A device, system and method for exchanging components between first and second fluids by direct contact in a microfluidic channel. The fluids flow as thin layers in the channel. One of the fluids is passed through a filter upon exiting the channel and is recycled through a secondary processor which changes the fluid's properties. The recycled fluid is reused for further exchange. The filter excludes blood cells from the recycled fluid and prevents or limits clogging of the filter. The secondary processor removes metabolic waste and water by diafiltration.