A novel elastometer for soft tissue

A novel device has been designed to allow a surgeon to determine the medium strain (5-25%) compressive properties of highly extensible soft tissue during a surgical procedure. The motivation for the instrument is the need for accurate knowledge of the elastic properties of vaginal tissue in vivo during corrective surgery for incontinence in women. Studies have shown that a surgical technique that adjusts the elastic nature of vaginal tissue can reduce urge and stress incontinence symptoms. The success of the surgical technique would be greatly enhanced by the introduction of an objective measure of the stiffness of vaginal tissue. The compressive deformation is achieved by folding and pinching (indenting) the tissue between two circular cylinders. The applied load and indentation depth are used to estimate the elastic properties of the sampled tissue. A linear material model has been developed and tested against commercially available elastomers. The limits of application of the linear material model were determined using FEA and results from the experimental testing. A basic nonlinear model is also presented that can determine the Neo-Hookean constant of the material. The simple algorithms developed allow immediate inversion of measurements to give elastic properties, thereby permitting multiple readings to be made during a surgical procedure, an outcome that would not be possible if FEA or similar numerical methods were needed for interpretation of the readings. Experimental and numerical results are compared to the analytical models and a discussion of initial design ideas is presented. The device is shown to yield elastic modulus of test materials with an error of less than 10%.