Quasi-Elastic Determination of Polymeric Material Moduli Using Vibrational OCT

The need to measure the mechanical properties of tissues and implants has been a goal of researchers since the 1970s. The pioneering work of Yamada [1] and Fung [2] illustrated how difficult this goal would be since the behavior of human extracellular matrix (ECM) depends on strain-rate, Poisson’s ratio, direction of testing and is time-dependent [3]. A variety of methods have been used to evaluate the mechanical properties of tissues over the last 40 years including uniaxial and biaxial tensile testing, indentation and rotational tests, ultrasound elastography (UE), optical cohesion tomography (OCT), optical cohesion elastography (OCE), and vibrational analysis combined with OCT [4-6]. Many of these techniques require the assumptions that the material is linearly elastic, Poisson’s ratio is close to 0.5 and that viscoelasticity does not dramatically affect the resulting properties. However, the behavior of most tissues is that of a non-linear viscoelastic material that has upward curvature to the stress-strain curve. These concerns makes determination of the stiffness (tangent to the stress-strain curve) and other mechanical properties very difficult to quantitatively analyze since the tangent to the stress-strain curve is constantly changing [3,5,6]. However, despite all of these problems, there is a need to be able to characterize the mechanical properties of tissues and implants, since this would give researchers valuable information about the properties of tissues and implants used as medical devices. In this paper, we will discuss the use of vibrational optical coherence tomography to determine the quasi-elastic modulus of implants and tissues.