POLYSULFONE COATING FOR HOLLOW-FIBER ARTIFICIAL LUNGS OPERATED AT HYPOBARIC AND HYPERBARIC PRESSURES

Carbon dioxide transfer is increased when the gas phase of a hollow fi ber membrane lung is operated at hypobaric pressures. Oxygen transfer is augmented by hyperbaric pressures. However, uncoated hollow fibers transmit gas bubbles into the blood when operated at a pressure greate r than 800 mmHg and may have increased plasma leakage when operated at hypobaric pressures. Ultrathin polymer coatings may avoid this proble m while reducing thrombogenicity. The authors coated microporous polyp ropylene hollow fibers with 380 mu m outer diameter and 50 mu m walls using 1, 2, 3, and 4% solutions of polysulfone in tetrahydrofuran by d ipping or continuous pull through. These fibers were mounted in small membrane lung prototypes having surface areas of 70 and 187 cm(2). In gas-to-gas testing, the longer the exposure time to the solution and t he greater the polymer concentration, the less the permeation rate. Th e 3% solutions blocked bulk gas flow. The coating was 1 mu m thick by mass balance calculations. During water-to-gas tests, hypobaric gas pr essures of 40 mmHg absolute were tolerated, but CO2 transfer was reduc ed to 40% of the bare fibers. Hyperbaric gas pressures of 2,100 mmHg a bsolute tripled O-2 transfer without bubble formation.