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We address the effect of elastic inhomogeneity on elastic modulus and hardness determinations made by depth-sensing indentations performed on individual particles embedded within a matrix of different elastic modulus. Finite element simulations and nanoindentation experiments are used to quantify the consequences of particle/matrix elastic inhomogeneity and we propose an adaptation of the Oliver-Pharr method that gives access to particle properties knowing those of the matrix. The method is suitable for any combination of matrix and particle elastic modulus and for any type of indenter, provided that the area of the tested particles along the surface of the sample is measured and that a large number of particles are probed. Further conditions for the implementation of the method are that testing conditions be such (i) that permanent deformation of the matrix is avoided, and (ii) that permanent deformation in each probed particle under the indenter is not affected by the matrix.

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Chalcogenide glass exhibits a wide transmission window in the infrared range, a high refractive index, and nonlinear optical properties; however, due to its poor mechanical properties and low chemical and environmental stability, producing three-dimensional microstructures of chalcogenide glass remains a challenge. Here, we combine the fabrication of arbitrarily shaped three-dimensional cavities within fused silica molds by means of femtosecond laser-assisted chemical etching with the pressure-assisted infiltration of a chalcogenide glass into the resulting carved silica mold structures. This process enables the fabrication of 3D, geometrically complex, chalcogenide-silica micro-glass composites. The resulting products feature a high refractive index contrast that enables total-internal-reflection guiding and an optical quality roughness level suited for applications in the infrared.

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Microprobe tips are commonly used to perform in-situ micromechanical tests within an electron microscope. In service, such tips have a tendency to accumulate along their surface a layer of deposited material. Tip cleanliness is crucial in order to obtain reliable and reproducible data; however, cleaning of such tips can be arduous, due to their fragility. The literature on appropriate tip cleaning methods is relatively sparse; we aim in this study to fill this gap by presenting an effective way to clean flat punch diamond microprobe tips within an electron microscope, based on mechanical scraping. Initial attempts to remove deposits from a contaminated diamond tip using two micro-brush samples, one containing silica needles and the other containing cementite lamellae, were unsuccessful, due to the adherence of the deposit to the surface of the tip and its apparently high hardness. The successful cleaning method consists of milling a silicon ridge by means of a focused ion beam, and then using this ridge to effectively scrape the deposits off the tip surface in a controlled and complete manner. This method avoids potential damage to the microprobe and can be implemented easily to clean flat punch tips rapidly within a scanning electron microscope.

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In this work, the macrotexture of dense Zn produced by laser powder bed fusion (LPBF) was studied and the mechanical properties for different tensile bar orientations were measured. The compressive strength of LPBF Zn scaffolds with five different unit cells was measured for a relative density of 20-51%. In addition, the response of mesenchymal stem cells to the LPBF Zn scaffolds was studied. The elastic modulus and yield strength of dense LPBF Zn were 110.0 ± 0.2 GPa and 78.0 ± 0.4 MPa, respectively in the vertical and 81.0 ± 0.4 GPa and 55.0 ± 0.7 MPa in the horizontal direction. This could be explained by the preferential orientation of the 〈0001〉 direction in the building plane. For LPBF Zn scaffolds, the plateau stress for the different unit cells varied between 8 and 33 MPa for a 30% relative density. Calcein staining, lactate production and DNA measurements over a 13-day period showed that mesenchymal stem cell viability was low for Zn scaffolds. This work forms a basis for further research into the LPBF texture formation of metals with hexagonal crystal structure, guides implant designers in scaffold unit cell and relative density selection and motivates further research into the cytocompatibility of LPBF Zn. STATEMENT OF SIGNIFICANCE: Laser powder bed fusion (LPBF) is a manufacturing technology which allows the seamless combination of porous and non-porous volumes in a metallic implant and is used in the orthopedic manufacturing industry today. The production of highly dense Zn with LPBF has been described earlier, but the mechanical properties of the resulting material have not been studied in detail yet. This study is the first to report on (i) the influence of different scanning strategies on the macrotexture of dense LPBF Zn and the resulting anisotropy of its mechanical properties, (ii) the relationship between the relative density and strength for LPBF Zn scaffolds with five different unit cells and (iii) the in vitro response of mesenchymal stem cells to these scaffolds.

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BACKGROUND: Microdialysis is a clinical method used to detect ischemia after microvascular surgery. Microdialysis is easy to use and reliable, but its value in most clinical settings is hampered by a 1- to 2-h delay in the delivery of patient data. This study evaluated the effectiveness of an increase in the microdialysis perfusion rate from 0.3 to 1.0 µL/min on the diagnostic delay in the detection of ischemia. METHODS: In eight pigs, two symmetric pure muscle transfers were dissected based on one vascular pedicle each. In each muscle, two microdialysis catheters were placed. The two microdialysis catheters were randomized to a perfusion rate of 0.3 or 1.0 µL/min, and the two muscle transfers were randomized to arterial or venous ischemia, respectively. After baseline monitoring, arterial and venous ischemia was introduced by the application of vessel clamps. Microdialysis sampling was performed throughout the experiment. The ischemic cutoff values were based on clinical experience set as follows: CGlucose < 0.2 mmol/L, CLactate > 7 mmol/L, and the lactate/pyruvate ratio > 50. RESULTS: The delay for the detection of 50% of arterial ischemia was reduced from 60 to 25 minutes, and for the detection of all cases of arterial ischemia, the delay was reduced from 75 to 40 minutes when the perfusion rate was increased from 0.3 to 1.0 µL/min. After the same increase in perfusion, the detection of 50% of venous ischemia was reduced from 75 to 40 minutes, and for all cases of venous ischemia, a reduction from 135 to 95 minutes was found. CONCLUSION: When using microdialysis for the detection of ischemia in pure muscle transfers, an increase in the perfusion rate from 0.3 to 1.0 µL/min can reduce the detection delay of ischemia.

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The aim of this randomized porcine study was to compare surface targeted temperature management (TTM) to endovascular TTM evaluated by cerebral diffusion-weighted magnetic resonance imaging (MRI): apparent diffusion coefficient (ADC), and by intracerebral/intramuscular microdialysis. It is well known that alteration in the temperature affects ADC, but the relationship between cerebral ADC values and the cooling method per se has not been established. Eighteen anesthetized 60-kg female swine were hemodynamically and intracerebrally monitored and subsequently subjected to a baseline MRI. The animals were then randomized into three groups: (1) surface cooling (n = 6) at 33.5°C using EMCOOLSpad®, (2) endovascular cooling (n = 6) at 33.5°C using an Icy® cooling catheter with the CoolGard 3000®, or (3) control (n = 6) at 38.5°C using a Bair Hugger™. The swine were treated with TTM for 6 hours followed by a second MRI examination, including ADC. Blood and microdialysate were sampled regularly throughout the experiment, and glucose, lactate, pyruvate, glycerol, and the lactate/pyruvate ratio did not differ among groups, neither intracerebrally nor intramuscularly. Surface cooling yielded a significantly lower median ADC than endovascular cooling: 714 (634; 804) × 10-6 mm2/s versus 866 (828; 927) × 10-6 mm2/s, (p < 0.05). The surface cooling ADC was lowered to a range usually attributed to cytotoxic edema and these low values could not be explained solely by the temperature effect per se. To what extent the ADC is fully reversible at rewarming is unknown and the clinical implications should be further investigated in clinical studies.

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