Microrobotic systems have the potential to revolutionise medicine and treatment in many applications including highly localized drug delivery, cancer therapies, such as hyperthermia and brachytherapy, minimally invasive surgery and cell transportation. Swimming microrobots, for example, are tiny machines that swim in the body's intravascular or interstitial fluids to perform biomedical operations. The application of microrobots in medicine requires a multidisciplinary delicate investigation. A current challenge in developing autonomous systems is to provide power and control for the microrobots. Magnetic actuation remains the most practical way for untethered powering and control of microrobots as it transfers power for movement and enables guidance for delivery. However, magnetic microrobots so far afford insufficient functionality to accomplish the foreseen tasks lacking, for example, the ability to sense their environment, make real-time decisions, and induce desired changes. Further, the effectiveness and flexibility of magnetic actuation drastically declines when controlling a team of microrobots since magnetic actuation provides an identical driving force for all devices in the team that makes the control of individual robots highly complicated. Additionally, the artificial microrobots lack the ability to sense the status of their mates in the group. The amount of medicine that can be carried by a single microrobot is not sufficient for an effective treatment, hence, a large group of microrobots should be utilised.
Alternatively, harnessing microorganisms, especially bacteria, as intelligent tiny robots provides a novel strategy for cargo delivery at micro-/nanoscale owing to their several advantages. These bacteria have a small size, swim fast and contain a system of sensors and actuators that automatically responds to environmental stimuli. The feasibility of biomicrorobotic systems has been studied in recent works. For example, drug-loaded microparticles have been attached to bacteria and driven to the target position.
We propose, for the first time, a biohybrid system composed of a magnetic microrobot (a "master") and groups of bacteria ("followers") to benefit from the subtle sensory system of bacteria along with their collective motility and precise magnetic navigation of the synthetic microrobot. In this system, a magnetic synthetic swimmer is functionalised with a chemical and controlled to trigger the tactic response of bacteria. The bacteria are attracted towards the chemical because of this tactic response. Therefore, the microrobot can lead them and direct them to a target position to deliver medicine. This research overcomes the insufficient functionality and communication of solitary artificial microrobots, challenges in artificial microrobotic swarm control, and instability and inaccuracy in the navigation of bacteria as bio micro/nanorobots. Chemotaxis and phototaxis-based motion of bacteria in response to the precisely controlled microrobot creates a platform, which can carry a large-volume cargo and have more sensitive local sensing such as biochemical and light to reach specific microenvironments to perform intricate applications in biomedicine and nanotechnology. This research would help efforts in creating a reliable microengineered system with multiple functions including propulsion, sensing, guidance, cargo delivery, and operation that move the micro/nanorobotics technology toward clinical trials more rapidly.
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