Microfluidic devices were utilized to study the behavior of highly viscous liquids surrounded by less viscous ones. This study mainly focuses on the lubrication transition of viscous threads flowing in sheaths of less viscous fluids, i.e., viscous core-annular flows. Miscible and immiscible fluid pairs with various viscosities, were tested in microchambers. A variety of flow patterns resulting from the viscous folding and capillary instabilities were observed and the relationships between flow morphologies and system parameters, including fluid viscosities, interfacial properties, flow rates of injection, and micro-cell geometry were examined. In addition, in order to fabricate microchannels more efficiently, a femtosecond laser was used to study the potential of ultrafast laser micromachining. Three disparate materials were tested to establish the ablation abilities of the laser. Each test piece was etched multiple times with different powers and the consequential geometrical parameters (height and width) of each etched trench were measured. The final result was shown on one master curve that works as a guideline for micromachining of tapered channels in transparent materials.