Piezoelectric Ceramic Applications: Micromixing in Biology and Medicine

Reducing the dimensions of macroscopic biological or chemical laboratories is advantageous, the small scale allowing the integration of various processes on one chip, analogous to integrated microelectronic circuitry. The microfluidic technology based on the “lab-on-a-chip” principle allows the usage of very small biological material quantities, decreases the quantity of reactives and waste and increases the speed in obtaining the results making use of automatization, integration, modularization and parallel processing (Southern, et al., 1999; Cai, et al., 2002). Such integration is prerequisite for a fully automated data management system covering all steps of a given chemical or biological process. Finally, the miniaturization results in enhanced precision by providing more homogenous reaction conditions in a shorter time (Pollack, et al., 1999; Hames & Higgins, 1990). Surface acoustic wave (SAW) devices as nano-pumps and micro-mixers used in microfluidic bio-medical applications are one of the uprising domains today. Surely, the conventional pumps cannot be used for the displacement of the very small liquid quantities on the substrate’s surface. To move such little liquid quantities in a “lab on a chip”, integrated nano-pumps on the substrate’s surface, are used. Using a piezoelectric substrate as support, SAWs are generated by application of an alternative signal with a suitable frequency and amplitude to a system of interdigital transducers (IDT). SAWs are launched on the substrate’s surface normally on the IDT lines and move like the water waves on the surface of a lake. This movement is used to move small drops of liquid on the substrate’s surface. Concerning the use of SAWs in micromixing applications, although the wavelengths are of the order of micrometers and wave amplitudes are of the order of nanometers, they are sufficient to produce fluidic nanocurrents inside the liquid droplets. These nanocurrents have chaotic movements that superimpose allowing mixing of their content. One of the applications of this microfluidic applications are “in situ” hybridization stations. In these stations, standard micro-meshes of DNA, proteins or other biological fluids are put in contact with a piezoceramic substrate supporting a SAW. Microagitation of the fluids during the incubation dramatically shortens the hybridization time (Toegl et al., 2003). 12