Abstract
The purpose of this study was to determine the impact of elevated temperature exposure in tissue banking on soft tissues. A secondary objective was to determine the relative ability of various assays to detect changes in soft tissues due to temperature deviations. Porcine pulmonary heart valve leaflets exposed to 37 °C were compared with those incubated at 52 and 67 °C for 10, 30 and 100 min. The analytical methods consisted of (1) viability assessment using the resazurin assay, (2) collagen content using the Sircol assay, and (3) permeability assessment using an electrical conductivity assay. Additionally, histology and two photon microscopy were used to reveal mechanisms of cell and tissue damage. Viability, collagen content, and permeability all decreased following heat treatment. In terms of statistical significance with respect to treatment temperature, cell viability was most affected (p < 0.0001), followed by permeability (p < 0.0001), and then collagen content (p = 0.13). After heat treatment, histology indicated increased apoptosis and two photon microscopy revealed a decrease in collagen fiber organization and an increase in elastin density. These results suggest that measures of cell viability would be best for assessing tissues where the cells are alive and that permeability may be best where cell viability is not intentionally maintained.
Highlights
Transplant of soft tissue for reconstructive surgery drives the need for processing methods that should have minimal impact on tissue structure and viability
We have previously examined the sensitivity of various analytical tests following a collagenase damage model on porcine pulmonary heart valves.[13]
Heart valve leaflets are organized in defined layers: fibrosa, spongiosa and ventricularis, which are composed of different ECM components such as collagen, elastin and proteoglycans.[14,23]
Summary
Transplant of soft tissue for reconstructive surgery drives the need for processing methods that should have minimal impact on tissue structure and viability. Modifications of the structure may compromise the mechanical responsiveness of the leaflet eventually leading to failure of aortic or pulmonary valve function. The collagen and elastin exist in a hydrated gel composed of proteoglycans. Collagen and elastin are wavy fibers that can straighten under small loads, allowing large extension of the tissue at low stress. Hydrated elastin is viscoelastic, demonstrated by creep or stress relaxation tests, due to the interaction of elastin molecules with water molecules. Stiffening of elastin occurs by loss of water content.[8] High level tensile properties of leaflets are entirely dominated by the functionally elastic behavior of the collagen and elastin fiber networks. Proteoglycans have a pronounced effect at low strains where
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