Cell reactions with biomaterials: the microscopies.

The methods and results of optical microscopy that can be used to observe cell reactions to biomaterials are Interference Reflection Microscopy (IRM), Total Internal Reflection Fluorescence Microscopy (TIRFM), Surface Plasmon Resonance Microscopy (SPRM) and Förster Resonance Energy Transfer Microscopy (FRETM) and Standing Wave Fluorescence Microscopy. The last three are new developments, which have not yet been fully perfected. TIRFM and SPRM are evanescent wave methods. The physics of these methods depend upon optical phenomena at interfaces. All these methods give information on the dimensions of the gap between cell and the substratum to which it is adhering and thus are especially suited to work with biomaterials. IRM and FRETM can be used on opaque surfaces though image interpretation is especially difficult for IRM on a reflecting opaque surface. These methods are compared with several electron microscopical methods for studying cell adhesion to substrata. These methods all yield fairly consistent results and show that the cell to substratum distance on many materials is in the range 5 to 30 nm. The area of contact relative to the total projected area of the cell may vary from a few per cent to close to 100% depending on the cell type and substratum. These methods show that those discrete contact areas well known as focal contacts are frequently present. The results of FRETM suggest that the separation from the substratum even in a focal contact is about 5 nm.