Designing and simulating a micro-robot for transporting filamentous cargos in Newtonian and viscoelastic fluids

Abstract

In recent years, there has been a notable surge in interest within the medical field towards minimally invasive procedures, with magnetic micro-robots emerging as a promising avenue. These micro-robots exhibit the capability to traverse various mediums, including viscoelastic and non-Newtonian fluids, facilitating targeted drug delivery and medical interventions. Many current designs, drawing inspiration from micro-swimmers found in biological systems such as bacteria and sperm, utilize a contact-based approach for transporting payloads. However, adhesion between the cargo and the carrier can complicate release at the intended site. In this thesis, our primary aim was to investigate the potential of a helical micro-robot for non-contact delivery of drugs or cargo. We conducted an extensive examination of the shape and geometrical parameters of the helical micro-robot, with a specific focus on its ability to transport passive filaments. Based on our analysis, we propose a novel design comprising three sections with alternating handedness, incorporating two pulling and one pushing microhelices, to improve the capture and transportation of passive filaments in Newtonian fluids using a non-contact approach. Subsequently, we simulated the process of capturing and transporting the passive filament and evaluated the functionality of the newly designed micro-robot. Initially concentrating on naturally straight filaments, we also demonstrated the micro-robot’s capability to capture filaments with intrinsic curvature and those with a spherical payload attached at one end. Our findings provide valuable insights into the mechanics of helical micro-robots and their potential applications in medical procedures and drug delivery. Furthermore, the proposed non-contact delivery method for filamentous cargo could pave the way for the development of more efficient and effective micro-robots for medical purposes. In the second phase of our project, recognizing that most biological fluids exhibit viscoelastic properties due to the presence of protein fibers, we proposed a viscoelastic model. Inspired by the viscoelastic structure of bovine vaginal fluid, we developed and initially characterized this model using creep and strain tests. Subsequently, in the proposed viscoelastic model, we investigated the functionality of the designed micro-robot in the viscoelastic fluid and compared its performance with that of the conventional single-handed helical micro-robot. It was observed that although the designed micro-robot is highly effective in transporting filamentous microcargo without contact in Newtonian fluid, its unique structure presents challenges when moving in viscoelastic fluid.