Second harmonic generation in collagen

Abstract

Ordered collagen in native, intact rat tail tendon has been studied by means of optical second harmonic generation (SHG). The two independent hyperpolarizability tensor elements of the collagen molecule, β₃ and β₁, have been found to be of opposite sign and roughly equal in absolute magnitude. Evidence is presented for a systematic variation in the ratio β₃/β₁ with age which may reflect the effects of progressive cross linking. Our experimental findings are in reasonably good agreement with a simple theory constructed on the basis of current models of the tendon structure, and thereby confirm this structure in the native, intact tissue. The many advantages of SHG for the structural study of intact partially ordered biological tissues are outlined.