A MEMS electrochemical bellows actuator for fluid metering applications

Abstract

We present a high efficiency wireless MEMS electrochemical bellows actuator capable of rapid and repeatable delivery of boluses for fluid metering and drug delivery applications. Nafion®-coated Pt electrodes were combined with Parylene bellows filled with DI water to form the electrolysis-based actuator. The performance of actuators with several bellows configurations was compared for a range of applied currents (1-10 mA). Up to 75 boluses were delivered with an average pumping flow rate of 114.40 ± 1.63 μL/min. Recombination of gases into water, an important factor in repeatable and reliable actuation, was studied for uncoated and Nafion®-coated actuators. Real-time pressure measurements were conducted and the effects of temperature, physiological back pressure, and drug viscosity on delivery performance were investigated. Lastly, we present wireless powering of the actuator using a class D inductive powering system that allowed for repeatable delivery with less than 2 % variation in flow rate values.

Figure 1

Illustration of operation concept of electrochemical bellows actuator. Actuator is shown housed within a reservoir to illustrate the case of fluid metering through an attached catheter.

Figure 2

Illustration detailing the electrode and bellows fabrication processes and bellows actuator assembly. A 2 convolution bellows is shown.

Figure 3

Photograph of: (a) Pt electrolysis electrode, (b) 2 convolution Parylene bellows, (c) assembled bellows actuator.

Figure 4

Circuit schematic for class D wireless inductive powering system.

Figure 5

(a) Real-time pressure measurements of a 2 convolution Nafion®-coated bellows actuator under constant current application; (b) Slope values for real-time pressure vs. time for different current values.

Figure 6

Comparison between recombined volume for uncoated and coated electrodes: (a) current controlled (10 mA) delivery for different ON/OFF times (Sheybani, Gensler et al. 5-9 June 2011) and (b) time controlled (2 min) flow rate delivery at different applied currents.

Figure 7

Comparison between rapid-fire bolus delivery using uncoated and coated 2 convolution bellows actuators (3 boluses at 10 mA, 15 sec ON/10 sec OFF, separated by 5 min OFF cycles (Sheybani, Gensler et al. 2011)).

Figure 8

Bolus delivery with a Nafion® coated, 2 convolution bellows actuator (at 10 mA current, 15 sec/1 min ON/OFF, modified from (Sheybani, Gensler et al. 2011)).

Figure 9

Bolus delivery with a Nafion® coated, 2 convolution bellows actuator (at 10mA current, 2 sec/1 min ON/OFF), inset: close-up for first 10 boluses delivered.

Figure 10

Bolus delivery using an actuator with an in-line check valve (at 10 mA current, 15 sec ON/ 60 sec OFF). After 15 boluses, the actuator is turned off. Inset shows average accumulated volume for 15 boluses.

Figure 11

Flow delivery results for of different viscosities of propylene glycol (at 8 mA constant current).

Figure 12

Current controlled flow delivery of cocaine (in 0.9 N saline) loaded in a pump at different concentrations (at 8 mA, 1.5 convolution bellows, modified from (Sheybani, Gensler et al. 2011)).

Figure 13

Flow delivery results for a range of physiologically relevant back pressures (at 5mA constant current).