There is limited information about age-specific structural and functional properties of human heart valves, while this information is key to the development and evaluation of living valve replacements for pediatric and adolescent patients. Here, we present an extended data set of structure-function properties of cryopreserved human pulmonary and aortic heart valves, providing age-specific information for living valve replacements. Tissue composition, morphology, mechanical properties, and maturation of leaflets from 16 pairs of structurally unaffected aortic and pulmonary valves of human donors (fetal-53 years) were analyzed. Interestingly, no major differences were observed between the aortic and pulmonary valves. Valve annulus and leaflet dimensions increase throughout life. The typical three-layered leaflet structure is present before birth, but becomes more distinct with age. After birth, cell numbers decrease rapidly, while remaining cells obtain a quiescent phenotype and reside in the ventricularis and spongiosa. With age and maturation–but more pronounced in aortic valves–the matrix shows an increasing amount of collagen and collagen cross-links and a reduction in glycosaminoglycans. These matrix changes correlate with increasing leaflet stiffness with age. Our data provide a new and comprehensive overview of the changes of structure-function properties of fetal to adult human semilunar heart valves that can be used to evaluate and optimize future therapies, such as tissue engineering of heart valves. Changing hemodynamic conditions with age can explain initial changes in matrix composition and consequent mechanical properties, but cannot explain the ongoing changes in valve dimensions and matrix composition at older age.
Mechanical loading protocols in tissue engineering (TE) aim to improve the deposition of a properly organized collagen fiber network. These conditioning protocols can result in tissue compaction [1], which may lead to loss of functionality of the tissue construct. A balance between the collagen deposition and compaction is desirable, yet difficult to achieve, due to the nonlinear coupling between mechanical loading, collagen modeling and compaction.
Small-diameter vessels tissue engineering (TE) seeks to provide viable replacements to the native ones. The approach involves seeding autologous cells onto a biodegradable scaffold material and delivering the suitable environmental factors (biochemical and biomechanical stimuli) during culture via a conditioning protocol. Still, these replacements appear to lack the native mechanical integrity. TE protocols should then be improved and optimized.
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