This diploma thesis presents design, development and implementation of a system for dosing of constant volumetric units of active drug ingredient (for example insulin). Implemented device should replace existing mechanical systems. The system was implemented using piezoelectric micropumps and a reservoir with a flexible membrane prototypes, recently developed in the LMSE (Laboratory of Microsensor Structures and Electronics). The main focus of presented thesis is on control electronic module, comprised of a microcontroller development board with touch-screen, a high voltage generator for driving the piezoelectric micropumps and a piezoresistive pressure sensor. During the dosing process, the piezoelectric micropump sucks drug ingredients from a reservoir, which is covered with a flexible membrane. The displaced volume causes a rise of vacuum pressure in the reservoir. This vacuum pressure is measured with a piezoelectric pressure sensor. The change of dosing volume can be calculated by monitoring the pressure drop and knowing the reservoir pressure vs. volume characteristic - also known as the reservoir characteristic. In addition to normal dosing operation, dedicated algorithms were programmed on a PC for accurate evaluation of reservoir characteristic. During measurement of reservoir characteristics, the micropump was replaced with a motorized syringe pump. The PC application synchronizes operation between microcontroller development board and a motorized syringe pump. Furthermore, this application also enables the download of calculated piecewise linear approximation description of reservoir characteristic to the microcontroller. For dispensing a single dose of active drug ingredient, the microcontroller initially measures the tank pressure. Based on this measurement, the tank characteristic piecewise linear approximation coefficients are evaluated and target tank pressure is calculated. The dosing process is stopped, when this target pressure value is achieved. Presented dosing approach is heavily dependent on quality of reservoir priming. Any residual air, contained in the dosing system causes a dosing error. Such residual air pockets can be detected by continuously monitoring the pressure drop - any sudden distortion in pressure drop will indicate presence of air in the system.
|
