Abstract
In this paper, we report a measurement method of viscoelastic properties of the grasped objects using a grasping forceps with sensors. Stiffness is one of the important information to distinguish the cancerous tissue from normal tissues because the mechanical properties of cancerous tissue change according to the grade of cancer. However, in laparoscopic surgery, it is difficult to acquire the tactile information including the stiffness. Thus, we have proposed a measurement method of stiffness by the special instrument used for the laparoscopic surgery to support surgeons. However, the viscoelasticity is not considered in the preceding method though organs are viscoelastic materials. We have already observed the stress relaxation, which is a viscoelastic phenomenon, using the grasping forceps with sensors. In this paper, we evaluated the viscoelasticity of the grasped object by measuring the stress relaxation and compared the viscoelastic properties acquired by the grasping forceps to those acquired by the conventional compression test. The grasped objects were expressed as viscoelastic materials with 3-element Maxwell model. The viscoelastic parameters, E_∞, E_1, and η_1, were calculated by fitting the theoretical curve using least squares approximation to the time response of the stress during the stress relaxation. The values of the viscoelastic parameters of 30% gelatin acquired by viscoelasticity measurement with forceps were E_∞ = 32 ± 5 kPa, E_1 = 13 ± 3 kPa, η_1 = 0.77 ± 0.41 MPa・s. Though E_∞ and E_1 were smaller than those acquired by the conventional compression test, the stress relaxation was observed and the relaxation time τ_1 was similar to that of the conventional compression test.
