Combining Colloidal ProbeAtomic Force and ReflectionInterference Contrast Microscopy to Study the Compressive Mechanicsof Hyaluronan Brushes.

We describe a method that combines colloidal probe atomicforcemicroscopy (AFM) and reflection interference contrast microscopy (RICM)to characterize the mechanical properties of thin and solvated polymerfilms. When analyzing polymer films, a fundamental problem in colloidalprobe AFM experiments is to determine the distance at closest approachbetween the probe and the substrate on which the film is deposited.By combining AFM and RICM in situ, forces and absolute distances canbe measured simultaneously. Using the combined setup, we quantifythe compressive mechanics of films of the polysaccharide hyaluronanthat is end-grafted to a supported lipid bilayer. The experimentaldata, and comparison with polymer theory, show that hyaluronan films are well-describedas elastic, very soft and highly solvated polymer brushes. The dataon these well-defined films should be a useful reference for the investigationof the more complex hyaluronan-rich coats that surround many livingcells. [ABSTRACT FROM AUTHOR]