Needle penetration test - qualifying examination of 3D printable silicones for vascular models in surgical practice

Background During cardiogenic shock blood circulation is minimal in the human body and does not suffice to survive. The extracorporeal life support system (ECLS) acts as a miniature heart-lung-machine that can be temporarily implanted over major vessels e.g. at the groin of the patient to bridge cardiogenic shock. To perform this procedure in an emergency, a proper training model is desirable. Therefore, a 3-dimensional-printable (3D) material must be found that mimics large vessel needle penetration properties. A suitable test bench for material comparison is desirable. Methods A test setup was built, which simulated the clinically relevant wall tension in specimens. The principle was derived from an existing standardized needle penetration test. After design, the setup was fabricated by means of 3D printing and mounted onto an universal testing machine. For testing the setup, a 3D printable polymer with low Shore A hardness and porcine aorta were used. The evaluation was made by comparing the curves of the penetration force to the standardized test considering the expected differences. Results 3D printing proved to be suitable for manufacturing the test setup, which finally was able to mimic wall tension as if under blood pressure and penetration angle. The force displacement diagrams showed the expected curves and allowed a conclusion to the mechanical properties of the materials. Although the materials forces deviated between the porcine aorta and the Agilus30 polymer, the graphs showed similar but still characteristic curves. Conclusions The test bench provided the expected results and was able to show the differences between the two materials. To improve the setup, limitations has been discussed and changes can be implemented without complications.

Insights in beachrock formation mechanism using multiproxy experimental data: Case study of Diolkos, Corinth, Greece

<p>Many studies have been published concerning the occurrence and formation mechanism of beachrocks around the world. However, there are only few quantified data on the precipitation mechanism and the parameters affecting it. The formation mechanism of beachrocks is directly related to their palaeoenvironmental significance, as it provides insights into sea level evolution and palaeogeographic evolution. In this study we corelate analytical data of natural and artificial beachrocks, which were created by the microbially induced carbonate precipitation (MICP) technique using sediments and ureolytic bacteria from the coastal zone of Diolkos, Corinth, Greece.</p><p>A multiproxy analysis was accomplished which included the mineralogical and geochemical analysis of both natural and artificial beachrocks, and the sedimentological and mechanical properties analysis of the artificial ones. This study focuses on four parameters that concern the cementation processes of artificial beachrocks: (a) sediment granulometry, (b) CaCO<sub>3 </sub>content, (c) bacteria type and (d) cement type. Diolkos, due to its location and history, presents great palaeo-geographic and geoarchaeological interest; for this reason, luminescence dating was accomplished on selected beachrock samples, in order to elucidate the relative sea level changes (RSL) and palaeogeographic evolution of the site.</p><p>For the artificial beachrocks formation, we conducted solidification test using ureolytic bacteria <em>Micrococcus yunnanensis sp.</em> and <em>Virgibacillus sp. </em>isolated from local sand samples. In order to determine the solidification of the beach sediments we estimated the unconfined compressive strength (UCS) by using needle penetration test on the surface of each sample. Furthermore, the precipitated CaCO<sub>3</sub> cement of the artificial beachrock samples, was calculated using HCl rinsing method. The artificial beachrocks were examined under SEM-EDS, XRD and XRF for their mineralogical and chemical composition accordingly.</p><p>Microscopy studies (optical and SEM-EDS) revealed that the cement of the artificial beachrock consists of calcite, in form of acicular sediment coating forming fans and multilayer concentrations. The cement in many cases was amorphous calcite crystals or microcrystalline, with thickness varying between 5 μm and 40 μm. The analysis from the artificial beachrock was correlated with the natural beachrock of Diolkos area. Our results revealed that the artificial beachrocks had different type of cement with microstratigraphy of an early digenesis. Moreover, amongst the artificial beachrocks, the sample with very well sorting (in terms of granulometry) has shown high values of CaCO<sub>3</sub> content, which corresponds to cement, a mean value of UCS 11 MPa and the best cement precipitation.</p>

Methods for in-situ HM characterization of claystone at the Mont Terri Rock Laboratory

<p>Claystones are considered to represent an important barrier rock in the context of nuclear waste storage. When cavities are opened underground, the rock mass in the near vicinity of the constructed repository is strongly affected by unloading, which is generally referred to as the Excavation Disturbed Zone (EDZ). This area is primarily characterized by newly formed unloading fractures, leading to an enhanced hydraulic transmissivity of the EDZ in comparison to the intact host rock. This phenomenon can affect the integrity of a geologic barrier as open fractures provide possible flow paths and endanger the long-term safety of underground storage facilities. A precise characterization of the EDZ is therefore essential for risk assessment and strategy development in terms of radioactive waste disposal.</p><p>In this study the Excavation Disturbed Zone (EDZ) of the Mont Terri Rock Laboratory is investigated with regard to hydraulic, mechanical and geophysical properties by using three simple field measuring devices, (1) portable permeameter, (2) microscope camera and (3) needle penetration test (NPT). The hydraulic aperture of accessible joints within the Opalinus Clay formation in the EZ-B niche is measured by a portable transient-airflow permeameter. The instrument was validated by flow-through experiments and is able to accurately determine hydraulic fracture apertures down to about 10 µm. In-situ measurements were carried out at 43 points and show a mean hydraulic aperture of 84 ± 23 µm, extending over a range from 20 to 100 µm. Fracture apertures do not change with increasing distance to the gallery in the accessible area of uncovered claystone.</p><p>For the same set of measuring points, the mechanical fracture aperture was determined by a digital microscope camera. Mechanical fracture apertures in the EZ-B niche ranged between 16 and 1400 µm with a mean value of 268 ± 276 µm. As comparable hydraulic apertures can be derived from the measured mechanical aperture by using empirical relations based on estimated joint surface roughness, the microscope camera represents a valuable alternative besides the air permeameter. The hydraulic characterization of the EDZ proves the existence of accessible fluid pathways within the Opalinus Clay of the Mont Terri Rock Laboratory, even about 15 years after tunnel excavation.</p><p>The mechanical and geophysical properties of the EDZ are investigated by a needle penetration test (NPT). Whereas the needle penetration index (NPI) is strongly influenced by bedding anisotropy, the influence of the EDZ is negligible. The NPT proves to be a suitable tool for estimating mechanical properties by using different empirical relations. Especially for the uniaxial compressive strength, a high correlation with literature values is observed. In contrast, geophysical parameters such as P-wave velocity cannot be reliably determined with this method. The obtained field data could be used as a reasonable input for numerical models that aim at investigating swelling and shrinking behavior of the Opalinus Clay with regard to self-sealing processes within the EDZ.</p>

Study on progression of deterioration in improved surplus soils

This study investigated the progression of deterioration in cement treated surplus soils with cement contents of 1.7, 3.5 and 5.3 % under soaked condition by conducting needle penetration test and measuring calcium ion distribution within soil specimens. It was found that deterioration has progressed throughout the specimen after 336 days soaking in all the cases. From the measurement of calcium ion distribution, it was identified that calcium has leached out from the centre to the surface of the specimens though that distribution did not follow a good correlation with localized strength distribution. It was understood that the progression of deterioration of improved surplus soils with lower cement contents cannot be explained only with the remaining amount of calcium.