Confocal laser scanning microscopy (CLSM) was utilized to explore noninvasively the
diffusion mechanisms of water-soluble, low molecular weight fluorescent probes in photopolymerized poly(ethylene glycol) (PEG) hydrogels. First, the simple case of 1-D diffusion in uniformly loaded PEG disks
was characterized. Dye distributions in PEG disks were imaged using CLSM during release experiments
and quantitatively evaluated through image analysis for comparison to Fickian diffusion models. Dye
diffusion coefficients were determined by fitting Fickian diffusion equations to experimentally measured
concentration profiles. Effective diffusion coefficients were on the order of 10-8 cm2/s, comparing favorably
to literature values. Second, the time-dependent distributions of two separate probes were monitored
simultaneously to explore the multicomponent tracking capabilities of CLSM in PEG hydrogels. Finally,
a more complex dye loading system was examined by embedding microparticles loaded with fluorescent
dye in PEG matrices and characterizing 3-D radial dye diffusion.
A simple and straightforward method for growing ultrathin, micropatterned polymer films on surfaces with precise thickness and spatial control is presented. A difunctional ene monomer and a difunctional thiol were photopolymerized on a surface terminated with thiol groups. The surface thiols participate in the polymerization, and a linear polymer is formed on the surface. Brush growth was spatially controlled by selectively polymerizing the monomers through a photomask, while the brush thickness was controlled by changing the ratio of thiol and ene monomers or by changing the monomer functionality. Further, the surface was passivated by attaching a patterned, cross-linked polymer film, which was then backfilled with another monomer, demonstrating the attachment of multiple functionalities on the surface in a controlled, photolithographically patternable manner. Thiol-ene polymerizations were carried out without an initiator and used to graft patterned, polymer films. The films were observed using scanning probe microscopy and characterized using ellipsometry.
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