(216am) Evidence of a Hydrophobic Region in Pluronic Brush Layers Formed On Silica Surfaces

The
action of pendant, polyethylene oxide (PEO) brush layers as nonfouling coatings
for biomedical materials is well understood. However progress toward clinical
application of stable, high density PEO coatings has historically been impeded
by the lack of cost effective, non-invasive methods for their preparation. Triblock
polymers featuring a hydrophobic, polypropylene oxide (PPO) or polybutadiene
(PB) centerblock flanked by two PEO side chains can be used to coat the
surfaces of hydrophobic biomedical materials, and in this way render them less
prone to protein adsorption and bacterial adhesion. Optimal coating requires
awarenesss of triblock aggregation properties, and for this purpose pyrene
fluorescence quenching was used to determine the critical aggregation
concentration of the triblocks used in this work. Coatings produced by radiolytic grafting of PEO-PB-PEO triblocks
to polyacrylonitrile membranes used in hemodialysis were evaluated in relation to impact on urea permeability through
the membrane. Neither the presence of
 PEO-PBD-PEO triblocks nor the irradiation process was observed to have any
effect on membrane permeability to urea. Beyond issues surrounding
biocompatibility, PEO coatings can potentially be used to entrap and later release bioactive peptides
for short-term medical device applications. In this context, pyrene
fluorescence quenching (Figure 1) was used to demonstrate the existence of a
hydrophobic inner region of PEO layers based on PEO-PPO-PEO triblocks,
substantially explaining the high affinity for entrapment previously recorded
for amphiphilic peptides.

Figure
1: Plot of
relative fluorescence intensity of pyrene at 395 nm for various Pluronic
coatings on R816 nanoparticles. Coatings were made at different concentrations,
denoted by the dilution factors. The dilution scheme is based on the CAC value
for each Pluronic. The error bars show the minimum and maximum values for each
data set of three samples.