Digital Light Processing of Multi-Materials with Extreme Stiffness Contrast

Biology is replete with examples of multi-materials (e.g., nacre, bones) known for their robustness, strength, and functionality. These properties are attributed to their precise hierarchical structure and stiffness mismatch. Over the years, synthetic polymers and composites, owing to their versatility, have garnered interest as mimics for these natural systems. This presentation will discuss the design and 3D printing of polymeric multi-materials with spatially controlled stiffness via digital light processing.

Orthogonal photoinitiation and curing of two independent polymer networks – polyethylene glycol-based bottlebrushes and epoxy-based resin – will be shown to result in super-soft and stiff domains, respectively. While the bottlebrush networks are formed via free radical polymerization, initiated by a shorter wavelength of light, the epoxy-based resin is cured via cationic ring-opening polymerization in the presence of visible light. The pivotal role of the photochemical components, polymerization mechanisms, and curing kinetics (role of exposure time and light intensity) on the printability of these materials will be discussed. Finally, the toughness, tensile strength, and elastic moduli of these multi-materials will be discussed in the context of biologically relevant hierarchical systems.