THE DESIGN AND FABRICATION OF AUTONOMOUS POLYMER-BASED
CHAPTER ONE
INTRODUCTION
1.1 Surface Tension-Confined Microfluidics
The field of microfluidics promises the capacity to automate sophisticated laboratory analyses into a diminutive platform that can be implemented by a user with minimal analytical experience negating the necessity for trained personnel and/or specialized equipment. Often an analogy is drawn towards the integrated circuit revolution which facilitated the automation of large-scale computation. Similarly, a great deal of optimism exists that microfluidics may have such an impact on chemistry, biology and medicine, resulting in a drastic decrease in the amount of expensive reagent or invasive fluid samples required while enabling higher degrees of throughput and parallelization.
Such microfluidic devices have been successfully developed. Researchers have effectively integrated an enzyme-linked immunosorbent assay into an on-chip platform (Sato et al., 2004) as well as developed chips for DNA analysis (Burns, 1998) and novel applications of microfluidics towards fuel cell development (Choban et al., 2004), among a plethora of other innovative utilizations. However, the fabrication methods traditionally employed to manufacture microfluidic devices tend to be cost ineffective and time intensive. In addition, fabrication techniques may require clean-room facilities or batch processing further complicating production scale-up. Consequently, current production techniques render exploiting this technology problematic for wide-scale deployment. This manuscript describes alternative fabrication techniques to mitigate the aforementioned problems.
Specifically, spontaneous surface tension-confined capillary pumping of fluids with appropriate surface tension and viscosity is enabled by patterning energetic discontinuities or topographical features upon a surface.
However, before surface tension-confined microfluidics can be employed towards solving problems in chemistry, biology and medicine, a thorough understanding of the underlying physics must be established. This task becomes non-trivial as fluidic miniaturization results in dramatic changes to the fundamental physics manifested at small length scales (Squires & Quake, 2005). For example, mass transport within microfluidic devices is a challenge as viscous dissipation dominates at small length scales rather than inertial effects. This implication suggests microfluidic flow is nearly devoid of convection enabling the elimination of non-linear terms in the Navier-Stokes equations for incompressible flow. Although the lack of inertia at small length scales seems to indicate the analysis of microfluidic fluid transport is straightforward, quite the opposite is true. Other non-linear phenomena that may not be as familiar at the macro scale become apparent as