Characterizing microscopic domains of birefringence in thin tissue sections

A tissue engineering problem that we anticipate will become increasingly of interest is how to grow protein layers and filaments in preferred orientations. For example, the polymerization of monomers into an oriented structure which may exert influence on adherent cells. In this paper, we report on an optical solution using polarized light measurements to probe the structure and orientation of fibers. In particular in this initial study, we measure the fast-axis orientation and retardance of micro-domains in thin sections of liver, muscle, and skin tissues using a polarizing microscope. The size of microdomains of iso-retardance is in the range 10-100 μm, which suggests that optical measurements with laser beams that are on the order of 1-mm in diameter or with unaging cameras with pixels sizes on the order of 100 s of μm will average over several microdomains and consequently complicate interpretation of measurements.