@mastersthesis{pearson96,
  author = {S. D. Pearson},
  title = {Mechanical Strength Studies of Steady-State Thermal and Pulsed Laser Tissue Welding},
  school = {Oregon Graduate Institute of Science and Technology},
  year = {1996},
  abstract = {Laser tissue welding is the process of binding two tissues together using laser irradiation with a mechanism that is still poorly understood. This study examined the mechanism of laser welding by determining the effects of heat and pulsed diode laser light on tissue. This includes yield strength tests, steady-state thermal contraction/expansion tests, and waterbath and laser welding experiments. \vskip2mm Yield strength measurements indicated that porcine aorta and intestine have great variations in yield due to structural and thickness variability. Waterbath heating experiments demonstrated that initial heating had little effect on average yield strength, while laser yield tests indicated a 20\% decrease in average yield strength. Also, yield strength was inversely proportional to number of pulses: i.e., the more pulses fired, the lower the yield strength. \vskip2mm Porcine aorta, intestine and elastin biomaterial react differently to immersion in hot water. Porcine intestine contracted at an exponential rate of 0.6$\pm$0.1\,s$^{-1}$ above a threshold temperature of 77$\pm$1$^\circ$C. Aorta contracted at two different rates, the first at a rate of 0.07$\pm$0.03\,s$^{-1}$ above a threshold temperature of 65$\pm$5$^\circ$C and the second at a slightly increasing linear rate of 0.0005$\pm$0.0001/s$^\circ$C. The elastin biomaterial actually elongated with increasing temperature at a linear rate of 0.036$\pm$0.006/s$^\circ$C. Laser contraction was performed on porcine aorta and intestine stained with 6.5\,mM ICG. Results show contraction occurred only after 10 pulses at irradiances above 75\mJper, and maximized at 2--3\mm. \vskip2mm Waterbath welds were performed on all five combinations of intestine, aorta, and heterograft at temperatures from 50--80$^\circ$C and times in the range of 3--15 minutes. All welds peaked at temperatures of 70--75$^\circ$C, and all intestine type welds peaked at 10 minutes. The others have time peaks beyond the times used in these studies. \vskip2mm Laser welds were attempted on all waterbath weld types with success in all types except aorta-aorta welds. Laser weld strengths peaked at staining concentrations of 1.6\,mM, irradiances of 42\,mJ/cm$^2$, and high pulse numbers (above 10 pulses). Peak laser weld strengths were 30--100\% of waterbath weld strengths. \vskip2mm Mechanical strength tests provided a basis for thermal effects on tissue strength. Thermal contraction/expansion studies produced different mechanisms for thermal changes in each tissue type. The waterbath and laser welding studies provided a basis for the strongest welds possible between each tissue type, as well as two viable methods to produce tissue welds. The welding tests also lead to separate mechanisms for welding due to large differences in peak welding times and temperatures.},
}