The Cellular Mechanism Of Photothermal Response During Laser Interaction With Skin

Photothermal response is the main form in infrared laser with biological tissue, however, the mechanism of generation, transmission and function is not very clear. The clinical application so far has to be counting on the experiences which make the process of laser treatment and therapeutic effect is difficult to manage and control. In order to clarify its mechanism, the photothermal effect has been studied in cellular level. In this present study, we employed the patch clamp to examine the photothermal effect induced by optical absorption in process of laser-tissue interaction in theory and experiment study.The most effective field in laser physiotherapy is skin disease. The related parameters, used infrared laser physiotherapy, are determined by the form of thermal. Based on such a premise, the two-layer model of skin is adoptive to calculate the temperature distribution, to compare the time of the beginning of the gasification of epidermis, and to study the cumulative of heat of different body part in photothemal effect according the optical properties of skin, The results showed that the optical properties of water, fat and hemoglobin, and thermal properties of skin played an important role in laser irradiation skin as well as the wavelength, energy density, and duration time of pulse, however, the experiments in cellular level are needed to do for know the role of chromophores.In order to confirm the mediated effect of water in photothermal response of laser-tissue interaction, the dual-wavelength laser (980nm and845nm) were chosen to study the mechanism in laser irradiation the cell. It is well known that water is the main chromophores (by weight) in biological tissue, it plays an important role in life; and the dual-wavelength laser is widely applied in study of laser medicine; the magnitude of absorption coefficients (0.502cm-1at980nm and0.0378cm-1at845nm) of this two wavelength lasers is10times difference, they can produce a correspondingly proportional absorption-driven temperature rises. Thus,980nm and845nm as two probe wavelengths have been chosen to assess the photofhermal effect during the activation of neurons by a continuous near-infrared laser irradiation.The photothermal effect can be assessed in two stages:the establishment and the dissipation of the absorption-driven temperature rises:In the establishment stage, because the duration time of laser irradiation (500ms) is longer than thermal relaxation time of water (17.6ms), and the spatial distance is far shorter than penetration depth of this two wavelength laser in water, the role of absoiption in axial direction and thermal diffusion in radial direction were take into account in theoretical study. According to the temperature-dependence of conductivity of solution, an open pipette method was employed to measure the absorption-driven temperature rises by fabricating a glass pipette which was filled with electrolyte solution, formed a several mega-ohm resistance and calibrated as a temperature sensor by using a pico-ampere current amplifier technique (patch clamp). The experiment results showed that ratio of temperature rises is about10times in absorption-driven temperature rises. In the dissipation stage (turn off the laser source), we used the theory of thermal diffusion to describe the dissipative process. The electrophysiological function of a living neuron cell in dissipative process was studied based on a patch clamp. This method can decrease the influence of photochemistry and photomechanics. Because all experimental conditions are kept as the same, while the wavelengths are switched, the results have the comparability of wavelength-dependence. The theoretical calculation and the experimental results showed that the optical properties of solution determined the photothermal effect in laser-tissue interaction, and then modulated the electrophysiological function of a living neuron cell. The results can be used to study the mechanism of photothermal effect in laser-tissue interaction.However, there is some difference between experiment results and theoretical results for the adoptive approximation method when we use the theoretical method to analyze the changes of current peak. The theoretical results are corrected in the following work. We analyzed the current change of Na ion channel with thermophoresis theory in the process of theoretical analysis. The ions displace along the gradient of temperature for laser irradiation, it will decrease the concentration of Na ions in local cell, then it will change the current intensity, and the physiological function is modulated.Finally, because the chromophores are the water (90%) and hemoglobin in blood, according to the optical properties of hemoglobin in vein, we made the vein imaging experiment with near infrared laser irradiation. This method can make the vein of opisthenar clearly, and may provide a lot of help for the clinical venipuncture, especially to the patients, whose blood vessels are not difficult to identify.