Optical Characterization of 3D Light-Driven Bio-Hybrid Actuators

Bio-hybrid actuators represent a promising field in robotics. The advantage of a 3-dimensional device is that it can better mimic a human muscle and achieve high performance, adaptability, and complexity of movement, matching the standards required in the robotics field ^[1].<br/>Muscle-based biohybrid systems are typically triggered electrically using electrodes. However, this approach has limitations, such as low spatial resolution and selectivity, potential tissue damage from inflammatory responses, and cumbersome wiring ^[2]. To address these issues, scientists are exploring light as an alternative trigger. Light stimulation offers high spatial and temporal resolution, low invasiveness, and can be controlled remotely. Methods like infrared radiation, semiconductor interfaces, and optogenetics have been successfully used to induce light-cell sensitivity. Another promising approach is the use of photoactive molecules. Recently, it has been demonstrated that an azobenzene molecule called Ziapin2 can modulate membrane capacitance and trigger muscle cells’ contraction upon light stimulation in 2D systems ^[3], due to its light-triggered isomeratation process in the cell’s membrane. Starting from this promising result, we infer that this stimulation approach may be used to induce the deformation and contraction of a 3D bio-hybrid actuator.<br/>Here we describe an example of a 3D bio-hybrid structure treated with Ziapin2 that is capable of contracting upon light stimulation. We studied and characterized the optical properties first of a 3D-printed hydrogel based on gelatin methacrylate. Subsequently, we encapsulated the skeletal cells inside the hydrogel to study Ziapin2 uptake and diffusion inside the cells and the hydrogel. Our focus was on optimizing the uptake of Ziapin2 to enhance its interaction with light, thereby achieving the most effective contractions. This study represents a significant step towards developing light-sensitive bio-hybrid actuators and a fundamental study of their optical properties.<br/><br/>[1] Sun, L. et al. Biohybrid robotics with living cell actuation. Chem. Soc. Rev. 49, 4043–4069 (2020).<br/>[2] Chen, C., Bai, X., Ding, Y. <i>et al.</i> Electrical stimulation as a novel tool for regulating cell behavior in tissue engineering. <i>Biomater Res</i> <b>23</b>, 25 (2019). https://doi.org/10.1186/s40824-019-0176-8<br/>[3] Venturino, I., Vurro, V., Bonfadini, S. <i>et al.</i> Skeletal muscle cells opto-stimulation by intramembrane molecular transducers. <i>Commun Biol</i> <b>6</b>, 1148 (2023). https://doi.org/10.1038/s42003-023-05538-y