Natural tissue valve prostheses having variably complaint leaflets

DETAILED DESCRIPTION These and other objectives are achieved by the present invention which, in a broad aspect, is directed to natural tissue valvular bioprosthetics having variably compliant valve leaflets and to methods for their production and use.
More particularly the present invention provides a novel tissue fixation process which may be used to produce valve leaflets that are variably compliant, exhibiting radially asymmetric flexing characteristics along the leaflet body.
Preferably, the valve leaflets will be fixed so as to provide a relatively stiffer base section adjacent to the annular margin of the valve assembly and a relatively flexible tip section adjacent to the commissures of the valve assembly.
This radial flexibility gradient along the valve leaflet allows it to move much more harmoniously in response to the flow of blood than valve leaflets fixed using traditional methods.
Moreover, the asymmetric flexibility of the valve leaflets tends to lower the in vivo pressure gradient necessary to open the valve while reducing the pressure drop and turbulence across the valve structure.
These improved hemodynamic properties result in a much more even distribution of mechanical stress across the tissue matrix of the leaflet thereby retarding the calcification of the leaflet tissue and associated deterioration of the prosthetic device.
Valve leaflets are made variably compliant during the fixation procedure of the present invention by subjecting different sections of each individual leaflet to different contact forces resulting in pressure.
Preferably the leaflet base, that is the section of the valve leaflet closer to the circumferential valvular margin or annulus, is chemically fixed while subjected to relatively high pressure.
At the same time, the leaflet tip section closer to the commissures is exposed to chemical fixatives under relatively low pressure.
The application of compressive force or pressure to a localized area during fixation increases the amount of cross-linking within the tissue matrix at that locale and compacts the fibrous protein structure, thereby increasing the local stiffness of the valve leaflet