A Chemical Toolbox for Stimuli-responsive Photoresins in 3D Printing

Three-dimensional printing (3DP) is an advanced manufacturing process that builds successive layers of materials to create objects from digital models. Without the need of molds, 3DP enables the rapid fabrication of complex and customizable products at low cost. Several 3DP techniques are available, being extrusion and vat photopolymerization some of the most used. Compared to extrusion, vat photopolymerization techniques stand out due to their efficiency in fabricating objects with minimal mechanical anisotropy and high resolution. These techniques are based on the spatiotemporal control of a polymerization reaction using light to build the polymer layers. However, most resins that are compatible with this manufacturing process are based on conventional acrylate monomers and have limited functionality. Inspired by the ability of natural systems to adapt to external conditions, several developments in polymer science have endowed polymers with the intrinsic ability to modify their properties under external stimuli, but it remains a challenge to incorporate this functionality into conventional 3D printable polymers. The objective of this research is to develop a chemical toolbox that expands the availability of stimuli-responsive photoprintable materials with improved processability and functionality. The first chapter provides a review of approaches in incorporating chemical interactions to improve the processability and functionality of 3D printable materials, including noncovalent interactions, dynamic covalent chemistry and click chemistry, and how this toolbox enables stimuli-responsive properties, such as self-healing. The second chapter describes the development of photoprintable polymer networks that include furan-maleimide Diels-Alder thermally reversible cycloadducts to enable self-healing in 3D printed objects, with up to a 99% self-healing efficiency, as observed in the recovery of mechanical strength, without affecting their detailed printed shape. The third chapter describes the use of ureas as pendant hydrogen bonding groups to provide noncovalent crosslinking, to enable fine tuning in the mechanical properties, and to endow the printed parts with self-healing properties. The fourth chapter describes the use of click and unclick reactions to facilitate the control in the integrity of a 3D printable polymer network, by photoprinting at 405 nm via thiol-ene, but enabling degradation at 365 nm via cleavage of ortho-nitrobenzyl ester. This research demonstrates the potential of using a chemical toolbox to develop advanced functionality in 3D photoprintable materials an enable delicate control of their properties.