Multifunctional evaluation of tissue engineered cartilage using nano-pulsed light for validation of regenerative medicine

There is a demand in the field of regenerative medicine for measurement technology that enables functions of engineered tissue to be determined. Articular cartilage, which has already been applied in clinical regenerative medicine, has specific mechanical functions. For meeting this demand, we previously proposed a noninvasive method for determination of the viscoelastic property based on photoacoustic measurements. However, characterization of the extracellular matrix of articular cartilage as well as determination of the viscoelastic property should be carried out for evaluation of regenerative medicine because the extracellular matrix plays an important role in the function of articular cartilage. The purpose of this study was to develop noninvasive measurement method for simultaneous evaluation of the viscoelastic properties by the photoacoustic method and characterization of the extracellular matrix of tissue engineered cartilage by the time-resolved autofluorescence spectroscopy. Third harmonic Q-switched Nd:YAG laser pulses were used as an excitation light source. Photoacoustic waves induced by the light pulses were detected using a piezoelectric transducer. The time-resolved fluorescence spectroscopy was obtained by using a photonic multichannel analyzer. The ratio of viscosity to elasticity 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. There were significant differences in the measured fluorescent parameters among the culture conditions of cartilage because chondrocytes produce a specific extracellular matrix depending on its culture condition. The specific extracellular matrix contained a specific type of collagen such as collagen type I or type II, which each have specific fluorescent features. The combination of time-resolved autofluorescence spectroscopy and the photoacoustic measurement is expected to become a useful evaluation method in regenerative medicine of articular cartilage.