Dynamic capillary systems towards disposable fluid probes

The basis of the proposed project is the investigation of novel polymer materials as major building blocks in capillary microfluidic networks. This comprises new concepts for capillary pumps as well as active and passive controlling elements in the microfluidic network. The aim is, to investigate dynamic capillary networks, where all actions necessary to supply and flush a reaction- or sensor-chamber like pumping, valving, and synchronization can be controlled in a direct and dynamic manner by means of a feedback control of flow properties. New soft polymer materials that became available recently have proved their ability to induce large changes in the thickness of the material, for example by the converse piezoelectric effect in cellular polymers, and complex three dimensional actuation modes, for example by Maxwell stresses in elastomers. Though these materials have been applied in a variety of transducers, little work yet has been devoted towards their use in actively controlled microfluidic devices. In the course of the project, piezoelectric polymer foams and actuating elastomers will thoroughly be examined for the utilization as controlling elements and actuators in microfluidic networks. A combination of surface (pre-) modification techniques and geometric changes of the channel diameter, dynamically controlled by the use of electroactive polymer actuators, will be employed to modify the capillary force and hence to control fluid flow through the microfluidic network. Open cell polymer foams will be explored for the use as capillary pumps. By adjusting the surface energy of the open cell foam and integrating a heating element underneath, it could serve as a dynamic controllable microfluidic pump. A fast feedback control of flow properties will be realized by implementation of flow velocity sensors in the fluid channel. Specifically developed control and read out electronics will allow direct and dynamic steering of flow properties. To demonstrate the potential of these new mechanisms for microfluidic components, microfluidic demonstrator chips will be realized with laser cut polymer foils using a stacked ("sandwich") design. Capable of handling multiple fluid samples in a controlled manner solely by capillary action, these systems will demonstrate the potential for applications in widespread industrial fields. For example, various applications in chemical and biological assays are under consideration, where a so called quartz-crystal-microbalance (QCM) sensor is used to track chemical reactions or to detect a specific biological component in a fluid sample. Up to now, these assays mostly require cumbersome electromechanical and fluidic connections to the flow-cells, usually containing the QCM sensor. Integration of a QCM in a capillary system, capable to steer liquid sample flows dynamically by feedback control of the flow properties, will result in a powerful and versatile microfluidic demonstration tool, which should be realizable at low cost and could thus be used as a disposable devices particularly suitable for medical applications..