Chemical advances in additive manufacturing

We are excited to bring forward this special themed issue of Polymer Chemistry to highlight chemical advances in additive manufacturing. The field of additive manufacturing has experienced an amazingly rapid growth, and 3D printers are now available to everyone from a hobbyist at home to professionals using high-end printers for medical and aerospace applications. Concurrently, there is a greater need for new chemistries and materials that are specifically designed for additive manufacturing processes. The contributions to this themed issue are representative of the latest developments in the chemical approaches that are used with additive manufacturing.

While resins and inks for additive manufacturing have historically been dominated by chemistry that involves radical or cationic polymerization, several of the contributions to this themed issue incorporated the various forms of highly efficient click reactions during and after the printing process. Shaochen Chen and co-workers report a new chemical strategy to 3D print polyurethanes that are not derived from toxic isocyanates (DOI: 10.1039/C9PY00999J). This approach used urethane formation via ring-opening of a cyclic carbonate to make precursors that could be photopolymerized using thiol–ene chemistry during a vat photopolymerization process to afford 3D printed objects. Andreas Heise and co-workers demonstrated a shear-thinning polypeptide hydrogel for material extrusion printing (DOI: 10.1039/C9PY00796B). After the entire printing process was completed, the nitrobenzyl protecting groups on cysteine were photo-cleaved to enable a subsequent catalyst free thiol–yne cross-linking of the hydrogel. Ronald Smaldone and co-workers show how base-catalyzed thiol-Michael addition is a mild reaction for curing hydrogels printed via material extrusion (DOI: 10.1039/C9PY00953A). Annalisa Chiappone and co-workers demonstrate how the reactions of thiols with bis(propargyl)fumarate can be used to 3D print objects in a vat photopolymerization process (DOI: 10.1039/C9PY00962K). The authors further showed that the printed objects can undergo a post-print functionalization by reacting an azide-functional dye with residual alkynyl functionalities present. Andrew Dove and co-workers designed new resins for vat photopolymerization with sustainability in mind (DOI: 10.1039/C9PY00950G). Several terpenes were identified that could undergo photo-initiated thiol–ene reactions for 3D printing complex shapes. The material properties of this new class of resin are reported in detail.

Other recent developments include new resins with tunable or responsive properties. Tim Long and co-workers demonstrate vat photopolymerization of ionic acrylates, acrylamides, and vinyl monomers to afford polymeric constructs with mechanical properties that were tunable based on the composition of the ionic or hydrogen bonding interactions (DOI: 10.1039/C8PY01792A). This method can be used to create water-dissolvable support scaffolds with complex 3D geometries. Ian Wong and co-workers used vat photopolymerization to fabricate a dual network hydrogel in which Fe³⁺ cation-polyacrylate supramolecular complexes were responsible for adhesive and self-healing properties of the hydrogel (DOI: 10.1039/C9PY00211A). Stephen Craig and co-workers demonstrated a mechanochromic silicone for material extrusion printing (DOI: 10.1039/C9PY01053J). The 3D printed materials exhibited color changes in response to relatively low tensile or compressive loads, and could be re-used upon the reversion of the spiropyran mechanophore back to its ring-closed form.

The next generation of new resins and inks for additive manufacturing will include chemistries, materials, or nanomaterials that have been previously unexplored in the field. Jeremiah Johnson and co-workers report new oxygen tolerant chemistries for enabling photo-controlled additive manufacturing (DOI: 10.1039/C9PY00022D). They demonstrate that trithiocarbonate iniferters can mediate radical polymerization of acrylates and acrylamides using visible light. Matthew Becker and co-workers demonstrate that macromolecular architecture can be used as a design parameter when synthesizing new resins for vat photopolymerization processes (DOI: 10.1039/C9PY00738E). In this case, they created biodegradable poly(propylene fumarate) star polymers that were used to print gyroidal scaffolds and medical screws. Mark Dadmun and co-workers are addressing a critical challenge in fused deposition modeling (FDM) – the relatively weak interfilament bonding that can result from FDM printing (DOI: 10.1039/C9PY00832B). The researchers successfully addressed this challenge by introducing graphene as a filler to enhance thermal conductivity to facilitate greater diffusion of the polymers at filament-filament interfaces.

We thank all of the authors for sharing their scientific contributions to our growing field in this themed issue!

Andrew J. Boydston

Alshakim Nelson

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