Optical imaging predicts mechanical properties during decellularization of cardiac tissue

Decellularization of xenogeneic hearts offers an acellular, naturally occurring, 3D scaffold that may aid in the development of an engineered human heart tissue. However, decellularization impacts the structural and mechanical properties of the extracellular matrix (ECM), which can strongly influence a cell response during recellularization. We hypothesized that multiphoton microscopy (MPM), combined with image correlation spectroscopy (ICS), could be used to characterize the structural and mechanical properties of the decellularized cardiac matrix in a noninvasive and nondestructive fashion. Whole porcine hearts were decellularized for 7 days by four different solutions of Trypsin and/or Triton. The compressive modulus of the cardiac ECM decreased to < 20% of that of the native tissue in three of the four conditions (range 2-8 kPa); the modulus increased by -150% (range 125-150 kPa) in tissues treated with Triton only. The collagen and elastin content decreased steadily over time for all four decellularization conditions. The ICS amplitude of second harmonic generation (SHG, ASHG) collagen images increased in three of the four decellularization conditions characterized by a decrease in fiber density; the ICS amplitude was approximately constant in tissues treated with Triton only. The ICS ratio (R(SHG), skew) of collagen images increased significantly in the two conditions characterized by a loss of collagen crimping or undulations. The ICS ratio of two-photon fluorescence (TPF, R(TPF)) elastin images decreased in three of the four conditions, but increased significantly in Triton-only treated tissue characterized by retention of densely packed elastin fibers. There were strong linear relationships between both the log of A(SHG) (R(2) = 0.86) and R(TPF) (R(2) = 0.92) with the compressive modulus. Using these variables, a linear model predicts the compressive modulus: E=73.9 × Log(A(SHG))+70.1 × R(TPF) - 131 (R(2) = 0.94). This suggests that the collagen content and elastin alignment determine the mechanical properties of the ECM. We conclude that MPM and ICS analysis is a noninvasive, nondestructive method to predict the mechanical properties of the decellularized cardiac ECM.