Biomedical Engineering Reference
In-Depth Information
Fig. 15.1.
Structural modifications induced in fibrillar collagen of connective tissue
by temperature rise. Normal triple helix collagen molecules are packed in a quarter-
staggered manner and connected by covalent bonds to form a collagen fibril (
left
).
When heat is applied, hydrolysis of intramolecular hydrogen bonds occurs, which
results in the unwinding of the triple helices (
middle
). The first step (1) leads to a
shrinkage effect parallel to the axis of the fibrils. At higher temperatures, covalent
cross-links connecting collagen strands break, resulting in a complete destruction of
the fibrillar structure (
right
) and causing relaxation of the tissue (step 2)
Laser tissue welding has been shown to possess several advantages com-
pared with conventional closure methods, such as reduced operation times,
fewer skill requirements, decreased foreign-body reaction and therefore
reduced inflammatory response, faster healing, increased ability to induce
regeneration, and an improved cosmetic appearance. Laser welding also has
the potential to form complete closures, thus making possible an immediate
watertight anastomosis, which is particularly important in the case of vas-
cular, genito-urinary tract, and gastrointestinal repairs. A watertight closure
also discourages the exit of regenerating axons and the entry of fibroblasts.
Lastly, laser welding can be used endoscopically and laparoscopically to ex-
tend the range of its applications to cases in which sutures or staples cannot
be used.
However, despite the large number of experimental studies reported in the
literature, very few of them have reached the clinical phase. This is mainly be-
cause of the lack of clear evidence of the advantages of laser-assisted suturing
against conventional methods, and because of a low reproducibility of results.
The damage induced in tissues by direct laser heating and heat diffusion and
the poor strength of the resulting welding are the main problems as far as
