Non-invasive multiphoton imaging of extracellular matrix structures

Multiphoton microscopy has become a powerful method for the artifact-free, nondestructive evaluation of deep-tissue cells and extracellular matrix (ECM) structures in their native environment. By interacting with highly non-centrosymmetric molecular assemblies such as fibrillar collagen, the non-linear process called second harmonic generation (SHG) has also proven to be an important diagnostic tool for the visualization of ECM compartments in situ with submicron resolution without the need for tissue processing. This review reports on applications of multiphoton-incluced autofluorescence and SHG microscopy to identify collagen and elastic fiber orientation in native, tissue-engineered and processed. as well as healthy and diseased, tissues and organs. SHG signal profiling was used to quantity ECM damage in various cardiovascular and exocrine tissues, as well as cartilage. These novel imaging modalities open the general possibility of high-resolution in situ and more important in vivo imaging of ECM structures, cells and intracellular organelles in living intact tissues. [GRAPHICS] Heart valve leaflets have a unique extracellular matrix that is organized in distinct layers, which can be non-destructively visualized by multiphoton imaging. (c) 2008 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim