Investigations on the Grasping Contact Analysis of Biological Tissues With Applications in Minimally Invasive Surgery

Abstract

Analytical and finite element methods are employed to determine the contact pressure on the surface of a tissue being grasped by an endoscopic grasper, in Minimally Invasive Surgery (MIS). Normally, an endoscopic grasper is corrugated (teeth-like) in order to grasp slippery tissues. It is highly important to avoid damage to the tissues while grasping and manipulation during endoscopic surgery. Therefore, it is essential to determine the exact contact pressure on the surface of the tissue. To this end, initially a comprehensive closed form, finite element and experimental analysis of grasping contact pressure on viscoelastic materials which have similar properties as that of biological tissues is studied. The behavior of a grasper with wedge-like teeth, when pressed into a linear viscoelastic material is examined. Initially, a single wedge penetrating into a solid is studied and then is extended to the grasper. The elastic wedge indentation is the basis of the closed form analysis and the effects of time are included in the equations by considering the corresponding integral operator from viscoelastic stress-stain relations. In addition, a finite element analysis is carried out in Ansys-10 software. Finally, the experimental results are presented to validate both analytical and FEM results. The results of this study provide a closed form expression for grasping contact pressure force and contact area along with the variations of stress in tissue obtained through FEM analysis. The variation of contact pressure and the rate of growth of the contact area with time are presented.

The Ovario-Protective Effect of Erythropoietin against Oxidative Damage Associated with Reperfusion Following Ovarian Torsion in Rat

“…In addition, it has been suggested that EPO can increase red blood cells leading to a reduction in cellular oxidative stress. According to the literature, EPO also exerts its beneficial effect in ischemic organs by prevention of apoptosis, probably by increasing Bcl2 and HSP70 expression Bonakdar et al, 2007). The time which the tissue exposing to ischemia is critical.…”

“…In their study reduction of medium oxygen content to <1% triggered a majority of cells to enter in apoptosis. It appears that the ovaries have high resistance to ischemia (Ming et al, 2001;Bonakdar et al, 2007). EPO is a protective tissue cytokine it's receptors have been shown to exist in lots of tissues.…”

“…The time which the tissue exposing to ischemia is critical. Calvillo et al (2003;Bonakdar et al, 2007), in an experimental study on myocardial cells showed that rhEPO prevents apoptosis when the cells exposed to extreme and prolonged hypoxia. In their study reduction of medium oxygen content to <1% triggered a majority of cells to enter in apoptosis.…”

“…To preserve the ovarian function, treatment of torsion should be as conservative as possible (Rousseau et al, 2008). RhEPO which was used in this study has several beneficial effects in ischemic organs (Sharples et al, 2004;Bonakdar et al, 2007;Calvillo et al, 2003;Wu et al, 2006). EPO is a potent antioxidant (Asli-Ardeh and AbbaspourGilandeh, 2008).…”

“…In the next two groups, the same procedure was performed and rhEPO (400 u kg −1 ) was administrated intraperitoneally 1 h after occlusion of the ovarian vessels. The dose of rhEPO was chosen based on the findings of Villa et al, 2003;Bonakdar et al, 2007).…”