Development and in vitro evaluation of a flow-adjustable elastic drug infusion pump

Passive-type drug infusion pumps have several advantages over active-type pumps including a simple drug chamber structure and relatively high operational stability. However, conventional passive-type infusion pumps also have several limitations compared to active ejection pumps, such as a fixed flowrate and monotonic flow pattern. To enhance the clinical feasibility of using passive-type drug infusion pumps, flow readjustment and flow regulation abilities are needed. This paper proposes a new portable elastic drug infusion pump that integrates the advantages of active and passive infusion pumps to improve clinical feasibility. The proposed infusion pump incorporates a passively driven drug chamber and an actively adjusted flow controller, which can adjust and regulate various target flowrates and adjust the flow pattern in accordance with the patient's time-varying physiological status. The proposed infusion pump uses the contraction force of an expanded elastic membrane to extract the drug from the drug chamber for delivery into the patient's body through an outlet catheter. It also utilizes a flow sensor, a flow resistor, and a motor-driven flow restrictor that can monitor the real-time flowrate through the outlet catheter and automatically regulate the actual flow-rate around the target value. Experiments on the proposed system resulted in actual injection rates of 0.49 +/- 0.03 (mean +/- standard deviation), 0.98 +/- 0.03, 1.49 +/- 0.04, and 1.99 +/- 0.03 ml/h when the target injection rate was set to 0.5, 1.0, 1.5, and 2.0 ml/h, respectively. During the entire period of operation from the fully filled state to the totally empty state, an inner-chamber pressure of >100 mmHg was maintained, which shows that the proposed infusion pump can stably maintain its target flowrate as the amount of drug remaining to be injected decreases. It appears that the proposed drug infusion pump can be applied to a wide variety of patient treatments that require short-term, accurate, and stable drug delivery.