Simultaneous morphological and stress-strain studies of the fibrous components in wet heart valve leaflet tissue.

Simultaneous morphological and stress-strain studies have been carried out on heart valve leaflet tissue maintained in its unaltered functional condition. A microtensile tissue testing device is described which inserts directly into the stage of an optical microscope fitted with a Nomarski interference contrast facility. Glutaraldehyde fixation of tissue subjected to different levels of loading reveals that the current stressed state of the collagen fibers is "frozen" in by crosslinking process, and as a consequence marked alterations in the preserved tissue properties are produced. This is shown to be relevant to the preparation of the glutaraldehyde treated heterograft heart valve. The mechanical roles of the collagen and elastin components are investigated and a "complementation" mechanism is postulated whereby the widely different mechanical properties of the two types of fibers are combined in a non-competing manner to produce a diversity of composite tissue characteristics.