Red and near-infrared light have been widely employed in optical therapies. Skin is the most common optical barrier in non-invasive techniques and in many cases it is the target tissue itself. Consequently, to optimize the outcomes brought by lightbased therapies, the optical properties of skin tissue must be very well elucidated. In the present study, we evaluated the dorsal skin optical properties of albino (BALB/c) and pigmented (C57BL/6) mice using the Kubelka-Munk photon transport model. We evaluated samples from male and female young mice of both strains. Analysis was performed for wavelengths at 630, 660, 780, 810 and 905 nm due to their prevalent use in optical therapies, such as low-level light (or laser) and photodynamic therapies. Spectrophotometric measurements of diffuse transmittance and reflectance were performed using a single integrating sphere coupled to a proper spectrophotometer. Statistic analysis was made by two-way ANOVA, with Tukey as post-test and Levenne and Shapiro-Wilks as pre-tests. Statistical significance was considered when p<0.05. Our results show only a slight transmittance increment (<10 %) as wavelengths are increased from 630 to 905 nm, and no statistical significance was observed. Albino male mice present reduced transmittance levels for all wavelengths. The organization and abundance of skin composing tissues significantly influence its scattering optical properties although absorption remains constant. We conclude that factors such as subcutaneous adiposity and connective tissue structure can have statistically significant influence on mice skin optical properties and these factors have relevant variations among different gender and strains.
Low-level laser therapy (LLLT) is commonly used to accelerate wound healing. Besides, the technique of imaging
the light distribution inside biological tissues permits us to understand several effects about light-tissue interaction.
The purpose of this study was to determine the relative attenuation coefficient of the light intensity in healthy and
burned skin rats during cutaneous repair following LLLT or not. Two burns about 6mm in diameter were
cryogenerated using liquid N2 on the back of 15 rats. Lesion L was irradiated by a He-Ne laser (λ= 632.8nm) and
fluence 1.0J/cm<sup>2</sup>; Lesion C was control and received sham irradiation. A healthy skin area (H) was also analyzed.
The lesions were irradiated at days 3, 7, 10 and 14 post-burning. The animals were euthanized at days 3, 10 and 31
and skin samples were carefully removed and placed between two microscope slides, spaced by z= 1mm. A laser
beam irradiated the sandwiched tissue from epidermis to dermis. A CCD camera was placed orthogonal to the beam
path and it photographed the distribution of the scattered light. The light decay occurred according to the Beer's
Law. Significance was accepted at p <0.01 by using t-Student test. Our results show that the light decay along any
direction was close to an exponential. Burned skin samples presented decay significantly faster than healthy skin
samples. Besides, attenuation coefficient changed during burning healing comparing treated and control lesions.
These findings suggest that the relative attenuation coefficient is a suitable parameter to optimize LLLT during
Severe burns cause extensive damage and are complicated by loss of body fluids, injury in the cutaneous vasculature and delayed wound healing. Low-intensity laser therapy (LILT) has been studied as an alternative method to accelerate wound healing. This study was carried out to evaluate LILT effects (λ= 660 nm) in rat burned skin with two different dose regimens. Thirty-six male adult Wistar rats with two burns created on their back using steam water were divided into 3 groups. In the fractioned dose laser group (FG), the lesions were irradiated with 1J/cm<sup>2</sup> on days 1, 3, 8 and 10; in the single dose laser group (SG), the lesions were irradiated with 4J/cm<sup>2</sup> on day 1. On control group (CG), lesions were not irradiated. Three animals per group were sacrificed on days 1, 3, 8, 10, 15 and 21 post-wounding and skin specimens were collected and processed to histomorphometry. At days 1, 3 and 8, statistical significant differences were not observed among groups. On the 10<sup>th</sup> day, mean values of the number of blood vessels for FG was significantly higher than CG. Irradiated groups showed a peak of new blood vessels formation at day 15 while for CG the peak was at day 21. The number of vessels in CG was significantly higher than FG and SG at day 21. These findings suggest that LILT may accelerate angiogenesis compared to control group, however, no significant differences were observed between laser groups with fractioned or single dose during all experiment.
We use the optical path difference (OPD) technique to quantify the organization of collagen fibers during skin repair of full-thickness burns following low-intensity polarized laser therapy with two different polarization incidence vectors. Three burns are cryogenerated on the back of rats. Lesion L is irradiated using the electric field vector of the polarized laser radiation aligned in parallel with the rat's occipital-caudal direction. Lesion L is irradiated using the electric field vector of the polarized laser radiation aligned perpendicularly to the aforementioned orientation. Lesion C is untreated. A healthy area labeled H is also evaluated. The tissue samples are collected and processed for polarized light microscopy. The overall finding is that the OPD for collagen fibers depends on the electric field vector of the incident polarized laser radiation. No significant differences in OPDs are observed between L and H in the center, sides, and edges of the lesion. Lesions irradiated using the electric field vector of the polarized laser radiation aligned in parallel with the rat's occipital-caudal direction show higher birefringence, indicating that collagen bundles in these lesions are more organized.
Low-intensity laser therapy (LILT) with adequate wavelength, intensity, and dose can accelerate tissue repair. However, there is still disperse information about light characteristics. Several works indicate that laser polarization plays an important role on the wound healing process. This study was conducted to verify the degree of linear polarization in normal and pathological rat skin samples. Artificial burns about 6 mm in diameter were created with liquid N<SUB>2</SUB> on the back of the animals. The degree of polarization was measured in normal and pathological skin samples. It was verified that linearly polarized light can survive in the superficial layers of skin and it can be more preserved in skin under pathological condition when compared with health skin. The present study supports the hypothesis that polarized laser radiation can be used to treat open wounds and improve the healing.