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Photochemical Tissue Bonding for Military Medical Applications

A two-wavelength laser and albumen stent easily repair separated vessels.

Joining severed vessels is a recurring problem in trauma and surgery. The basic technology of joining vessels using sutures has been available for centuries, but remains a slow and tedious process. A complete system for micro-anastomosis of vessels was developed that involves a laser in a clinically useful form factor, and a novel albumen stent to support the vessel during the surgery.

The novel laser uses two wavelengths, each with its own power setting. A red aiming beam (1 mW at 0.639 microns) creates a spot on the vessel wall, allowing the surgeon to target specific areas. A 1.9-micron beam is then fired at 300 mW to bond the damaged area. The result is a strong, watertight junction.

Photothermal bonding is attractive because no highly reactive chemical species are involved. To deliver light to a tissue, the light must be absorbed by water. A 1.9-micron emission uses only low power levels, and the penetration depth of 100 microns is sufficient to generate a physically robust bond, but too low to damage healthy tissue underneath.

The novel stent is made from human albumen, concentrated to 38% instead of the more customary 25%, because 38% is optimal for laser welding. The albumen provides both support and glue for the repair. It is necessary to closely match the diameter of the stent with the vessel to be repaired. This leads to a close alignment of the vessel edges, which improves and speeds healing. These stents are biodegradable – any non-irradiated albumen will dissolve in freely flowing blood within a minute.

Possible improvements are to use a green light as opposed to red in the aiming beam. This will provide a greater contrast on the vessel wall. Using an LED instead of a coherent light beam would reduce speckling, and allow the unit to run cooler.

This work was done by Dennis McCal of nLIGHT Photonics Corp. and Scott Prahl of the Oregon Medical Laser Center for the Air Force Office of Scientific Research. For more information, download the Technical Support Package (free white paper) at www.medicaldesignbriefs.com/briefs. AFRL-0134

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