WO 2018/046962 A1 - Force sensor plate

The present invention provides a force sensor plate for use in a training apparatus for simulating minimally invasive surgery. The force sensor plate comprises: a frame configured to support a tissue-sheet through which an incision can be made to simulate minimally invasive surgery using at least one surgical tool; and a sensor system configured to sense the force and/or torque applied to the tissue-sheet at the incision by the at least one surgical tool.status: publishe

Stretching the limits of biaxial testing: Material characterization of biological tissues with subcritical dimensions

Biaxial testing, planar or extension inflation, is the method of choice to test soft biological tissue. In some cases, sample dimensions prohibit the use of the aforementioned setups. For cerebral bridging veins, samples with a diameter as small as 0.5 mm [1] can be obtained. To successfully characterise tissues of that size, a new test setup was developed. This setup applies a combination of uniaxial and simple shear deformations to obtain transversely isotropic, fibre reinforced (GOH) [2] material properties for this type of tissue. To validate our method, a finite element (FE) model was built in Abaqus 6.14-1. A virtual testing sample was modelled as a 2D planar deformable shell, with GOH material parameters. Homogeneous boundary conditions were imposed, allowing uniaxial extension followed by simple shear deformation. The reaction forces and strain data were used as virtual experimental data and given as input to a fitting procedure to determine the GOH material parameters. Using a least squares nonlinear optimization algorithm in Matlab R2015a (lsqnonlin), the difference between experimental and model stress for each loading direction was minimized. Figure1 shows the applied deformations in the FE model and Table 1 shows the results of the fitting procedure. Future work will be to adapt the FE models to more realistic conditions, upon which this methodology will be applied to actual biological tissue, in casu human bridging veins.status: publishe

Full characterization of small samples of anisotropic biological soft tissue: Combining microindentation, uniaxial tensile testing and two rail-shear testing

status: publishe

Combination of uniaxial tensile testing and two rail shear testing for small samples of biological soft tissue: Feasibility study

status: publishe

The sensitivity to inter-subject variability of the bridging vein entry angles for prediction of acute subdural hematoma

Acute subdural hematoma (ASDH) is one of the most frequent traumatic brain injuries (TBIs) with high mortality rate. Bridging vein (BV) ruptures is a major cause of ASDH. The KTH finite element head model includes bridging veins to predict acute subdural hematoma due to BV rupture. In this model, BVs were positioned according to Oka et al. (1985). The aim of the current study is to investigate whether the location and entry angles of these BVs could be modelled using data from a greater statistical sample, and what the impact of this improvement would be on the model's predictive capability of BV rupture. From the CT angiogram data of 78 patients, the relative position of the bridging veins and their entry angles along the superior sagittal sinus was determined. The bridging veins were repositioned in the model accordingly. The performance of the model, w.r.t. BV rupture prediction potential was tested on simulations of full body cadaver head impact experiments. The experiments were simulated on the original version of the model and on three other versions which had updated BV positions according to mean, maximum and minimum entry angles. Even though the successful prediction rate between the models stayed the same, the location of the rupture site significantly improved for the model with the mean entry angles. Moreover, the models with maximum and minimum entry angles give an insight of how BV biovariability can influence ASDH. In order to further improve the successful prediction rate, more biofidelic data are needed both with respect to bridging vein material properties and geometry. Furthermore, more experimental data are needed in order to investigate the behaviour of FE head models in depth.status: publishe

Collagen fibre orientation in human bridging veins

Bridging veins (BVs) drain the blood from the cerebral cortex into dural sinuses. BVs have one end attached to the brain and the other to the superior sagittal sinus (SSS), which is attached to the skull. Relative movement between these two structures can cause BV to rupture producing acute subdural haematoma, a head injury with a mortality rate between 30 and 90%. A clear understanding of the BVs microstructure is required to increase the biofidelity of BV models when simulating head impacts. Twelve fresh BV samples draining in the superior sagittal sinus (SSS) from a single human cadaver were cut open along their length and placed on an inverted multiphoton microscope. To ensure that the BVs were aligned with the axial direction an in-house built, uniaxial tension set-up was used. Two scans were performed per sample. Before the first scan, a minor displacement was applied to align the tissue; then, a second scan was taken applying 50% strain. Each BV was scanned for a length of 5 mm starting from the drainage site into the SSS. Imaging was performed on a Zeiss LSM780 microscope with an 25[Formula: see text] water immersion objective (NA 0.8), coupled to a tunable MaiTai DS (Spectraphysics) pulsed laser with the wavelength set at 850 nm. Second harmonic and fluorescence signals were captured in forward and backward direction on binary GaAsP (BiG) detectors and stored as four colour Z-stacks. Prior to the calculation of the local orientations, acquired Z-stacks were denoised and enhanced to highlight fibrillar structures from the background. Then, for each Z-plane of the stack, the ImageJ plugin OrientationJ was used to extract the local 2D orientations of the fibres based on structure tensors. Two kinds of collagen architectures were seen. The most common (8[Formula: see text]12 samples) was single layered and had a uniform distribution of collagen. The less common (4[Formula: see text]12 samples) had 2 layers and 7 to 34 times thicker collagen bundles on the outer layer. Fibre angle analysis showed that collagen was oriented mainly along the axial direction of the vessel. The von Mises fittings showed that in order to describe the fibre distribution 3 components were needed with mean angles [Formula: see text] at [Formula: see text] 0.35, 0.21, [Formula: see text] 0.02 rad or [Formula: see text] 20.2[Formula: see text], 12.1[Formula: see text], [Formula: see text] 1.2[Formula: see text] relative to the vessel's axial direction which was also the horizontal scan direction.status: publishe