# 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
No improvement in bonding strength was achieved with an application of a 5% albumin solution. In turn, [PERSON] et al. [43] reported that leakage of liquid solder solutions occurred during surgery, creating an obstacle to the regeneration process. In agreement with this, [PERSON] et al. [47] observed that the disruption of low-viscosity solder solutions occurred at the solder midline. However, regarding semi-solid solder solutions, the same authors reported that these solutions withstand higher pressures in the solder area than at the interface, due to higher protein concentrations. The application of a semi-solid solder solution in arterial laser welding is illustrated in Figure 5. As illustrated by the black dots, although laser welding is a highly localized process, a heat-affected zone (HAZ) was generated around the welding site, which agrees well with the aforementioned concerns regarding thermal damage. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Bonding Materials and Solders** & **Advantages** & **Drawbacks** \\ \hline Fibrin glue [40] & Reduces inflammatory tissues and easy application & Low tensile strength, infection risk \\ \hline Cyanoacrylate glue [40; 58] & High tensile strength and easy application & Requires support stay sutures, causes fibrosis, foreign-body toxicity \\ \hline Polyethylene glycol (PEG) [40] & Nontoxic, biocompatible and reduces scar tissue & Slow degradation process (over 20 months) \\ \hline Albumin-based solution [40; 47; 78] & In nerve repairs, protects the epinephrine, increases bonding strength, reduces thermal damage & Leakage of fluid solder, thermal damage still present, viral infection risk, becomes brittle \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Advantages and drawbacks of solders and bonding materials used in vascular and nerve repairs. Figure 5: Transverse cross-section of an artery repaired by laser welding, with the application of a semi-solid solder solution [47]. [PERSON] et al. [77] and [PERSON] et al. [72] focused their works on minimizing solder leakage by using biodegradable polymers as carrier material for the liquid solders and by studying solder viscosity, respectively. In agreement with the previous researches, [PERSON] et al. [49] reported that the application of semi-solid solders provides higher protein density and cohesive bonding when compared to fluid solders. The authors also reported that porous polymer scaffolds can be used to prevent solder leakage. In turn, [PERSON] et al. [40] confirmed the possibility of including support cross-linking agents, such as genipin, in albumin-based solutions to improve their flexibility and reduce brittleness. The improvement of solder properties by adding other elements had already been tested some years earlier by [PERSON] et al. [76], who introduced heparin in an albumin-based solder with the purpose of reducing microvessel thromboses. More recently, [PERSON] et al. [78] reported the effectiveness of using carrier membranes with bovine serum albumin (BSA) solder linked by covalent cross-linking bindings and indocyanine green (ICG) dye to improve bonding strength and to prevent liquid solder leakage. In fact, the addition of laser-activated dyes in solder solutions (ICG and fluorescein isothiamate), enabling the use of lower energy outputs due to selective laser absorption, which minimizes the associated thermal damage, had already been reported in previous works, such as [PERSON] et al. [56], [PERSON] et al. [43], and [PERSON] et al. [51]. Besides the welding parameters and the use of solder solutions, the welding process is also influenced by other issues. Specifically, handling laser welding in three-dimensional (3D) approaches requires specific surgical skills due to the necessary manipulation of the vascular and nervous elements, which may lead to injury aggravation and procedure repetition [50; 51]. To avoid manual surgical manipulation in the laser-welding procedure, [PERSON] et al.