Self-propelled catalytic micro- and nanomotors have been the subject of intense study over the past few years, but it remains a continuing challenge to build in an effective speed-regulation mechanism. Movement of these motors is generally fully dependent on the concentration of accessible fuel, with propulsive movement only ceasing when the fuel consumption is complete. Here we report a demonstration of control over the movement of self-assembled stomatocyte nanomotors via a molecularly built, stimulus-responsive regulatory mechanism. A temperature-sensitive polymer brush is chemically grown onto the nanomotor, whereby the opening of the stomatocytes is enlarged or narrowed on temperature change, which thus controls the access of hydrogen peroxide fuel and, in turn, regulates movement. To the best of our knowledge, this represents the first nanosized chemically driven motor for which motion can be reversibly controlled by a thermally responsive valve/brake. We envision that such artificial responsive nanosystems could have potential applications in controllable cargo transportation.
We report the self-assembly
of a biodegradable platinum nanoparticle-loaded
stomatocyte nanomotor containing both PEG-b-PCL and
PEG-b-PS as a potential candidate for anticancer
drug delivery. Well-defined stomatocyte structures could be formed
even after incorporation of 50% PEG-b-PCL polymer.
Demixing of the two polymers was expected at high percentage of semicrystalline
poly(ε-caprolactone) (PCL), resulting in PCL domain formation
onto the membrane due to different properties of two polymers. The
biodegradable motor system was further shown to move directionally
with speeds up to 39 μm/s by converting chemical fuel, hydrogen
peroxide, into mechanical motion as well as rapidly delivering the
drug to the targeted cancer cell. Uptake by cancer cells and fast
doxorubicin drug release was demonstrated during the degradation of
the motor system. Such biodegradable nanomotors provide a convenient
and efficient platform for the delivery and controlled release of
therapeutic drugs.
Ionic liquid (IL)-based polyelectrolytes (PILs), referred to as polymeric ILs, polymerised ILs, or poly(IL)s are a new subclass of polymer materials. They are distinct from conventional polyelectrolytes due to their unique physico-chemical properties originated from a dense packing of ILs in the macromolecular architecture. Mixtures of PILs and solvents, in particular, water have attracted a great deal of interest especially in terms of their compatibilities depending on temperature, namely, thermoresponsiveness of PIL/solvent mixtures. Apart from static compatibility, such as the compatibility of PILs with solvents, which do not change largely by a temperature change, there are mainly two types of dynamic phase changes, an upper critical solution temperature (UCST)-and a lower critical solution temperature (LCST)-type phase behaviour. Some PILs dissolved in solvents homogenise upon heating; this behaviour is classified as UCST behaviour. On the other hand, only in the last two years have PIL/water mixtures with LCST been discovered. This article summarises rapidly growing studies on the design of thermoresponsive PIL systems with water or organic solvents. The hydrophobicity/hydrophilicity balance of the starting IL monomers features the phase behaviour of the resulting polyelectrolytes, and some IL monomers that show thermoresponsive phase behaviour in solvents were found to maintain their thermoresponsiveness even after the polymerisation. Based on their unique combination of properties derived from an ionic and thermoresponsive nature, these thermoresponsive PILs will attract considerable interest, and their wide applications are expected in the fields of separation, sensing and desalination.
A cationic polyelectrolyte based
on the styrenic ionic liquid tributyl-4-vinylbenzylphosphonium
pentanesulfonate was found to undergo a lower critical solution temperature
(LCST)-type phase transition in aqueous solutions. This phase transition
occurs in a wide temperature range in terms of polymer concentration
as well as type and concentration of externally added salts. Anion
exchange and salting out effects are responsible for the flexible
phase transition temperature.
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