G. Tae et al., Hydrogels with controlled, surface erosion characteristics from self-assembly of fluoroalkyl-ended poly(ethylene glycol), MACROMOLEC, 34(18), 2001, pp. 6409-6419
Poly(ethylene glycol) (PEG) (M-w = 6k, 10k, and 20k g/mol) terminated at bo
th ends by hydrophobic fluoroalkyl segments (-(CH2)(2)CnF2+1, n = 6, 8, or
10) was synthesized and demonstrated to self-assemble into hydrogels with p
hase behavior and mechanical and erosion properties that can be systematica
lly varied by molecular design. With increasing fluoroalkyl length relative
to PEG length, the phase behavior of these polymers in aqueous solution ch
anges from the single-phase behavior of familiar associative thickeners, to
sol-gel coexistence, to precipitation. For those polymers that exhibit sol
-gel coexistence, the equilibrium gel concentration (or swelling ratio of t
he gel phase) and the modulus of the gel phase are governed by the length o
f the PEG midblock, whereas the relaxation time is determined by the hydrop
hobe length. The erosion characteristics of these hydrogels correlate with
their phase behavior. The gels of sol-gel coexisting species exhibit surfac
e erosion in an open system with a slow dissolution rate controlled by the
end-group length; in contrast, hydrogels from polymers that show single-pha
se behavior exhibit bulk erosion that is relatively fast, Therefore, the mo
lecular structure of this class of polymers produces hydrogels whose mechan
ical and erosion properties can be tailored for desired applications. Based
on the established biocompatibility of PEG, the degree to which the charac
teristics of the gel phases can be tailored, and the surface erosion charac
teristics that can be achieved, these materials might have applications in
implantable drug-release depots.