# Piezoelectric Silicon Micropump for Drug Delivery Applications
###### Abstract  
Subcutaneous injection is crucial for the treatment of many diseases. Especially for regular or continuous injections, automated dosing is beneficial. However, existing devices are large, uncomfortable, visible under clothing, or interfere with physical activity. Thus, the development of small, energy efficient and reliable patch pumps or implantable systems is necessary and research on microelectromechanical system (MEMS) based drug delivery devices has gained increasing interest. However, the requirements of medical applications are challenging and especially the dosing precision and reliability of MEMS pumps are not yet sufficiently evaluated. To enable further miniaturization, we propose a precise 5 \(\times\) 5 mm\({}^{2}\) silicon micropump. Detailed experimental evaluation of ten pumps proves a backpressure capability with air of 12.5 \(\pm\) 0.8 kPa, which indicates the ability to transport bubbles. The maximal water flow rate is 74 \(\pm\) 6 \(\mu\)L/min and the pumps' average blocking pressure is 51 kPa. The evaluation of the dosing precision for bolus deliveries with water and insulin shows a high repeatability of dosed package volumes. The pumps show a mean standard deviation of only 0.02 mg for 0.5 mg packages, and therefore, stay below the generally accepted 5% deviation, even for this extremely small amount. The high precision enables the combination with higher concentrated medication and is the foundation for the development of an extremely miniaturized patch pump. micropump; piezoelectric diaphragm pump; drug delivery; microdosing; patch pump; insulin delivery +
Footnote †: journal: Applied Physics Letters  
1 Fraunhofer EMFT Research Institution for Microsystems and Solid State Technologies, 80686 Munich, Germany; [EMAIL_ADDRESS] (H.L. );  
[EMAIL_ADDRESS] (D.Z. );  
[EMAIL_ADDRESS] (M.W. );  
[EMAIL_ADDRESS] (Y.C. );  
[EMAIL_ADDRESS] (M.R.) [EMAIL_ADDRESS] (M.R.) [EMAIL_ADDRESS] (M.R.) [EMAIL_ADDRESS] (M.R.) [EMAIL_ADDRESS] (M.R.) marin.richter@emft. leads to a better therapeutic result with limited side effects for specific cancer treatments and studies show that a delivery adapted to the circadian rhythm is beneficial [7,8]. Even though research pushes towards automated, small dosing units for patch applications or implantation, there is still improvement necessary [9]: existing patch pumps for insulin delivery are large enough to be visible under clothing. Furthermore, the accuracy of currently available pumps is lower compared to durable pumps [10, 11, 12, 13]. The improvement of the dosing accuracy as well as further miniaturization is therefore desirable. The drug delivery application demands for well-adapted properties under challenging conditions [9]. The device needs to be utmost reliable with high dosing accuracy and dosing stability, even against backpressure. In addition to demanding fluidic requirements, patch pumps need to be cost-efficient, since they are often at least partly disposable and need to compete with the cost of conventional therapy. Further miniaturization of delivery systems is possible based on micropumps that enable small and lightweight systems for energy efficient delivery. Since the production is mostly based on standard, large scale processes, e.g., MEMS processes, costs are low if production numbers are sufficiently high. However, the use of micropumps implies new challenges. For instance, the transport of air bubbles that is usually unproblematic for macroscopic actuators, can lead to the failure of a micro diaphragm pump, since air is compressible and acts as a fluidic capacitance in the chamber of the displacement pump [14]. Additionally, surface tension becomes extremely relevant and the microfluidic actuator needs to be capable of moving the liquid meniscus through the system while overcoming resulting capillary forces [15, 16, 17]. Bubble tolerance of diaphragm pumps can be achieved with adapted designs towards a large compression ratio, the ratio between displaced volume and dead volume, that enables to overcome high air backpressure [14].