Piezoelectric Normally Open Microvalve with Multiple Valve Seat Trenches for Medical Applications

Claudia Patricia Durasiewicz,Wolfgang Hölzl,Sophia Thekla Güntner,Gabriele Schrag,Philipp Klaus Maier

doi:10.3390/app11199252

Abstract

Microfluidic systems for medical applications necessitate reliable, wide flow range, and low leakage microvalves for flow path control. High design complexity of microvalves increases the risk of possible malfunction. We present a normally open microvalve based on energy-efficient piezoelectric actuation for high closing forces and micromachined valve seat trenches for reliable valve operation. A comprehensive investigation of influencing parameters is performed by extensive fluidic 3D finite element simulation, derivation of an analytical closed state leakage rate model, as well as fabrication and test of the microvalve. Additional valve seat coating and a high force actuator are introduced for further leakage reduction. The microvalve has a wide-open flow range as well as good sealing abilities in closed state. Extensive fatigue tests of 1 × 106 actuation cycles show that additional coating of the valve seat or increased actuator strength promote sealing performance stability. Analytical calculations of leakage are suitable to estimate experimentally obtained leakage rates and, along with computational fluidic dynamic (CFD) simulations, enable future microvalve design optimization. In conclusion, we demonstrate that the presented normally open microvalve is suitable for the design of safe and reliable microfluidic devices for medical applications.

Highlights

While passive microvalves show diode-like fluid path opening at forward pressure and closing at backwards pressure [3] or serve as constant flow regulators [4], active microvalves based on piezoelectric [5,6], shape memory alloy [7,8], phase change [9,10], or other actuation mechanisms [3] allow for opening and closing of fluid paths in an arbitrary, flexible and dedicated manner
This work provides a detailed investigation of normally open (NO) microvalve development for medical applications, where many intricate requirements in flow performance, biocompatibility, hermetic sealing, and device reliability call for sophisticated solutions
We introduce a piezoelectric microvalve with multiple trenches serving as a valve seat and omit any movable soft sealing components in the valve chamber as an important step towards the reliable operation of the microfluidic device

Summary

Introduction

Microfluidic systems for lab-on-chip applications, implantable or wearable medical devices often necessitate active flow path control that is achieved by using microvalves [1,2].While passive microvalves show diode-like fluid path opening at forward pressure and closing at backwards pressure [3] or serve as constant flow regulators [4], active microvalves based on piezoelectric [5,6], shape memory alloy [7,8], phase change [9,10], or other actuation mechanisms [3] allow for opening and closing of fluid paths in an arbitrary, flexible and dedicated manner. External control of active microvalves enables functionalities like controlled dosing of drugs [11,12], mixture of reagents [10,13], confinement of a high pressure fluid to other volumes [14,15], as well as handling of small fluid volumes in medical devices and implants [16,17,18,19,20] Such active flow path control can be achieved by piezoelectrically actuated microvalves, which are either of normally open (NO) or normally closed type, defined by their function in a non-actuated state [3], and typically consist of a piezoactuator, a valve diaphragm, and a valve seat [2]. Medical applications like wearable drug dosing devices or implants require hermetic sealing of the device, low risk of component failure, as well as biocompatibility of all wetted surfaces [21]

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Results

Conclusion