# Piezoelectric Silicon Micropump for Drug Delivery Applications
## 4 Conclusions  
In the presented preliminary experiments, the introduced piezoelectric micro diaphragm pump proves well adapted for drug delivery applications. Its relatively large compression ratio (compared to other state of the art MEMS pumps) enables self-priming as well as the transport of bubbles, though the dosing precision is not independent of bubbles. The fluidic performance meets the requirements of microfluidic drug delivery. The water flow rate of 74 uL/min \(\pm\) 6 uL/min allows the delivery of 10 U of insulin (0.1 mL drug solution) within 45 s, which is in the same range as macroscopic automated dosing units on the market [24]. The blocking pressure of 51 kPa of the pumps is high enough to overcome the physiological backpressure as well as additional flow restrictions due to clogging of the injection site. The pumps show a high repeatability of package dosing. However, the precision decreases slightly with insulin compared to the transport of DI water. The higher surface tension of insulin solution increases the pressure necessary to transport air bubbles through the chamber. The decrease of precision shows that a pump that doses more independently from bubbles is desirable for the transport of insulin solution. Such a fluidic actuator can be achieved with design modifications towards a further decrease of the valve's capillary pressure and a higher compression ratio. The increased compression ratio requires a smaller pump chamber to decrease the dead volume. In future design adaptations, the compatibility of such a pump with higher concentrated drugs, and therefore, liquids with a higher viscosity, needs to be evaluated carefully. In subsequent development steps, the integration of our pump with a miniaturized, capacitive volume control will enable closed-loop control of the dosing unit, which allows for higher dosing accuracy even with occurring disturbances. Nevertheless, the presented experimental results already show that even small packages of approximately 0.5 mg are dosed as precise as commercial pumps dose larger packages of 5 mg. Hence, the 5 \(\times\) 5 mm\({}^{2}\) silicon micropump is suitable for a precise dosing of a U100 insulin. Furthermore, this high precision enables a combination with higher concentrated drugs, which limits the needed reservoir size as well as reduces the volume to be dosed. This enables a lower energy consumption and therefore smaller batteries. Hence, the overall size of the delivery device can be significantly reduced. The development of small and comfortable patch pumps or even implantable systems is therefore attainable. Conceptualization, A.B., J.H., H.L. and M.R. ; methodology, A.B. and M.W. ; software, M.W. and D.Z. ; validation, A.B., M.W. and D.Z. ; formal analysis, A.B., H.L., M.W. and D.Z. ; investigation, A.B., Y.C. and D.Z. ; resources, A.B., Y.C., H.L., M.R. and M.W. ; data curation, M.W. and D.Z. ; writing--original draft preparation, A.B., H.L. and D.Z. ; writing--review and editing, A.B., J.H., M.R., H.L., M.W. and D.Z. ; visualization, A.B., M.W. and D.Z. ; supervision, J.H. and M.R. ; project administration, A.B. and H.L. ; funding acquisition, A.B., H.L. and M.R. All authors have read and agreed to the published version of the manuscript. This research is part of the Moore4 Medical project, which has received funding within the Electronic Components and Systems for European Leadership Joint Undertaking (ECSEL JU) in collaboration with the European Union's H2020 Framework Program (H2020/2014-2020) and National Authorities, under Grant Agreement H2020-ECSEL-2019-IA-876190 www.moore4 medical.eu (accessed on 27 August 2021). Not applicable. The actuator stroke and fluidic test data that support the findings of this study are available in Fordatis--Research Data Repository of Fraunhofer-Gesellschaft with the identifier [[http://dx.doi.org/10.24406/fordatis/143](http://dx.doi.org/10.24406/fordatis/143)]([http://dx.doi.org/10.24406/fordatis/143](http://dx.doi.org/10.24406/fordatis/143)) (accessed on 27 August 2021).