Hydrogels with controlled, surface erosion characteristics from self-assembly of fluoroalkyl-ended poly(ethylene glycol)

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.