Perfluorocarbon (PFC)
nanoemulsions, droplets of fluorous solvent stabilized by surfactants
dispersed in water, are simple yet versatile nanomaterials. The orthogonal
nature of the fluorous phase promotes the formation of nanoemulsions
through a simple, self-assembly process while simultaneously encapsulating
fluorous-tagged payloads for various applications. The size, stability,
and surface chemistry of PFC nanoemulsions are controlled by the surfactant.
Here, we systematically study the effect of the hydrophilic portion
of polymer surfactants on PFC nanoemulsions. We find that the hydrophilic
block length and identity, the overall polymer hydrophilic/lipophilic
balance, and the polymer architecture are all important factors. The
ability to modulate these parameters enables control over initial
size, stability, payload retention, cellular internalization, and
protein adsorption of PFC nanoemulsions. With the insight obtained
from this systematic study of polymer amphiphiles stabilizing PFC
nanoemulsions, design features required for the optimal material are
obtained.
Stimuli-responsive
materials are exploited in biological, materials,
and sensing applications. We introduce a new endogenous stimulus,
biomacromolecule crowding, which we achieve by leveraging changes
in thermoresponsive properties of polymers upon high concentrations
of crowding agents. We prepare poly(2-oxazoline) amphiphiles that
exhibit lower critical solution temperatures (LCST) in serum above
physiological temperature. These amphiphiles stabilize oil-in-water
nanoemulsions at temperatures below the LCST but are ineffective surfactants
above the LCST, resulting in emulsion fusion. We find that the transformations
observed upon heating nanoemulsions above their surfactant’s
LCST can instead be induced at physiological temperatures through
the addition of polymers and protein, rendering thermoresponsive materials
“crowding responsive.” We demonstrate that the cytosol
is a stimulus for nanoemulsions, with droplet fusion occurring upon
injection into cells of living zebrafish embryos. This report sets
the stage for classes of thermoresponsive materials to respond to
macromolecule concentration rather than temperature changes.
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