Background Connective tissue disorders (CTDs) are a heterogeneous group of disorders often presenting with a variety of comorbidities including musculoskeletal, autonomic, and immune dysfunction. Some CTDs such as hypermobile Ehlers-Danlos syndrome (hEDS), which is one of the most common, have been associated with neurological disorders requiring surgical intervention. The frequency of these comorbidities in these populations and their subsequent requirement for neurosurgical intervention remains unclear. Methods Based on our initial experience with this population, we investigated the presentation rates of specific comorbidities and neurosurgical interventions in a cohort of individuals referred to our institution for evaluation and neurosurgical management of issues secondary to diagnosed or suspected CTDs from 2014 to 2023. Primary diagnoses were made by referring physicians or institutions based on clinical presentation and standard-of-care criteria. We evaluated relationships between diagnoses and surgical interventions by multivariate correlation and intersection plots using the UpSetR package. Results Of 759 individuals, we excluded 42 based on incomplete data. From the remaining (total cohort, N = 717), 460 (64%) individuals were diagnosed with hEDS, 7 were diagnosed with a CTD other than hEDS, and 250 lacked a formal CTD diagnosis. We found that individuals with hEDS had a higher frequency of certain comorbidities, such as Mast Cell Activation Disorder and Postural Orthostatic Tachycardia Syndrome, and neurosurgical intervention compared to individuals without a CTD diagnosis (unaffected). Of the total cohort, 426 (59%) were diagnosed with Chiari I Malformation, which shared a significant overlap with hEDS. Of those who elected to undergo surgery ( n = 612), 61% required craniocervical fusion (CCF). Notably, of the 460 individuals diagnosed with hEDS, 404 chose surgical intervention, of which, 73% required CCF for craniocervical instability. Conclusion In this retrospective study of individuals referred to our institution for evaluation of CTDs potentially requiring neurosurgical intervention, we defined the frequency of presentation of specific comorbidities that we commonly encountered and revealed the rate at which they required neurosurgical intervention.
When a fluid is pumped into a cavity in a confined elastic layer, at a critical pressure, destabilizing fingers of fluid invade the elastic solid along its meniscus (Saintyves, Dauchot, and Bouchaud, 2013). These fingers occur without fracture or loss of adhesion and are reversible, disappearing when the pressure is decreased. We develop an asymptotic theory of pressurized highly elastic layers trapped between rigid bodies to explain these observations, with predictions for the critical fluid pressure for fingering, and the finger wavelength. We also show that the theory links this fluid-driven fingering with a similar transition driven instead by transverse stretching of the elastic layer. We further verify these predictions by using finite-element simulations on the two systems which show that, in both cases, the fingering transition is first-order (sudden) and hence has a region of bistability. Our predictions are in good agreement with recent observations of this elastic analog of the classical Saffman-Taylor interfacial instability in hydrodynamics.
If a chain is initially at rest in a beaker at a height h1 above the ground, and the end of the chain is pulled over the rim of the beaker and down towards the ground and then released, the chain will spontaneously "flow" out of the beaker under gravity. Furthermore, the beads do not simply drag over the edge of the beaker but form a fountain reaching a height h2 above it. We show that the formation of a fountain requires that the beads come into motion not only by being pulled upwards by the part of the chain immediately above the pile, but also by being pushed upwards by an anomalous reaction force from the pile of stationary chain. We propose possible origins for this force, argue that its magnitude will be proportional to the square of the chain velocity, and predict and verify experimentally that h2 is proportional to h1.
Abstract Liquid crystal elastomers exhibit very rich elastic behaviour because they couple elastic fields and mobile liquid crystal order. One striking phenomenon is the formation of textured deformations: a homogenous elastomer sometimes responds to a macroscopically homogenous imposed strain by forming a spatially fine mixture of very different deformations (a texture) that average to the imposed strain. This occurs because some large strains can be accommodated by rotation of the liquid crystal order, so they cost little energy to impose, while other equally large (or smaller) strains cannot and hence are energetically expensive. If one of these latter strains is imposed macroscopically, the elastomer's energy is lowered if it can form a fine mixture of larger but lower energy strains that average to the imposed deformation. Great progress has been made in understanding this behaviour over the last 10 years. Here, we review the key theoretical ideas and highlight several predicted textures which merit experimental attention. This review assumes little prior knowledge of elasticity or liquid crystal elastomers so hopefully it will be accessible to both non-elasticians and elasticians from other fields, notably the study of martensite which is a highly analogous system but with small strains and discrete broken symmetries rather than large strains and continuous broken symmetries. Keywords: liquid crystalelastomertexture deformationelasticity
Spontaneous material shape changes, such as swelling, growth or thermal expansion, can be used to trigger dramatic elastic instabilities in thin shells. These instabilities originate in geometric incompatibility between the preferred extrinsic and intrinsic curvature of the shell, which may be modified by active deformations through the thickness and in plane, respectively. Here, we solve the simplest possible model of such instabilities, which assumes the shells are shallow, thin enough to bend but not stretch, and subject to homogeneous preferred curvatures. We consider separately the cases of zero, positive and negative Gauss curvature. We identify two types of supercritical symmetry-breaking instability, in which the shell's principal curvature spontaneously breaks discrete up/down symmetry and continuous planar isotropy. These are then augmented by inversion instabilities, in which the shell jumps subcritically between up/down broken symmetry states and rotation instabilities, in which the curvatures rotate by 90° between states of broken isotropy without release of energy. Each instability has a thickness-independent threshold value for the preferred extrinsic curvature proportional to the square root of Gauss curvature. Finally, we show that the threshold for the isotropy-breaking instability is the same for deep spherical caps, in good agreement with recently published data.
Liquid crystal elastomers (LCEs) can undergo large reversible contractions along their nematic director upon heating or illumination. A spatially patterned director within a flat LCE sheet, thus, encodes a pattern of contraction on heating, which can morph the sheet into a curved shell, akin to how a pattern of growth sculpts a developing organism. Here, we consider theoretically, numerically, and experimentally patterns constructed from regions of radial and circular director, which, in isolation, would form cones and anticones. The resultant surfaces contain curved ridges with sharp V-shaped cross sections, associated with the boundaries between regions in the patterns. Such ridges may be created in positively and negatively curved variants and, since they bear Gauss curvature (quantified here via the Gauss–Bonnet theorem), they cannot be flattened without energetically prohibitive stretch. Our experiments and numerics highlight that, although such ridges cannot be flattened isometrically, they can deform isometrically by trading the (singular) curvature of the V angle against the (finite) curvature of the ridge line. Furthermore, in finite thickness sheets, the sharp ridges are inevitably non-isometrically blunted to relieve bend, resulting in a modest smearing out of the encoded singular Gauss curvature. We close by discussing the use of such features as actuating linear features, such as probes, tongues, and grippers. We speculate on similarities between these patterns of shape change and those found during the morphogenesis of several biological systems.
The connection between macroscopic deformation and microscopic chain stretch is a key element in constitutive models for rubber-like materials that are based on the statistical mechanics of polymer chains. A new micro-macro chain stretch relation is proposed, using the Irving–Kirkwood–Noll procedure to construct a Cauchy stress tensor from forces along polymer chains. This construction assumes that the deformed polymer network remains approximately isotropic for low to moderate macroscopic stretches, a starting point recently adopted in the literature to propose a non-affine micro-macro chain stretch relation (Amores et al., 2021). Requiring the constructed Cauchy stress to be consistent with the stress tensor derived from the strain energy density results in a new chain stretch relation involving the exponential function. A hybrid chain stretch relation combining the new chain stretch with the well-known affine relation is then proposed to account for the whole range of stretches in experimental datasets. Comparison of the model predictions to experimental data in the literature shows that the two new micro-macro chain stretch relations in this work result in two-parameter constitutive models that outperform those based on existing chain stretches with no increase in the number of fitting parameters used.
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