Abstract: A system is disclosed for priming an ultrafiltration unit (10) connected to a blood source, without requiring a pump in the blood line. An ultrafiltration unit (10) is provided having an ultrafiltration membrane which separates a blood compartment from an ultrafiltrate compartment, a blood inlet port (12), a blood outlet port (14), a second inlet port (16) communicating with the ultrafiltrate compartment, and an ultrafiltrate outlet port (18). A feedback tube (38) connects the blood outlet port (14) to the second input port (16). Priming solution (36) is introduced to the blood inlet port (12) and a vacuum is applied to the ultrafiltrate outlet port (18). The priming solution (36) is drawn through the blood compartment, through the ultrafiltrate compartment, out the ultrafiltrate outlet port, and to drain.

Abstract: A bundle (12) of hollow fiber (34) is formed by winding a length of hollow fiber around a core (38) from an arm (20) that is in a plane at an acute angle with respect to the longitudinal axis of the core and is between opposite ends of the core. Relative rotation is provided between the longitudinal axis of the core and the position of the winding arm. During winding of the hollow fiber around the core, there is an increase in the ratio of (a) the angular velocity of the wind and (b) the relative rotational velocity between the longitudinal axis of the core and the position of the winding arm. In this manner, the void fraction of radially-outward annuli of the wound bundle is less than the void fraction would be if the ratio remained constant.