<title>Laser solder repair technique for nerve anastomosis: temperatures required for optimal tensile strength</title>

Abstract

Laser-assisted repair of nerves is often unsatisfactory and has a high failure rate. Two disadvantages of laser assisted procedures are low initial strength of the resulting anastomosis and thermal damage of tissue by laser heating. Temporary or permanent stay sutures are used and fluid solders have been proposed to increase the strength of the repair. These techniques, however, have their own disadvantages including foreign body reaction and difficulty of application.To address these problems solid protein solder strips have been developed for use in conjunction with a diode laser for nerve anastomosis. The protein helps to supplement the bond, especially in the acute healing phase up to five days post-operative. Indocyanine green dye is added to the protein solder to absorb a laser wavelength ('8OO nm) that is poorly absorbed by water and other bodily tissues. This reduces the collateral thermal damage typically associated with other laser techniques.An investigation of the feasibility of the laser-solder repair technique in terms of required laser irradiance, tensile strength of the repair, and solder and tissue temperature is reported here. The tensile strength of repaired nerves rose steadily with laser irradiance reaching a maximum of 105 10 N.cm2 at 12.7 W.cm2 . When higher laser irradiances were used the tensile strength of the resulting bonds dropped. Histopathological analysis of the lasersoldered nerves, conducted immediately after surgery, showed the solder to have adhered well to the perineurial membrane, with minimal damage to the inner axons of the nerve. The maximum temperature reached at the solder surface and at the solder/nerve interface, measured using a non-contact fibre optic radiometer and thermocouple respectively, also rose steadily with laser irradiance. At 12.7 W.cm2 , the temperatures reached at the surface and at the interface were 85 4 and 68 4 °C respectively.This study demonstrates the feasibility of the laser-solder repair technique for nerve anastomosis resulting in improved tensile strength. The welding temperature required to achieve optimal tensile strength has been identified.

Surgical adhesives for laser-assisted wound closure

“…The irradiance of 15 W/cm 2 for the maximum strength is much higher than previously reported for liquid or solid solders. 17,21,22 This increase is believed to be due to scattering of the laser light in the adhesive and the packing density of the solder. 7 Sacrificing some of the tissue repair strength for increased adhesive control and flexibility can be advantageous in surgical procedures with irregular geometries.…”

“…The combination of serum albumin and indocyanine green dye ͑ICG͒ has shown promising results. 3,[7][8][9][10][11][12][13][14][15][16][17] The albumin solder is denatured at the repair site during laser welding to enhance the adhesion of the adjacent tissue edges. The resulting denatured solder is nonimmunogenic 14 and is gradually absorbed in the normal wound healing process.…”