The discrimination of type I and type II collagen and the label-free imaging of engineered cartilage tissue

Using excitation polarization-resolved second harmonic generation (SHG) microscopy we measured SHG intensity as a function of the excitation polarization angle for type I and type II collagens We determined the second order susceptibility (chi((2))) tensor ratios of type I and II collagens at each pixel and displayed the results as images We found that the chi((2)) tensor ratios can be used to distinguish the two types of collagen In particular we obtained chi(zzz)/chi(zxx) = 1 40 +/- 004 and chi(xzx)/chi(zxx) = 0 53 +/- 010 for type I collagen from rat tail tendon and chi(zzz)/chi(zxx) = 114 +/- 009 and chi(xzx)/chi(zxx) = 029 +/- 011 for type II collagen from rat trachea cartilage We also applied this methodology on the label-free imaging of engineered cartilage tissue which produces type I and II collagen simultaneously By displaying the chi((2)) tensor ratios in the image format the variation in the chi((2)) tensor ratios can be used as a contrast mechanism for distinguishing type I and II collagens (C) 2010 Elsevier Ltd All rights reserved