Abstract
The ability of traditional tensile tests to determine mechanical properties of human tissue can be affected by several factors, which may include failure within the clamping area of standard clamp designs. The use of custom-designed 3D printed clamps seems to provide success in preventing tissue failure and minimizing slippage during testing. Additionally, due to the nonhomogeneous characteristics of tissue, the mechanical properties often vary along the length of specimens, therefore a full-field measurement technique is required to capture the complete behavior of the tissue. Non-contact imaging techniques can be used to quantify full-field deformation during the test, allowing behavior to be quantified in different regions of the sample. Digital image correlation (DIC) is investigated in this work and is able to calculate strain by comparing successive images taken during the sample deformation. In order to measure changes in the pictures, the analyzed surface must have a well-defined high-contrast random pattern. Currently, methods for tensile testing of human tissues combined with DIC typically use an airbrush to create a random pattern on the tissue surface. Replication of this existing technique can be challenging based on the lack of control of the paint applied by the airbrush. This work presents an approach for tensile testing of well-preserved human tissue using 3D printed clamps and DIC. The samples investigated in this work include plantar fascia and Achilles tendons to analyze the performance of the proposed clamp design in thin and thick human tissue. The failure of thin and thick well-preserved human tissue was reached with a maximum load of 1124.9 N and 2167.08 N, respectively. The 3D printed clamps showed signs of clamping-related failure during the test even after increasing the infill percentage and adjusting the clamp layer orientation. The samples were dyed in methylene blue and painted with a user-defined random pattern. A custom resin roller generated by OpenSCAD was used to paint the surface of the plantar fascia allowing standardization of the creation of a random pattern on the sample surface. However, the curvature of the Achilles tendon in the most distal region where it attaches to the calcaneus bone (i.e. heel bone) precluded use of the roller. Therefore, a random pattern was hand-painted instead. The hand-painted random pattern had a performance similar to the pattern made by the resin roller which followed commercial roller characteristics. Results of this study can be used in the future to help standardize tensile testing techniques for mechanical evaluation of human tissue.
