| Telechelic polymers with hydrophilic midblocks (poly(ethylene glycol), PEG) and hydrophobic end groups (fluoroalkyl, Rf) are synthesized and explored as candidates for in situ forming hydrogels. Relevant physical properties are characterized to guide rational design of polymers for specific biomedical applications.; With increasing fluoroalkyl length relative to PEG length, the phase behavior changes from single-phase behavior, to sol-gel coexistence, to an insoluble precipitate. For sol-gel coexisting polymers, the equilibrium gel concentration and the modulus of the gel phase are governed by PEG length, whereas the relaxation time is determined by fluoroalkyl length. The erosion characteristics correlate with their phase behavior: the gels of sol-gel coexisting species exhibit surface erosion with slow dissolution rate controlled by the end-group length, whereas gels showing single-phase behavior exhibit bulk erosion that is relatively fast.; Aqueous solutions of Rf-PEGs exhibit ordering transitions with increasing concentration. The hydrophobic cores of the micelle-like aggregates order into a body-centered-cubic structure, and the aggregated state is determined by fluoroalkyl length only. This micelle packing effect is manifested in the viscoelastic properties changes: appearance of a new low frequency elastic plateau and a yielding behavior in creep.; The gel phase of sol-gel coexisting polymers can be transformed into an injectable state by the addition of a bio-tolerable organic solvent, such as N-methyl pyrrolidone, and it can be restored to a hydrogel state quickly after injection by removal of the organic solvent by diffusion. Release of Human growth hormone (hGH) using this injectable formulation reveals that hGH remains stable inside the hydrogel formed, and more than 2 weeks of prolonged release of hGH pretreated with zinc is obtained without irreversible aggregation.; Rf-PEGs that exhibit sol-gel equilibrium or precipitated gel phase provide a facile route to hydrophilic modification of poly(tetrafluoroethylene) (PTFE) surfaces. Dip coating of PTFE into 1 wt % Rf-PEGs in ethanol, followed by immersing into water, converts the PTFE surface to hydrophilic. The lifetime of this modification is correlated to the phase behavior of the bulk gel state, and stable in various shear rates. An Rf-PEG insoluble in water gave a stable modification over a period of weeks. |
