Optimization of novel thermally activated single-use valves and pumps for minimally invasive transdermal drug delivery and Lab-on-Chip applications
Degree NameDiploma in Engineering Sciences
This thesis reports on the optimization of microfluidic devices based on a novel temperature sensitive elastomer composite. The composite consists of expandable microspheres confined in a polydimethylsiloxane (PDMS) matrix and allows to design highly integrated active liquid handling networks. Devices employing this composite can be fabricated entirely of low-cost materials on a wafer-level scale. Upon heating the microspheres increase their volume expanding the composite. In contrast to other approaches complicated localization of the actuator material is avoided by using embedded heat sources to geometrically define expansion. The work presented focuses on the theoretical and experimental investigation of embedded microheater performance, based on which innovative heater designs are proposed. In addition, fluid temperature is measured during device operations. Partial fluid entrapment during operation and resulting high alignment precision during fabrication are addressed by using specially designed heaters. Devices with microheaters based on printed circuit board (PCB) technology as thermal power source are analyzed and simulated using finite element modelling (FEM). Heater trace width and spacing are adjusted to produce custom temperature profiles. Temperature dependence of fluorescence for RhodamineB is adapted to compare fabricated heater shapes with simulation results. The potential problem of excessive temperature increase of the fluid as a consequence of the actuation principle is investigated using fluorescence based thermometry. Direct fluid temperature measurements for typical actuation currents are performed on pure PDMS dummies and composite based active devices. An intermediate gold layer as well as custom machined PDMS observation windows are introduced for active devices to enable the measurement process. Fluid temperatures of up to 43℃ on dummy devices and up to 35℃ on composite based devices are measured in the fluidic system during similar operation conditions.