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.