Biaxial failure properties of planar living tissue equivalents

Quantification of the mechanical properties of living tissue equivalents (LTEs) is essential for assessing their ultimate functionality as tissue substitutes, yet their delicate nature makes failure testing problematic. For this study, we evaluated the validity of using an inflation device for quantifying the biaxial tensile failure properties of extremely delicate fibroblast-populated collagen gels (CGs) and fibrin gels (FGs). Small samples were circularly clamped and then inflated until rupture. Each sample assumed an approximately spherical shape and burst at its center indicating effective clamping. After two weeks in culture, all LTEs tested were fragile, but the FGs were significantly stronger and more extensible than the CGs (ultimate tensile strength 6.0 kPa +/- 2.0 kPa vs. 2.8 kPa +/- 0.7 kPa; failure strain 3.5 +/- 0.9 vs. 0.26 +/- 0.05, n = 4). After an additional 11 days of culture, the strength of the FGs increased significantly (26.5 kPa +/- 12.7 kPa), and the extensibility decreased (1.9 +/- 0.8, n = 3). This study demonstrates that subtle differences in the properties of LTEs can be measured using inflation methods with minimal sample handling and without having to grow the tissues into anchors or cut the specimens.