Suvranu De Rahul
Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180 USA.
Comput Methods Appl Mech Eng. 2017 Feb 1;314:71-84. doi: 10.1016/j.cma.2016.07.026.
A multi-physics model has been developed to investigate the effects of cellular level mechanisms on the thermomechanical response of ultrasonically activated soft tissue. Cellular level cavitation effects have been incorporated in the tissue level continuum model to accurately determine the thermodynamic states such as temperature and pressure. A viscoelastic material model is assumed for the macromechanical response of the tissue. The cavitation model based equation-of-state provides the additional pressure arising from evaporation of intracellular and cellular water by absorbing heat due to structural and viscoelastic heating in the tissue, and temperature to the continuum level thermomechanical model. The thermomechanical response of soft tissue is studied for the operational range of frequencies of oscillations and applied loads for typical ultrasonically activated surgical instruments. The model is shown to capture characteristics of ultrasonically activated soft tissue deformation and temperature evolution. At the cellular level, evaporation of water below the boiling temperature under ambient conditions is indicative of protein denaturation around the temperature threshold for coagulation of tissues. Further, with increasing operating frequency (or loading), the temperature rises faster leading to rapid evaporation of tissue cavity water, which may lead to accelerated protein denaturation and coagulation.
已开发出一种多物理场模型，以研究细胞水平机制对超声激活软组织热机械响应的影响。细胞水平的空化效应已被纳入组织水平的连续介质模型中，以准确确定诸如温度和压力等热力学状态。假定组织的宏观力学响应采用粘弹性材料模型。基于空化模型的状态方程通过吸收组织中结构和粘弹性加热产生的热量，提供了细胞内和细胞间水分蒸发产生的额外压力，并将温度纳入连续介质水平的热机械模型。针对典型超声激活手术器械的振荡频率和施加负载的工作范围，研究了软组织的热机械响应。该模型被证明能够捕捉超声激活软组织变形和温度演变的特征。在细胞水平上，环境条件下低于沸点温度的水分蒸发表明在组织凝固温度阈值附近蛋白质发生变性。此外，随着工作频率（或负载）的增加，温度上升得更快，导致组织腔水分快速蒸发，这可能会加速蛋白质变性和凝固。
