Additive manufacturing of highly entangled polymer networks

Incorporation of polymer chain entanglements within a single network can synergistically improve stiffness and toughness, yet attaining such dense entanglements through vat photopolymerization additive manufacturing [e.g., digital light processing (DLP)] remains elusive. We report a facile strategy that combines light and dark polymerization to allow constituent polymer chains to densely entangle as they form within printed structures. This generalizable approach reaches high monomer conversion at room temperature without the need for additional stimuli, such as light or heat after printing, and enables additive manufacturing of highly entangled hydrogels and elastomers that exhibit fourfold- to sevenfold-higher extension energies in comparison to that of traditional DLP. We used this method to print high-resolution and multimaterial structures with features such as spatially programmed adhesion to wet tissues. Editor’s summary When three-dimensional (3D) printing polymers, there is a trade-off between fast hardening, which ensures the strength and fidelity of the printed shape, and a slower reaction rate, which allows for more downstream processing but may not be compatible with some printing methods such as vat polymerization. Dhand et al. designed monomers that can be partially reacted using fast photo-initiated polymerization followed by a slow, redox initiated process, thus forming long polymer chains with dense entanglements. The key to the process is to keep the content of the initiators at a low level. The method enables the printing of objects with functional monomers, complex shapes, and multiple materials. —Marc S. Lavine