Bioinspired rational design of multi-material 3D printed soft-hard interfaces

TL;DR

This study uses bioinspired design principles and multi-material 3D printing to create durable soft-hard interfaces with enhanced strength and toughness, mimicking natural hierarchical and interlocking structures.

Contribution

It introduces novel bioinspired interfacial designs using voxel-based 3D printing, combining gradients and interlocking mechanisms to improve mechanical performance.

Findings

Gyroid and particle designs showed highest strength and toughness.

Gradient transitions and interdigitated connections reduce strain concentrations.

Combining gyroid architecture with particles yields near-maximum strength and 50% toughness increase.

Abstract

Durable interfacing of hard and soft materials is a major design challenge caused by the ensuing stress concentrations. In nature, soft-hard interfaces exhibit remarkable mechanical performance, with failures rarely happening at the interface but in the hard or soft material. This superior performance is mechanistically linked to such design features as hierarchical structures, multiple types of interlocking, and functional gradients. Here, we mimic these strategies to design efficient soft-hard interfaces using voxel-based multi-material 3D printing. We designed several types of soft-hard interfaces with interfacial functional gradients and various types of bio-inspired interlocking mechanisms. The geometrical designs were based on triply periodic minimal surfaces (i.e., octo, diamond, and gyroid), collagen-like triple helices, and randomly distributed particles. We utilized a combination of the finite element method and experimental techniques, including uniaxial tensile tests, quad-lap shear tests, and full-field strain measurement using digital image correlation, to characterize the mechanical performance of different groups. The analysis of the best performing designs (i.e., the gyroid, collagen, and particle designs) suggests that smooth interdigitated connections, compliant gradient transitions, and either decreasing or constraining the strain concentrations regions between the hard and soft phases led to simultaneously strong and tough interfaces. Increasing the gradient length was only beneficial when the resulting interface geometry reduced strain concentrations (e.g., in collagen and particles). Combining the gyroid-based architecture with a random distribution of particles yielded the best-performing soft-hard interface, with strengths approaching the upper limit of the possible strengths and up to 50% toughness enhancement as compared to the control group.