Effects of laser irradiation on collagen organization in chemically induced degenerative annulus fibrosus of lumbar intervertebral disc

Abstract

Background and Objective: The number of in vitro experimental studies was carried out with the use of intact tissues to establish a mechanism of laser-tissue interaction. However, in the process of degeneration, both biochemical composition and behavior of the disc were altered drastically. The objective of this study was to evaluate the role of the main matrix components in laser modification of annulus fibrosus (AF) under IR laser irradiation. Study Designs/Materials and Methods: The samples of AF in a motion segment after hyaluronidase treatment, trypsin digestion and glycation by glyceraldehyde were heated in hydrothermal bath (95°C, 2 min) or irradiated by laser at 1.56 μm. Specimens were imaged by cross-polarization optical coherence tomography (CP-OCT), and then analyzed by differential scanning calorimery (DSC). Results and Discussion: According to CP-OCT and DSC data non-significant alteration was revealed in AF after hyaluronidase treatment, glycation led to stabilization of annulus collagen and trypsin digestion resulted in a noticeable impairment of collagen fibrils. Laser treatment induced subsequent damages of AF matrix but these damages cannot be explained by laser heating only. The specificity of chemical modification of AF matrix has an influence on a character of collagen network alteration due to IR laser effect. Minimal and maximal alterations are observed for hyaluronidase and trypsin treated samples respectively. Glyceraldehyde fixed samples showed failure of the collagen structure after moderate laser treatment; at the same time thermal denaturation of collagen macro-molecules was negligible. We assume that a mechanical effect of laser irradiation plays an important role in laser-induced annulus collagen modification and propose the scheme of physico-chemical process occurring under non-uniform IR laser treatment in AF tissue. Conclusion: CP-OCT and DSC techniques allow us to record the alteration of collagen network organization as a result of chemical modification. There were detected significant and specific effects of the biochemical composition and material properties on the response of AF collagen network on laser irradiation. The results go in accordance with our hypothesis that the primary effect of laser influence on collagen network under tension is the mechanical damage of collagen fiber. © 2008 Wiley-Liss, Inc.