Micro propulsion in liquid by oscillating bubbles

Abstract

This paper presents a micro propelling mechanism that may be possibly used to propel a micro medibot (medical robot) that can swim inside of animal/human bodies. A key contribution of this work is that, to our best knowledge, for the first time we microfabricate micro propelling devices based on bubble oscillation and prove the propelling mechanism in micro scale. The measured propelling speed is up to 45 mm/s and the generated propelling force is estimated to be up to 6 µN, which is strong enough not only to propel the propelling device itself but also to carry a large attached object of even several millimeters.

Mini and Micro Propulsion for Medical Swimmers

“…In Figure 2, the inertia propulsion methods are located in the large Re region while the viscous propulsion methods are in the low Re region. More specifically, the bubble type (putt-putt boat type) swimmers are using momentum transfer through the microstreaming formed by bubble oscillation [19,20]. The micro robots that harness natural organisms or use the artificial cilia/flagella (regardless of motion types, corkscrew motion, or flexible oar motion) generate propulsion via viscous stress interaction [17,18,[21][22][23][24][25][26].…”

“…Leoni et al [40] first realized this model experimentally with optical tweezers and compared the experimental results with the numerical solution. [19], 1′-acoustic scallop (Re is based on oscillating speed and amplitude), 2-oscillating micro bubble (Re is based on body speed and size) [20], 2′-oscillating micro bubble (Re is based on oscillating speed and amplitude), 3-artificial magnetic bacteria flagella [21], 4-artificial magnetic nanostructured propeller [22], 5-magnetically actuated colloidal [23], 6-magnetotactic bacteria propeller [24], 7-flagella-based propulsion [25] [17], and 19-Escherichia coli [18]. Note that the triangles denote inertia dominant propulsion, the squares denote viscous dominant propulsion, and the circles means the propulsion mechanisms cannot be clearly classified.…”

“…As the latter Reynolds number of the generated flow is proportional to the operating frequency, it is high enough for the inertia to come into play to generate a net momentum transfer between the surrounding water and the "scallop" by oscillation of the bubble meniscus. Later, Feng et al [20] used a similar concept but in a much smaller scale by fabricating the micro scallop with a micron bubble (470 μm × 60 μm × 80 μm).The device is fabricated based on micro photolithography. This propulsion operated at the oscillation-based Reynolds number of around 700 and the body-based Reynolds number of about 24.…”

Vibrational modes prediction for water-air bubbles trapped in circular microcavities

“…8,9 In the case of robust control, these phenomena are of crucial importance for precise flow and object manipulation in various geometries, including microchambers 10,11 and microchannels. 3,[12][13][14][15] Other applications of oscillating bubbles to be mentioned are micropumps, 16 microtweezers, [17][18][19] microfilters, 20 microrotors, 21 biosensors, 22 microswimmers, [23][24][25] and sorting. [26][27][28] An extensive literature exists on theoretical predication of dynamics as well as resonant and dissipative behavior of spherical bubbles, capitalizing on the well-known Minnaert 29 frequency.…”

Experimental characterization of Drobot: Towards closed-loop control

“…The former-related to fluidic assembly [8] as well as to surface-tension-based microrobotics [3]-has seen for instance the use of oscillating bubbles to propel swimming robots [9], [10], of air bubbles to create Marangoni stresses driving cells in bulk liquid [11] and of opticallyactuated bubbles in oil as microrobots [12]. Varel recently described a rotating table based on water droplets moving unidirectionally along a circular track micromachined onto a substrate subject to vertical oscillations [13].…”