Design, fabrication and actuation of magneto-acoustic microrobots: een deel magnetisch, een ander deel akoestisch, allebei fantastisch

Abstract

Bridging the fictional world of "Fantastic Voyage" to modern-day clinical applications, microrobots extend the outreach of minimally-invasive surgeries. Recent micromanipulation strategies have led to a plethora of microrobotic designs that remotely harvest energy from external sources. Such remote actuation empowers microrobots to perform various tasks in hardto-reach environments such as biological vasculatures, microfluidic channels and cell cultures. Besides, these microrobots have the potential to replace large-scale mechanical instruments and make clinical procedures less invasive. However, there are considerable challenges in the synthesis and actuation of microrobots in order to be deployed for the aforementioned applications. Unlike macro-scale robots, microrobots cannot be easily tethered and powered with external peripheral electronics. Hence, microrobots derive energy from indirect physical forces (e.g., magnetism, acoustics, optics) or chemical reactions (e.g., peroxide decomposition, photocatalysis of noble metals, glucose oxidation) in order to move autonomously. The prevalence of existing clinical technologies like magnetic resonance and medical ultrasound imaging complement magnetics and acoustics, respectively, as indirect physical means of contactless manipulation.Among the two means of indirect actuation, magnetic actuation is the most popular approach employed to power microrobots. Inspired from the swimming mechanics of microorganisms (e.g., Escherichia coli, Spermatozoa, Spirulina platensis) countless designs of magnetically-powered microrobots have been reported over the past decade. Despite this popularity, it becomes challenging to design and fabricate different components of microrobots at micro-and nano-scale that move in response to magnetic forces. Moreover, various forms of magnetic actuation require heavy, bulky and power-consuming permanent or electromagnets as hardware. These hardware requirements often impose thermal constraints due to energy dissipation, or electrical bandwidth constraints which may limit speed of the applied actuation. In order to overcome these limitations, acoustic manipulation strategies are investigated as alternative means for contactless actuation of microrobots. Particularly, the versatile nature of acoustic manipulation strategies benefits diverse scenarios that range from i microfluidic-and levitation-based systems, to bubble-powered microrobots. Furthermore, acoustic microrobots can also collaborate with the traditional magnetic actuation and give rise to a hybrid magneto-acoustic micromanipulation strategy. This doctoral thesis describes a mix of magnetically-and acoustically-powered microrobots, and their respective actuation strategies. The chapters presented in this thesis embark the reader on a journey starting with the long-established magnetic microrobots, pass through different pit stops of acoustic microrobotic systems, and finally end where magnetic and acoustic microrobots join forces. This doctoral thesis is divided into four parts and ei...