Development of a Method Using Photoacoustic Measurement for Evaluation of the Viscoelasticity of Articular Cartilage in Regenerative Medicine

Abstract

We propose a method for noninvasive viscoelastic characterization of biological tissue using photoacoustic measurement. The relaxation time (η/G , η being viscosity and G being elasticity) of laser-induced photoacoustic signals agreed with intrinsic relaxation parameters measured using a conventional rheometer with a correlation coefficient over 0.99 when the density of a gelatin model was changed in the range of 5-25 % as samples. We also applied this measurement method to tissue-engineered cartilage cultured for various periods (up to 12 weeks). Longer culture period resulted in greater viscoelasticity, which is equivalent to shorter relaxation time. The correlation between relaxation times of the photoacoustic signals and biochemical characteristics of the cultured cartilage revealed that the cartilage acquired viscoelasticity during the process of formation of an extracellular matrix such as collagen. This study demonstrated the usefulness of photoacoustic measurement for evaluating the viscoelastic properties of actual cultured cartilage using a tissue-engineering technique.