## 3 Results and Discussion
### Fatigue Test  
A reliable and safe microfluidic device design is required in medical applications in order to minimize the risk of device failure. Hence, the stability of the microvalves' performance is investigated by subjecting them to fatigue testing as described in Section 2.4.  
Immediately after fatigue testing, we inspect the microvalve's piezoceramic actuator optically and by measurement of its electric capacitance in order to detect critical failure in the form of cracks. Valves with piezoceramic actuator failure are excluded from subsequent fluidic characterization. The changes in maximum open flow, NO flow, and leakage after fatigue testing compared to observed performances after manufacturing are summarized in Table 3.  
None of the 4 high force design valves show failure of the piezoceramic actuator, but a total of 5 out of the 10 tested microvalves with a 0.2 mm thick piezoceramic actuator experience material cracking of the piezoceramic (three basic design valves and two coated valves). To confirm increased robustness of the actuator with increased actuator thickness, further investigations with an increased number of samples are needed and are planned for future work.  
Characterization of the active open flow rate shows only small changes (Table 3). The average change of NO flow rates at 100 kPa is zero for microvalves with coating, and is increased slightly for the basic design; for the high force design valves, the flow rates increases notably. Microvalves with coating exhibit the lowest change in leakage after fatigue testing, whereas an increase of 14% of leakage rates is observed for high force design valves, and a strong increase of 123% is found for valves of the basic design.  
Though standard deviations of the measured changes in leakage rates are high, a tendency of the stability of the tested designs can be deduced. Both design adaptions of the basic design, the coated as well as the high force design, show lower increase in leakage rates after the fatigue tests. The valve seat coated with Parylene-C seems to favor a good seal of the valve diaphragm to the seat even after fatigue. Comparing valves of the high force design to those of the basic design, the stiffer actuator capable of higher compression  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Microwave Design Variants** & **Fatigue Tested Valves** & **Piezoceramic Actuator Failures** & **Change of Max. Open Flow, 20 kPa** & **Change of NO Flow, 100 kPa** & **Change of Leakage, 20 kPa** \\ \hline Basic design & 5 & 3 & (\(-6\pm 3\))\% & (\(8\pm 4\))\% & (\(123\pm 62\))\% \\ Coated design & 5 & 2 & (\(-2\pm 2\))\% & (\(0\pm 11\))\% & (\(3\pm 13\))\% \\ High force design & 4 & 0 & (\(6\pm 4\))\% & (\(18\pm 8\))\% & (\(14\pm 15\))\% \\ \hline \end{tabular}
\end{table}
Table 3: Results of \(1\times 10^{6}\) actuation fatigue test. Listed as piezoceramic actuator failures are observed material failures of the PZT in form of cracks. Change in fluidic performance is given for valves with functional piezoceramic actuator.  
forces appears to exhibit higher robustness against fatigue testing regarding piezoceramic actuator failure as well as an increase in leakage rate. A larger number of samples for testing would be necessary for future studies to increase the statistical relevance of the results and further substantiate these findings.