Monitoring changes of viscoelasticity during blood coagulation with acoustic sensors

In our previous work we demonstrated the general suitability of surface and bulk acoustic wave (SAW and BAW) structures for recording the continuous change of fluidic behavior in the course of blood coagulation processes [Guhr et al.,2005]. Special advantage can be taken from the direct impact of fluid consistence on SAW and BAW device parameters (e. g. resonator frequency, quality factor, impedance). Beside the ability of continuous detection of coagulation process further tests can be realized with SAW and BAW devices as was shown in an acoustic version of thrombelastography [Guhr et al.,2006]. In this paper, we make the proposal to describe the observed features of blood in the frame of non-Newtonian behavior. Therefore we distinguish between acoustic monitoring of shear viscosity and shear elasticity changes during the whole process of haemostasis. The goal is to get more detailed insight into the ongoing biological process. That approach is suggested from modeling of resonance-antiresonance behavior of thickness shear-mode resonators (TSM), also called quartz crystal microbalance (QCM). The response of resonance and antiresonance parameters can be significantly different from each other, depending on the shear viscosity and elasticity of the loaded fluid. For example, the frequency shifts of both resonances have the same or the opposite sign when changing the viscosity or the elasticity, respectively. The results of modeling the QCM response to viscoelastic loading are used for the interpretation of time dependent measurement signals of the coagulation process.