# Piezoelectric Silicon Micropump for Drug Delivery Applications
###### Abstract
To enable the use of micropumps for drug delivery application, a sufficient dosing accuracy has to be guaranteed. However, up to date, micropumps presented in research are not tested extensively with respect to their dosing precision and reliability [9]. The only extensively tested, MEMS based patch pump system is the Jewel Pump developed by DeBiotech. The integration of a double limiter concept, several pressure sensors and the pre-tension of the passive flap valves enable stable dosing even at varying temperature, inlet and outlet pressure, or medium's viscosity as well as a quick error detection [18, 19, 20]. [PERSON] et al. [13] confirm a high dosing accuracy compared to other insulin pump systems, and an exceptionally fast error detection. To further evaluate the usability of micropump based delivery systems, a detailed experimental characterisation of the fluidic properties, as well as the dosing precision and robustness of the fluidic actuator are necessary. However, the little volume of dosed packages and the small measured flow rates make an experimental evaluation extremely challenging. The norm IEC 60601-2-24 [21] regulates the assessment of dosing accuracy for drug dosing devices, also including patch pumps. Unfortunately, the proposed gravimetric measurement is not described in detail and data are to be presented in a trumpet curve, which is often criticised by the scientific community [22]. In addition, the norm allows for a run-in period of up to one day that does not reflect the clinical application where accurate dosing is required at all times [22, 23]. Hence, several improvements to the experimental assessment of dosing accuracy are proposed to evaluate insulin delivery systems: It is common to depict the average deviation of the dosed volume within a given observation time, or the accuracy of single doses [10, 11, 12, 13, 23, 24, 25]. While optical flow detection that evaluates the volume in an accurate capillary is also used [25], most studies rely on gravimetric measurements [11, 13, 23]. It is necessary to minimize the influence of evaporation and condensation, both to cover the surface of the reservoir with oil [11, 13, 23] as well as an evaporation trap are adequate methods [26]. Furthermore, hydrostatic pressure can influence the measurement, which is why the inlet and outlet reservoir should be levelled [23]. Even if drift is prevented with all means, drift correction is indispensable for accurate data analysis. In this work, we use a gravimetric measurement based on the introduced studies to evaluate the dosing precision of our piezoelectric micropump. The 5 \(\times\) 5 \(\times\) 0.6 mm\({}^{3}\) small pump is specifically designed for the requirements of drug delivery, including fluidic performance such as flow and pressure capability, as well as the ability to transport bubbles. The precision of package dosing is investigated with water and insulin solution. Therewith, we evaluate the reproducibility of bolus dosing and investigate additional challenges caused by the change of the transported medium. This preliminary study is designed to investigate a general feasibility and reveal necessary improvements. The accuracy of an integrated pump in a closed-loop controlled dosing unit is the subject of subsequent studies.