# Dry Test Methods for Micropumps
## 1 Introduction
Alternatively, functional testing with gas is an attractive approach for several types of microfluidic devices, notably passive flow regulators [17], micropumps [18; 19], gas sensing [20; 21], or gas flow sensors [22; 23]. The functional testing of BioMEMS can be therefore a critical risk for the project, and the associated cost may be not compatible with the reimbursement strategy of the medical device. Determining the functional test approach during the early development phase can be a determinant factor to market the device. An interesting example is the functional testing approach for pin-constrained biochips. Indeed, the increase in density and surface area of biochips generates, as for integrated circuits, higher defect densities, which reinforce the need for postproduction tests. [PERSON] et al. developed innovative techniques that address fundamental biochip operations, such as droplet dispensing, droplet transportation, mixing, splitting, and capacitive sensing. Functional testing is performed through parallel droplet pathways and leads to qualified regions where synthesis tools can map microfluidic functional modules [24]. The present paper describes the Design-for-Testability of an insulin micropump dedicated to type 1 diabetes care. Diabetes is a chronic, metabolic disorder characterized by high blood sugar levels (hyperglycemia), which leads to severe damage over time. Type 1 diabetes, also known as insulin-dependent diabetes, is a chronic condition in which the beta cells of the pancreas produce little or no insulin. For people with type 1 diabetes, daily insulin administration is essential for their survival. Traditionally, the most common route of insulin administration in patients with diabetes is by subcutaneous injection using an insulin syringe or a pen. The most advanced insulin delivery systems are patch pumps that deliver, through a thin cannula placed subcutaneously, rapid-acting insulin 24 h a day to match body requirements. These pumps can be programmed to deliver basal and bolus insulin doses. The rates of basal insulin delivery can be programmed based on individual patient requirements. Insulin pumps can also deliver bolus insulin to minimize postmeal high blood sugar level excursions [25]. Recent trends include connectivity to a Continuous Glucose Monitoring system (CGM) that transmits glucose readings to the device. The artificial pancreas or closed-loop system consists of an automated insulin delivery system, a CGM, and an insulin delivery algorithm. Such a system aims to deliver a continuous and precise dose of insulin to mimic physiologic insulin secretion by the pancreatic beta cells [26]. Hemoglobin A1C and glucose control are better controlled, and the daily insulin dosage is reduced together with hypoglycemia risk and glycemic variability to ultimately improve patient satisfaction and quality of life. The device considered here is a disposable MEMS micropump powered by a piezo actuator. The system is a membrane micropump with two passive check valves. Due to the high potency of insulin, the production test will verify that the system presents any risks of over- and under-delivery during use. Figure 1 presents an exploded view of the volumetric piezoelectric micropump with two passive check valves considered here to illustrate the Design-for-Testability method [27; 28]. The micropump can deliver basal insulin in increments of 0.02 units (U) of U100 insulin per hour with high accuracy. Each pump stroke infuses 0.2 microliters of insulin with a maximum error of 3%, making it compatible with a highly concentrated insulin formulation (up to 500 U/mL (U-500) insulin). The device is made of a triple stack of wafers bonded together by Au-Au thermocompression: one silicon-on-insulator plate with the micromachined pump and valve structures and top and cover silicon plates with through holes (see Figure 1). Two square silicon membranes comprising piezoresistive strain gauges obtained by boron implantation are used to measure the pressure in the pumping chamber and at the outlet of the micropump.