Title : Viscoelasticity of synthetic polymers and soft tissues using VOCT
Abstract:
My lab has developed a new technique to noninvasively measure the elastic and viscous properties of synthetic and natural polymers using infrared light and acoustic sound applied transversely to the surface of materials. The technique termed vibrational optical coherence tomography (VOCT) measures the resonant frequencies of materials and calculates the elastic modulus from the deformation in-phase with the applied force. The viscous component is obtained from the ratio of the width of the deformation decay peak at the half-height divided by the peak height after the sample is unloaded. For silicone rubber, the viscous component of the viscoleastic behavior is much smaller then that of soft tissues including skin and cornea. The elastic modulus of both silicone, skin, and cornea are all about 2 MPs but skin and cornea have much higher viscous components (up to 65% of the elastic components) compared to silicone at strain rates of about 50 Hz. At strain rates of above 200 Hz silicone, skin, and cornea all behave almost purely elasticially with viscous components below about 5% of the elastic modulus. It is concluded that the high water content and viscoelasticity of skin and cornea help these tissues dissipate large amounts of energy at low loading frequencies preventing premature mechanical failure. The high value of viscous modulus of tissuesat low frequencies reflect water contents of up to 80% by volume. At low loading frequencies water is displaced form the spaces between collagen fibers in tissues dissipating some of the applied energy. At high strain rates, tissues behave almost purely elastically when water remains bound to the surface of the collagen fibers during loading. The ability to noninvasively measure the viscoelasticity of polymers and tissues provides a method to anlayze the effects of processing of implants and chnages that couur during disease.
