How Hollow Are Thermoresponsive Hollow Nanogels?
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Abstract
A main challenge in colloid science
is the development of smart
delivery systems that store and protect actives from degradation and
allow release in response to an external stimulus like temperature.
Hollow nanogel capsules made of temperature-sensitive polymers are
particularly promising materials. The stimuli-sensitive void size,
shell thickness, and permeability determine cargo storage and its
release behavior. Thus, determination and control of these morphological
parameters are of outmost relevance for the design of new, functional
drug delivery vehicles. Here we investigate quantitatively void size
and shell thickness of hollow nanogels at different states of swelling
by means of small-angle neutron scattering (SANS) employing contrast
variation. We demonstrate the structure-sensitivity dilemma: hollow
nanogels with a slightly cross-linked shell reveal distinct temperature
sensitivity but possess nearly no void (14% of the initial core volume)
and are thus hardly “hollow”. Nanogels with a stiff
shell are indeed hollow (albeit with smaller void as compared to the
core size of the template) but less temperature sensitive