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Purpose The aim of this study was to evaluate skull replacement options after decompressive craniectomy by systematically investigating which combination of geometrical properties and material selection would result in a mechanical response comparable in stiffness to that of native skull bone and a strength as high or higher than the same. Materials and methods The study was conducted using a Finite Element Model of the top part of a human skull. Native skull bone, autografts and commercial implants made of PEEK, solid titanium, two titanium meshes and a titanium-ceramic composite were modeled under a set load to evaluate deformation and maximum stress. Results The computational result showed a large variation of the strength and effective stiffness of the autografts and implants. The stiffness of native bone varied by a factor of 20 and the strength by a factor of eight. The implants span the entire span of the native skull, both in stiffness and strength. Conclusion All the investigated implant materials had a potential for having the same effective stiffness as the native skull bone. All the materials also had the potential to be as strong as the native bone. To match inherent properties, the best choice of material and thickness is thus patient specific, depending on the quality of the patient's native bone. [ABSTRACT FROM AUTHOR]

Abstract: A mechanical model for analyses of rapid deformation and fracture in three-dimensional fiber materials is derived. Large deformations and fractures are handled in a computationally efficient and robust way. The model is truly dynamic and computational time and memory demand scales linearly to the number of structural components, which make the model well suited for parallel computing. The specific advantages, compared to traditional continuous grid-based methods, are summarized as: (1) Nucleated cracks have no idealized continuous surfaces. (2) Specific macroscopic crack growth or path criteria are not needed. (3) The model explicitly considers failure processes at fiber scale and the influence on structural integrity is seamlessly considered. (4) No time consuming adaptive re-meshing is needed. The model is applied to simulate and analyze crack growth in random fiber networks with varying density of fibers. The results obtained in fracture zone analyses show that for sufficiently sparse networks, it is not possible to make predictions based on continuous material assumptions on a macroscopic scale. The limit lies near the connectivity , where is the ratio between the average fiber segment length and the total fiber length. At ratios the network become denser and at the limit , a continuous continuum is approached on the macroscopic level. [Copyright &y& Elsevier]

Background: The Y111C/KCNQ1 mutation causes a dominant-negative effect in vitro but a benign clinical phenotype in a Swedish long QT syndrome population. Objective: The purpose of this study was to investigate the origin (genealogic, geographic, genetic, and age) of the Y111C/KCNQ1 mutation in Sweden. Methods: We identified 170 carriers of the Y111C/KCNQ1 mutation in 37 Swedish proband families. Genealogic investigation was performed for all families. Haplotype analysis was performed in 26 probands, 21 family members, and 84 healthy Swedish controls, using 15 satellite markers flanking the KCNQ1 gene. Mutation age was estimated using ESTIAGE and DMLE computer software and regional population demographic data. Results: All probands were traced back to a northern river valley region. A founder couple born in 1605/1614 connected 26 of 37 families. Haplotyped probands shared 2–14 (median 10) uncommon alleles, with frequencies ranging between 0.01 and 0.41 (median 0.16) in the controls. The age of the mutation was estimated to 24 generations (95% confidence interval 18; 34), that is, 600 years (95% confidence interval 450; 850) assuming 25 years per generation. The number of now living Swedish Y111C mutation carriers was estimated to approximately 200–400 individuals for the mutation age span 22–24 generations and population growth rates 25%–27%. Conclusion: The Y111C/KCNQ1 mutation is a Swedish long QT syndrome founder mutation that was introduced in the northern population approximately 600 years ago. Enrichment of the mutation was enabled by a mild clinical phenotype and strong regional founder effects during population development of the northern inland. The Y111C/KCNQ1 founder population constitutes an important asset for future genetic and clinical studies. [Copyright &y& Elsevier]

Abstract: The heat transfer equation was used to model the heat distribution in an intervertebral disk during ultrasound (US) exposure. The influence of thermal and acoustic parameters was studied to get a quantitative understanding of the heat transfer in the system. Heating of collagen to 65°C or above will lead to denaturation and is believed to stabilize and contract the outer part of the disk in a herniated disk. In our model, the US intensity was approximated by a Gaussian distribution and nonlinear propagation was excluded. The effect of self-heating and cooling of the transducer was also studied. The simulations were performed using the finite element method. From this model, it can be concluded that it is possible to heat parts of the disk to treatment temperature using a focused 5-mm diameter US probe. The physical constraints on the piezocrystal set the limit of the size of the treatment volume. (E-mail: johan.persson@ort.lu.se) [Copyright &y& Elsevier]

Thermal intradiscal therapy for chronic low back pain, using a catheter inserted into the intervertebral disc, is becoming more popular in the treatment of low back pain. The aim of this study was to investigate the possibility of heating the nucleus pulposus of the intervertebral disc with high-intensity focused ultrasound (US) or HIFU. Two specific situations were considered, invasive transducers that would be in contact with the annulus fibrosus of the disc, and noninvasive transducers that could be used externally. Theoretical simulations were performed to find the optimal parameters of US transducers and then experimental studies were done using transducers made to these specifications. These experiments confirmed that it was possible to heat the discs with HIFU. Two orthogonal transducers resulted in a superior temperature distribution than using just one transducer. It is, therefore, feasible to consider thermal treatment of the nucleus pulposus of the disc using noninvasive US. (E-mail: Johan.Persson@ort.lu.se) [Copyright &y& Elsevier]

This study evaluates the Ottosen–Stenström–Ristinmaa (OSR) incremental fatigue damage model for predicting fatigue life in powder bed fusion with laser beam (PBF-LB) Ti6Al4V notched specimens. To fit the OSR model, we conduct constant-amplitude tension-compression fatigue tests on PBF-LB Ti6Al4V specimens with as-built surface. Our results highlight a relatively low scatter in fatigue life data for PBF-LB Ti6Al4V across different studies, a critical factor for reliable design against fatigue failure. The study suggests that the stress gradient effect is influenced by the as-built surface, which carries load differently from the target build geometry due to surface undulations. The OSR model effectively captures the characteristics of Wöhler curves for various notch geometries and stress ratios. We validate the OSR model with out-of-phase tension-torsion tests, demonstrating that it provides safe fatigue life predictions for nonproportional loads. Overall, our findings show that the OSR model offers conservative fatigue life predictions for PBF-LB Ti6Al4V, underscoring its practical utility and reinforcing the suitability of PBF-LB Ti6Al4V for aircraft applications. • Time-domain model predicts fatigue life for AM Ti6Al4V under nonproportional loads. • Fatigue life scatter for PBF-LB Ti6Al4V is surprisingly low across studies. • The stress gradient effect is influenced by surface roughness in as-built PBF-LB. • Conservative fatigue predictions observed for critical load conditions. • PBF-LB Ti6Al4V shows potential for reliable design in demanding aircraft applications. [ABSTRACT FROM AUTHOR]

• LES of turbulent flow of concentrated fiber suspension is carried out. • An increase in fiber concentration highly affects the variation in flow regimes. • Visualization of vortical structures helped to understand these variations. • Turbulent intensity and Reynolds stress are obtained for different concentrations. Large eddy simulation (LES) of turbulent flow of concentrated fiber suspension or pulp is carried out to investigate the flow and turbulence structures in a channel. The simulations are carried out for the turbulent flow of Eucalyptus pulp suspension using OpenFOAM for three fiber concentrations (c = 1.5, 2.0 and 2.5) and six different Reynolds numbers (6 ≤Re s ≤ 16,600). It is observed that the variation in flow regime is similar in the two lower fiber concentrations while the flow regime is highly affected by fiber concentration for c = 2.5. Visualizations of vortical structures for different Reynolds numbers and fiber concentrations are used to investigate different flow regimes. Variation of apparent viscosity with Reynolds number and fiber concentration is also presented to show its effect on the turbulent properties of fiber suspension flow. It is shown that the deviation of turbulent velocity profile from that of a Newtonian flow increases with an increase in Reynolds number and fiber concentration. Also, the extend of buffer layer increases at higher Re. Using the calculated turbulent velocity profile, the values of constant in logarithmic velocity profile is proposed for fiber suspension. Finally, a discussion is presented on the variation of turbulent intensities and Reynolds stress with Reynolds number and fiber concentration. [ABSTRACT FROM AUTHOR]