Baoxing Xu1

1, University of Virginia, Charlottesville, Virginia, United States

Soft-hard material integration is ubiquitous in biological materials and structures in nature and has also attracted growing attention in the bio-inspired design of advanced functional materials, structures and devices. The inherent physical distinction between these soft and hard phases has led to fundamental differences in their mechanical behavior (e.g. usually more than two orders of magnitude difference in Young’s modulus) but is harnessed well in biological structures through elegant and facile integrated organizations with unprecedented functions as a whole. In essence, the unique properties of soft-hard integrated natural or man-made materials, structures and devices are closely underpinned by the soft-hard interactions, where the rotation of hard phases in a soft matrix has been considered to be very critical and plays a significant role in the entire mechanical properties and functionalities. In the present study, inspired by the Nacre, a typical hard-soft material integrated structure, where the hard inorganic aragonite is embedded into the organic biopolymer soft matrix, we design a soft-hard composite that exhibits a negative Poisson’s ratio by leveraging the unique rotation of hard particles in the soft matrix. A mechanics theory is established to quantitatively describe the rotation of hard particles in a soft elastic matrix and to incorporate with the overall negative Poisson’s ratio of soft-hard composites. The designed soft-hard composites are manufactured using 3D printing technique to validate the structural design and mechanical performance.