1 research outputs found
Spatially Resolved Tracer Diffusion in Complex Responsive Hydrogels
Thermosensitive composite hydrogels that consist of a
poly(acrylamide)
hydrogel matrix with embedded micrometer-sized poly(<i>N</i>-isopropylacrylamide) microgel beads are promising models for complex,
heterogeneous gels. We investigate the coupling of the microgel beads
with the gel matrix and the formation of interpenetrating networks
inside the microgels by confocal two-focus fluorescence correlation
spectroscopy (2fFCS). This technique serves to study the effects of
the heterogeneous structure of the composite hydrogels on the diffusive
mobility of nanoscopic dextran tracers within the gels. Our investigations
reveal that the formation of interpenetrating networks inside the
embedded microgel beads depends on their cross-link density: whereas
interpenetrating networks are formed inside weakly cross-linked beads,
they are not formed inside strongly cross-linked beads. If the formation
of interpenetrating networks occurs, the temperature-dependent swelling
and deswelling of the beads is obstructed. In addition, the mobility
of dextran tracers inside the embedded microgel beads is hindered
compared to those in free beads and in the surrounding gel matrix.
Surprisingly, the surrounding poly(acrylamide) hydrogel matrix swells
inhomogeneously when the embedded poly(<i>N</i>-isopropylacrylamide)
beads collapse upon heating. This indicates the formation of pores
near the surface of the collapsed beads, offering promising means
to tailor composite hydrogels for applications as membranes with tunable
permeability. Our experiments also demonstrate the utility of 2fFCS
to study spatially resolved diffusion in complex environments, which
is of great interest in biomaterials research