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Silicone-based materials can be applied on ship hulls to serve as foul release coatings. Depending on the application, coatings are not likely to have a uniform thickness. Pull-off tests of epoxy studs from silicone coatings with a thickness gradient found that for the thickest coatings, release initiated at the edge and proceeded inward with no bias in the peeling direction, and as the thickness decreased the release initiated on the thin side of the coating. Release mechanism and critical pull-off force were also affected. In this work, finite element models were developed to predict the detailed stress field at the silicone/epoxy interface in silicone coatings with a thickness gradient. Average coating thickness, thickness gradient, and Poisson's ratio were varied to determine changes in the value and location of the peak interface stress and determine the properties that produce the highest peak interface stress, which should correspond to the lowest critical pull-off force. While the peak stress increased with increasing thickness gradients in all cases, the optimal geometric properties depended on the Poisson's ratio of the coating, so the specific material chosen is an important factor. The location of the peak stress was nearly always on the thin side of the coating when a thickness gradient was present, although the exact location (i.e., edge or interior) also depended on the Poisson's ratio.

Objective To characterize the clinical phenotype, genetic origin, and muscle pathology of patients with the FKRP c.1387A>G mutation. Methods Standardized clinical data were collected for all patients known to the authors with c.1387A>G mutations in FKRP. Muscle biopsies were reviewed and used for histopathology, immunostaining, Western blotting, and DNA extraction. Genetic analysis was performed on extracted DNA. Results We report the clinical phenotypes of 6 patients homozygous for the c.1387A>G mutation in FKRP. Onset of symptoms was G patients revealed a 500-kb region of shared homozygosity at 19q13.32, including FKRP. All 4 muscle biopsies available for review showed end-stage dystrophic pathology, near absence of glycosylated α-dystroglycan (α-DG) by immunofluorescence, and reduced molecular weight of α-DG compared with controls and patients with homozygous FKRP c.826C>A limb-girdle muscular dystrophy. Conclusions The clinical features and muscle pathology in these newly reported patients homozygous for FKRP c.1387A>G confirm that this mutation causes congenital muscular dystrophy. The clinical severity might be explained by the greater reduction in α-DG glycosylation compared with that seen with the c.826C>A mutation. The shared region of homozygosity at 19q13.32 indicates that FKRP c.1387A>G is a founder mutation with an estimated age of 60 generations (∼1,200–1,500 years).

BACKGROUND Depression is a highly prevalent mental health issue that exacts significant economic, societal, personal and interpersonal costs. Innovative internet-delivered interventions have been designed to increase accessibility to and cost-effectiveness of treatments. These treatments have mainly targeted mild to moderate levels of depression. The increased risk associated with severe depression, particularly of suicidal ideation often results in this population being excluded from research studies. As a result, effectiveness of iCBT in more severely depressed cohorts is less researched. OBJECTIVE To examine the effect of iCBT on symptoms of severe depression, comorbid symptoms of anxiety and levels of work and social functioning. METHODS Retrospective consent was provided by participants with elevated scores (>28 severe depression symptoms) on the Beck Depression Inventory (BDI-II) who accessed an iCBT intervention (Space from Depression) with support for 8 weeks. Data was collected at baseline, post-treatment and 3-month follow-up on the primary outcome the Beck Depression Inventory-II (BDI-II), and secondary outcomes; the Generalized Anxiety Disorder-7 (GAD-7) and the Work and Social Adjustment Scale (WSAS). RESULTS Significant change was observed on all measures between pre- and post- measurement, and maintained at 3-month follow-up. Clinical improvement was observed for participants on the BDI-II from pre- to post- measurement and suicidal ideation also reduced from pre- to post- measurement. CONCLUSIONS Space from Depression was found to decrease symptoms of depression and anxiety and increase work and social functioning for individuals with severe depression symptoms. The intervention also demonstrated its potential to decrease suicidal ideation. Further investigation is required to determine why some individuals improve, and others do not. ICBT may have the potential to be used as an adjunct treatment for severe depression symptoms, but participants may require further treatment if they receive iCBT as a standalone. Although promising, further research is needed to support the utility of Space from Depression for use in or as an adjunct to treatment for severe depression.

An end-to-end, mechanism-based concussion risk model, linking head motion to axonal injury, has been demonstrated to predict concussion outcomes with greater sensitivity and specificity than external correlates such as peak head acceleration. The development of this model was driven by the need to more accurately translate head-worn sensor measurements into injury assessment in near-real time. The full end-to-end model is a detailed multi-scale model, composed of complex components (e.g., a human head finite element model), is computationally expensive, and requires specialized software. For practicality, this research-level model must be simplified into a standalone, fast-running algorithm that can be embedded on the microprocessor of a head-worn sensor. This article describes the development of a simplified, fast-running algorithm that delivers comparable results to those of the full end-to-end model. The dynamic axonal response of the human head finite element model to head motion is mathematically modeled using a lumped parameter system fitted to the finite element model response for a range of head motions. The other component models of the full end-to-end model were similarly reduced. For the same head kinematic scenarios, the probabilities of concussion obtained from the end-to-end model and from the simplified algorithm are compared well.

Past concussion studies have focused on understanding the injury processes occurring on discrete length scales (e.g., tissue-level stresses and strains, cell-level stresses and strains, or injury-induced cellular pathology). A comprehensive approach that connects all length scales and relates measurable macroscopic parameters to neurological outcomes is the first step toward rationally unraveling the complexity of this multi-scale system, for better guidance of future research. This paper describes the development of the first quantitative end-to-end multi-scale model that links gross head motion to neurological injury by integrating fundamental elements of tissue and cellular mechanical response with axonal dysfunction. The model quantifies axonal stretch (i.e., tension) injury in the corpus callosum, with axonal functionality parameterized in terms of axonal signaling. An internal injury correlate is obtained by calculating a neurological injury measure (the average reduction in the axonal signal amplitude) over the corpus callosum. By using a neurologically based quantity rather than externally measured head kinematics, the end-to-end model is able to unify concussion data across a range of exposure conditions and species with greater sensitivity and specificity than correlates based on external measures. In addition, this model quantitatively links injury of the corpus callosum to observed specific neurobehavioral outcomes that reflect clinical measures of mild traumatic brain injury. This comprehensive modeling framework provides a basis for the systematic improvement and expansion of this mechanistic-based understanding, including widening the range of neurological injury estimation, improving concussion risk correlates, guiding the design of protective equipment, and setting safety standards.

Enveloped viruses attach to host cells by binding to receptors on the cell surface. For many viruses, entry occurs via membrane fusion after a sufficient number of receptors have engaged ligand proteins on the virion. Under conditions where the cell surface receptor densities are low, recruitment of receptors may be limited by diffusion rather than by receptor-ligand interactions. We present a receptor-binding model that includes the effects of receptor availability at the viral binding site. The receptor binding and unbinding kinetics are coupled to receptor diffusion across the cell membrane. We find numerical solutions to our model and analyze the viral entry probabilities and the mean times to entry as functions of receptor concentration, receptor diffusivity, receptor binding stoichiometry, receptor detachment rates, and virus degradation/detachment rates. We also show how entry probabilities and times differ when receptors bind randomly or sequentially to the binding sites on the viral glycoprotein spikes. Our results provide general insight into the biophysical transport mechanisms that may arise in viral attachment and entry.

As revealed by techniques of structural biology and single-molecule experimentation, the protein shells of viruses (capsids) are some of nature’s best examples of highly symmetric multiscale self-assembled structures, with impressive mechanical properties of strength and elasticity. Mechanical models of viral capsids built “from the bottom up,” i.e., from all-atom models in the context of molecular dynamics and normal mode analysis, have chiefly focused on unforced vibrational capsid dynamics. Due to the size of viral capsids, which can contain several hundred thousand atoms, the computer power needed for these types of methods has only recently reached the level required for all-atom simulations of entire viral capsids. Coarse-grained normal mode analysis has provided a simplified means of studying the unforced vibrational dynamics of viral capsids. Recent focus on “top-down” mechanical models of viral capsids based on two- and three-dimensional continuum elasticity have provided a theoretical complement to single molecule experiments such as atomic force microscopy, and have advanced the fundamental understanding of the forced mechanics. This review serves to assess the current state of modeling techniques for the study of the mechanics of viral capsids, and to highlight some of the key insights gained from such modeling. In particular, a theme is established of a link between shape—or geometry—and the global mechanical properties of these hierarchical multiscale biological structures.

A detailed 3D finite element model (FEM) of the sheep thorax was developed to predict heterogeneous and volumetric lung injury due to blast. A shared node mesh of the sheep thorax was constructed from a computed tomography (CT) scan of a sheep cadaver, and while most material properties were taken from literature, an elastic–plastic material model was used for the ribs based on three-point bending experiments performed on sheep rib specimens. Anesthetized sheep were blasted in an enclosure, and blast overpressure data were collected using the blast test device (BTD), while surface lung injury was quantified during necropsy. Matching blasts were simulated using the sheep thorax FEM. Surface lung injury in the FEM was matched to pathology reports by setting a threshold value of the scalar output termed the strain product (maximum value of the dot product of strain and strain-rate vectors over all simulation time) in the surface elements. Volumetric lung injury was quantified by applying the threshold value to all elements in the model lungs, and a correlation was found between predicted volumetric injury and measured postblast lung weights. All predictions are made for the left and right lungs separately. This work represents a significant step toward the prediction of localized and heterogeneous blast lung injury, as well as volumetric injury, which was not recorded during field testing for sheep.

The elastic properties of capsids of the cowpea chlorotic mottle virus have been examined at pH 4.8 by nanoindentation measurements with an atomic force microscope. Studies have been carried out on WT capsids, both empty and containing the RNA genome, and on full capsids of a salt-stable mutant and empty capsids of the subE mutant. Full capsids resisted indentation more than empty capsids, but all of the capsids were highly elastic. There was an initial reversible linear regime that persisted up to indentations varying between 20% and 30% of the diameter and applied forces of 0.6-1.0 nN; it was followed by a steep drop in force that is associated with irreversible deformation. A single point mutation in the capsid protein increased the capsid stiffness. The experiments are compared with calculations by finite element analysis of the deformation of a homogeneous elastic thick shell. These calculations capture the features of the reversible indentation region and allow Young's moduli and relative strengths to be estimated for the empty capsids. © 2006 by The National Academy of Sciences of the USA.

Viral capsids undergo significant mechanical deformations during their assembly, maturation, and infective life-span. In order to characterize the mechanics of viral capsids, their response to applied external forces is analyzed in several experimental studies using, for instance, Atomic Force Microscope (AFM) indentation experiments. In recent years, a broader approach to study the mechanics of viral capsids has leveraged the theoretical tools proper of continuum mechanics. Even though the theory of continuum elasticity is most commonly used to study deformable bodies at larger macroscopic length scales, it has been shown that this very rich theoretical field can still offer useful insights into the mechanics of viral structures at the nanometer scale. Here we show the construction of viral capsid continuum mechanics models starting from different forms of experimental data. We will discuss the kinematics assumptions, the issue of the reference configuration, the material constitutive laws, and the numerical discretization necessary to construct a complete Finite Element capsid mechanical model. Some examples in the second part of the chapter will show the predictive capabilities of the constructed models and underline useful practical aspects related to efficiency and accuracy. We conclude each example by collecting several key findings discovered by simulating AFM indentation experiments using the constructed numerical models.

Viral capsids undergo significant mechanical deformations during their assembly, maturation, and infective life-span. In order to characterize the mechanics of viral capsids, their response to applied external forces is analyzed in several experimental studies using, for instance, Atomic Force Microscope (AFM) indentation experiments. In recent years, a broader approach to study the mechanics of viral capsids has leveraged the theoretical tools proper of continuum mechanics. Even though the theory of continuum elasticity is most commonly used to study deformable bodies at larger macroscopic length scales, it has been shown that this very rich theoretical field can still offer useful insights into the mechanics of viral structures at the nanometer scale. Here we show the construction of viral capsid continuum mechanics models starting from different forms of experimental data. We will discuss the kinematics assumptions, the issue of the reference configuration, the material constitutive laws, and the numerical discretization necessary to construct a complete Finite Element capsid mechanical model. Some examples in the second part of the chapter will show the predictive capabilities of the constructed models and underline useful practical aspects related to efficiency and accuracy. We conclude each example by collecting several key findings discovered by simulating AFM indentation experiments using the constructed numerical models.

Recent Atomic Force Microscope (AFM) nanoindentation experiments measuring mechanical response of the protein shells of viruses have provided a quantitative description of their strength and elasticity. To better understand and interpret these measurements, and to elucidate the underlying mechanisms, this paper adopts a course-grained modeling approach within the framework of three-dimensional nonlinear continuum elasticity. Homogeneous, isotropic, elastic, thick shell models are proposed for two capsids: the spherical Cowpea Chlorotic Mottle Virus (CCMV), and the ellipsocylindrical bacteriophage $\phi 29$. As analyzed by the finite element method, these models enable parametric characterization of the effects of AFM tip geometry, capsid dimensions, and capsid constitutive descriptions. The generally nonlinear force response of capsids to indentation is shown to be insensitive to constitutive details, and greatly influenced by geometry. Nonlinear stiffening and softening of the force response is dependent on the AFM tip dimensions and shell thickness. Fits of the models capture the roughly linear behavior observed in experimental measurements and result in estimates of Young's moduli of $\approx$280--360 MPa for CCMV and $\approx$4.5 GPa for $\phi 29$., Comment: 24 pages, 10 figures, submitted to Biophysical Journal

The current rapid growth in the use of nanosized particles is fueled in part by our increased understanding of their physical properties and ability to manipulate them, which is essential for achieving optimal functionality. Here we report detailed quantitative measurements of the mechanical response of nanosized protein shells (viral capsids) to large-scale physical deformations and compare them with theoretical descriptions from continuum elastic modeling and molecular dynamics (MD). Specifically, we used nanoindentation by atomic force microscopy to investigate the complex elastic behavior of Hepatitis B virus capsids. These capsids are hollow, ∼30 nm in diameter, and conform to icosahedral (5-3-2) symmetry. First we show that their indentation behavior, which is symmetry-axis-dependent, cannot be reproduced by a simple model based on Föppl-von Kármán thin-shell elasticity with the fivefold vertices acting as prestressed disclinations. However, we can properly describe the measured nonlinear elastic and orientation-dependent force response with a three-dimensional, topographically detailed, finite-element model. Next, we show that coarse-grained MD simulations also yield good agreement with our nanoindentation measurements, even without any fitting of force-field parameters in the MD model. This study demonstrates that the material properties of viral nanoparticles can be correctly described by both modeling approaches. At the same time, we show that even for large deformations, it suffices to approximate the mechanical behavior of nanosized viral shells with a continuum approach, and ignore specific molecular interactions. This experimental validation of continuum elastic theory provides an example of a situation in which rules of macroscopic physics can apply to nanoscale molecular assemblies. © 2010 by the Biophysical Society.

A series of recent nanoindentation experiments on the protein shells (capsids) of viruses has established atomic force microscopy (AFM) as a useful framework for probing the mechanics of large protein assemblies. Specifically these experiments provide an opportunity to study the coupling of the global assembly response to local conformational changes. AFM experiments on cowpea chlorotic mottle virus, known to undergo a pH-controlled swelling conformational change, have revealed a pH-dependent mechanical response. Previous theoretical studies have shown that homogeneous changes in shell geometry can play a significant role in the mechanical response. This article develops a method for accurately capturing the heterogeneous geometry of a viral capsid and explores its effect on mechanical response with a nonlinear continuum elasticity model. Models of both native and swollen cowpea chlorotic mottle virus capsids are generated from x-ray crystal structures, and are used in finite element simulations of AFM indentation along two-, three-, and fivefold icosahedral symmetry orientations. The force response of the swollen capsid model is observed to be softer by roughly a factor of two, significantly more nonlinear, and more orientation-dependent than that of a native capsid with equivalent elastic moduli, demonstrating that capsid geometric heterogeneity can have significant effects on the global structural response.

We report nanoindentation experiments by atomic force microscopy on capsids of the Hepatitis B Virus (HBV). HBV is investigated because its capsids can form in either a smaller T=3 or a bigger T=4 configuration (see figure), making it an ideal system to test the predictive power of continuum elastic theory to describe nanometer-sized objects. It is shown that for small, consecutive indentations the particles behave reversibly linear and no material fatigue occurs. For larger indentations the particles start to deform non-linearly. The experimental force response fits very well with finite element simulations on coarse grained models of HBV capsids. Furthermore, this also fits with thin shell simulations guided by the Foppl- von Karman (FvK) number (the dimensionless ratio of stretching and bending stiffness of a thin shell). Both the T=3 and T=4 morphology are very well described by the simulations and the capsid material turns out to have the same Young's modulus, as expected. The presented results demonstrate the surprising strength of continuum elastic theory to describe indentation of viral capsids.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Viral capsids are self assembled nano-containers with remarkable material properties. They combine extreme simplicity of construction with both, toughness and resilience protecting the viral genome, and with complex functionality that the virus needs for targeting and infecting new host cells. We have experimentally, with atomic force microscopy, and numerically, with finite element analysis, studied viral shells under external mechanical stress. While gently probing bacteriophage Φ29 shells with small forces, we could measure linear response properties and estimate a Young's modulus for the shell proteins. In images we observed patterns following symmetry elements. When we irreversibly destroyed the shells in a controlled fashion with higher applied forces, we found that the capsids fractured along well-defined lines revealing trimers as stable building blocks. Similar experiments on capsids of the cowpea chlorotic mottle virus (CCMV) at pH 4.8 revealed an initial reversible linear regime up to indentations of ∼ 20% of the diameter followed by irreversible deformation. At a pH 6.0, the response of the shell changes dramatically and becomes soft. Modeling predicts that the nature of structural failure is determined by a simple and universal physical characteristic, namely, the Foppl-von Karman (FvK) number, a dimensionless control parameter that emerges from the continuum theory of thin shells.