Research on evolution process of full-layer incision of skin tissue under different laser incidences
Yuxin Chena*, Jun Huanga*, Kehong Wanga*, Xiaopeng Lia, Yunfeng Ruib, Wentao Fanc,
a School of Material Science and Technology, Nanjing University of Science and Technology, Nanjing, China
b Department of Orthopaedics, Southeast University, Zhongda Hospital, Nanjing, China
c First school of clinical medicine, Nanjing Medical University, Nanjing, China
*Corresponding author: Kehong Wang, E-mail:wkh1602@126.com, Jun Huang, E-mail:huangjun@njust.edu.cn,Yuxin Chen, Email: chenyuxin1602@njust.edu.cn
Abstract :Considering difficulties of achieving vertical incidence of beam in different positions of skin, it’s significant to study potential effects of incidence angles of laser on incisions. Surgical platform with a 1064nm continuous fiber laser was established. Incident angle was adopted and real-time temperature fluctuations in laser operating area could be monitored. The rats were treated with laser at day 0 and day 3 after incision modeling, and H&E, Masson, Sirius Red and Immuno-histochemical staining and enzyme-linked immunosorbent assay were adopted at day 3,7,14 to analyze the performance of healing. Laser with energy density of 67.54J/mm2 can effectively accelerate wound healing in vivo, in which laser with incident angle around 60° can effectively avoid scar hyperplasia. Therefore, the use of low energy laser with small deflection angle has a good clinical application prospect in promoting wound healing.
Key words:Laser tissue welding; Wound healing; Incident angles; Laser automated surgical platform; Collagen remodeling
Introduction
The skin is the largest organ of the human body, playing a role in maintaining the fluids and electrolytes homeostasis, resisting physical and chemical damage, as well as preventing microbial infections [1]. Regrettably, full-thickness skin defects are prone to occur under various injury factors, such as large-scale burns, traumatic injuries, diabetic ulcers, and vascular lesions, which seriously harmed not only the life quality of patients, but also the medical economy. Current therapeutic interventions remain far from ideal repair[2].
Medical laser is known as an epoch-making progress in traditional surgery, and has become a special and effective means of diagnosis and treatment in many medical fields[3-4]. In recent years, laser has made great progress in the field of biomedicine, especially in minimally invasive surgery, due to its excellent monochromatic properties, collimation and flexible energy density [5-6]. The thermal effect produced by laser acting on biological tissue with different wavelength and energy is also different, so different types of tissue normally need different kinds of lasers [7,23-25]. The surgical application and safety procedures of lasers are related to the degree of thermal damage [8-9]. The degree of thermal damage is not only a function of laser parameters, such as power density, duration, pulse width, etc., but also depends on the absorption and scattering properties of tissues and thermophysical parameters such as thermal conductivity and thermal diffusivity of tissues [10-11]. Once the heat source is determined, the tissue temperature distribution changes can be calculated according to the heat transport equations and various assumed conduction and convection boundary conditions [12-13]. An increase in temperature can lead to cell inactivation, protein denaturation, and even vaporization and cutting of tissues [14]. Medical laser technology, a non-contact skin tissue suture has the advantage of high immediate tensile strength [15], fast recovery, low infection and less scar tissue and so on which has outstanding application potential in surgery, obstetrics and gynecology and cosmetic surgery[16]. However, in practical applications, the location of the full-layer incision in the skin tissue is relatively flexible, which cannot guarantee that the laser can be vertically incident. Therefore, it is of great significance to study the evolution rule of microstructure, collagen degeneration[17] process and content changes of important cytokines in the process of bonding full-layer incision of skin tissue by different laser incidences in order to accelerate the prognostic process for achieving the clinical progress of laser induced full-layer incision connection technology[18-19]. Since the thickness of skin tissue is small and the photo-thermal effect between laser and skin tissue is sensitive [20], the evolution process of microstructure corresponding to different layers of skin is an important reference to judge the healing situation of samples. Similarly, the change of macro morphology is inevitably based on the change of microstructure morphology. In this study, continuous low-power laser was performed on the back of living SD rats by different laser incident angles. The macro-morphology, microstructure morphology, fibroblast morphology, endothelial growth factor content, and the distribution of type I and III collagen were continuously characterized at fixed periods. The laser bonding processes of skin tissue was further investigated from the microscopic mechanism of healing, also the potential of laser bonding incisions in different positions have been verified theoretically and experimentally.
Materials and Methods
On the basis of great researches before, we constructed a comprehensive welding system which could meet all basic demands during the laser welding processes, as shown in Fig.1. The skin tissue connection machine used in this study consists of three parts: a laser working system, a thermograph, and an overall control system. The laser working system consists of 1064nm Nd:YAG consecutive fiber lasers, a workbench and relevant clamping devices. The thermograph consists of a Fortic near-infrared thermal imager and a control subsystem. The overall control system consists of the temperature output data processing subsystems of a laser control system and a thermal imager. The overall control system in Fig.2.1 can adjust and set the laser parameters in real time and monitor the temperature changes of skin tissues, and can regulate tissue injuries and the macroscopic condition of welding. In order to guarantee the accuracy and scientificity of experimental data, we also carry out the experiments in an ultra-clean laser surgery area, as shown in Fig.1.