" descriptor also harkens back to the chaotic advection mechanism of efficient streamline multiplication. The fractal pattern produced by the advective assembler in Figure 2d is reminiscent of the voxel-by-voxel pattern achieved by the nozzle arrays.…”

Polysiloxane Inks for Multimaterial 3d Printing of High‐Permittivity Dielectric Elastomers

“…This inaccuracy is an inherent issue of the printing technique, which can only be overcome by coextrusion processes. [4,10,11] The breakdown occurred at the edge of one of the middle layers of the printed structure. Typical for carbon black-based electrodes, the electrical discharge burns the surrounding dielectric.…”

“…Magnetic, pneumatic, pH, and light-induced actuators have been successfully printed in DOI: 10.1002/adfm.202313167 various configurations by extrusion-based processes, such as direct ink writing (DIW). [1][2][3][4][5] Yet, despite intense research, successful examples of printed electricallydriven dielectric elastomer actuators (DEA) remain rare. [6,7] While hydraulically amplified actuators can be 3D printed by inkjet printing, the ink requirements imposed by DIW create a significant challenge for DEA.…”