Pellet Printing for Soft Devices

Abstract

Rapid prototyping of soft devices is often limited by manual fabrication and additive manufacturing methods that are costly, material-restricted, or require extensive post-processing. Fused Granulate Fabrication (FGF) offers a rapid, scalable alternative by extruding thermoplastic pellets through a screw-based extruder directly onto the build surface, enabling continuous, high-throughput printing. It also supports a broad range of materials, from rigid plastics to silicone-soft elastomers (Shore 6A). Reliable printing of airtight pneumatic soft structures with a volumetric flow rate up to 5 mm³/s was achieved by addressing the root causes of inconsistent extrusion and stringing through integrated hardware, material, and parameter optimizations. Mechanical performance of thermoplastic styrenic block copolymer pellets was characterized, revealing good elastic recovery and Mullins-effect-induced softening. Fatigue testing of FGF-printed pneumatic actuators demonstrated durability over 100,000 bending cycles, and behavior was cross-validated with numerical simulations using Ogden hyperelastic models. Demonstrated applications include a pneumatically actuated robotic hand with 15 segments, a multi-chamber robotic fish with an articulated fin, and a soft pressure cuff for blood pressure monitoring. FGF enables the fabrication of airtight, functional soft devices using commercially available thermoplastic pellets, offering a versatile, cost-effective, and scalable alternative to traditional soft device manufacturing methods.