Membranes in Extracorporeal Blood Oxygenation Technology

Abstract

The development and implementation of the extracorporeal membrane oxygenation (ECMO) technique for the treatment of patients in critical conditions make it possible to effectively and safely support gas exchange processes in the blood for a long time. One of the main components of the ECMO unit is a gas permeable membrane which is a barrier separating the blood from the gas phase. Since the 1950s, the development of this technology has been aimed at improving the safety and duration of use of membranes, which led to the creation of oxygenators that provide life support for several weeks. This review is devoted to the development of the extracorporeal membrane oxygenation technology including the choice of materials, methods to improve their hemocompatibility, and approaches to the design of the membrane contactor.

The Evaluation of the Hemocompatibility of Polymer Membrane Materials for Blood Oxygenation

“…One of the most effective methods for the treatment of acute respiratory failure is extracorporeal membrane oxygenation (ECMO) or "iron lung" based on providing a systemic bloodstream using a centrifuge pump and extracorporeal oxygen saturation of blood and elimination of carbon dioxide dissolved in blood using membrane gas exchange [1,2]. This technology is used for life support when conducting longterm open-heart surgeries; when performing heart, lung, liver, and cardiopulmonary complex transplant surgeries as well as in case of traumas associated with massive blood loss [1].…”

“…The key element of modern ECMO technology is an oxygenator, a hollow-fiber membrane contactor, in which a polymer membrane in the form of a hollow fiber separates gas (oxygen or air) and liquid (blood) phases [1,2]. Generally, a gas flow is supplied onto the internal surface of the fiber, and the external surface of the membrane is washed with blood.…”

“…The efficiency and duration of operation of an ECMO oxygenator directly depend on the properties of the material such as hemocompatibility (absence of structural and functional abnormalities of the cells of blood and its plasma composition upon contact with the material) and thromboresistance (the prevention of spontaneous coagulation of blood and formation of blood clots on the surface of the material). So-called diffusion membranes (generally, composite), in which a thin nonporous (diffusion) layer of a hemocompatible polymer is applied onto the surface of porous hollow fibers are used for the long-term (up to several days and even weeks) applications of ECMO technology [2]. Oxygen that passed through the polymer membrane dissolves in blood in the molecular form by the dissolution-diffusion mechanism, while carbon dioxide dissolved in blood desorbs through the membrane to the gas phase.…”

“…Oxygen that passed through the polymer membrane dissolves in blood in the molecular form by the dissolution-diffusion mechanism, while carbon dioxide dissolved in blood desorbs through the membrane to the gas phase. The efficiency of oxygen transport to blood and transfer of carbon dioxide in the diffusion mode depends on the surface area of the membrane and permeability of the surface diffusion layer of the polymer, e.g., its thickness and permeability of the polymer material [1,2]. In state-of-the-art oxygenators, polypropylene or polymethylpentene (PMP) is generally used as the porous hollow fiber [1,2], while various modifications of cross-linked polydimethylsiloxane (PDMS) with grafted biocompatible thromboresistant coatings containing heparin or phosphoryl choline are used as the material of the diffusion coating [1,2], which makes it possible to achieve the duration of operation of some oxygenators of up to 30 days upon performing ECMO [2].…”

“…(1) For PDMS, the following upper boundary of permeability is specified in the published sources [7]: oxygen permeability coefficient P(O 2 ) = 600 Barrer (1 Barrer = 10 −10 cm 3 (STP) cm cm −2 s −1 cmHg −1 ), although this value may be substantially lower in the real material of the coating due to the different densities of the crosslinks. Here, other materials currently applied for continuous layers have substantially lower oxygen and carbon dioxide permeability coefficients [2].…”