Morphomechanics of dermis-A method for non-destructive testing of collagenous tissues

Background

Collagenous tissues store, transmit and dissipate elastic energy during mechanical deformation. In skin, mechanical energy is stored during loading and then is dissipated, which protects skin from mechanical failure. Thus, energy storage (elastic properties) and dissipation (viscous properties) are important characteristics of extracellular matrices (ECMs) that support the cyclic loading of ECMs without tissue failure.

Methods

Uniaxial stress-strain measurements on decellularized human dermis have been made and compared to results of a non-destructive technique involving optical coherence tomography (OCT) combined with vibrational analysis. In addition, Poisson's ratio has been determined for tensile deformation of decellularized dermis.

Results

The modulus of decellularized dermis measured using standard tensile stress-strain tests and that determined from calculations derived from natural frequency measurements give similar results. It is also observed that Poisson's ratio for dermis is between 0.38 and 0.63 after correction for changes in volume that occur during tensile deformation. These results suggest that the assumption that dermis and other ECMs deform at constant volume is incorrect and will lead to differences in the calculated modulus by conventional tensile stress-strain measurements.

Conclusions

It is proposed that OCT in conjunction with vibrational analysis is a convenient way to non-destructively measure the modulus of decellularized dermis, ECMs and other materials that have a positive curvature to their stress-strain curves. Tensile deformation of dermis and possibly other ECMs is associated with an increase in Poisson's ratio consistent with a model of fluid expulsion from collagen fibrils during stretching. The value of Poisson's ratio should be considered in analyzing the mechanical properties of ECMs since at least dermis appears to be compressible during tensile deformation. Fluid expression during tensile deformation may play a role in mechanotransduction in skin in a similar manner to cartilage and bone tissue.

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