Designing the pressure-dependent shear modulus using tessellated granular metamaterials.

Jammed packings of granular materials display complex mechanical response. For example, the ensemble-averaged shear modulus 〈G〉 increases as a power law in pressure p for static packings of soft spherical particles that can rearrange during compression. We seek to design granular materials with shear moduli that can either increase or decrease with pressure without particle rearrangements even in the large-system limit. To do this, we construct tessellated granular metamaterials by joining multiple particle-filled cells together. We focus on cells that contain a small number of bidisperse disks in two dimensions. We first study the mechanical properties of individual disk-filled cells with three types of boundaries: periodic boundary conditions (PBC), fixed-length walls (FXW), and flexible walls (FLW). Hypostatic jammed packings are found for cells with FLW, but not in cells with PBC and FXW, and they are stabilized by quartic modes of the dynamical matrix. The shear modulus of a single cell depends linearly on p. We find that the slope of the shear modulus with pressure λ_{c}<0 for all packings in single cells with PBC where the number of particles per cell N≥6. In contrast, single cells with FXW and FLW can possess λ_{c}>0, as well as λ_{c}<0, for N≤16. We show that we can force the mechanical properties of multicell granular metamaterials to possess those of single cells by constraining the end points of the outer walls and enforcing an affine shear response. These studies demonstrate that tessellated granular metamaterials provide a platform for the design of soft materials with specified mechanical properties.

Effect of Anti-TNF Treatment on Mooren's Ulcer: A Case Series and Review of the Literature.

PURPOSE: To report the efficacy of systemic anti-TNF agents in Mooren's ulcer. DESIGN: Retrospective, consecutive case series. METHODS: We report on clinical characteristics and outcome of five patients with Mooren's ulcer with anti-TNF treatment. RESULTS: During a mean follow-up of 30 months, relief of symptoms and arrest of corneal melting were observed in all eyes. Systemic corticosteroid treatment could be discontinued or reduced to threshold levels. No patient experienced adverse effects on bDMARDs. CONCLUSIONS: Our results suggest that bDMARDs are effective in Mooren's ulcer unresponsive to conventional treatment. This is in line with accumulating evidence in the current literature. Therefore, more targeted immunomodulatory approaches might be an effective first-line therapy in the future.

Dorsal root ganglia hypertrophy as in vivo correlate of oxaliplatin-induced polyneuropathy.

PURPOSE: To investigate in vivo morphological and functional correlates of oxaliplatin-induced peripheral neuropathy (OXA-PNP) by magnetic resonance neurography (MRN). METHODS: Twenty patients (7 female, 13 male, 58.9±10.0 years) with mild to moderate OXA-PNP and 20 matched controls (8 female, 12 male, 55.7±15.6 years) were prospectively enrolled. All patients underwent a detailed neurophysiological examination prior to neuroimaging. A standardized imaging protocol at 3.0 Tesla included the lumbosacral plexus and both sciatic nerves and their branches using T2-weighted fat-saturated sequences and diffusion tensor imaging. Quantitative assessment included volumetry of the dorsal root ganglia (DRG), sciatic nerve normalized T2 (nT2) signal and caliber, and fractional anisotropy (FA), mean diffusivity (MD), axial (AD) and radial diffusivity (RD). Additional qualitative evaluation of sciatic, peroneal, and tibial nerves evaluated the presence, degree, and distribution of nerve lesions. RESULTS: DRG hypertrophy in OXA-PNP patients (207.3±47.7mm3 vs. 153.0±47.1mm3 in controls, p = 0.001) was found as significant morphological correlate of the sensory neuronopathy. In contrast, peripheral nerves only exhibited minor morphological alterations qualitatively. Quantitatively, sciatic nerve caliber (27.3±6.7mm2 vs. 27.4±7.4mm2, p = 0.80) and nT2 signal were not significantly changed in patients (1.32±0.22 vs. 1.22±0.26, p = 0.16). AD, RD, and MD showed a non-significant decrease in patients, while FA was unchanged. CONCLUSION: OXA-PNP manifests with morphological and functional correlates that can be detected in vivo by MRN. We report hypertrophy of the DRG that stands in contrast to experimental and postmortem studies. DRG volume should be further investigated as a biomarker in other sensory peripheral neuropathies and ganglionopathies.

Posterior interosseous neuropathy: Supinator syndrome vs fascicular radial neuropathy.

OBJECTIVE: To investigate the spatial pattern of lesion dispersion in posterior interosseous neuropathy syndrome (PINS) by high-resolution magnetic resonance neurography. METHODS: This prospective study was approved by the local ethics committee and written informed consent was obtained from all patients. In 19 patients with PINS and 20 healthy controls, a standardized magnetic resonance neurography protocol at 3-tesla was performed with coverage of the upper arm and elbow (T2-weighted fat-saturated: echo time/repetition time 52/7,020 milliseconds, in-plane resolution 0.27 × 0.27 mm2). Lesion classification of the radial nerve trunk and its deep branch (which becomes the posterior interosseous nerve) was performed by visual rating and additional quantitative analysis of normalized T2 signal of radial nerve voxels. RESULTS: Of 19 patients with PINS, only 3 (16%) had a focal neuropathy at the entry of the radial nerve deep branch into the supinator muscle at elbow/forearm level. The other 16 (84%) had proximal radial nerve lesions at the upper arm level with a predominant lesion focus 8.3 ± 4.6 cm proximal to the humeroradial joint. Most of these lesions (75%) followed a specific somatotopic pattern, involving only those fascicles that would form the posterior interosseous nerve more distally. CONCLUSIONS: PINS is not necessarily caused by focal compression at the supinator muscle but is instead frequently a consequence of partial fascicular lesions of the radial nerve trunk at the upper arm level. Neuroimaging should be considered as a complementary diagnostic method in PINS.

Diffusion Tensor Imaging Adds Diagnostic Accuracy in Magnetic Resonance Neurography.

OBJECTIVE: The aim of this study was to determine whether quantitative diffusion tensor imaging (DTI) adds diagnostic accuracy in magnetic resonance neurography. MATERIALS AND METHODS: This prospective study was approved by the institutional review board. We enrolled 16 patients with peripheral polyneuropathy of various etiologies involving the upper arm and 30 healthy controls. Magnetic resonance neurography was performed at 3 T using transverse T2-weighted (T2-w) turbo spin echo and spin echo planar imaging diffusion-weighted sequences. T2-weighted normalized signal (nT2), fractional anisotropy (FA), apparent diffusion coefficient (ADC), radial diffusivity (RD), and axial diffusivity (AD) of the median, ulnar, and radial nerves were quantified after manual segmentation. Diagnostic performance of each separate parameter and combinations of parameters was assessed using the area under the receiver operating characteristic curve (AUC). Bootstrap validation was used to adjust for potential overfitting. RESULTS: Average nT2, ADC, RD, and AD values of the median, ulnar, and radial nerve were significantly increased in neuropathy patients compared with that in healthy controls (nT2, 1.49 ± 0.05 vs 1.05 ± 0.05; ADC, 1.4 × 10(-3) ± 2.8 × 10(-5) mm(2)/s vs 1.1 × 10(-3) ± 1.3 × 10(-5) mm(2)/s; RD, 9.5 × 10(-4) ± 2.9 × 10(-5) mm(2)/s vs 7.2 × 10(-4) ± 1.3 × 10(-5) mm(2)/s; AD, 2.3 × 10(-3) ± 3.7 × 10(-5) mm(2)/s vs 2.0 × 10(-3) ± 2.2 × 10(-5) mm(2)/s; P < 0.001 for all comparisons). Fractional anisotropy values were significantly decreased in patients (0.51 ± 0.01 vs 0.59 ± 0.01; P < 0.001). T2-weighted normalized signal and DTI parameters had comparable diagnostic accuracy (adjusted AUC: T2-w, 0.92; FA, 0.88; ADC, 0.89; AD, 0.84; RD, 0.86). Combining DTI parameters significantly improved the diagnostic accuracy over single-parameter analysis. In addition, the combination of nT2 with DTI parameters yielded excellent adjusted AUCs up to 0.97 (nT2 + FA). CONCLUSIONS: Diffusion tensor imaging has high diagnostic accuracy in peripheral neuropathy. Combining DTI with T2 can outperform T2-w imaging alone and provides added value in magnetic resonance neurography.