Hybrid bio-robotics: from the nanoscale to the macroscale

Rafael Mestre Castillo

Samuel Sánchez Ordóñez

Hybrid bio-robotics is a discipline that aims to integrate biological entities with synthetic materials to overcome existing challenges in the field of soft robotics, incorporating features of biological systems that have been optimized over millions of years of natural evolution and are not easy to reproduce artificially. This thesis covers various aspects of this type of devices from the nanoscale to the macroscale, focusing on enzymatically propulsive nano- and micromotors, as well as bioactuators and biorobots based on skeletal muscle tissue. In the field of enzymatic nanomotors there is a need to find better models that can describe the dynamics of their movement in order to understand their underlying propulsion mechanisms. In this thesis, we focus on several examples of nano- and micromotors that show complex movement dynamics and propose different strategies that can be used to analyze and characterize this movement. However, the true inventive and innovative capacity of this thesis lies in the development and application of bioactuators and biorobots based on muscle tissue, as well as in the improvement of their fabrication using 3D printing technologies. We demonstrate that this technique can produce functional and aligned muscle fibers that can be stimulated and contracted with electrical pulses. However, for the application of these biorobots in regenerative medicine, it is necessary that the tissue resembles human musculoskeletal tissue as much as possible, consisting of millions of individual and fine fibers. To improve the current state of the art, this thesis presents a new method to manufacture thin, individual and functional muscle fibers that do not fuse together, based on a co-axial 3D printing system, mimicking the native structure of human muscle tissue and with potential industrial interest in the field of regenerative medicine (muscle tissue transplants for patients with degenerative diseases or serious accidents) and, of course, in biomedical research to understand the development of human muscle tissue. Additionally, this thesis presents the design, manufacture and application of a muscle force measurement platform, with numerous applications in pharmacology and cosmetics for drug testing. With this platform, we study the adaptability of muscle tissue after training with electrical pulses. In collaboration with a cosmetics company, we demonstrate the application of this platform for testing active ingredients, measuring muscle contractions, their dynamics and relaxation time after adding the product. These experiments are also performed on bioprinted muscle models with human (and mouse) cells and with young and aged models, demonstrating its versatility to mimic different stages of tissue formation for testing active ingredients, not only cosmetic, but also pharmacological for diseases such as muscular dystrophy. Finally, the thesis ends with the fabrication of a muscle-based bio-robot capable of swimming on the surface of a liquid. These hybrid biorobots are presented as the future of robotics, using biological systems to take advantage of the characteristics optimized by nature, such as the adaptability of muscle tissue according to specific needs.

The work carried out in this PhD thesis has two direct and timely applications with industrial and commercial impact. On the one hand, this thesis deals with the fabrication of a 3D-bioprinted force measurement platform for skeletal muscle tissue of either mouse or human origin (Chapter 4). A practical example of an industrial application of this technology was carried out with the help of the cosmetics company Lipotec™ Active Ingredients, which resulted in the successful market release of a cosmetics product and a scientific publication1. On the other hand, it deals with the improvement of 3D bioprinting technologies to properly mimic the three-dimensional structure of skeletal muscle tissue, focusing on a novel application using a co-axial printing system that can bioprint individual and thin fibres, much like they exist in our own body (Chapter 3). The approach of this work will be of interest for tissue engineering and 3D bioprinting companies, as it allows to obtain more faithful models of skeletal muscle tissue for drug testing. Protection of the intellectual property concerning this technology is being sought through a patent application (see below for further details).

Hybrid Bio-robotics; Biological Entities; Synthetic Materials; Soft Robotics; Biological Systems; Enzymatically Propulsive Nano- and Micromotors; Bioactuators; Biorobots; Skeletal Muscle Tissue; Enzymatic Nanomotors; Movement Dynamics; Propulsion Mechanisms; Complex Movement Dynamics; Bioactuator Development; Biorobot Development; 3D Printing Technologies; Functional Muscle Fibers; Aligned Muscle Fibers; Electrical Pulse Stimulation; Muscle Contraction; Regenerative Medicine; Human Musculoskeletal Tissue; Individual Muscle Fibers; Co-axial 3D Printing System; Native Structure of Human Muscle Tissue; Industrial Interest; Muscle Tissue Transplants; Degenerative Diseases; Serious Accidents; Biomedical Research; Human Muscle Tissue Development; Muscle Force Measurement Platform; Pharmacology Applications; Cosmetics Applications; Drug Testing; Muscle Tissue Adaptability; Electrical Pulse Training; Active Ingredients Testing; Muscle Contractions; Dynamics; Relaxation Time; Bioprinted Muscle Models; Human Cells; Mouse Cells; Young Models; Aged Models; Versatility; Tissue Formation Stages; Muscular Dystrophy; Muscle-Based Bio-robot; Swimming Biorobot; Future of Robotics; Biological Systems; Adaptability of Muscle Tissue.