Bio-hybrid soft robots with self-stimulating skeletons

Abstract

Bioinspired hybrid soft robots combining living actuation and synthetic components are an emerging field in the development of advanced actuators and other robotic platforms (i.e. swimmers, crawlers, walkers). The integration of biological components offers unique properties (e.g. adaptability, response to external stimuli) that artificial materials cannot replicate with accuracy, being skeletal and cardiac muscle cells the preferred candidates for providing contractile actuation. Here, we present a skeletal-muscle-based swimming biobot with a 3D-printed serpentine spring skeleton that provides mechanical integrity and self-stimulation during the cell maturation process. The restoring force inherent to the spring system allows a dynamic skeleton compliance upon spontaneous muscle contraction, leading to a novel cyclic mechanical stimulation process that improves the muscle force output without external stimuli. Optimization of the 3D-printed skeletons is carried out by studying the geometrical stiffnesses of different designs via finite element analysis. Upon electrical actuation of the muscle tissue, two types of motion mechanisms are experimentally observed: i) directional swimming when the biobot is at the liquid-air interface and ii) coasting motion when it is near the bottom surface. The integrated compliant skeleton provides both the mechanical self-stimulation and the required asymmetry for directional motion, displaying its maximum velocity at 5 Hz (800 micrometer second−1, 3 body length second−1). This skeletal muscle-based bio-hybrid swimmer attains speeds comparable to cardiac-based bio-hybrid robots and outperforms other muscle-based swimmers. The integration of serpentine-like structures in hybrid robotic systems allows self-stimulation processes that could lead to higher force outputs in current and future biomimetic robotic platforms.

Biohybrid robotics: From the nanoscale to the macroscale

“…(iv) Speed of the swimmer at different frequencies and (v) hydrodynamics FEA simulations of the flow around the skeleton during a contraction, showing a heterogeneous distribution of the flow lines due to the asymmetry in the design, which leads to motion. Adapted with permission from Guix et al (2020)…”

“…Although the biohybrid swimmer did not attain very fast speeds compared to other examples in the literature due to the difficulty of motion at low Reynolds number, it represents the first biohybrid swimmer based on skeletal muscle in coculture with motor neurons, which could offer scalability to bioengineer larger and more efficient multicellular robots. Recently, Guix et al presented a biohybrid swimmer based on a 3D‐printed spring serpentine skeleton and skeletal muscle (Figure 8d) (Guix et al, 2020). The compliant nature of the spring skeleton provided an extra level of mechanical stimulation due to its restoring force when spontaneous contractions occurred during maturation, yielding larger force than tissues matured in static conditions.…”

A Manta Ray-Inspired Biosyncretic Robot with Stable Controllability by Dynamic Electric Stimulation

“…Because of the potential advantages of biological actuation, different living actuators have been adopted to explore the development of biosyncretic robots [24,25]. The frequent biological materials used for robotic actuation include movable microorganisms [26], insect dorsal vascular tissues (DV tissues) [23,27,28], mammalian cardiomyocytes [29][30][31][32][33][34], and skeletal muscle cells [35][36][37][38][39][40]. Among these materials, bacteria and DV tissues can generate an effective actuation force with robustness, but their use is challenging in terms of customizing the actuator size for adaptation to different robots [18].…”