3D printing of resilient biogels for omnidirectional and exteroceptive soft actuators

Abstract

Soft robotics greatly benefits from nature as a source of inspiration, introducing innate means of safe interaction between robotic appliances and living organisms. In contrast, the materials involved are often nonbiodegradable or stem from nonrenewable resources, contributing to an ever-growing environmental footprint. Furthermore, conventional manufacturing methods, such as mold casting, are not suitable for replicating or imitating the complexity of nature’s creations. Consequently, the inclusion of sustainability concepts alongside the development of new fabrication procedures is required. We report a customized 3D-printing process based on fused deposition modeling, printing a fully biodegradable gelatin-based hydrogel (biogel) ink into dimensionally stable, complex objects. This process enables fast and cost-effective prototyping of resilient, soft robotic applications from gels that stretch to six times their original length, as well as an accessible recycling procedure with zero waste. We present printed pneumatic actuators performing omnidirectional movement at fast response times (less than a second), featuring integrated 3D-printed stretchable waveguides, capable of both proprio- and exteroception. These soft devices are endowed with dynamic real-time control capable of automated search-and-wipe routines to detect and remove obstacles. They can be reprinted several times or disposed of hazard-free at the end of their lifetime, potentially unlocking a sustainable future for soft robotics.

Fluid-driven hydrogel actuators with an origami structure

“…Compared with molding methods ( Shintake et al., 2017 ; Yuk et al., 2017 ; Zhang et al., 2018 ; Hardman et al., 2022 ), this facile fabrication strategy is capable of fabricating 3D thin-walled hollow hydrogels with complex shapes and structures. Unlike 3D printing methods for hydrogels (including direct-ink-write ( Cheng et al., 2019 ; Heiden et al., 2022 ) and stereolithography ( Mishra et al., 2020 ; Mishra et al., 2021 ; Takishima et al., 2021 )), its equipment is readily available and low cost. The thickness and mechanical properties of the formed thin-walled hydrogels can be regulated by adjusting the forming time and the processes of ion diffusion and hydrogel crosslinking, including the concentration of the precursor solution, the concentration of initiators, properties of template materials, shape of templates, and so on.…”

“…( Cheng et al., 2019 ) and Heiden et al. ( Heiden et al., 2022 ) realized multidirectional bending actuation through a multiple-chamber structure. However, 3D printing methods for hydrogels always require specialized printers, and there are only limited ink materials with applicable crosslinking networks can be used, which restrict their wide applications ( Wu et al., 2019 ; Hardman et al., 2022 ).…”

Bioinspired Structures for Soft Actuators

“…In terms of soft actuator fabrication, FDM has been used to manufacture pneumatic actuators from thermoplastic polyurethane, [ 142 ] ionic polymer‐metal composite (IPMC) actuators from thermoplastic nafion, [ 152 ] and biodegradable sensors and actuators from hydrogels. [ 153 ] The FDM process can conveniently produce complex inner structures with soft materials but is restricted by the low resolution and use of high temperature.…”

Stretchable reflective coating for soft optical waveguides and sensors

“…The fabricated sensors could detect strains up to 100% and be tolerant to bending at curvature radii larger than 6 cm 19 . Recently, Heiden et al 3D printed biodegradable stretchable waveguides based on a gelatin-based hydrogel 20 . Despite the excellent results in terms of stretchability of the components, several issues must still be addressed both for waveguides used as connecting optical components and as strain sensors.…”