The present invention relates generally to a sample processing device, such as a microfluidic device, comprising a substrate, wherein the substrate comprises a plurality of channels configured to transport a fluid, and wherein the plurality of channels are substantially coated with lubricin, or a functional variant thereof. Also disclosed herein are methods of manufacturing such devices, methods of preventing fouling of a channel in a device using lubricin, or a functional variant thereof and methods of controlling the electrokinetic flow of an analyte through a channel that is substantially coated with lubricin, or a functional variant thereof. Also disclosed herein is chromatographic material for the electrophoretic and/or chromatographic separation of an analyte, wherein the chromatographic material is substantially coated with lubricin, or a functional variant thereof..