Birefringence and Second Harmonic Generation on Tendon Collagen Following Red Linearly Polarized Laser Irradiation

Abstract

Regarding the importance of type I collagen in understanding the mechanical properties of a range of tissues, there is still a gap in our knowledge of how proteins perform such work. There is consensus in literature that the mechanical characteristics of a tissue are primarily determined by the organization of its molecules. The purpose of this study was to characterize the organization of non-irradiated and irradiated type I collagen. Irradiation was performed with a linearly polarized HeNe laser (λ = 632.8 nm) and characterization was undertaken using polarized light microscopy to investigate the birefringence and second harmonic generation to analyze nonlinear susceptibility. Rats received laser irradiation (P = 6.0 mW, I = 21.2 mW/cm(2), E ≈ 0.3 J, ED = 1.0 J/cm(2)) on their healthy Achilles tendons, which after were extracted to prepare the specimens. Our results show that irradiated samples present higher birefringence and greater non-linear susceptibility than non-irradiated samples. Under studied conditions, we propose that a red laser with polarization direction aligned in parallel to the tendon long axis promotes further alignment on the ordered healthy collagen fibrils towards the electric field incident. Thus, prospects for biomedical applications for laser polarized radiation on type I collagen are encouraging since it supports greater tissue organization.

Low-level laser therapy for spinal cord injury in rats: effects of polarization

“…They attributed this to the changes in molecular order and aggregation states of the collagen fibers. 45 With linearly polarized laser, the tendon was irradiated once in their work, while the spinal cord was irradiated daily for five consecutive days in our work. Similar alteration of the fibrotic structure, which affects direction of photon scattering, could take place in the spinal cord examined in this study.…”

Biomechanical and structural response of healing Achilles tendon to fatigue loading following acute injury

“…From photoelastic theory, the specimen’s peak-to-peak intensity and thickness can be related to determine tissue birefringence (Buckley et al, 2013a; Glazer, 1996; Timoshenko, 1969). Birefringence is a term used to describe the structural anisotropy of a tissue (i.e., the difference in index of refraction between its fast and slow axes) (Silva et al, 2013). As shown previously (Timoshenko, 1969), the intensity of light detected through the analyzer is given by the equation $$I_c=I_p{\text{sin}}^{2}false(2\alpha false){\text{sin}}^{2}true(\frac{\mathrm{\Delta }}{2}true)$$ where I c is the intensity of light detected by the camera, I p is the intensity of light passing through the polarizer, α is the angle between P and the tendon’s slow axis (i.e., the aligned axis of the tendon), and Δ is the phase difference of light passing through the tendon.…”

Experimental burns: Comparison between silver sulfadiazine and photobiomodulation

“…18 It is important to remember that better organization of collagen fibers implies a better appearance of the scar, as a consequence of a better cicatricial process. 8,19 With respect to the systemic effect, there is no record of its occurrence in skin lesions using photobiomodulation.…”