| dc.description.abstract | A new biaxial testing machine that is designed to experimentally investigate soft tissues is presented. The system is able to perform uniaxial, biaxial and simple shear tests as defined in a theoretical framework proposed by our collaborator. Proof-Of-Principle experiments have been carried out on silicone membrane. Testing protocols are also discussed in this research. In addition, this research studies the various clamping methods for soft tissues. A novel clamp design for mechanical testing of soft biologic tissue that combines pins with serrated clamps to successfully decrease the occurrence of test sample slippage while reducing imposed stress concentrations at the clamping sites. The uniaxial tensile test is a standard method to obtain the mechanical properties of biological tissues and tissue-engineered constructs. Various clamping techniques have been developed in the past few decades to address the difficulty of imposing appropriate boundary conditions on soft tissues during mechanical testing. Two criteria for a successful clamping mechanism are (i) prevention of test specimen slippage, and (ii) prevention of test specimen failure outside the gage region. Informed by an extensive review of the related literature, this study presents a novel clamp design for mechanical testing of soft tissue. This design was validated by performing 40 uniaxial tensile tests on rat abdominal wall muscles using strain rates of 1% per second or 10% per second. Load and displacement data were acquired at the grips. The clamping area on the tissue sample was marked with India ink to track potential slippage of the sample during testing. Ultimate tensile strength and the corresponding stretch were calculated when the maximum load was achieved. With fine tuning of the torque applied to the clamping grips, the success rate of the tensile tests reached over 90%. In this research, multiple strain measurement techniques for soft tissues are evaluated. Particularly, we investigated the strain measurement from both sides of soft biological tissue under uniaxial tensile test. Strain measurement is an important step in mechanical characterization of the mechanical behavior of soft tissues.
Various strain measurement techniques have been developed in the past few decades. However, most of the research about strain measurement on soft tissues are focused on only one side of the tissue (usually the side with less connective tissues). But what happened to the other side? After a brief review of the strain measurement on soft tissues, especially skins, this study presents measurement from both sides of rat skins under uniaxial loading environment. The motion of the four black markers glued on each side of soft tissues were tracked through optical approach. Finite element method was used to calculate the deformation of the quadrilateral formed by the markers. Twelve uniaxial tests were conducted and used for data analysis. Strain at both sides of the specimens were measured and compared. In general, when the stretch increased, the strain along the stretching direction (Exx) of both sides increased. However, the strain at the transverse direction (Eyy) and shear strain (Exy) behaved quite differently between the two sides. Thus, it might be necessary to take into consideration both sides when characterizing soft tissue mechanical properties. | |
