Conductive polylactic-acid filament for dose monitoring in syringe-less wearable infusion pump

We have demonstrated the use of conductive polylactic acid (PLA) filament for dose monitoring in a syringe-less wearable infusion pump. A channel reservoir is inlaid with conductive PLA filament. As the liquid medium is dispensed via gas pressurization by an built-in electrolysis chamber, the effective impedance of the conductive PLA filament/liquid medium column changes as well. This allows the dispensed volume to be monitored via the output voltage across a series resistor. Using 5 V sinusoidal input voltage, the output voltage decreased from ∼1.3 to ∼0.13 V as the dispensed volume of 0.1 mol/L PBS increased from 0 to 1000 μL. Similarly, the output voltage for insulin analog decreased from ∼0.64 to 0.126 V for the same volume displaced. Repeated dispensing runs with 0.1 mol/L PBS showed good consistency (standard deviation less than 10 mV). The rate of change of the output voltage with elapsed time varied accordingly for the different flow rates (0.25–1.00 mL/h or ∼4–17 μL/min). At electrolysis voltages of 1.5 and 5 V, the respective output voltage were 1.04 and 0.33 V. These corresponded to flow rates of ∼3 and 10 mL/h (∼50 and 160 μL/ min).