Mesh migration following abdominal hernia repair: a comprehensive review.

PURPOSE: This study reviewed the literature regarding mesh migration in abdominal hernia repair. The aim of this study is to interrogate incidence, common type of abdominal hernia repair leading to migration, patterns of mesh migration, and materials associated with migration. METHODS: A comprehensive literature review was conducted. PubMed and MEDLINE were searched for relevant articles in the English literature. We employed Ovid syntax from 1949 to January 2010, the Cochrane Library, Google and Google Scholar. The clinical trial database Clinicaltrials.gov was reviewed. Letters to the editor were reviewed to extract cross-references. Multiple keywords were used alone and in combination to extract all relevant articles. RESULTS: In total, 287 unique English citations were reviewed. Of these, 84 articles were selected and consisted of 3 case series, 77 case reports, 2 literature reviews, 1 retrospective study, and 1 prospective, observational study. In an analysis of available cases, the average age was 59.8 ± 13.8 years with a male predominance (76.2%). The index hernia repair was inguinal in 62.9%, incisional/ventral in 28.1%, umbilical in 6.7%, and other in 2.2%. Within the inguinal hernia group, 51.8% were open repairs, 42.9% were laparoscopic, and 1.8% were robotic. Implicated mesh materials included polypropylene, PTFE, and composite mesh. Migration commonly affected multiple organs (31.5%). CONCLUSIONS: It is likely that more cases of mesh migration will appear in the literature. Reports are heterogeneous and highlight the diversity of this complication. A standardized method of reporting is needed to develop guidelines and recommendations for this presentation.

Size effect and stability of polarized fluid phases.

The existence of a ferroelectric fluid phase for systems of 1000-2000 dipolar hard or soft spheres is well established by numerical simulations. Theoretical approaches proposed to determine the stability of such a phase are either in qualitative agreement with the simulation results or disagree with them. Experimental results for systems of molecules or particles with large electric or magnetic dipole moments are also inconclusive. As a contribution to the question of existence and stability of a fluid ferroelectric phase this simulation work considers system sizes of the order of 10 000 particles, thus an order of magnitude larger than those used in previous studies. It shows that although ferroelectricity is not affected by an increase of system size, different spatial arrangements of the dipolar hard spheres in such a phase are possible whose free energies seem to differ only marginally.

Influence of short range potential on field induced chain aggregation in low density dipolar particles.

We investigate, by Monte Carlo simulation, the effect of the steepness of the short range repulsive potential on mesostructure formation in dipolar particles submitted to a strong external field. Columnar clusters made of several dipolar chains are only observed when the short-range potential is sufficiently steep. The confinement of the dipolar liquid in a slit geometry instead of bulk conditions suppresses the formation of columns.

Low density mesostructures of confined dipolar particles in an external field.

Mesostructures formed by dipolar particles confined between two parallel walls and subjected to an external field are studied by Monte Carlo simulations. The main focus of the work is the structural behavior of the Stockmayer fluid in the low density regime. The dependence of cluster thickness and ordering is estimated as a function of density and wall separation, the two most influential parameters, for large dipole moments and high field strengths. The great sensitivity of the structure to details of the short-range part of the interactions is pointed out. In particular, the attractive part of the Lennard-Jones potential is shown to play a major role in driving chain aggregation. The effect of confinement, evaluated by comparison with results for a bulk system, is most pronounced for a short range hard sphere potential. No evidence is found for a novel "gel-like" phase recently uncovered in low density dipolar colloidal suspensions [A. K. Agarwal and A. Yethiraj, Phys. Rev. Lett. 102, 198301 (2009)].

A computational study of electrolyte adsorption in a simple model for intercalated clays.

A pillared interlayered clay is represented by a two-dimensional quenched charged disordered medium, in which the pillar configuration is produced by the quench of a two-dimensional electrolyte and the subsequent removal of the anions (that act as a template). The cation charge is counterbalanced by a neutralizing background that is an ideal representation of the layer's negative charge in the experimental system. In this paper we investigate the adsorption of electrolyte particles in this charged disordered medium resorting both to the use of the replica Ornstein-Zernike equation in the hypernetted chain approximation and grand canonical Monte Carlo simulations. The theoretical approach qualitatively reproduces the simulated behavior of the adsorbed fluids. Theoretical estimates of the material porosities obtained for various types of pillar distributions are in good agreement with the simulation. We investigate the influence of the matrix on correlation functions and adsorption isotherms.

Self-organization of confined dipolar particles in a parallel field.

Monte Carlo simulations of a Stockmayer fluid confined between two parallel walls are performed to investigate self-organization of magnetic nanocrystals in a field parallel to the walls as a function of density, field strength, and wall separation. In order to study the formation of mesoscopic structures, a large number of up to 12,000 particles have to be used. The particles organize into periodically spaced cylindrical-like columns whose width typically varies between 5 and 9 particle diameters at low density. At small heights the columns are quenched due to the parallel walls, while larger wall separations can accommodate several layers of columns in good agreement with experiments. An increase in density entails a clear increase in column thickness, whereas an increase in field strength seems to have the opposite effect.

Mesoscopic void structures in cobalt nanocrystal films formed from drying concentrated colloidal solutions.

Here we report the formation of void (hole) structures when concentrated colloidal solutions of magnetic nanocrystals are subjected to a magnetic field during slow evaporation. This presents a new type of solid mesostructure obtained by self-assembly of nanocrystals. The voids are characterized by a cylindrical shape with either circular or elliptical base. We show that the morphology of these patterns is essentially controlled by the fraction of the volume occupied by the magnetic phase to the total volume of the film. Monte Carlo simulations carried out using a Stockmayer fluid model agree remarkably well with the experiments for the formation of void structures in the range of considered volume fractions.

Defining a transcriptional fingerprint of murine splenic B-cell development.

B-cell development occurs in a stepwise fashion that can be followed by the expression of B cell-specific surface markers. In this study, we wished to identify proteins that could contribute to the changes in expression of such markers. By using RNA from freshly isolated B220+ cells, we hoped to reduce the effect of artifacts that occur during the isolation and amplification steps necessary to use flow cytometry analysis-sorted subsets in microarray experiments. Analyses comparing expression patterns from B220+ 2-week bone marrow (pro-B, pre-B, immature B cells), 2-week spleen (predominantly transitional cells) and 8-week spleen (mainly mature B cells) yielded hundreds of genes. We also examined the B cell-activating factor (BAFF)-dependent effects on immature splenic B cells by comparing expression patterns in the spleen between 2-week A/J vs 2-week A/WySnJ mice, which lack functional BAFF receptor signaling. Genes that showed the expression differences between spleen and bone marrow samples were then analyzed through quantitative PCR on B-cell subsets isolated using two different sorting protocols. A comparison of the results from our study with the results from other analyses showed not only some overlap of preferentially expressed genes but also an expansion of other genes potentially involved in B-cell development.

Self-organization of magnetic nanoparticles: a Monte Carlo study.

To understand the self-organization of magnetic nanocrystals in an applied field, we perform Monte Carlo simulations of Stockmayer fluids confined between two parallel walls. The system is examined in the gas-liquid coexistence region of its phase diagram and the field is applied perpendicular to the walls. Gibbs ensemble simulations are carried out to determine the phase coexistence curves of the confined Stockmayer fluid. In canonical simulations, different types of organizations appear dependent on particle density: columns, walls, and elongated and spherical holes. The morphology and size of structures are in good agreement with results obtained by free energy minimization and experiments. The influence of a distribution of particle sizes on the particle organization is investigated.

Structure and thermodynamics of a two-dimensional Coulomb fluid in the strong association regime.

The behavior of a two-dimensional neutral Coulomb fluid in the strong association regime (low density, high ionic charge) is explored by means of computer simulation and the hypernetted chain integral equation. The theory reproduces reasonably well the structure and thermodynamics of the system but presents a no-solution region at temperatures well above the computer simulation estimates of the metal-insulator transition. In contrast with hypernetted chain predictions for the three-dimensional Coulomb fluid, here the breakdown of the solution is not accompanied by divergences in any physical quantity.

Orientational order in high density dipolar hard sphere fluids.

Taking advantage of recent estimates, by one of us, of the critical temperature of the isotropic-ferroelectric transition of high density dipolar hard spheres, we performed new Monte Carlo simulations in the close vicinity of these estimates and applied histogram reweighting methods to obtain refined values of the critical temperatures from the crossing of the fourth-order cumulant for different system sizes. The ferroelectric line is determined in the density range rho*=0.80-0.95, and the onset of columnar ordering is located.

Phase transition in two-dimensional dipolar fluids at low densities.

Monte Carlo computer simulations of a quasi two-dimensional (2D) dipolar fluid at low and intermediate densities indicate that the structure of the fluid is well described by an ideal mixture of self-assembling clusters. A detailed analysis of the topology of the clusters, of their internal energy and of their size (or mass) distributions is used to obtain approximations to their partition functions. Within the scope of these approximations, the results of this work suggest that the 2D dipolar fluid undergoes a phase transition from a dilute phase characterized by a number of disconnected clusters to a condensed phase characterized by a network or spanning (macroscopic) cluster that includes most of the particles in the system.

Expression of the mouse fragilis gene products in immune cells and association with receptor signaling complexes.

The mouse genome possesses five genes encoding proteins homologous to human Leu-13. The Leu-13 protein associates with immune cell receptor activation complexes: a monoclonal antibody against Leu-13 induces T and B cells to form homotypic aggregates, inhibits activation-induced proliferation and induces the shedding of L-selectin. The mouse fragilis proteins have not been previously analyzed as components of the immune response. Antibody and nucleic acid reagents were generated that are specific for each of the five fragilis gene products. Expression of some of these genes (fragilis and fragilis3) is wide spread in a variety of mouse immune (and nonimmune) tissues while others (fragilis5) appear to be much more restricted. These proteins have been predicted to span the membrane twice with both amino- and carboxyl-terminal sequences extracellular: we show that a highly conserved loop of the protein between the transmembrane domains is intracellular. The fragilis proteins are associated with tetraspanin proteins CD81 and CD9: B cell activation positions fragilis into lipid rafts along with the CD81, CD19, and CD21. The mouse functional equivalent to human Leu-13 may not be single gene product, but instead may require the contribution of multiple fragilis proteins.

The ferroelectric transition of dipolar hard spheres.

We investigate by Monte Carlo simulation the size dependence of the variation of the polarization and the dielectric constant with temperature for dipolar hard spheres at the two densities rho sigma3=0.80 and 0.88. From the crossing of the fourth-order cumulant for different system sizes first more precise estimates of the ferroelectric transition temperatures are obtained. Theoretical approaches, when predicting an ordering transition, are shown to generally overestimate the critical temperature.

Overexpression of RANKL implicates IFN-beta-mediated elimination of B-cell precursors in the osteopetrotic bone of microphthalmic mice.

The microphthalmic (mi) mouse possesses a dominant negative mutation in the microphthalmia-associated transcript factor (MITF) transcription factor. These animals are characterized by reduced numbers of peripheral mast and natural killer (NK) cells, are osteopetrotic because of osteoclast reduction and malfunction, lack functional melanocytes, and are deficient for maturing B-cells within the bone marrow. Granulocyte precursor cells, however, are functionally maintained within the mi bone marrow. A central question has been whether the B-cell deficiency of the mi mouse marrow is caused by the absence of an MITF-controlled gene product or because of the compromised, osteopetrotic environment. In this report, we examined mi marrow by performing transcriptional mapping analyses of candidate genes whose products are instrumental for functional osteoclast and B-cell development. Surprisingly, the expression of a subset of such genes including RANKL, stromal-derived factor (SDF-1), B-cell lymphotactin chemokine (BLC), and RANK was dramatically enhanced in the mi marrow. Normal and mutant marrow were also analyzed by subtractive transcript cloning, which identified a number of known and unknown genes with altered transcriptional activity. One such unknown mouse gene possesses a human counterpart that is interferon-beta (IFN-beta) inducible, suggesting the osteopetrotic marrow is enriched for IFN-beta, a cytokine that is known to eliminate B-cell precursors. A model is proposed suggesting excess RANKL sets off a cascade of cytokine production including IFN-beta that leads to the preferential elimination of B-cell precursors in the marrow of osteopetrotic marrow.

Quasi-two-dimensional dipolar fluid at low densities: Monte Carlo simulations and theory.

We studied a quasi-two-dimensional dipolar fluid in the chaining regime using Monte Carlo canonical simulations and theoretical analyses. The self-assembled clusters were characterized by measuring their internal energy, conformational properties, and equilibrium length distributions. We generalized and used equilibrium polymer theory to describe the structure of the chains and rings observed in the simulations. The scaling forms of the length distribution functions predicted by theory were found to describe adequately the simulation results. Finally, we discuss how this type of analysis may be used to establish the existence and mechanisms of phase transitions in dilute dipolar fluids.

Adsorption of a diatomic molecular fluid into random porous media.

Structural and thermodynamic properties of a homonuclear hard dumbbell fluid adsorbed into a disordered hard sphere matrix are studied by means of integral equation techniques and computer simulation. In particular, we have rewritten the replica Ornstein-Zernike equations to deal with orientational degrees of freedom and we have solved them in two different approaches: the hypernetted chain equation and a semiempirical extension of Verlet's approximation. We have also derived direct expressions to calculate the chemical potential in these approximations. Comparison with grand canonical Monte Carlo results shows that both theoretical treatments describe adequately the physical behavior of the system, Verlet's approach being, however, clearly superior in accordance with previous findings for equilibrated hard core mixtures.

Genetic control of susceptibility to experimental Lyme arthritis is polygenic and exhibits consistent linkage to multiple loci on chromosome 5 in four independent mouse crosses.

C3H/He mice infected with Borrelia burgdorferi develop severe arthritis and are high antibody responders, while infected C57BL/6 and BALB/c mice develop mild arthritis and less robust humoral responses. Genetic analysis using composite interval mapping (CIM) on reciprocal backcross populations derived from C3H/HeN and C57BL/6N or C3H/HeJ and BALB/cAnN mice identified 12 new quantitative trait loci (QTL) linked to 10 murine Lyme disease phenotypes. These QTL reside on chromosomes 1, 2, 4, 6, 7, 9, 10, 12, 14, 15, 16, and 17. A reanalysis of an F(2) intercross between C57BL/6N and C3H/HeN mice using CIM identified two new QTL on chromosomes 4 and 15 and confirmed the location of seven previously identified loci. Two or more experimental crosses independently verified six QTL controlling phenotypes after B. burgdorferi infection. Additionally, Bb2 on chromosome 5 was reproduced in four experimental populations and was linked to the candidate locus Cora1. Evidence of four distinct QTL residing within the 30-cM region of chromosome 5 encompassing the previously mapped Bb2 and Bb3 loci was shown by CIM. Interestingly, some alleles contributing to susceptibility to Lyme arthritis were derived from C57BL/6N and BALB/cAnN mice, showing that disease-resistant strains harbor susceptibility alleles.

Phase diagram of a symmetric binary fluid in a porous matrix.

The phase behavior of a binary symmetric fluid in thermal equilibrium with a porous matrix has been studied with the optimized random phase approximation and grand canonical Monte Carlo simulations. Depending on the matrix properties and the matrix-fluid and fluid-fluid interactions we find three types of phase diagram characterized by a tricritical point, a tricritical point with a triple point, or a critical end point. Small changes in the properties of the matrix or in the interactions are demonstrated to lead to drastic modifications of the phase diagram of the fluid, in qualitative agreement with observations in experimental studies. We show, in particular, that the change between the different types of phase diagram is triggered not only by the fluid-fluid interactions (internal parameters) but also by the properties of the matrix and of the matrix-fluid potentials (external parameters).

Functional characterization of Pactolus, a beta-integrin-like protein preferentially expressed by neutrophils.

Murine Pactolus is a beta-integrin-like molecule expressed exclusively on the surface of granulocytes. Cell surface expression of Pactolus is dramatically increased following activation of bone marrow neutrophils with known agonists, and cross-linking of cell surface Pactolus, suggesting the bulk of the protein is in intracellular stores. The mature protein is found in two forms depending upon the extent of N-linked glycosylation. There is no evidence to suggest that Pactolus requires an associated alpha chain for expression. In some mouse strains, a truncated form of the protein is predicted based upon alternative splicing: this form, however, is unstable and rapidly degraded after synthesis. Differences in the quantities of these Pactolus mRNA isoforms have defined two alleles. BALB/c and C3H/HeJ mice possess allele B and preferentially express the truncated, unstable product, whereas C57BL/6 mice possess allele A and only produce the membrane-bound form. Sequence analysis has shown the difference between these two alleles is due to a single base pair difference at the splice acceptor site for the truncated product. The increased expression of the membrane form of Pactolus by granulocytes of C57BL/6 mice suggests a compensatory adhesion function that is reduced in cells from the low producing strains.