3D Printing of Supramolecular Polymer Hydrogels with Hierarchical Structure

Abstract

Liquid crystalline hydrogels are an attractive class of soft materials to direct charge transport, mechanical actuation, and cell migration. When such systems contain supramolecular polymers, it is possible in principle to easily shear align nanoscale structures and create bulk anisotropic properties. However, reproducibly fabricating and patterning aligned supramolecular domains in 3D hydrogels remains a challenge using conventional fabrication techniques. Here, a method is reported for 3D printing of ionically crosslinked liquid crystalline hydrogels from aqueous supramolecular polymer inks. Using a combination of experimental techniques and molecular dynamics simulations, it is found that pH and salt concentration govern intermolecular interactions among the self‐assembled structures where lower charge densities on the supramolecular polymers and higher charge screening from the electrolyte result in higher viscosity inks. Enhanced hierarchical interactions among assemblies in high viscosity inks increase the printability and ultimately lead to greater nanoscale alignment in extruded macroscopic filaments when using small nozzle diameters and fast print speeds. The use of this approach is demonstrated to create materials with anisotropic ionic and electronic charge transport as well as scaffolds that trigger the macroscopic alignment of cells due to the synergy of supramolecular self‐assembly and additive manufacturing.

The Martini Model in Materials Science

“…[ 264 ] The simulations showed that DMAP molecules interfere with the monomer‐monomer interactions at the fiber ends by first penetrating in between the monomer porphyrin cores and then facilitating monomer dissociation from the fiber end. [ 264 ] Other supramolecular material systems that have been simulated with Martini include supramolecular block copolymers, [ 267,268 ] peptide‐based supramolecular polymers chemically linked to spiropyran‐based networks, [ 269 ] poly‐catenanes, [ 270 ] peptoid‐based nanomaterials, [ 271 ] supramolecular macrocycle fibers, [ 272 ] responsive conjugated polymers, [ 273 ] platinum complexes, [ 274,275 ] supramolecular polymer hydrogels, [ 276 ] and light‐harvesting double‐walled nanotubes. [ 277 ]…”

On the progress of 3D-printed hydrogels for tissue engineering

“…These materials can be made possible due to the synergistic capabilities of supramolecular self-assembly and 3D printing. [ 9 , 100 ] A consequence of this multi-material and multi-cellular strategy is the provision for new types of geometric orientation synergistic with the cell differentiation process.…”

Enhancing Peptide Biomaterials for Biofabrication

“…However, in the translation of synthetic peptide materials to bioinks, these key predictors are often under-reported and seemingly inconsistent. In reported studies of SAP bioinks, measures of printability such as viscosity [ 80 , 81 , 82 , 104 ], loss tangent [ 80 , 81 , 102 ], shear-thinning [ 81 , 82 , 103 ], achievable height [ 81 , 82 , 99 , 103 ] and filament assessments [ 81 , 82 , 103 ], were briefly discussed. This demonstrates the adoption of printability measures into the SAP bioink field; however, the lack of standard printability outcomes and the inconsistency in relationships of printability and predictors such as viscosity [ 81 , 82 ] limit the understanding of key material properties for future development.…”

“…Progress into biomaterial molecular modelling and design principles may improve the clinical translation of materials by predicting outcomes without significant labour-intensive bench time. Molecular modelling [ 80 , 81 , 82 , 83 , 84 ], design principles [ 85 , 86 , 87 , 88 , 89 , 90 , 91 ] and predictive gelation models [ 90 ] of synthetic peptide materials are being increasingly reported, indicating a future ramp-up of high-throughput peptide biomaterial discovery. Synthetic self-assembling peptide (SAP) hydrogels are peptide sequences that self-assemble via supramolecular interactions to spontaneously immobilise fluid, creating a highly hydrated scaffold [ 92 ].…”

“…Synthetic peptide materials give rise to complex biomimetic structures with bioactivity, resulting in controlled cell-scaffold interactions [ 96 , 97 ]. Furthermore, recent reports have demonstrated the translation of synthetic SAP biomaterials into bioinks [ 80 , 81 , 82 , 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 ]. This demonstrates the potential of synthetic SAP design for biofabrication of organs and tissues, and ultimately clinical translation ( Figure 1 ).…”