A Polymeric 3D Printing Material System Exhibiting an Extensive Range of Mechanical Properties

In nature, structures and systems frequently employ multiple materials with significantly varying stiffnesses to optimize their overall mechanical performance and functionality. The integration of such highly dissimilar materials in multi-material 3D printing promises to substantially enhance the design space across various applications, including biomedical devices, mechanical metamaterials, and soft robotics. However, materials with extreme mechanical property differences typically exhibit also substantial differences in their chemical and physical properties, such as surface energy and thermal expansion coefficients. This often leads to reduced adhesion and thermal interfacial stresses, rendering them incompatible with each other and, consequently, limiting the design space. In this work, we propose a polymeric thiol-ene elastomer material system that spans a large range (e.g., ~5 orders of magnitude in the elastic modulus) of mechanical properties while maintaining compatible chemical and physical properties. The extremes —specifically, the soft and stiff materials that can be mixed at any ratio—exhibit the same photo-crosslinking mechanism but vary in crosslinking densities, resulting in significantly different mechanical properties. This material system is compatible with various 3D printing technologies, as demonstrated through vat photopolymerization and direct ink writing. The ability to print materials with extreme differences together enables improved structural performances in applications such as soft electronics and shock absorption.