Motility analysis of bacteria‐based microrobot (bacteriobot) using chemical gradient microchamber

Abstract

A bacteria-based microrobot (bacteriobot) was proposed and investigated as a new type of active drug delivery system because of its useful advantages, such as active tumor targeting, bacteria-mediated tumor diagnosis, and therapy. In this study, we fabricated a bacteriobot with enhanced motility by selective attachment of flagellar bacteria (Salmonella typhimurium). Through selective bovine serum albumin (BSA) pattering on hydrophobic polystyrene (PS) microbeads, many S. typhimurium could be selectively attached only on the unpatterned surface of PS microbead. For the evaluation of the chemotactic motility of the bacteriobot, we developed a microfluidic chamber which can generate a stable concentration gradient of bacterial chemotactic chemicals. Prior to the evaluation of the bacteriobot, we first evaluated the directional chemotactic motility of S. typhimurium using the proposed microfluidic chamber, which contained a bacterial chemo-attractant (L-aspartic acid) and a chemo-repellent (NiSO4 ), respectively. Compared to density of the control group in the microfluidic chamber without any chemical gradient, S. typhimurium increased by about 16% in the L-aspartic acid gradient region and decreased by about 22% in the NiSO4 gradient region. Second, we evaluated the bacteriobot's directional motility by using this microfluidic chamber. The chemotactic directional motility of the bacteriobot increased by 14% and decreased by 13% in the concentration gradients of L-aspartic acid and NiSO4 , respectively. These results confirm that the bacteriobot with selectively patterned S. typhimurium shows chemotaxis motility very similar to that of S. typhimurium. Moreover, the directional motilities of the bacteria and bacteriobot could be demonstrated quantitatively through the proposed microfluidic chamber.

Propulsion and Chemotaxis in Bacteria‐Driven Microswimmers

“…The simulations of the model produces 3D trajectories and motility characteristics that resemble those of experiments. The model, in combination with the signaling pathway models of bacterial chemotaxis, also traces out the chemotaxis behavior of bacteria‐driven microswimmers reported by recent studies 14, 17, 20, 21, 22, 23, 24, 25. The agreement between simulation and experiment implies that our model assumptions are reasonable and the model captures the fundamental biophysical mechanisms of the system.…”

“…Most of the studies on bacteria‐driven microswimmers adopt a similar design, which is a sphere‐shaped microbead driven by single or multiple flagellated bacteria attached to it in random locations and orientations 2, 6, 9, 11, 12, 13, 14, 17, 20, 21, 22, 23, 24, 25. This particular design is chosen for its easier fabrication, characterization, and analysis, and also isotropic physical properties, such as drag coefficient, in all orientations.…”

“…Over the past decade, numerous studies have been conducted on harnessing the flagellated bacteria, such as E. coli and S. marcescens , as propellers for biohybrid microswimmers,1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 aiming to develop a new type of targeted drug delivery system for tumor therapy 14, 16, 18, 19. Recently, efforts have also been made to guide the motion of such bacteria‐driven microswimmers through taxis‐based14, 17, 20, 21, 22, 23, 24, 25 and magnetic steering16, 26 approaches. Among these studies, the most common way to integrate bacteria into biohybrid microswimmers is attaching intact bacterial cells onto the surfaces of synthetic microstructures, such as polystyrene microbeads, where the attachment could be enabled either by physical attraction2 or through chemical bonding 14.…”

“…Such natural sensing abilities of bacteria are considered to be ideal guiding mechanisms for the motion of biohybrid microsystems, especially for healthcare applications in the human body, where chemical cues are ubiquitous. Thus far, the taxis‐based guiding method constitutes the major way to regulate the otherwise highly stochastic motion of bacteria‐driven microswimmers, which has been studied both in vitro17, 20, 21, 22, 23, 24, 25 and in vivo 14, 16. Chemotaxis, one of the most common taxis behaviors in bacteria, has been well understood36 and its signaling pathway has been mathematically modeled 37, 38, 39, 40, 41, 42, 43.…”

Development of bacteria-actuated microrobots using the surface modification of microstructures

“…Moreover, some other groups proposed a neodymium-iron-boron microrobot, which is composed of neodymium-iron-boron with dimensions 250 μm × 130 μm × 10 μm, is actuated and stirred by a system of 6 macro-scale electromagnets, and observed micro-robot translation speeds can exceed 10 mm/sec [16]. Third, S. typhimurium and E. coli can be recognize the some bacterial chemotactic chemicals, chemo-attractant (L-aspartic acid) and chemo-repellent (NiSO 4 ), by their chemoreceptors and show positive or negative motility against a chemotactic chemicals by flagella motor [17].…”