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The promising idea of using self-propelled particles in fields such as microfabrication and environmental remediation has led to the appearance of a plethora of different approaches for their motion during the past years. [1] Among them, the combination of living swimmers and nanocontainer cargos is especially attractive [2]. However, the usual necessity of a fuel in the environment hinders their application in biological tissue and consequently, their bio-medical usage. Here, we propose a novel propulsion mechanism based solely on the refraction of light in the volume of micro-scale particles.
In order to understand these artificial swimmers, numerical simulations were undertaken to identify optimized geometries and refractive index distributions of particles. In particles with broken symmetry, a resultant directional photon momentum transfer is intiating a propulsion force, which in turn can be enhanced by the inclusion of a GRadient of refractive INdex (GRIN).
We demonstrate fabrication of such artificial swimmers by femtosecond laser lithography based on two photon polymerization (TPP). The versatility of TPP along with the well-suited fabrication polymer Ormocomp allow replicating any of the numerically suggested particles, especially those containing GRIN distributions. We demonstrate the directional motion of the fabricated artificial swimmers under collimated illumination, with the GRIN particles outperforming their homogeneous counterparts.
With this first proof-of-principle we pave the way for numerous applications this new generation of fuel-free, refraction-driven self propelled swimmers.
[1] M. Guix, S. M. Weiz, O. G. Schmidt, M. Medina‐Sánchez, Part. Part. Syst. Charact. 35, 1700382 (2015).
[2] Á. Barroso et al., Biomedical Microdevices 17, 26 (2015);A. Barroso et al., SPIE Newsroom (2015); doi:10.1117/2.1201507.006023
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