Biocompatibility of Membrane-Based Therapeutic Treatments

Inadequate membrane biocompatibility elicits a variety of responses, including activation of the coagulation and complement system, activafion of platelets and leukocytes, production of cytokines and free oxygen radicals, and accumulation of bradykinin. Although they initiate locally, these responses cause systemic changes to the blood and the body behavior. They may also change the surface and transport properties of the membranes used. However, it should be recalled that the treatment of bio(in)compatibility is not solely related to the biomaterials used but rather depends also on the blood fluid dynamics in the membrane device and the whole extracorporeal blood circulation loop, as well as on how blood is handled in extracorporeal circulation. 

Blood clotting at artificial surfaces has been, and still is, a major problem in extracorporeal blood treatments. Within milliseconds fi om blood contact with an artificial surface, plasma proteins (e.g., fibrinogen) adsorb on it (Basmadjian et al. 1997), the intrinsic coagulation pathway is activated, platelets adhere to the surface or aggregate and release factors that further activate the intrinsic coagulation pathway, thus promoting thrombogenesis. 

Complement activation has been associated with leukostasis in the pulmonary vasculature, granulocytopenia, anaphylactoid reactions, hypotension, pyrogenic reactions, amyloid formation in the joints of long-term renal patients, and cardiopulmonary complications (Chenoweth, 1988). This has led to the development of surface-modified RC membranes less complement activating (see Section 18.4.1.2). However, the controversial results obtained in many reported clinical trials comparing treatments of renal failure with membranes known to activate or not to activate complement have not yet shown a significant impact on patients mortality or morbidity. 

3 Drug-Mediated Amplification of Contact-Phase Activation 

T parameter related to tortuosity accounting for the fact that the diffusive path length is greater than membrane thickness 

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