An object/test material interaction microti iridic device comprising a sample inlet adapted to receive a fluid sample comprising a plurality of objects, an outlet adapted to output the fluid sample from the device, at least one internal surface defining a flow cavity within the device, wherein the flow cavity extends between and is connected to the sample inlet and the outlet for flow of the fluid sample through the flow cavity, the flow cavity comprises a test area to which at least one test material is attached and which is situated in the flow cavity for flow of the fluid sample over the test area, and the flow cavity has an aspect ratio which, when the flow cavity is substantially filled by the fluid sample, provides a substantially constant shear force between the test area and the fluid sample flowing over the test area. The invention further comprises a system incorporating the device, methods of use of the device and system, and methods of analysing interactions.