• DOI:10.1038/s41567-021-01291-3
• Corpus ID: 236154766

Rechargeable self-assembled droplet microswimmers driven by surface phase transitions

@article{Cholakova2021RechargeableSD,
  title={Rechargeable self-assembled droplet microswimmers driven by surface phase transitions},
  author={Diana Cholakova and Maciej Lisicki and Stoyan K. Smoukov and Slavka S. Tcholakova and E Emily Lin and Jianxin Chen and Gabriele De Canio and Eric Lauga and Nikolai Denkov},
  journal={Nature Physics},
  year={2021}
}

• D. Cholakova, M. Lisicki, +6 authors N. Denkov
• Published 15 July 2021
• Engineering
• Nature Physics

1Department of Chemical and Pharmaceutical Engineering, Faculty of Chemistry and Pharmacy, Sofia University, Sofia, Bulgaria. 2Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland. 3Active and Intelligent Materials Lab, School of Engineering and Materials Science, Queen Mary University of London, London, UK. 4Department of Applied Chemistry, School of Science, Northwestern Polytechnical University, Xi’an, People’s Republic of China. 5Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, UK. ✉e-mail: [e-mail]; [e-mail]; [e-mail]; [e-mail] Due to their relative simplicity, natural microswimmers1,2 and their artificial counterparts3–5 are convenient systems for studying the complex behaviour of active matter. Indeed, intricate nanomachinery governs movement, from cell shaping and division to the propulsion of microorganisms in biology6. Developments in molecular machines3 including nanocars7 foreshadow such life-like complexity in artificial swimmers, but fabrication and integration from molecular to nanoand microscales is non-trivial: ‘a major challenge is finding robust ways to couple and integrate the energy-consuming building blocks to the mechanical structure’8. To this end, promising non-biological artificial muscles have already achieved programmable movement9 and phase-transition-driven two-way elastic deformation10. Combinatorial approach methodology to multifunctionality11 has resulted in self-sensing muscles12, and bottom-up synthesis techniques can be used to synthesize single molecules into polymer shapes13. A number of mechanisms for artificial swimmers have been used, including prominently chemical power14—catalytic particles creating bubbles, self-electrophoresis or releasing slightly dissolving compounds to drive Marangoni flows (for example, camphor boats)15. Others are driven by physical effects—thermophoresis16 or external acoustic17, magnetic18 and electric19 fields, and they serve as a basis for the theoretical understanding of ‘active matter’20. Three main classes have emerged that are relatively easy to make in large quantities and are therefore accessible for the study of large ensembles of microparticle swarms. The first class—catalytic Janus microswimmers5—use catalysts on one side of their surface (for example, Pt or Pd) to decompose hydrogen peroxide in the surrounding solution, creating microor nanobubbles, and self-propel while the chemical fuel lasts. The second major class of artificial microswimmers21 uses light-absorbing Janus particles to induce local heating and asymmetric demixing in a binary lutidine/water mixture, thus generating spatial concentration gradients that induce self-diffusiophoretic motion of the particles. Both types of system have been extensively studied, but the need of toxic peroxide or lutidine prevents the study of such swimmers interacting with biological microswimmers in their native environment. The third class of microswimmers are compatible with biological media and exploit external light or magnetic fields to create motion. Differential light absorption on relatively easy to fabricate Janus particles has been used for thermophoresis. Such swimmers have achieved ~50 μm s−1 speeds with hollow particles, which allow loading with drugs for targeted delivery22. More recently, emulsion-based Pickering immobilization was employed to scale up and simplify the fabrication of such metal-containing Janus particles, capable of thermophoretic swimming23. Their potential beyond drug delivery also extends to therapies such as thrombosis ablation treatment24. Magnetic swimmers require more involved microfabrication of intricate screw-type structures25, which, however, can be controlled in deep tissues without restrictions for transparency or complications of light absorption. Therefore, they have excellent properties for the studies of mixed artificial and biological swimmers. Magnetic microrobots picked, encapsulated and delivered cells to Rechargeable self-assembled droplet microswimmers driven by surface phase transitions