RAFT-Mediated 3D Printing of Polylactones/Itaconate Elastomers with Polypeptide Surface Functionalization

Reversible addition-fragmentation chain transfer (RAFT) polymerization has gained interest in vat photopolymerization, particularly for enabling postprinting surface functionalization via reactivation of the RAFT agent. In this work, we report the development of RAFT photopolymerizable resins containing up to 50% renewable content using sustainable dimethyl or dibutyl itaconate as primary monomers combined with hydroxyethyl acrylate as a reactive comonomer. A 4-arm polyester cross-linker end-functionalized with itaconic acid (IA), poly-(caprolactone-co-valerolactone)-IA, was synthesized and incorporated into the resin formulation. Photorheology confirmed efficient polymerization, and mechanical characterization revealed elastomeric properties for networks derived from dimethyl itaconate. Digital light processing (DLP) of this formulation enabled the 3D printing of flexible structures, including microneedles. The presence of pendant carboxylic acid groups in the cross-linker imparted pH-responsiveness to the printed objects, allowing for reversible swelling and size changes in response to environmental pH, demonstrating 4D behavior. Leveraging the controlled nature of RAFT polymerization, a two-stage printing approach was employed. After printing with the itaconate-based ink, a switch to a methacrylated polylysine ink enabled surface biofunctionalization. Successful grafting of polylysine was confirmed by atomic force microscopy (AFM) and FTIR spectroscopy. Preliminary results demonstrate antimicrobial activity of the cationic surfaces, as well as the ability to spatially control surface functionalization, exemplified by patterned attachment of fluorescent polylysine.