<title>Dynamic simulations of tissue welding</title>

Abstract

The exposure of human skin to near-infiared radiation is numerically simulated using coupled laser, thermal transport and mass transport numerical models. The computer model LATIS is applied in both one-dimensional and two-dimensional geometries. Zones within the skin model are comprised of a topical solder, epidermis, dermis, and fatty tissue. Each skin zone is assigned initial optical, thermal and water density properties consistent with values listed in the literature. The optical properties of each zone (ie. scattering, absorption and anisotropy coefficients) are modeled as a kinetic function of the temperature. Finally, the water content in each zone is computed from water diffusion where water losses are accounted for by evaporative losses at the air-solder interface. The simulation results show that the inclusion of water transport and evaporative losses in the model are necessary to match experimental observations. Dynamic temperature and damage distributions are presented for the skin simulations. P

Infrared skin damage thresholds from 1940-nm continuous-wave laser exposures

“…Although this layer does not absorb the laser energy directly, the layer was found to affect predicted outcomes for longer exposure times, where significant thermal diffusion occurred in regions beyond the dermis during the laser exposure time. Parameters for the fat layer were obtained from 12 Thermal and optical properties of the skin layers were estimated using equations derived by Takata, Zaneveld, and Richter 9 with the assumption of 80% water content in the dermis and 30% in epidermis, as did Chen et al 3 The absorption coefficient does change fairly rapidly between 1940 and 2000 nm. This difference was programmed into the model for comparison of the two studies.…”

“…6,10,11 Models that represent the skin as a two-or three-layer construct, with a Beer's law absorption term for the laser energy deposition, have been shown to accurately predict the opticalthermal response of the tissue. 3,9,12 Thermal diffusion solutions are most often computed through finite element or finite difference methods. Increased accuracy has been demonstrated when temperature-dependent surface cooling associated with the evaporation of water is included.…”

Infrared skin damage thresholds from 1319-nm continuous-wave laser exposures

“…[21][22][23][24] Models that represent the skin as a two-or three-layer construct, with a Beer's law absorption term for the laser energy deposition, have been shown to accurately predict the optical-thermal response of the tissue. 5,19,25 Thermal diffusion solutions are most often computed through finite element or finite difference methods. Increased accuracy has been demonstrated when temperature-dependent surface cooling associated with the evaporation of water is included.…”

Experimental and Computational Laser Tissue Welding Using a Protein Patch

“…This result agrees with previous studies. 5,6,12 The patches provided sufficient hydration to allow evaporation to occur and prevented desiccation. The uniform thickness and composition of the patches resulted in consistent absorption of the laser energy, yielding only small variation in peak surface temperatures for a given laser fluence.…”

“…This problem has been addressed by employing a numerical model of the laser-tissue interaction based on experimentally obtained surface temperature data. [5][6][7] The combination of experiment and simulation enables characterization of the status of the tissue and the progression of the weld.…”