posted on 2016-06-13, 14:48authored byAnnie Xi Lu, Yijing Liu, Hyuntaek Oh, Ankit Gargava, Eric Kendall, Zhihong Nie, Don L. DeVoe, Srinivasa R. Raghavan
We describe the creation of polymeric
microcapsules that can exhibit autonomous motion along defined trajectories.
The capsules are made by cross-linking aqueous microdroplets of the
biopolymer chitosan using glutaraldehyde. A coflow microfluidic tubing
device is used to generate chitosan droplets containing nanoparticles
(NPs) with an iron (Fe) core and a platinum (Pt) shell. The droplets
are then incubated in a Petri dish with the cross-linking solution,
and an external magnet is placed below the Petri dish to pull the
NPs together as a collective “patch” on one end of each
droplet. This results in cross-linked capsules (∼150 μm
in diameter) with an anisotropic (patchy) structure. When these capsules
are placed in a solution of H2O2, the Pt shell
of the NPs catalyzes the decomposition of H2O2 into O2 gas, which is ejected from the patchy end in
the form of bubbles. As a result, the capsules (which are termed micromotors)
move in a direction opposite to the bubbles. Furthermore, the micromotors
can be steered along specific paths by an external magnet (the magnetic
response arises due to the Fe in the core of the NPs). A given micromotor
can thus be directed to meet with and adhere to an inert capsule,
i.e., a model cargo. Adhesion occurs due to the soft nature of the
two structures. Once the cargo is picked up, the micromotor-cargo
pair can be moved along a specific path to a destination, whereupon
the cargo can be released from the micromotor. We believe these soft
micromotors offer significant benefits over their existing hard counterparts
because of their biocompatibility, biodegradability, and ability to
encapsulate a variety of payloads.