3D printed soft composites with tunable hyperelastic properties

The ability to precisely control spatially varying mechanical properties of soft materials is an emerging need towards the development of functionally graded biomimetic compliant structures. Multi-material additive manufacturing has proven to be an effective method to achieve this goal, however commonly used methods are expensive and limited in material capabilities. This work presents novel soft composites, consisting of a silicone matrix and thermoplastic elastomer reinforcements, fabricated through low-cost extrusion-based additive manufacturing. A customized 3D printer with direct ink write (DIW) and fused filament fabrication (FFF) capabilities is used to print composites with a sinusoidal reinforcement pattern. This parametric pattern allowed us to quantitatively analyze how the frequency and amplitude parameters influenced the hyperelastic behavior of the composites. Spatially varying hyperelastic property control capability is then demonstrated through spatial variation of reinforcement geometry. Information from these samples is used to develop a method of efficiently modeling the design-property relationships of these composites allowing us to predict hyperelastic behavior based on given design parameters. Finally, the capability of this approach to realize as-designed property variations is evaluated. The presented multi-material composites exhibit a broad range of spatially controllable stiffness and strain hardening behavior, owing to their compliant reinforcements with complex design and their unconventional interfacial nature. This approach opens up possibilities to create soft structures to be used in various applications including soft wearables, flexible electronics and tissue phantoms.