3D printing soluble solids via PISA

Abstract

Polymer-Induced Self Assembly (PISA) is a technique that often involves the use of a macro chain transfer agent (macro-CTA) polymerized through reversible addition–fragmentation chain transfer (RAFT), which is then chain extended with a monomer to induce phase separation during block copolymer formation. The process results in the in situ generation of nanostructures with various morphologies. Prior studies have indicated that increasing the functionality of RAFT macro-CTAs can cause the formation of flower or loop-like coronas during polymer self-assembly, enabling physical crosslinks between particles and gel formation. This study focuses on developing a PISA resin for 3D printing using a difunctional macro-CTA, with the expectation that physical crosslinks between difunctional macro-CTAs would allow printed parts to maintain their shape without the need for a crosslinker. In this research, a difunctional poly(ethylene glycol) (PEG) macro-CTA was chain extended with diacetone acrylamide (DAAm) in water and 3D printed via digital light projection (DLP) using lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) as a photoinitiator and phenol red as a photoabsorber. Resins were printed with or without the addition of 2.5 wt% N′N-methylene bisacrylamide (MBAc) crosslinker. The DAAm PISA frog without crosslinker, being water-insoluble, completely dissolved in N,N-dimethylformamide (DMF) while the one with crosslinker did not. Controlled dissolution of the part architecture was achieved by printing components containing both crosslinked and uncrosslinked resins. Atomic Force Microscopy (AFM) images displayed interlocked particle (worm-like) morphologies and/or phase-separated domains, indicating self-assembly during the printing process. Scanning Electron Microscopy (SEM) imaging of these physically crosslinked, 3D printed PISA polymers revealed a vasculature-like network, which holds potential for use an scaffolds in tissue engineering applications.