PISA printing from CTA functionalized polymer scaffolds†

This study investigates DLP 3D printing using RAFT polymerization-induced self-assembly (RAFT PISA) printing, focusing on the impact of CTA (chain transfer agent) groups per scaffold on PISA printing times and mechanical properties of printed objects. We synthesized a solvophilic polymer scaffold from DMA (N,N-dimethylacrylamide) and HEAm (2-hydroxyethyl acrylamide) in a 90 : 10 molar ratio, suitable for CTA functionalization and solubility in various solvents. Employing an aqueous, oxygen-tolerant PET RAFT process, we achieved a target degree of polymerization (DP) of 10 000, introducing varying amounts of CTA groups by esterification (chain transfer agent functionalized scaffold or CFS), with the highest graft density resulting in a scaffold with an average of 74 CTA groups. This process was additionally repeated with a DP 500 scaffold by grafting with varying densities of CTAs. Photocurable DLP (digital light projection) resins based on the chain extension of core-forming DAAm (diacetone acrylamide) from the CFS macro-CTA were then prepared and used to print 3D objects. This study revealed that the increased number of CTA groups per scaffold decreased the normal exposure time for PISA printing when compared to our previous work which employed a difunctional macro-CTA. In mechanical property assessments, conducted across different DPs and CTA graft densities, we observed trends in modulus, strain-to-break, and toughness. The increasing modulus trend ceased beyond a DP of 500, suggesting a balance between the amounts of DAAm and CTA-functional scaffolds. Additionally, parts with higher graft densities demonstrated increased stiffness due to a higher density of physical crosslinks. The study also explored the dissolution behavior of these parts in DMF, with parts showing varying degrees of swelling and dissolution depending on their DP and CTA graft density. These findings indicate a significant advancement in the 3D PISA printing technique, offering new insights into the optimization of printing times and mechanical properties, potentially revolutionizing applications in areas like biomedical implants and tissue engineering scaffolds.