The present invention provides a device for concentrating a blood fraction. The device includes an ultrafiltration unit connected to a fluid delivery system for delivering the blood fraction to be concentrated into the ultrafiltration unit. The device also includes a purge fluid delivery system for expelling concentrate from the ultrafiltration unit. In one embodiment, the device accommodates multiple cycles of concentration. A blood fraction concentration method is also provided. The device and method of the present invention are particularly useful for preparing a plasma concentrate suitable for use in a coagulum-based wound sealant.