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Background Tissue grasping damage often occurs in minimally invasive surgery, which would increase the postoperative recovery time and the risk of surgical complications. The purpose of this study was to evaluate the relationship between liver tissue trauma and compression stress magnitude and duration during tissue clamping operation. Methods The clamping experiments of liver tissues in vivo were conducted by using a universal soft tissue mechanical testing machine under different clamping stress magnitudes and durations. The rabbit liver was used to simulate human liver. A minimally invasive surgery grasper was used in these tests to simulate the real tissue-surgical operation condition. A pathological grading system was created to quantitatively assess the trauma within the liver tissue. The hyperbolic regression models were utilized to predict the trauma degree of liver tissue. Findings Obvious hyperemia, hemorrhage, hepatic capsule rupture and inflammatory cell infiltration appeared in the clamping sites of the liver. Assessment results indicated that the trauma degree increased nonlinearly with the increasing clamping stress and duration time. There exist safe thresholds, in which the severe trauma of the studied tissue can be avoided during grasping operation. Interpretation The results could provide the safety margins and the trauma prediction models for surgeons during grasping and palpation tasks in minimally invasive surgery.

Experimental observations in the open literature indicate that soft tissues are slightly compressible, and this characteristic affects not only their overall elastic response but also their damage evolution and failure mechanism. In this study, we find that the compressibility of liver tissues is also closely related to the initial specimen volume according to the confined compression tests: the samples with smaller initial volume exhibit more compressible behavior compared to the larger ones. To include this initial-volume dependent effect, we developed a novel volumetric strain energy model with two variables, i.e., the bulk modulus and the compressibility factor. A detailed scheme was proposed as well to identify these two parameters, and the relationship between the bulk modulus and the initial volume was clarified. Findings from this study will help to deepen the understanding of the biomechanical properties of soft tissues. Statement of significance Liver is a highly vascular organ and traditionally assumed to be an incompressible medium. However, through the confined compression tests, we found that the samples with smaller initial volumes exhibit more compressible behavior. Hence, we developed a novel strain energy density model to characterize the initial-volume dependent hyperelastic response, and found that the bulk modulus of liver tissues is positively related to the initial volume. Our results suggest that the compressibility of liver tissues should be considered in the future study of liver biomechanics.

In this article, the tensile properties of gastric wall were investigated by using biomechanical test and theoretical analysis. The samples of porcine stomach strips from smaller and greater curvature of the stomach were cut in longitudinal and circumferential direction, respectively. The loading-unloading, stress relaxation, strain creep, tensile fracture tests were performed at mucosa-submucosa, serosa-muscle and intact layer, respectively. Results showed that the biomechanical properties of the porcine stomach depended on the layers, orientations and locations of the gastric wall and presented typical viscoelastic, nonlinear and anisotropic mechanical properties. During loading-unloading test, the stress of serosa-muscle layer in the longitudinal direction was 15-20% more than that in the circumferential direction at 12% stretch ratio, while it could reach about 40% for the intact layer and 50% for the mucosa-submucosa layer. The results of stress relaxation and strain creep showed that the variation degree was obviously faster in the circumferential direction than that in the longitudinal direction, and the ultimate residual values were also different for the different layers, orientations and locations. In the process of fracture test, the serosa-muscle layer fractured firstly followed by the mucosa-submucosa layer when the intact layer was tested, the longitudinal strips firstly began to fracture and the required stress value was about twice as much as that in the circumferential strips. The anisotropy and heterogeneity of mechanical characterization of the porcine stomach were related to its complicated geometry, structure and functions. The results would help us to understand the biomechanics of soft organ tissue.

Background During clamping operation for minimally invasive intestinal surgery, patients often suffer from small intestine trauma. This phenomenon will lead to various complications, increase recovery time and cause pain for patients. Methods In this paper, preliminary simulations of small intestine clamping operations in the minimally invasive surgery were made by conducting compression tests under different clamping stresses, durations and loading rates. A pathological grading system was designed after microscope observation to quantitatively evaluate the trauma of small intestine tissue. Findings Results showed that different traumas: inflammatory cell infiltration, hyperemia, hemorrhage and rupture between serosa and muscularis, as well as villi destruction could be observed on the clamping sites of the small intestine tissue. When the clamping parameters (clamping stress, duration and loading rate) increased, the degree of the tissue trauma increased. There existed safe thresholds for clamping operations, at which severe trauma of small intestine tissues could be avoided in the clamping process. Interpretation As the clamping parameters increased, the strain, that is the deformation of the small intestine tissue increased. The increase in the deformation would induce the aggravation of trauma degree.

The contact characteristic between finger and objects changes due to the different deformation of a fingerprint when the finger slides in different directions. To understand this mechanism better, a new type of experimental setup was designed, and specific tests were conducted. We analyzed the regularity of the friction coefficient in two sliding directions. When the finger was sliding on surfaces with different roughness values, normal forces, and contact angles, the fingerprint deformation was captured by the Asana microscope. The following were inferred from the conducted experiments. Firstly, the friction coefficient decreases with increasing sample roughness and normal force. Secondly, the friction coefficient first decreases and then increases with increasing contact angle. Thirdly, the distance between the fingerprints increases when the finger is dragged, leading to an increase in contact area, thereby improving the friction coefficient. Finally, the result will be opposite to the previous inference when the finger is squeezed hard for fingerprinting.

Radial fretting tests on human femur cortical bone with a ball-on-flat configuration were carried out in vitro under different normal contact loads. The kinetics behaviors and damage characteristics of the cortical bone were analyzed using the load versus displacement (F–D) curves. The fretting scars were examined using laser confocal scanning microscopy (LCSM) and scanning electron microscopy (SEM). A nano-indenter was used to characterize the mechanical property of the osteon of the cortical bone. Morphologies showed that the primary damage form was due to micro-cracking. Around the osteon, three kinds of micro-crack configurations were observed; i.e. annular cracks—located at the concentric lamellae; radial cracks—initiated from the Harversion canal; and interstitial cracks—initiated and propagated between the interstitial lamellae. Plenty of interstitial cracks occurred in the wear scar, which indicated that the interstitial tissue was the weak zone in the structure of cortical bone. In addition, the contact stresses under the radial fretting condition were calculated by the finite element method analysis (FEMs) and the behaviors of cracking were explained. The results demonstrated that the stress concentration that occurred around the Harversian canal and osteon system resulted in a better resistance than that from the interstitial tissue. The concentric lamellae presented a better radial-fretting resistance and contact fatigue resistance than that from the interstitial lamellae.

Dental microwear has been used for decades to reconstruct the diets of fossil hominins and bioarchaeological populations. The basic theory has been that hard-brittle foods (e.g., nuts, bone) require crushing and leave pits as they are pressed between opposing cheek-tooth surfaces, whereas soft-tough foods (e.g., grass blades, meat) require shearing and leave scratches as they are dragged along opposing surfaces that slide past one another. However, recent studies have called into question the efficacy of microwear as an indicator of diet. One issue has been the limited number of in vitro studies providing empirical evidence for associations between microwear pattern and chewing behavior. We here describe a new study using a chewing simulator, the BITE Master II, to examine the effects of angle of approach between opposing teeth and food consistency on microwear surface texture. Results indicate that opposing teeth that approach one another: 1) perpendicular to the occlusal plane (crushing) result in pits; 2) parallel to the occlusal plane (shearing) result in striations in the direction of movement; and 3) oblique to the occlusal plane (45°) result in both striations and pits. Results further suggest that different food types and abrasive loads affect the propensity to accumulate microwear features independent of feature shapes.

Fretting wear tests of bonded MoS2 coating under radial and composite fretting mode have been carried out on a new fretting rig. The maximum applied load was respectively 200N, 400N and 800N with a constant loading speed of 12mm/min. Dynamic analyses in combination with microscopic examinations through SEM and XPS have been performed. Experimental results showed that such MoS2 coating exhibited an excellent radial fretting damage resistance, and its damage strongly depended upon the applied maximum loads and inclined angle under composite fretting condition. The fretting damage mechanism of MoS2 coating also discussed under different fretting modes. The XPS analysis revealed that the oxidation of MoS2 crystal was played an important role in damage. The fretting wear of MoS2 coating was mainly represented by the mechanism of delamination and oxidation wear under composite fretting conditions.