A material deposition system for additive manufacturing including an extruder and a measuring device for measuring the viscosity and/or other rheological properties of a build material contained within the extruder. The measuring device may provide feedback to a controller for controlling one or more parameters depending on the measured viscosity and/or other rheological properties of the build material within the extruder. Two or more feed materials may be supplied to the extruder and a mixing device may be configured to mix the feed materials within the extruder to create a blended deposition material. The mixing device may be operatively coupled to the measuring device for simultaneously measuring the viscosity and/or other rheological properties of the materials during mixing. The controller may be configured to independently control one or more parameters associated with the materials depending on the viscosity and/or other rheological properties measured by the measuring device.