Background and Objective:Recent studies have indicated that chondrocyte viability decreases with prolonged or repeated laser irradiation. To optimize laser-mediated cartilage reshaping, the heating process must be finely controlled. In this study, we use high-power Nd:YAG laser irradiation ( ס 1.32 m) combined with cryogen spray cooling (CSC) in an attempt to reshape porcine septal cartilage while enhancing chondrocyte viability. Study Design/Materials and Methods: Chondrocyte viability was determined after high-power (50 W/cm 2 ) Nd:YAG-mediated cartilage reshaping with and without cryogen spray cooling (CSC) and correlated with dynamic measurements of tissue optical and thermal properties. Results: After 1.5 to 2.0 seconds of laser exposure, characteristic changes in diffuse reflectance (indicating the onset of accelerated stress relaxation) was observed in both laser only and laser with CSC specimens. After 2 seconds of laser exposure, specimens in both groups retained the curved shape for up to 14 days. After one laser exposure, chondrocyte viability was 94.35 ± 6.1% with CSC and 68.77 ± 20.1% (P < 0.05) without CSC. After two laser exposures, a similar trend was observed with CSC (70.18 ± 16.44%) opposed to without CSC (28 ± 45%; P < 0.05). Conclusion: CSC during high-power laser irradiation allows rapid heating while minimizing extreme front surface temperature elevations and axial thermal gradients. Laser irradiation with CSC can be used to effectively reshape cartilage tissue with the additional advantage of increasing chondrocyte viability. Lasers Surg.
Abstract. The effect of' tissue micro-architecture and water content on ablation rates in bone is examined. Precisely machined and prepared porcine calvarial lamellar and cortical bone were ablated with a Holmium-YAG laser (k=2.1/~m). Lamellar and cortical bone differ substantially in their tissue micro-architecture. Both are porous hard tissues, which differ predominantly in size and distribution of pores within the bone matrix. These hard tissues were ablated under physiological (wet) and chemically dehydrated conditions. The ablation rates over the range of energy densities examined assumes many linear characteristics. Ablation rate (as a function of fluence) is considerably higher for dehydrated cortical bone (4.7ttm cm e J-1) compared to fresh cortical bone (1.49 #m cm 2 J-1). This trend is also observed in lamellar bone (2.31/~m cm 2 J-1 for wet and 0.37~m cm 2 J-1 for dry). Under both physiological and dehydrated conditions, cortical bone was ablated faster. Mechanisms accounting for these observations are discussed.
The Pockels’ effect has been demonstrated in thermally evaporated polycrystalline thin films of ZnS. The strongly (111)-oriented films were found to have an electro-optic constant of r41 = 3.3 × 10−13 m/V for fields perpendicular to the (111) planes. Extinction ratios of up to 85% have been observed in an optical waveguide modulator. Analysis indicates a stress-related birefringence that manifests itself upon temperature change. The temperature coefficient of stress in the polycrystalline films was found to be 3.0×105 N m−2/°C.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.