3D Printed Biomimetic Soft Robot with Multimodal Locomotion and Multifunctionality.

Soft robots can outperform traditional rigid robots in terms of structural compliance, enhanced safety, and efficient locomotion. However, it is still a grand challenge to design and efficiently manufacture soft robots with multimodal locomotion capability together with multifunctionality for navigating in dynamic environments and meanwhile performing diverse tasks in real-life applications. This study presents a 3D-printed soft robot, which has spatially varied material compositions (0-50% particle-polymer weight ratio), multiscale hierarchical surface structures (10 nm, 1 µm, and 70 µm features on 5 mm wide robot footpads), and consists of functional components for multifunctionality. A novel additive manufacturing process, magnetic-field-assisted projection stereolithography (M-SL), is innovated to fabricate the proposed robot with prescribed material heterogeneity and structural hierarchy, and hence locally engineered flexibility and preprogrammed functionality. The robot incorporates untethered magnetic actuation with superior multimodal locomotion capabilities for completing tasks in harsh environments, including effective load carrying (up to ∼30 times of its own weight) and obstacle removing (up to 6.5 times of its own weight) in congested spaces (e.g., 5 mm diameter glass tube, gastric folds of a pig stomach) by gripping or pushing objects (e.g., 0.3-8 times of its own weight with a velocity up to 31 mm/s). Furthermore, the robot footpads are covered by multiscale hierarchical spike structures with features spanning from nanometers (e.g., 10 nm) to millimeters. Such high structural hierarchy enables multiple superior functions, including changing a naturally hydrophilic surface to hydrophobic, hairy adhesion, and excellent cell attaching and growth properties. It is found that the hairy adhesion and the engineered hydrophobicity of the robot footpad enable robust navigation in wet and slippery environments. The multimaterial multiscale robot design and the direct digital manufacturing method enable complex and versatile robot behaviors in sophisticated environments, facilitating a wide spectrum of real-life applications.

Magnetic Field-Assisted Stereolithography for Productions of Multimaterial Hierarchical Surface Structures.

Natural organisms provide inspirations for various functional structures and surfaces with significant applications in multidisciplinary fields. These biological systems are generally composed of multiscale surface structures with high geometric complexity and a variety of materials, making it challenging to replicate their characteristics in engineering. This study presents a novel multiscale multimaterial 3D printing method, magnetic field-assisted stereolithography (M-SL), for fabricating hierarchical particle-polymer structures with surface features ranging from a few nanometers to millimeters or even centimeters. Taking inspiration from nature, this study describes the design and fabrication of a bioinspired multiscale hierarchical surface structure, which is characterized of microscale cones, nanoscale pores, and surface wrinkles at a few nanometers. To understand the fundamental physics underlying the hierarchical surface structure fabrication in the proposed M-SL process, the complexities among the M-SL process parameters, material parameters, and printed geometries are discussed. The accuracy of the developed printing method is investigated by comparing the printed geometries and digital designs. Effects of the printed hierarchical surface structure on hydrophobicity and cell viability were characterized and discussed. It was found that the highly hierarchical surface structure changed the polymer composite surface from hydrophilic (contact angle: ∼38°) to hydrophobic (∼146°). In addition, the hierarchical surface structure also created a better environment for cell attachment and growth, with 900% more living cells at 72 h after cell seeding, compared with cells on the nonstructured smooth surface. Local and selective cell seeding can also be enabled by the surface structure design. Experimental results validated the effectiveness of the M-SL 3D printing method on fabricating multimaterial functional objects with hierarchically structured surfaces for a wide spectrum of applications.