A modified lap test to more accurately estimate interfacial shear strength for bonded tissues

Effective attachment to relevant anatomical surfaces has long been a critical issue for tissue replacement or repair. This is especially true for cartilage repair where adequate, reliable initial fixation to surrounding tissue and joint surfaces has been a dominant factor affecting clinical outcomes. Due to ease of application and ability to replicate dimensions and rates across multiple experiments, the single-lap test in tension has become a common method to assess interfacial strength for cartilage and other tissues in apposition. The standard single-lap configuration does not, however, provide a true measure of shear strength. The presence of a bending moment and resulting bond rotation create an uneven stress environment; specimens typically fail due to peel stresses at the edges of the interface. This report describes finite element analysis of variations to the single-lap method in which supports were added to either side of the bond interface. These results were then experimentally validated using photochemically bonded articular cartilage. Both the finite element and experimental results show that the addition of supports helps mitigate edge stresses and produces a more uniform stress distribution across the bond interface. Adding supports to prevent bond rotation, even for specimens not fixed to the supports, still produces a better estimate of shear strength than the traditional, non-supported configuration. These findings allow selection of a single-lap approach to more closely approximate shear strength even in those situations where it is not feasible or otherwise desirable to fix the tissue specimens to supports.