Date

July 1995

Document Type

Thesis

Degree Name

M.S.

Department

Dept. of Applied Physics

Institution

Oregon Graduate Institute of Science & Technology

Abstract

Laser tissue welding is a sutureless method of wound closure that has been used successfully in nerve, skin, and arterial anastomoses. After heating generated by laser exposure, a glue is formed between tissue edges that forms a weld upon cooling. The advantages of laser welding over traditional wound closure are no foreign body reaction and less scar formation. However, traditional methods of laser welding have a minimal surface area of tissue to weld, such as in anastomoses. Also, excess heating occurs with the use of traditional surgical CW lasers such as the Argon and C0[subscript]2. These studies used an artificial biomaterial made mostly of elastin and fibrin to weld to porcine aorta, which allowed greater surface area for welding and measurement of optical properties of the weld site. Also, a pulsed diode laser was used to maintain thermal confinement and therefore minimize excess heating. Steady state thermal experiments indicated that the elastin-based biomaterial was thermally stable up to 100°C. Welds between biomaterial and aorta were successful between 65-80°C with pressures of SN/cm² for immersions of 5 minutes. Photosensitive dyes with high absorption at the laser wavelength are added to the weld site to increase heating and to minimize thermal damage to surrounding unstained tissue. The intimal surface of porcine aorta was stained with indocyanine green dye to efficiently absorb 808nm diode laser light. A 5mg/ml solution of indocyanine green dissolved in water penetrated 200µm into the intimal side of porcine aorta. Transmission measurements of stained aorta were made using radiant exposures of 6-129mJ /mm² and using pulse durations of 0.5-5 ms. Transmission increases and reaches a maximum of 80-85% with successive pulses for radiant exposures greater than ~25 mJ /mm², indicating that the absorption coefficient, and therefore heating, of stained tissue decreases with repetitive pulses. Thermal measurements of the surface of stained aorta using a photothermal radiometer were made for radiant exposures of 38-120mJ/mm². Temperature rises of 10-100°C were measured after one pulse. Thermal measurements of samples from different aortas, each stained with new solutions of ICG, showed the wide variability in the heating of tissue, and therefore the variability in concentration of ICG for different samples. Simultaneous transmission and thermal measurements were made of stained aorta to eliminate sample variability and to compare the absorption coefficients calculated from each measurement. As in previous transmission measurements, transmission increased over pulses, indicating a decrease in absorption. However, the surface temperature, and therefore the absorption coefficient remained constant over repetitive pulses. It was postulated that ICG was undergoing a photochemical change with repeated exposure to laser light. This change was thought to be a change in effective depth of the ICG since the penetration depth of ICG was the only hard to measure quantity in our calculations. The effective depth of stain is inversely proportional to the fourth root of the pulse number. Laser welds of stained aorta to biomaterial were attempted by sandwiching the samples between glass slides and applying pressures ranging from 4-20N/cm² for 5 ms pulse durations and 86 mJ /mm² radiant exposure. Welds were successful for pressures above 11 N/cm².

Identifier

doi:10.6083/M4HD7SKD

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