Gold Nanorod-Collagen Nanocomposites as Photothermal Nanosolders for Laser Welding of Ruptured Porcine Intestines

Surgical site infection and postoperative leakage are complications that may develop following colorectal surgery and result in fatal consequences. Rapid, fluid-tight wound closure through laser tissue welding (LTW) can reduce postoperative leakage and thus decrease infection. Laser tissue welding involves generation of localized heat by exposing an exogenous chromophore to near-infrared (NIR) irradiation in order to seal wounds. In this study, we generated gold nanorod (GNR)-collagen nanocomposites (NCs) for laser-facilitated welding of ruptured intestinal tissue. The fluid content, stiffness, elasticity, and laser-induced temperature response of these nanocomposites were modulated to optimize laser-induced tissue fusion and minimize tissue damage. In addition, the effect of laser operating parameters including power density, femtosecond pulsed wave (PW) or continuous wave (CW) laser, and exposure duration were all studied. Laser power density and treatment duration significantly affected the temperatures reached during welding, as well as tissue weld strength and burst pressure. CW laser was found to induce significantly higher temperatures of the nanocomposites during treatment than PW laser, but the differences in weld strength and burst pressure for the two laser types were insignificant. This suggests that PW lasers can result in robust welds while minimizing potential thermal damage compared to CW lasers. The ultimate tensile strength of welded ruptured tissue was returned to as high as 68% of the native tissue strength through laser treatment, and laser treatment with these nanocomposites restored up to 64% of native tissue leak pressure and 42% of burst pressure. To the best of our knowledge, the laser power densities used (≤2.50 W/cm²) are among the lowest reported for laser tissue welding, and the laser configuration and use require very little surgical skill. Our results indicate that GNR-collagen nanocomposites are promising photothermal biomaterials in laser tissue welding applications

Nitration Kinetics of Cellulose Fibers Derived from Wood Pulp in Mixed Acids

A model has been developed to describe the reaction kinetics of single cellulose fibers (SCFs) in mixtures of nitric acid, sulfuric acid, and water during the production of highly nitrated nitrocellulose. Experiments were performed to provide insight into factors affecting the rate and extent of reaction for the nitration of wood-pulp-derived cellulose fibers in mixed acids and to provide kinetic data for model evaluation and kinetic parameter estimation. This work provided considerable information regarding the nature of the chemical reaction, and demonstrated that fiber properties do not play a significant role in the reaction kinetics or extent of reaction. This finding is particularly important because it allows for much broader range of wood pulps to be considered for industrial-scale nitration than have historically been used. A semiempirical kinetic model was developed to describe the conversion of cellulose to nitrocellulose as an equilibrium controlled reaction using these results. This kinetic model yielded excellent agreement with experimental results over the entire range of temperatures, fiber types, and reaction times studied