Mechanical Characterization of an In-Body Tissue-Engineered Autologous Collagenous Sheet, Biosheet, for Application as an Aortic Valve Reconstruction Material

Abstract

The reconstruction of the aortic valve using glutaraldehyde-treated autologous pericardium is known as “aortic valve neo-cuspidization” (AVNeo). In-body tissue architecture (iBTA), a cell-free, in vivo tissue-engineering that can produce autologous implantable tissues of the desired shape by subcutaneously embedding specially designed molds, was used to develop sheet-like collagenous tissues called “Biosheets.” Cylindrical molds with line slits arranged in an alternating (n=30) or parallel (n=36) pattern were subcutaneously embedded in goats (n=12) for several months. The tubular tissues formed in the molds were dried and then cut in the longitudinal direction, thus forming the sheet-like Biosheets (5×7 cm). The success rate was 97.6% when using the alternating-pattern molds and 97.2% for the parallel molds. Thickness mapping of the Biosheets showed that their entire surface, except for the line-projection portions, was smooth without any defects. The average wall thickness could be controlled over a range of ca. 0.2–0.5 mm by changing the size of the gap (0.75–1.5 mm) in the molds. The alternating slit-patterned Biosheets were found to be almost isotropic in their mechanical properties (ultimate tensile strength, fracture strain, and Young’s modulus). Although the composition of the Biosheet wall was heterogeneous in terms of its density, the breaking force of all the alternating-patterned Biosheets increased almost linearly with the thickness within the range of the thickness of glutaraldehyde-treated human pericardium, and was larger than that of human aortic valve leaflets. Therefore, the alternating-patterned Biosheets may be used as an alternative aortic leaflet material in AVNeo.