Embodiments of the invention provide a gravity-fed blood purifier device for removing waste particles from blood. In one embodiment, the blood purifier device includes a pair of end plates and a first cylindrical tube located between the end plates. The blood purifier device also includes a porous tube contained within the space defined by the first cylindrical tube. An inlet provides unpurified red blood cells into blood purifier device. An electrode generates a negative potential across the porous tube to repel red blood cells so that the waste particles pass through the porous tube and the red blood cells do not. An outlet can be coupled to one of the end plates to receive the purified red blood cells.