Size-Dependent Locomotion Ability of Surface Microrollers on Physiologically Relevant Microtopographical Surfaces.

Controlled microrobotic navigation inside the body possesses significant potential for various biomedical engineering applications. Successful application requires considering imaging, control, and biocompatibility. Interaction with biological environments is also a crucial factor in ensuring safe application, but can also pose counterintuitive hydrodynamic barriers, limiting the use of microrobots. Surface rolling microrobots or surface microrollers is a robust microrobotic platform with significant potential for various applications; however, conventional spherical microrollers have limited locomotion ability over biological surfaces due to microtopography effects resulting from cell microtopography in the size range of 2-5 µm. Here, the impact of the microtopography effect on spherical microrollers of different sizes (5, 10, 25, and 50 µm) is investigated using computational fluid dynamics simulations and experiments. Simulations revealed that the microtopography effect becomes insignificant for increasing microroller sizes, such as 50 µm. Moreover, it is demonstrated that 50 µm microrollers exhibited smooth locomotion ability on in vitro cell layers and inside blood vessels of a chicken embryo model. These findings offer rational design principles for surface microrollers for their potential practical biomedical applications.