Pulse-driven microfluidic pumps with varying depth flow channels for fine flow rate tuning*

The delivery of liquid pharmaceuticals across the skin has been based on powered infusion pumps and syringes for over half a century. Both types of devices pose significant limitations for patients, including injection site pain, bulkiness, and embarrassment. To address some of these limitations, we have developed featherweight, wearable, arterial pulse-driven microfluidic infusion pump devices. Small changes in microfluidic channel design parameters like channel length and width have sometimes resulted in a change in the character of the correlation between the driving heart rate and blood pressure and the resulting device flow rate. To address this, we allowed the channel depth to vary along its length, hypothesizing that this would result in finer control over the precise flow rate produced by a given device. To test this hypothesis, we developed a pump prototype with a slanted channel with a depth varying from 40 to 80 μm that yielded a constant flow rate of 0.2 μL/s regardless of the driving heart rate or blood pressure. The results from this device provide evidence that varying-depth flow channel devices may expand the number of achievable flow rates in our devices, compared to constant depth devices, allowing for finer control over device flow rates.