Usefulness of photoacoustic measurements for evaluation of biomechanical properties of tissue-engineered cartilage.

There is a demand in the field of regenerative medicine for measurement technology that enables functions of engineered tissue to be determined. For meeting this demand, we previously proposed a noninvasive method for determination of the viscoelasticity of a tissue phantom based on photoacoustic measurements. The purpose of this study was to verify the usefulness of the photoacoustic measurement method for evaluation of the viscoelastic properties of actual engineered tissue and to determine the correlation between biochemical characteristics and photoacoustic signals. The relaxation times measured by the photoacoustic method agreed well with the intrinsic viscoelastic parameters with a correlation coefficient of 0.98 when tissue-engineered cartilage tissues cultured for various periods (up to 12 weeks) were used as samples. By comparison of the results of biochemical analyses and biomechanical studies, we proved that the photoacoustic signal is a good indicator for evaluating extracellular matrix formation in order to determine the characteristics of tissue-engineered cartilage. To our knowledge, this is the first report on noninvasive and time-dependent viscoelastic evaluation of engineered tissue for determining functions of engineered tissues.