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Aqueous solutions of a methylcellulose, ranging from 0.30 to 2.49 wt %, were studied by means of micro differential scanning calorimetry (micro DSC) and rheology. The effects of polymer concentration on the thermodynamic properties of these solutions were examined through a heating process and a following cooling process at a fixed rate of 1 °C/min. Upon heating, an endothermic peak was observed at about 63 °C, which was independent of polymer concentration. The total energy defined by the endothermic peak area was found to be a linear function of polymer concentration. On the other hand, when samples were cooling from about 90 °C, a broad exothermic peak appeared at about 33 °C, and the peak height and its broadness increased with polymer concentration. A shoulder was observed above the peak temperature of 33 °C, and the shoulder became more prominent with increasing polymer concentration to eventually appear as a second peak at about 40 °C. The thermal analysis results clearly show that the association of methylcellulose molecules in water is thermorevesible but the dissociation occurred at much lower temperatures than the association temperatures. The viscoelastic properties of these solutions correlated excellently with the results obtained from the micro thermal analysis. Thermodynamic mechanisms involved in the association and the dissociation are proposed.

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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.