Author's School

School of Engineering & Applied Science

Author's Department/Program

Biomedical Engineering


English (en)

Date of Award

January 2009

Degree Type


Degree Name

Master of Arts (MA)

Chair and Committee

Donald Elbert


The lower critical solution temperature: LCST) behavior of poly(ethylene glycol): PEG) in aqueous sodium sulfate solutions was exploited to fabricate hydrogel microspheres under mild conditions without the use of other monomers, polymers, surfactants or organic solvents. Reactive PEG derivatives underwent thermally induced phase separation to produce spherical PEG-rich domains that coarsened pending gelation, resulting in stable hydrogel microspheres that were polydisperse in size. The degree of reaction prior to phase separation, reaction rate within the PEG-rich domains, and duration of the reaction were independently varied to elucidate their effects on final microsphere size and gain insight regarding the mechanism of formation. It was found that both the time required to reach the gel point during coarsening and the extent of crosslinking after gelation impacted the final size of the microspheres. Power law analyses of microsphere sizes revealed the mean radius of PEG-rich droplets to grow with time to the 1/4th power until gelation. Together with dynamic light scattering data, this suggested that a percolation-to-cluster transition occurred soon after phase separation by off-critical spinodal decomposition. This technique of producing PEG microspheres with controlled sizes has considerable potential for an array of applications, including the production of modular scaffolds for tissue engineering.


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