# Overview on the Evolution of Laser Welding of Vascular and Nervous Tissues
## 2 Laser Welding of Vascular and Nervous Tissues
### Welding Parameters and Bonding Conditions  
An overview of the main researches conducted in vascular and nervous laser welding over the last 30 years is presented in Table 5. The laser type and the main parameters tested in these works are displayed in the table. The research has been mainly focused on optimizing the inverse relation existing between the laser power and the exposure time by testing different laser types (different wavelengths). Regarding the laser operation mode, continuous wave (CW) was used in most of the studies, although the laser was often performed as a sequence of consecutive pulses (not short-pulse laser mode) by the actuation of a switch device, like, for example, a foot switch. For this reason, the table presents the weld time, which corresponds to the total time per weld, the time of each pulse, and the interval between consecutive pulses. It should be noted that the tested conditions are not generalizable, since they strongly depend on the specific application, and consequently, on the interaction mechanisms between the laser radiation and the welded tissues. The application of external bonding materials, protein solutions (solders), and dyes in the weld region has also been intensively studied (Figure 4). \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Study**} & \multicolumn{2}{c}{**Laser Welding**} & \multicolumn{2}{c}{**Histologic Examination**} \\ \cline{2-4}  & **CO\({}_{2}\)** & **Argon** & \\ \hline [PERSON] et al. [44] & - & x & \begin{tabular}{c} Minimal inflammatory response, near normal collagen content, \\ absent of aneurysm formation \\ \end{tabular} \\ \hline [PERSON] et al. [57] & - & x & \begin{tabular}{c} Absent of hematomas, false aneurysms or luminal dilatation, and \\ minimal inflammatory response \\ \end{tabular} \\ \hline [PERSON] et al. [71] & - & x & \begin{tabular}{c} Minimal inflammatory response and near-normal collagen content \\ \end{tabular} \\ \hline [PERSON] et al. [41] & - & x & \begin{tabular}{c} Absent aneurysm formation \\ \end{tabular} \\ \hline [PERSON] et al. [45] & x & - & Absent foreign body reaction, minimized scar tissue formation \\ \hline [PERSON] et al. [46] & x & - & \begin{tabular}{c} Minimized tissue thermal damage and no foreign body reactions \\ \end{tabular} \\ \hline [PERSON] et al. [42] & - & x & \
\begin{tabular}{c} Absent aneurysm formation although with no complete \\ regeneration of the elastic lamina \\ \end{tabular} \\ \hline [PERSON] et al. [47] & x & - &
\begin{tabular}{c} Minimal thermal necrosis and welding strength increase \\ \end{tabular} \\ \hline [PERSON] et al. [50] & x & - & Good functional recovery with no nerve dehiscence \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Overview of histological results of CO\({}_{2}\) and argon repairs over conventional suturing. The materials referred to above improve the technical parameters and reduce the thermal damage, enabling the achievement of higher weld strength [43; 46; 72; 76]. [PERSON] et al. [45] concluded that the amount and concentration of structural proteins is directly correlated with the bonding strength of the welded repair. This correlation has been recently corroborated by [PERSON] et al. [78]. The different types of bonding materials and solders reported to be used in nervous and vascular repairs are displayed in Table 6. Although the biodegradable glues (fibrin and cyanoacrylate glues and polyethylene glycol)  
Figure 4: Schematics of laser welding of a nervous tissue, with the application of a solder and a light absorbing dye [40].