The present invention provides a medical device and a method for the selective separation of a biological sample of a mammal into a first portion and a second portion. It comprises a first layer comprising a first reservoir for receiving the biological sample and for retaining the first portion of the sample, and a second layer comprising a second reservoir for receiving the second portion of the sample. Between the first layer and the second layer a third layer is provided, wherein the third layer comprises a plurality of channels configured to provide a fluid communication between the first reservoir and the second reservoir. Furthermore, between the first layer and the second layer a fourth layer adjacent to the third layer is provided, wherein the fourth layer comprises and/or is configured as a separation layer. At least the third and fourth layer are configured to selectively separate the biological sample between the first reservoir and the second reservoir into the first portion and the second portion of the sample. According to the invention, the layers are to be understood to be stackable in a substantially vertical plane, forming a three-dimensional layered structure.