A parameter-free total Lagrangian smooth particle hydrodynamics algorithm applied to problems with free surfaces

This paper presents a new Smooth Particle Hydrodynamics computational framework for the solution of inviscid free surface flow problems. The formulation is based on the Total Lagrangian description of a system of first-order conservation laws written in terms of the linear momentum and the Jacobian of the deformation. One of the aims of this paper is to explore the use of Total Lagrangian description in the case of large deformations but without topological changes. In this case, the evaluation of spatial integrals is carried out with respect to the initial undeformed configuration, yielding an extremely efficient formulation where the need for continuous particle neighbouring search is completely circumvented. To guarantee stability from the SPH discretisation point of view, consistently derived Riemann-based numerical dissipation is suitably introduced where global numerical entropy production is demonstrated via a novel technique in terms of the time rate of the Hamiltonian of the system. Since the kernel derivatives presented in this work are fixed in the reference configuration, the non-physical clumping mechanism is completely removed. To fulfil conservation of the global angular momentum, a posteriori (least-squares) projection procedure is introduced. Finally, a wide spectrum of dedicated prototype problems is thoroughly examined. Through these tests, the SPH methodology overcomes by construction a number of persistent numerical drawbacks (e.g. hour-glassing, pressure instability, global conservation and/or completeness issues) commonly found in SPH literature, without resorting to the use of any ad-hoc user-defined artificial stabilisation parameters. Crucially, the overall SPH algorithm yields equal second order of convergence for both velocities and pressure

A Particle Model for Prediction of Cement Infiltration of Cancellous Bone in Osteoporotic Bone Augmentation.

PMC3693961Femoroplasty is a potential preventive treatment for osteoporotic hip fractures. It involves augmenting mechanical properties of the femur by injecting Polymethylmethacrylate (PMMA) bone cement. To reduce the risks involved and maximize the outcome, however, the procedure needs to be carefully planned and executed. An important part of the planning system is predicting infiltration of cement into the porous medium of cancellous bone. We used the method of Smoothed Particle Hydrodynamics (SPH) to model the flow of PMMA inside porous media. We modified the standard formulation of SPH to incorporate the extreme viscosities associated with bone cement. Darcy creeping flow of fluids through isotropic porous media was simulated and the results were compared with those reported in the literature. Further validation involved injecting PMMA cement inside porous foam blocks - osteoporotic cancellous bone surrogates - and simulating the injections using our proposed SPH model. Millimeter accuracy was obtained in comparing the simulated and actual cement shapes. Also, strong correlations were found between the simulated and the experimental data of spreading distance (R2 = 0.86) and normalized pressure (R2 = 0.90). Results suggest that the proposed model is suitable for use in an osteoporotic femoral augmentation planning framework.JH Libraries Open Access Fun

Repetitive domain of Clostridium difficile toxin B exhibits cytotoxic effects on human intestinal epithelial cells and decreases epithelial barrier function

We have used recombinant repetitive domain of Clostridium difficile toxin B obtained from two different strains, rec-TcdB3(10463) and rec-TcdB3(8864) and a model intestinal epithelial cell line(s) to characterize their cytotoxic and cytopathic effect and influence on tight-junction organization. Both recombinant receptor binding domains caused intestinal epithelial cell damage, decreased transepithelial electrical resistance and induced translocation of ZO-1 from tight-junction proteins although less efficiently as holotoxins. Recombinant repetitive TcdB domains also caused stimulation of interleukin IL-8 synthesis in HT-29 cells. This is the first description of glucosyltransferase independent toxicity of TcdB and these C-terminal mediated effects may contribute to the pathophysiology of C difficile infection. (C) 2010 Elsevier Ltd. All rights reserved