Use of Polarized Light Microscopy to Measure Internal Strains of Collagenous Tissues.

Extract

When studying connective tissues, it is often necessary to develop an understanding of their internal mechanics. In the aortic valve, studying of the internal strains of the leaflet material has provided insight into the means through which these largely avascular tissues survive up to 3 billion loading cycles during their functional lifespan. Even the inert, “dead” bioprosthetic valve replacements can withstand hundreds of millions of cycles before wearing out. The durability of the natural and prosthetic valves is therefore highly dependent on their microstructure and internal micromechanics.

Conventional microscopy has shown the aortic valve leaflet to consist of two structural layers, the fibrosa and ventricularis, separated by a loose central spongiosa rich in proteoglycans (figure 1). Both layers are highly organized, consisting of layers of elastin and collagen fibers. As the valve leaflets stretch and bend during opening and closure, these collagen fiber layers elongate, compress and shear in response to the applied external forces.