Directed self-assembly of thermoplastic elastomers via 3D printing for mechanically tailored soft architectures

Many biological systems utilize self-assembled hierarchically ordered structures to achieve complex functional properties. However, current methods cannot scalably achieve this level of control over structure and function across multiple length scales in synthetic systems. Here, we make progress towards bridging this gap by demonstrating the use of material extrusion 3D printing to induce tunable alignment of a commercial cylinder-forming polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) thermoplastic elastomer along a controlled print path. We show that the extent of nanostructure alignment and resulting anisotropy can be tuned via the shear and extensional forces applied to the material during 3D printing. In addition, we show that post-printing thermal annealing plays a critical role in maximizing domain alignment via relaxation of trapped stresses. Ultimately, we have demonstrated the ability to induce up to 85x greater tensile modulus along the print direction compared to perpendicular to the print direction. By designing custom print paths for these soft and mechanically anisotropic materials, we enable fabrication of soft architectures with tailored macroscopic mechanical behavior such as controlled localization of strain and bending upon deformation.