Fabrication of High Aspect Ratio Poly(ethylene glycol)-Containing Microstructures by UV Embossing

Abstract

The fabrication of high aspect ratio (5 and above) microstructures based upon UV embossing of mixtures containing poly(ethylene glycol) diacrylate (PEGDA) is described. UV embossing is a quick and convenient replication technique using low pressure and room temperature. The biocompatibility and cell- and protein-resistance of PEGDA make deep three-dimensional (3-D) micropatterned PEGDA films potentially useful for many biological applications such as protein delivery, tissue engineering, drug delivery, and biosensors. Microarrays of deep microchannels and microcups separated by PEGDA walls with aspect ratios of 7 and 5, respectively, were successfully embossed. UV embossing was found to faithfully replicate the lateral periodicity and height of the mold. We also successfully UV embossed a mixture having equal weight proportions of hydrophilic PEGDA and hydrophobic poly(propylene glycol) diacrylate and demonstrated the use of this microarray of microcups for encapsulation of a model protein (bovine serum albumin) within a UV cured PEGDA hydrogel; a protein encapsulated within a hydrogel 3-D microarray was fabricated. Although high aspect ratio UV embossing has many attractive features, it is a difficult process to implement, requiring precise control and optimization of mold, process, and material parameters. Successful high aspect ratio UV embossing was achieved using two molds: a rigid nickel mold and a silicone rubber mold. The latter did not require any surface treatment, but the nickel mold was found to require coating with a cured silicone resin to obtain a suitable nonstick surface. The UV exposure time was controlled to optimize the hardened resin strength while avoiding excessive brittleness. Peel-off of the hardened microstructures was performed at a small angle to avoid breakage of the molded structures. A mold release additive was necessary for successful demolding. Trimethylolpropane triacrylate, a high shrinkage monomer, also facilitated demolding.

Direct Patterning of Protein‐ and Cell‐Resistant Polymeric Monolayers and Microstructures

“…To create PEG microstructures, photolithographic methods have been used. [19,23] However, the cost and complexities associated with photolithography provides a barrier to its widespread application for cell and protein patterning. In another approach, polymeric deposition of a PEG-based comb polymer was used to generate topographical changes, but no direct control over feature height was demonstrated.…”

Synthesis of Stimuli-Sensitive Hydrogels in the μm and sub-μm Range by Radiation Techniques and their Application

“…A direct means of patterning is photolithography [20]. In summary, one can say that photo-cross-linking is a very successful and often applied technique.…”

Live Lymphocyte Arrays for Biosensing

“…Micropatterning of hydrogels has drawn attention as a simple means to direct cell adhesion/growth/function on surfaces, by combining control of surface chemistry and topography. Previous studies have demonstrated the utility of capillary-force lithography/molding under polydimethylsiloxane (PDMS) stamps, [41][42][43][44] molding over microstructured silicon substrates, [45] UV embossing, [46] and photolithographic crosslinking [47][48][49][50] as facile means to create topographically structured PEG hydrogels, including "microwell" microstructures. Because lymphocytes are nonadherent, nonanchorage-dependent cells, [40] we …”