Rigid Skin Research Articles

Quantitative analysis of the upwelling behavior of methane bubbles in nature and numerical simulations

In recent years, methane gas released from the seafloor has been considered a sub-oceanic resource, and comprehending the dynamics of methane bubbles in the ocean has garnered increasing attention. Therefore, in this study, we conducted a quantitative analysis of the behavior of ascending methane bubbles with and without a hydrate layer. The bubbles were filmed at two natural gas seep sites and reproduced by numerical simulations using two-dimensional motion analysis software. The simulations were performed with gas bubbles and methane hydrate (MH)1 bubbles spouting from a nozzle in a computational domain filled with pure water to assess the validity of image analysis for in-situ data, whereas numerical models and physical properties were utilized for the current two-phase (gas-liquid) simulations. The rising velocity, size, circumference, circularity, and maximum diameter of the methane bubbles were examined to understand the effects of the MH layer on the statistical and stochastic features of ascending methane bubbles. Based on the statistics of the above variables, the gas bubbles had a higher rising velocity and smaller circularity than the MH bubbles when the bubble sizes were identical. In addition, stochastic analysis indicated that the circularity of the MH bubble was uniquely determined by their size, due to the more rigid skin of the MH bubbles compared to that of gas bubbles. Consequently, discrepancies in bubble dynamics between methane gas and MH bubbles were clarified in this study.

An exploration into surface wrinkling in 3D printing inspired orthotropic bilayer systems

Surface instability, termed wrinkling, might occur in compressed bilayer systems constituted by an external rigid skin resting on an internal soft substrate, where wrinkling is favored by the rigidity contrast between the two layers. In this paper, the same instability mechanism is explored by considering a substrate characterized by an orthotropic elastic response. By varying the orientation of the principal axes of the substrate’s material, the critical strain of wrinkling and the wrinkles’ wavelength can be tuned during compression. Theoretical formulations for wrinkling are discussed along with the results obtained by linear bifurcation and geometrically nonlinear analyses carried out with two-dimensional finite element models. To experimentally validate the results, the intrinsic properties of Fused Deposition Modeling (FDM) 3D printing technology are leveraged: bilayer objects are manufactured by printing continuous outer shells (corresponding to the rigid skin) along the borders, while the inner raster is shaped with a porous infill pattern, forming a substrate with an orthotropic elastic response.

Primeiro relato de predação de um jacaré-coroa (Paleosuchus trigonatus) por uma lontra (Lontra longicaudis)

ABSTRACT Lontra longicaudis is a semi-aquatic predator which mainly feeds on fish and crustaceans, but which can opportunistically predate mammals, birds, and reptiles. In the Amazon, this species is sympatric with Paleosuchus trigonatus, one of the smallest species of crocodilians, whose possible means of defense is a very rigid skin, which causes adults to have few predators. Here we report the first documented case of predation of P. trigonatus by L. longicaudis.

Pore development in viscoelastic foods during drying.

In this paper, we present a numerical model that can describe the pore formation/cavitation in viscoelastic food materials during drying. The food material has been idealized as a spherical object, with a core/shell structure and a central gas-filled cavity. The shell represents a skin as present in fruits/vegetables, having a higher elastic modulus than the tissue, which we approximate as a hydrogel. The gas-filled pore is in equilibrium with the core hydrogel material, and it represents pores in food tissues as present in intercellular junctions. The presence of a rigid skin is a known prerequisite for cavitation (inflation of the pore) during drying. For modeling, we follow the framework of Suo and coworkers, describing the inhomogeneous large deformation of soft materials like hydrogels - where stresses couple back to moisture transport. In this paper, we have extended such models with energy transport and viscoelasticity, as foods are viscoelastic materials, which are commonly heated during their drying. To approach the realistic properties of food materials we have made viscoelastic relaxation times a function of Tg/T, the ratio of (moisture dependent) glass transition temperature and actual product temperature. We clearly show that pore inflation only occurs if the skin gets into a glassy state, as has been observed during the (spray) drying of droplets of soft materials like foods.

Stiff Skin Syndrome: Clinical Exploration, Pathophysiology and Therapeutic Advances in a Rare Connective Tissue Disease

Stiff Skin Syndrome, also known as "diffuse stiff skin syndrome" or "Scleroderma-like syndrome with focal contracture", is a rare and complex clinical entity in the spectrum of connective tissue diseases. This disorder is characterized by progressive and diffuse infiltration of connective tissue into the skin and underlying tissues, resulting in extreme skin stiffness and limited joint mobility. In addition to its cutaneous and joint manifestations, stiff skin syndrome can affect multiple internal organs, making it a clinical entity of great multidisciplinary relevance. This article aims to provide a comprehensive review of stiff skin syndrome, addressing its epidemiology, clinical manifestations, etiopathogenesis, differential diagnosis, and current therapeutic options. Recent research that has shed light on the underlying molecular mechanisms and emerging therapies that are being developed to improve the quality of life of patients affected by this disease are highlighted. In addition, the importance of a comprehensive evaluation and an interdisciplinary therapeutic approach to optimize the clinical management of individuals with rigid skin syndrome is highlighted.

The intriguing molecular dynamics of Cer[EOS] in rigid skin barrier lipid layers requires improvement of the model

Omega-O-acyl ceramides such as 32-linoleoyloxydotriacontanoyl sphingosine (Cer[EOS]) are essential components of the lipid skin barrier, which protects our body from excessive water loss and the penetration of unwanted substances. These ceramides drive the lipid assembly to epidermal-specific long periodicity phase (LPP), structurally much different than conventional lipid bilayers. Here, we synthesized Cer[EOS] with selectively deuterated segments of the ultralong N-acyl chain or deuterated or 13C-labeled linoleic acid and studied their molecular behavior in a skin lipid model. Solid-state 2H NMR data revealed surprising molecular dynamics for the ultralong N-acyl chain of Cer[EOS] with increased isotropic motion toward the isotropic ester-bound linoleate. The sphingosine moiety of Cer[EOS] is also highly mobile at skin temperature, in stark contrast to the other LPP components, N-lignoceroyl sphingosine acyl, lignoceric acid, and cholesterol, which are predominantly rigid. The dynamics of the linoleic chain is quantitatively described by distributions of correlation times and using dynamic detector analysis. These NMR results along with neutron diffraction data suggest an LPP structure with alternating fluid (sphingosine chain-rich), rigid (acyl chain-rich), isotropic (linoleate-rich), rigid (acyl-chain rich), and fluid layers (sphingosine chain-rich). Such an arrangement of the skin barrier lipids with rigid layers separated with two different dynamic “fillings” i) agrees well with ultrastructural data, ii) satisfies the need for simultaneous rigidity (to ensure low permeability) and fluidity (to ensure elasticity, accommodate enzymes, or antimicrobial peptides), and iii) offers a straightforward way to remodel the lamellar body lipids into the final lipid barrier.

Concurrent Topology Optimization for Maximizing the Modal Loss Factor of Plates with Constrained Layer Damping Treatment.

Damping performance of the plates with constrained layer damping (CLD) treatment mainly depends on the layout of CLD material and the material physical properties of the viscoelastic damping layer. This paper develops a concurrent topology optimization methodology for maximizing the modal loss factor (MLF) of plates with CLD treatment. At the macro scale, the damping layer is composed of 3D periodic unit cells (PUC) of cellular viscoelastic damping materials. At the micro scale, due to the deformation of viscoelastic damping material affected by the base and constrained layers, the representative volume element (RVE) considering a rigid skin effect is used to improve the accuracy of the effective constitutive matrix of the viscoelastic damping material. Maximizing the MLFs of CLD plates is employed as the design objectives in optimization procedure. The sensitivities with respect to macrodesign variables are formulated using the adjoint vector method while considering the contribution of eigenvectors, while the influence of macroeigenvectors is ignored to improve the computational efficiency in the mesosensitivity analysis. The macro and meso scales design variables are simultaneously updated using the Method of Moving Asymptotes (MMA) to find concurrently optimal configurations of constrained and viscoelastic damping layers at the macro scale and viscoelastic damping materials at the micro scale. Two rectangular plates with different boundary conditions are presented to validate the optimization procedure and demonstrate the effectiveness of the proposed concurrent topology optimization approach. The effects of optimization objectives and volume fractions on the design results are investigated. The results indicate that the optimized layouts of the macrostructure are dependent on the objective mode and the volume fraction on the meso scale. The optimized designs on the meso scale are mainly related to the objective mode. By varying the volume fraction on the macro scale, the optimized designs on the meso scale are different only in their detailed size, which is reflected in the values of the equivalent constitutive matrices.

Preconditioning process for dermal tissue decellularization using electroporation with sonication.

Decellularization to produce bioscaffolds composed of the extracellular matrix (ECM) uses enzymatic, chemical and physical methods to remove antigens and cellular components from tissues. Effective decellularization methods depend on the characteristics of tissues, and in particular, tissues with dense, complex structure and abundant lipid content are difficult to completely decellularize. Our study enables future research on the development of methods and treatments for fabricating bioscaffolds via decellularization of complex and rigid skin tissues, which are not commonly considered for decellularization to date as their structural and functional characteristics could not be preserved after severe decellularization. In this study, decellularization of human dermal tissue was done by a combination of both chemical (0.05% trypsin-EDTA, 2% SDS and 1% Triton X-100) and physical methods (electroporation and sonication). After decellularization, the content of DNA remaining in the tissue was quantitatively confirmed, and the structural change of the tissue and the retention and distribution of ECM components were evaluated through histological and histochemical analysis, respectively. Conditions of the chemical pretreatment that increase the efficiency of physical stimulation as well as decellularization, and conditions for electroporation and sonication without the use of detergents, unlike the methods performed in previous studies, were established to enable the complete decellularization of the skin tissue. The combinatorial decellularization treatment formed micropores in the lipid bilayers of the skin tissues while removing all cell and cellular residues without affecting the ECM properties. Therefore, this procedure can be widely used to fabricate bioscaffolds by decellularizing biological tissues with dense and complex structures.

Multi-scale analysis of the flexural behaviour of 3D printed cellular polymer materials: Comparison between morphing and sandwich beams

Cellular materials with tailorable properties are increasingly being used as a controllable morphing mechanism in airfoils. Nonetheless, the flexural properties of this mechanism change depending on the configuration. Thus, the aim of this paper is to identify and analyse parameters tailoring these properties. A multi-scale analysis that models reliably the behaviour of 3D printed structures is developed. Three scales are considered. The microscopic scale, where the properties of the 3D-printed material are measured. The mesoscopic scale, where mechanical properties of four different patterns, selected for their current use in morphing applications, are estimated via numerical homogenisation. The macroscopic scale, where the global bending behaviour of cellular beams is studied. Then, the mechanical behaviour of cantilever cellular beams is studied while varying their skin rigidity. Results indicate that the skin rigidity is a critical parameter tailoring the core’s behaviour. Rigid skins force the morphing airfoil to behave like a sandwich structure, while compliant skins induce a more complex behaviour.

Modeling of a Complete Morphing Mechanism Covered by a Paneled Morphing Skin

Abstract Presented in this paper is a method for modeling and simulation of a complete morphing mechanism. The said mechanism has a rigid panel morphing skin that morphs along with a driving mechanism. The said skin is made of segmented panels, inspired by fish scales. Since the gaps between these panels are undesirable, a gapless design is introduced in this paper by using shape-memory polymer (SMP) joints. This paper aims to solve two fundamental problems for the entire system: (1) motion control and (2) force control. The motion control is addressed through the kinematic modeling of two equations including (a) the passive rigid panels and (b) the passive rigid panels to the active mechanism. Force control is achieved through force modeling. This is to develop a relationship of the SMP deformations to the required actuator forces. The experiment is carried out to determine the SMP forces versus deformation, and simulations are conducted to investigate how a complete morphing mechanism behaves. It also reveals that the workspace and singularity of the original mechanism will change after covered by a morphing skin. The developed method sheds light on the design of a complete morphing mechanism.

Zinc and Its Transporters in Epigenetics.

Epigenetic events like DNA methylation and histone modification can alter heritable phenotypes. Zinc is required for the activity of various epigenetic enzymes, such as DNA methyltransferases (DNMTs), histone acetyltransferases (HATs), histone deacetylases (HDACs), and histone demethylases, which possess several zinc binding sites. Thus, the dysregulation of zinc homeostasis can lead to epigenetic alterations. Zinc homeostasis is regulated by Zinc Transporters (ZnTs), Zrt- and Irt-like proteins (ZIPs), and the zinc storage protein metallothionein (MT). Recent advances revealed that ZIPs modulate epigenetics. ZIP10 deficiency was found to result in reduced HATs, confirming its involvement in histone acetylation for rigid skin barrier formation. ZIP13 deficiency, which is associated with Spondylocheirodysplastic Ehlers-Danlos syndrome (SCD-EDS), increases DNMT activity, leading to dysgenesis of dermis via improper gene expressions. However, the precise molecular mechanisms remain to be elucidated. Future molecular studies investigating the involvement of zinc and its transporters in epigenetics are warranted.

An analytical solution for elastic buckling analysis of stiffened panel subjected to pure bending

In this study, an analytical solution has been developed for the elastic buckling analysis of stiffened panels subjected to pure bending, and the effect of main geometric parameters of the stiffened panels on buckling strength has been investigated. A simplified model of stiffened panels has been proposed for buckling analysis, where an elastically built-in boundary condition replaces the skin's effect on buckling of the stiffened panels. The equilibrium method with a conventional rigid skin assumption and a new flexible skin assumption is developed for the simplified model to analytically capture the buckling behaviour of the stiffened panels. To consider the non-rigid rotation effect of flexible skin on buckling of stiffened panels, a new parameter, the effective width of stiffened panels, has been introduced, and a finite element (FE) assisted method has been employed to obtain its value for different stiffened panels. The results show that the flexible skin assumption significantly enhances the accuracy of buckling strength prediction compared with the conventional rigid skin assumption, and the maximum difference between analytical results and corresponding FE simulations is decreased from 12.2% with rigid skin assumption to only 3.9%. Based on the proposed analytical solution, effects of main geometric parameters of the stiffened panels (the stiffened panel length and width, the stiffener height, and the ratio of the skin thickness to the stiffener thickness) on their buckling coefficients have been discussed. Increasing stiffened panel length and/or reciprocal of stiffener height leads to an initial abrupt decrease of the buckling coefficient until reaching a stable level. When the stiffened panel width increases, the buckling coefficient first increases and then remains stable, whereas increasing thickness ratio leads to the increase of the buckling coefficient.

Smart Patterned Surface with Dynamic Wrinkles.

Patterned surfaces are fundamentally important to physics, chemistry, materials, and biology science, endowing significant functions and thus bearing broad and fantastic applications whether in natural or man-made events. Among the various methods for patterning surfaces, wrinkling or buckling offers a powerful alternative to prepare surface patterns because of its spontaneous nature, versatility, easy preparation in large-scale, and capability to be responsive to various stimuli. In particular, patterned surfaces with dynamic wrinkles can tailor the encoded surface properties on demand and can provide a promising alternative for smart surfaces, which has potential for wide applications in enhanced and tunable optical or photoelectric devices, responsive microstructures, switchable wettability, smart adhesion and friction, and so on. The concept of smart patterned surfaces based on dynamic wrinkles is fundamental and versatile, and it is expected that there will be extensive future work based on this concept in generalizing this work to other smart materials and systems, and in using dynamic pattern systems to tune not only morphology but also functional properties encoded in the system's topography. In this Account, we present recent progress on smart surfaces with dynamic wrinkle patterns, including their design, preparation, and potential applications. First, we provide a brief introduction of a basic concept for mechanical instability induced wrinkle patterns and outline the general strategies and mechanics for dynamic wrinkles. Then, we discuss how the wrinkling and dewrinkling processes of a rigid skin bound to a soft substrate in bilayers or gradient layer systems occur by controlling the mechanical properties and geometric characteristics of the top and bulk layers, thereby paving the way for a smart patterned surface using chemical and physical approaches. Next, we discuss various chemical and physical stimuli, including light, temperature, pH, and chemicals, which can be harnessed into an extensive library of complex dynamic wrinkles. We highlight recent advances in preparing multiresponsive dynamic wrinkling patterns by adjusting the intrinsic properties of the skin layers (i.e., Young's modulus and cross-linking density) via dynamic chemistry, such as the Diels-Alder reaction, photodimerization, and supramolecular chemistry. Then, we outline how functional inclusions, such as photothermic or photoelectric additives and magnetic nanoparticles, can enable the composite elastic substrate as a dynamic platform for various functional top-layers to fabricate a smart surface for a desired function. In particular, photothermally reconfigurable wrinkle systems were investigated, where the carbon nanotube (CNT) served to efficiently convert its absorbed light energy into heat, hence actuating a real-time response of a near-infrared light (NIR)-sensitive wrinkle pattern and providing access to the development of advanced optoelectronic devices. In addition, based on their unique characteristics, applications of dynamic wrinkle patterns for smart displays, memory, flexible electronics, dynamic gratings, tunable adhesion, friction, and wettability are presented. Finally, we conclude by offering our perspective on future developments of this rapidly evolving field.

Design of commercial hexagonal honeycombs of equal out-of-plane shear moduli

In the present paper the hexagonal honeycombs with double vertical walls (commercial), which usually are used as cores in sandwich plates, and the rigid skin effect are considered. Loaded in out-of-plane shear, the core is designed to have an identical macroscopic behavior in both planes, that is G13 = G23. Using a general parameterization of their geometry and imposing the necessary conditions together with some restrictions, the relations between geometrical parameters are first sought analytically in some simplified hypotheses. Then, considering a 3D finite element model and the optimization module in ANSYS, the more accurate geometry representation of the possible out-of-plane isotropic commercial honeycombs and their effective elastic constants were obtained. The numerical results are discussed by comparing them to the ones given by the classic analytical models. The results provide new insights into understanding the mechanics of honeycombs and designing new types of cellular materials which may fulfill some supplementary conditions than the existing ones.

Development and dosimetric assessment of a patient-specific elastic skin applicator for high-dose-rate brachytherapy

PurposeThe purpose of this study was to develop a patient-specific elastic skin applicator and to evaluate its dosimetric characteristics for high-dose-rate (HDR) brachytherapy. Methods and MaterialsWe simulated the treatment of a nonmelanoma skin cancer on the nose. An elastic skin applicator was manufactured by pouring the Dragon Skin (Smooth-On Inc., Easton, PA) with a shore hardness of 10A into an applicator mold. The rigid skin applicator was printed using high-impact polystyrene with a shore hardness of 73D. HDR plans were generated using a Freiburg Flap (FF) applicator and patient-specific rigid and elastic applicators. For dosimetric assessment, dose-volumetric parameters for target volume and normal organs were evaluated. Global gamma evaluations were performed, comparing film measurements and treatment planning system calculations with various gamma criteria. The 10% low-dose threshold was applied. ResultsThe V120% values of the target volume were 56.9%, 70.3%, and 70.2% for HDR plans using FF, rigid, and elastic applicators, respectively. The maximum doses of the right eyeball were 21.7 Gy, 20.5 Gy, and 20.5 Gy for the HDR plans using FF, rigid, and elastic applicators, respectively. The average gamma passing rates were 82.5% ± 1.5%, 91.6% ± 0.8%, and 94.8% ± 0.2% for FF, rigid, and elastic applicators, respectively, with 3%/3 mm criterion. ConclusionsPatient-specific elastic skin applicator showed better adhesion to irregular or curved body surfaces, resulting in better agreement between planned and delivered dose distributions. The applicator suggested in this study can be effectively implemented clinically.

Cellulose Acetate Polymeric Membrane Fabrication by Nonsolvent-Induced Phase Separation Process: Determination of Velocities of Individual Components

Abstract In this work, the velocities of individual components during the immersion process using mathematical modeling of a nonsolvent-induced phase separation process are investigated. For this purpose, a mass average velocity correction factor was defined as the ratio of mass average velocity in the absence of a zero polymer velocity assumption to the mass average velocity with zero polymer velocity assumption. The velocities were computed and the result was coherent with observations of a considered case study. It was concluded that the polymer moves towards the interface, as the sign of the polymer velocity at early moments of immersion was positive, which is in accord with accumulation and vitrification of the polymer at the interface. The positive sign of the solvent and the negative sign of nonsolvent are in accord with the observations as solvent leaves the cast film and nonsolvent penetrates into the film. The reduction of velocity values to the order of magnitude of diffusivities is in accord with the limiting role of the rigid skin layer for mass exchanges. Relatively large velocity values of the solvent rather than the nonsolvent imply that much more solvent is probably left in the cast film rather than the nonsolvent enters into it as observed by densification of the cast film.

Variable-Friction Finger Surfaces to Enable Within-Hand Manipulation via Gripping and Sliding

The human hand is able to achieve an unparalleled diversity of manipulation actions. One contributor to this capability is the structure of the human finger pad, where soft internal tissue is surrounded by a layer of more rigid skin. This permits conforming of the finger pad around object contours for firm grasping, while also permitting low-friction sliding over object surfaces with a light touch. These varying modes of manipulation contribute to the common ability for in-hand-manipulation, where an object (such as a car key) may repositioned relative to the palm. In this letter, we present a simple mechanical analogy to the human finger pad, via a robotic finger with both high- and low-friction surfaces. The low-friction surface is suspended on elastic elements and recesses into a cavity when a sufficient normal force is applied (∼1.2 to 2.5 N depending on contact location), exposing the high-friction surface. We implement one “variable friction” finger and one “constant friction” finger on a 2-DOF gripper with a simple torque controller. With this setup, we demonstrate how within-hand rolling and sliding of an object may be achieved without the need for tactile sensing, high-dexterity, dynamic finger/object modeling, or complex control methods. The addition of an actuator to the finger design allows controlled switching between variable-friction and constant-friction modes, enabling precise object translation and reorientation within a grasp, via simple motion sequences. The rolling and sliding behaviors are characterized with experimentally verified geometric models.

Water Ion Interactions at Crude-Oil/Water Interface and Their Implications for Smart Waterflooding in Carbonates

Summary Smart waterflooding (SWF) through tailoring of injection-water salinity and ionic composition is receiving favorable attention in the industry for both improved and enhanced oil recovery (EOR) in carbonate reservoirs. Surface/intermolecular forces, thin-film dynamics, and capillary/adhesion forces at rock/fluid interfaces govern crude-oil liberation from pores. On the other hand, stability and rigidity of oil/water interfaces control the destabilization of interfacial film to promote coalescence between released oil droplets and to improve the oil-phase connectivity. As a result, the dynamics of oil recovery in smart waterflood is caused by the combined effect of favorable interactions occurring at both oil/brine and oil/brine/rock interfaces across the thin film. Most of the laboratory studies reported so far have been focused on only studying the interactions at rock/fluid interfaces. However, the other important aspect of characterizing water ion interactions at the crude oil/water interface and their impact on film stability and oil-droplet coalescence remains largely unexplored. A detailed experimental investigation was conducted to understand the effects of different water ions at the crude-oil/water interface by using several instruments such as Langmuir trough, interfacial shear rheometer, Attension tensiometer, and coalescence time-measurement apparatus. The reservoir crude oil and four different water recipes with varying salinities and individual ion concentrations were used. Interfacial tension (IFT), interface pressures, compression energy, interfacial viscous and elastic moduli, oil-droplet crumpling ratio, and coalescence time between crude-oil droplets are the major experimental data measured. The IFTs are found to be the largest for deionized (DI) water, followed by the 10-times-reduced-salinity seawater and 10-times-reduced-salinity seawater enriched with sulfates. Interfacial pressures gradually increased with compressing surface area for all the brines and DI water. The compression energy (integration of interfacial pressure over the surface-area change) is the highest for DI water, followed by the lower-salinity brine containing sulfate ions, indicating rigid interfaces. The transition times of interfacial layer to become elastic-dominant from viscous-dominant structures are found to be much shorter for brines enriched with sulfates, once again confirming the rigidity of interface. The crumpling ratios (oil drop wrinkles when contracted) are also higher with the two recipes of DI water and sulfates-only brine to indicate the same trend and to confirm elastic rigid skin at the interface. The coalescence time between oil droplets was the least in brines containing sufficient amounts of magnesium and calcium ions, while the highest in DI water and sulfate-rich brine, respectively. These results, therefore, showed a good correlation of coalescence times with the rigidity of oil/water interface, as interpreted from different measurement techniques. This study, thereby, integrates consistent results obtained from different measurement techniques at the crude-oil/water interface to demonstrate the importance of both salinity and certain ions, such as magnesium and calcium, on crude-oil-droplets coalescence, and to improve oil-phase connectivity in smart waterflood.

Novel approaches for the assembly simulation of rigid Skin Model Shapes in tolerance analysis

While the modelling of nominal assemblies is sufficiently solved in modern computer-aided design tools, the assembly simulation for parts considering geometrical deviations is still an important research issue. Particularly in tolerance analysis, the assessment of the effects of geometrical part deviations on the part assembly behaviour is of central importance. Though established assembly simulation approaches for parts with geometrical deviations cover a moderate range of real assembly problems, they are not suitable for all assembly simulation problems. To overcome this shortcoming, a general framework and new approaches for the assembly simulation of Skin Model Shapes for the use in tolerance analysis are presented. The application of these assembly simulation approaches is highlighted in generalized case studies and recommendations for their use in tolerance simulations are derived.

Restrictive dermopathy: Report of two cases

Restrictive dermopathy is a rare entity that is fatal in the neonatal period itself. The rigidity of the skin leads to erosions, contractures, and restriction of respiratory movements. Diagnosis is often made clinically with classical features such as low-set ears, micrognathia, small, and persistently open fixed “o”-shaped mouth, translucent, shiny, rigid skin with prominent superficial blood vessels, and pseudocontractures of limb joints. We report two cases of restrictive dermopathy observed in our center within 2 years period and suggest that this condition may not be as rare as believed.