Tuning the size and stiffness of inflatable particles

We describe size-varying cylindrical particles made from silicone elastomers that can serve as building blocks for granular materials with tunable structural and mechanical properties. The particle size variation, which is achieved by inflation, gives rise to changes in stiffness under compression. We design and fabricate inflatable particles that can become stiffer <i>or</i> softer during inflation, depending on key parameters of the particle geometry, such as the ratio of the fillet radius to the wall thickness, <i>r</i>/<i>t</i>. We also conduct numerical simulations of the inflatable particles and show that they only soften during inflation when localization of large strains occurs in the regime <i>r</i>/<i>t</i> → 0. This work introduces novel particle systems with tunable size and stiffness that can be implemented in particle packings for soft robotic applications.