The membrane inner surface plays a crucial role in the anti-coagulation requirements of the patient during treatment, because this surface directly contacts the patient's blood. There are many possibilities to reduce the activation of the coagulation system. Among them, we have improved the membrane by creating a hydrophilic gel layer on the membrane surface, to which optimum conditions of hydrophilic agent including its concentration are applied.

If platelets directly touch a membrane surface, it is possible to stimulate platelet activation, leading to platelet adhesion to the membrane surface. The coagulation system is also highly susceptible to such activation. The hydrophilic gel layer on the APS membrane inner surface is designed to cushion the platelets and other blood components from activation caused by blood-membrane interaction.