A scalable microfluidic extraorporeal lung assist device for preterm neonates
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Respiratory distress syndrome is a leading source of morbidity and mortality in preterm infants. The pathophysiology of Respiratory Distress Syndrome (RDS) is centered on decreased lung compliance secondary to insufficient surfactant production. Treatment of severe RDS is currently managed with mechanical ventilation, which has shown decreases in mortality. However, mechanical ventilation is also associated with complkations due to barotrauma, volutrauma, and 02 toxicity, which can lead to irreversible lung injury or death in an immature lung. Extracorporeal membrane oxygenation (ECMO) is a system that oxygenates blood independently from the lungs and allows the lungs to continue to mature undisturbed. ECMO has shown potential for being an effective neonatal respiratory assist device, but current designs are limited by low surface area-to-volume ratios of the blood-gas interface, increased risk of thromboembolic events, and plasma-protein leakage through membrane pores. Microelectromechanical systems (MEMS) is a new technology that can be used to fabricate channels that mimic lung vasculature. Studies have shown that ECMO made with MEMS technology can be designed to provide high surface area-to-volume ratios of the blood gas interface and decreased shear-stress of blood flow. However, no study has been able to attain physiologically-relevant levels of blood oxygenation due to limits in blood flow. Preterm neonates have a cardiac output of approximately 221 ml/min/kg. To design an ECMO device for clinical use, it must be able to ultimately achieve flow rates that match the cardiac output of preterm neonates. Additionally, adequate oxygenation must be achieved at physiologically relevant flow rates. This study characterizes the effects of blood flow rate on oxygenation through a MEMS ECMO device and investigates the potential to scale this device to reach physiologically relevant blood flow rates in preterm neonates. The MEMS ECMO devices were fabricated by etching vascular patterns on silicon wafers with photolithography. The processed silicon wafers were subsequently used as casts to imprint the vascular pattern onto PDMS. A PDMS oxygen chamber separated by a semi-permeable membrane was attached to the vascular channels by using plasma bonding. This study reports on the verification of oxygen transfer rates and oxygen concentration as a function of blood flow rates across devices constructed from two vascular channel depths. For both channel depths, oxygen transfer rates increased with increased flow rates while oxygen concentration decreased with increasing flow rates. A novel approach to the scaling of an ECMO device was also developed. The design and fabrication of the new device capable of higher blood flow rates is reported.
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