Pellet Printing for Soft Devices

Abstract

Rapid prototyping of soft devices is limited by manual fabrication and additive manufacturing methods that are material-restricted or require extensive post-processing steps. Fused Granulate Fabrication offers a rapid, scalable alternative by extruding thermoplastic pellets through a screw-based extruder directly onto the build surface, enabling continuous, high-throughput printing. FGF also supports the printing of a broad range of materials, from rigid plastics to silicone-soft elastomers (Shore hardness 6A). In this study, we achieved reliable 3D printing of airtight pneumatic soft structures with a volumetric flow rate up to 5 mm\textsuperscript{3}/s by addressing the root causes of inconsistent extrusion and stringing through hardware, material, and parameter optimizations. We characterized the mechanical performance of thermoplastic styrenic block copolymer pellets, revealing their elastic recovery and Mullins-effect-induced softening. Our additively manufactured pneumatic actuators demonstrated durability over 100,000 bending cycles, which we cross-validated with numerical simulations using Ogden hyperelastic models. We demonstrate a pneumatically actuated robotic hand with 15 individually addressable segments, a multi-chamber robotic fish with an articulated fin, and a soft pressure cuff for blood pressure monitoring. FGF enables the digital fabrication of large (tens of centimeters), airtight, functional soft devices using commercially available thermoplastic pellets, offering a versatile, cost-effective, and scalable alternative to soft lithography with mechanical properties comparable to silicone elastomers.