The potential of liquid marbles for biomedical applications: a critical review

Liquid marbles (LM) are freestanding droplets covered by micro/nanoparti- cles with hydrophobic/hydrophilic properties, which can be manipulated as a soft solid. The phenomenon that generates these soft structures is regarded as a different method to generate a superhydrophobic behavior in the liquid/ solid interface without modifying the surface. Several applications for the LM have been reported in very different fields, however the developments for bio- medical applications are very recent. At first, the LM properties are reviewed, namely shell structure, LM shape, evaporation, floatability and robustness. The different strategies for LM manipulation are also described, which make use of magnetic, electrostatic and gravitational forces, ultraviolet and infrared radiation, and approaches that induce LM self-propulsion. Then, very distinc- tive applications for LM in the biomedical field are presented, namely for diagnostic assays, cell culture, drug screening and cryopreservation of mam- malian cells. Finally, a critical outlook about the unexplored potential of LM for biomedical applications is presented, suggesting possible advances on this emergent scientific area. The authors acknowledge funding from the European Research Council grant agreement ERC-2012-ADG 20120216-321266 for project ComplexiTE. N. M. Oliveira acknowledges the financial support from Portuguese Foundation for Science and Technology - FCT (Grant SFRH/BD/73172/2010), from the financial program POPH/FSE from QREN.