Numerical Analyses of Microchannels Filling in a Lab-on-Chip Device Available to Purchase

A prototype of a Lab-on-Chip (LoC) device manufactured by ST Microelectronics Inc., which is intended to be a diagnostic platform for DNA analysis, has been analyzed. In particular, the dynamics of the filling process was evaluated by means of a 3-D numerical model. Measurements of wettability were also conducted by evaluating the surface tension of the examined liquids and their contact angles on the solid substrates. Two different filling conditions were simulated: pure capillarity and a pressure of 1.5 kPa applied to the inlet. Results in terms of filling time, fluids velocities and percentage of air entrapped in the channels were analyzed. The numerical model revealed the presence of 3.4% of air in the channels (localized in the corner regions), when the pressure of 1.5 kPa was applied. In case of zero pressure, the top corners of the central channel got completely wetted, thus reducing the amount of air to 2.7%. The results showed that capillary forces are dominant during the filling of channels with dimensions smaller than 200 μm. General parameters used to have an insight into the kind of forces leading a fluid-dynamic process are the Reynolds (Re) and Capillary (Ca) numbers, ratios between inertial and viscous forces, and viscous and surface forces, respectively. The computed maximum values in our simulations were Re = 60 and Ca = 0.018, showing the predominance of surface forces on both viscous and, indirectly, inertial ones.