Multi-material 3D printed composites inspired by nacre: a hard/soft mechanical interplay

Structural materials are used extensively in nature where mechanical function is required. These structures are composites consisting of soft and, in some cases, hard phases precisely distributed over different length scales. Bio-inspiration aims at producing materials with structure, design and/or mechanical properties adopted from biological tissues. To reproduce complex structures found in nature, additive manufacturing (AM) using three-dimensional printing (3DP) is an attractive method to assemble complex topologies with resolutions approaching the micro and nano-composition. Specifically, high-resolution MultiJetPrinting (MJP) 3D printing allows the simultaneous deposition of soft and hard photo curable plastic resins. Nacre is a prevalent example of a complex biological composite material organization that can test the ability of MJP to manufacture a bio-inspired engineering structure, where the organization of materials in nacre is optimized to avoid catastrophic failure. However, the compositional and organization information translated from biology to an engineered composite is lacking. The aim of this study was to develop a novel digital workflow for the generation of hybrid composites inspired by nacre. The interplay between a number of manufacturing parameters including material volume fraction in the composite, printing direction and resultant mechanical behaviour was evaluated. Stress transfer mechanism during mechanical loading was shown to dictate overall composite mechanics of the nacre inspired composite and optimized to enhance work of failure compared to the base materials. The use of generative design and MJP produced effective nacre with enhanced mechanical properties. In addition, the tough composites herein reported are sufficiently flexible to output any biologically inspired material with improved mechanical performance for engineering applications.