Ambulatory Lung Assist Device Oxygenates and Removes Carbon Dioxide from Blood Across a Silicone-Coated Porous Membrane
David M. Hoganson1, Jennifer Anderson1, Brian Orrick2, Joseph P. Vacanti1; 1Massachusetts General Hospital, Boston, MA; 2Alito Therapeutics, Boston, MA
Comment on this Abstract
Objective: Transplantation is a current treatment for patients with end stage lung disease. An implantable lung assist device would allow ambulation and hospital discharge and is currently under development as a bridge to or an alternative to lung transplantation. The device has a gas permeable membrane that exchanges oxygen and carbon dioxide between a gas chamber and blood in a network of channels which were computationally designed to replicate the function of a vascular network. Optimizing the membrane material is critical to achieve adequate gas transfer, minimize size of the assist device and avoid plasma leakage.
Methods: In-vitro testing of the lung assist device (18cm2 surface area) was performed with three different membranes. An uncoated porous polycarbonate (PC) membrane (1.0μm pores, 12μm thick) was used as a control membrane as it has excellent gas transfer but is unacceptable for this application as it allows some plasma leakage. Two fluid impermeable membranes, a thin silicone membrane (63μm thick) and a silicone-coated porous PC membrane (1.0μm pores, 14.8μm thick with coating) were tested as potential membranes for the device. Anticoagulated porcine blood was pumped through the channel network of the lung assist device while oxygen flowed through the gas chamber (40ml/min). Gas transfer was assessed at blood flow rates of 0.6, 1.0, 2.0, 4.0 and 8.0 ml/min using blood gas analysis (n=4 for each flow rate and membrane type).
Results: The oxygen transfer was similar between all groups and increased with increasing blood flow. For the silicone-coated PC membrane, oxygen transfer varied from 0.05 +/- 0.01 to 0.24 +/- 0.19 ml/min, similar to the uncoated PC membrane (0.05 +/- 0.01 to 0.21 +/- 0.1 ml/min) and the silicone membrane (0.05 +/- 0.01 to 0.25 +/- 0.08 ml/min) for the given blood flow range. The carbon dioxide transfer through the lung assist device is shown in Figure 1. An effective lung assist device may need to remove 20% of CO2 generated at rest or 50 ml/min of CO2. With the silicone coated porous membrane, the lung assist device would have 0.64 m2 surface area and 1.4 L/min blood flow.
Conclusion: The lung assist device with a silicone-coated porous membrane oxygenates and removes carbon dioxide at rates similar to an uncoated porous membrane. A scaled-up version of this technology may serve as a bridge to or an alternative to lung transplantation for patients with end stage lung disease and become a platform for the development of a tissue engineered lung.
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