Silicon Micropore-Based Parallel Plate Membrane Oxygenator

Abstract

Extracorporeal membrane oxygenation (ECMO) is a life support system that circulates the blood through an oxygenating system to temporarily (days to months) support heart or lung function during cardiopulmonary failure until organ recovery or replacement. Currently, the need for high levels of systemic anticoagulation and the risk for bleeding are main drawbacks of ECMO that can be addressed with a redesigned ECMO system. Our lab has developed an approach using microelectromechanical systems (MEMS) fabrication techniques to create novel gas exchange membranes consisting of a rigid silicon micropore membrane (SμM) support structure bonded to a thin film of gas-permeable polydimethylsiloxane (PDMS). This study details the fabrication process to create silicon membranes with highly uniform micropores that have a high level of pattern fidelity. The oxygen transport across these membranes was tested in a simple water-based bench-top set-up as well in a porcine in vivo model. It was determined that the mass transfer coefficient for the system using SµM-PDMS membranes was 3.03 ± 0.42 mL O₂ min^-1 m^-2 cm Hg^-1 with pure water and 1.71 ± 1.03 mL O₂ min^-1 m^-2 cm Hg^-1 with blood. An analytic model to predict gas transport was developed using data from the bench-top experiments and validated with in vivo testing. This was a proof of concept study showing adequate oxygen transport across a parallel plate SµM-PDMS membrane when used as a membrane oxygenator. This work establishes the tools and the equipoise to develop future generations of silicon micropore membrane oxygenators.

Keywords: -Artificial lung; -Heart lung bypass; -Respiratory assist device; -Silicon micropore membrane; Extracorporeal membrane oxygenator.

Figure 1

Schematic of the fabrication of the silicon micropore membranes (1A) and of the PDMS transfer process (1B) to achieve 3–5 micron thick PDMS layer bonded to the silicon micropore membranes

Figure 2

Diagram (A) and picture (B) of experimental setup to measure oxygen diffusion into water

Figure 3

The SμM membrane was fabricated with the windows of pores as seen under bright field and individual pores as seen by SEM imaging (A and B). A thin layer of PDMS was bonded to the surface of the membrane and imaging was accomplished with SEM (C). This shows both the rigid silicon support structure and a gas permeable membrane consisting of PDMS.

Figure 4

O₂ permeability for three separate flow cells ± SD. Combining all flow cells, average gas permeability was found to be 1.71 ml O₂ STP/min/m²/cm Hg ± 1.03 ml O₂ STP/min/m²/cm Hg (n=7 for each of the three flow cells).

Figure 5

Picture of flow cell with top and bottom half of the blood flow path exposed after in vivo test.

Figure 6

Comparison of model output with experimental water data (A, left) and experimental blood data (B, right) showing the partial pressure of oxygen at a particular water or blood flow rate at a certain sweep gas pressure before and after (both experimentally and model-predicted) the device.

Figure 7

Oxygen transport and pressure drop as a function of channel height showing increasing channel height results in less oxygen transport (starting O₂ concentration of 58 mm Hg) and a lower total pressure drop across the membrane portion of the device.