Fig.5
Pathological examination of wound
tissue (A) Representative images of
evolution of microstructure during healing processes by H&E staining
(\(\times 400\)). (B) Quantitative data of width of wound gap after the
two stages of laser welding at different time points (n ¼ 3). Data
represent mean \(\pm\) SD; *, P < 0.05, **, P < 0.01.
Overall collagen proliferation during wound healing
In Masson’s Trichrome staining,
collagen fiber is represented by blue coloration, as depicted in Fig.6.
On the third day after the first laser welding, it was observed that
collagen deposition in the 90° laser group concentrated mainly in the
dermis, becoming more pronounced near the subcutaneous fat layer.
Alterations in the structure of some subcutaneous fat were visible,
including finer, smaller fat particles and larger fibroblast nuclei. In
contrast, the 60° laser group displayed significant collagen deposition
distributed within the dermis and epidermis surrounding the wound, with
this group demonstrating the most substantial deposition area according
to the intensity of the blue shades in Fig.6.
By day 7, there was a noticeable difference from the initial stage of
laser welding. The collagen distribution in all three laser groups was
finer and more even compared to day 3, signifying that most deposited
collagen underwent further remodeling to form a dense network post the
second laser welding—an indicative feature of extraordinary healing
performances. However, incision marks were still visible in the
cross-section provided by Fig.6, indicating that the wound was yet to
fully heal and remained in the fibroblast proliferation phase. In
conclusion, the densest collagen network was found in the 90° laser
group, followed by the 60° and 30° laser groups respectively.
14 days into the healing process, notable changes were observed.
Firstly, collagen in both the 90° and 30° laser groups had further
proliferated, and fibroblast levels essentially returned to normal. The
90° laser group showed only slight gaps in collagen, and the dermis area
affected by the laser exhibited complete newly formed fine collagen
tissue. In contrast, the samples in the 60° laser group demonstrated
restoration closer to the original collagen texture, closely resembling
the dermis collagen of normal skin. This suggests that the samples in
the 90° and 30° laser groups may require an extended healing cycle due
to their overly fine collagen network and fibroblast levels lower than
the pre-treatment state. These conditions could result in decreased
elasticity of the collagen network and potential abnormal proliferation
post-collagen cracking [43-45]. Such phenomena might be caused by
the concentrated energy of the 90° laser, which, besides promoting
fibroblast proliferation, also inflicts additional thermal damage,
causing the destruction and potential loss of biological activity in
some hematopoietic cells and integrins. Although the healing process was
significantly enhanced, it remained challenging to ensure the thickening
and hardening of the collagen scaffold post the epithelial regeneration
stage.