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When a poroelastic gel is released from a patterned mold, surface stress drives deformation and solvent migration in the gel and flattens its surface profile in a time-dependent manner. Specifically, the gel behaves like an incompressible solid immediately after removal from the mold, and becomes compressible as the solvent is able to squeeze out of the polymer network. In this work, we use the finite element method (FEM) to simulate this transient surface flattening process. We assume that the surface stress is isotropic and constant, the polymer network is linearly elastic and isotropic, and that solvent flow obeys Darcy’s law. The short-time and long-time surface profiles can be used to determine the surface stress and drained Poisson’s ratio of the gel. Our analysis shows that the drained Poisson’s ratio and the diffusivity of the gel can be obtained using interferometry and high-speed video microscopy, without mechanical measurement.

Subcritical fracture of materials can take place below the critical failure condition by slow accumulation of internal damage. While subcritical fracture accounts for most of the structural failures in use, it is challenging to understand its microscopic origin or predict/prevent it in time, due to the lack of current non-destructive detection methods with suitable resolution. We use simultaneous space-time-resolved multispeckle diffusing wave spectroscopy (MSDWS) measurements and mechanophore mapping to investigate the fracture of polydimethylsiloxane elastomers. We identify a fracture precursor in the form of large-scale strain rate acceleration, detected over a ~cm2 sample area, long time (up to hundreds of seconds) before macroscopic fracture, which we attribute to the far-field elastic deformation induced by localized molecular damage (over a ~ 0.01 mm2 sample area). While the evolution of local damage is currently detectable only by mechanochemistry, the resulting strain rate field is readily observable by MSDWS with ordinary imaging and image processing tools. As tested in different conditions and for various materials, our work shows that MSDWS is a powerful tool to characterize and predict microscopic damage, well before it becomes critical., We thank the French CNES, CNRS, ANR (see grant numbers in the Funding section), and ANRT (grant No. 2014/0109) for financial support. LC acknowledges support from the Institut Universitaire de France.

BACKGROUND: Papillary thyroid carcinoma (PTC) is typically treated with surgical resection, even in recurrent cases. However, some cases of recurrent PTC are refractory to the conventionally used locoregional radiotherapy and resection methods. 125I seed permanent brachytherapy has emerged as a promising alternative for such PTCs, but no effective brachytherapy protocol has been reported for tumors with a huge volume, liquefaction, necrosis, and skin invasion. CASE PRESENTATION: A 47-year-old man presented with recurrence 8 years after 2 thyroidectomy procedures for PTC and recurrent PTC. The tumor measured 6 × 7 × 8 cm3 and exhibited liquefaction, necrosis, and skin invasion. The patient was treated at our hospital from December 2017 to November 2018. He received one round of 125I seed temporary brachytherapy and 4 rounds of 125I seed permanent implantation. The activity of the seeds was 0.3–3.0 mCi, and the total dose delivered to the tumor was 145 Gy. The recurrent tumor was successfully removed by 125I seed brachytherapy guided with a 3D-printed template and ultrasound and CT scanning. The refractory tumor healed uneventfully after 125I seed brachytherapy without recurrence over the 25-month follow-up. CONCLUSIONS: To the best of our knowledge, this is the first reported case of a large thyroid carcinoma that was effectively treated by 3D-printed template-guided 125I seed brachytherapy.

Stress intensity factor due to applied screw dislocation density for a periodic array of cracks

Cavitation is a common damage mechanism in soft solids. Here, we study this using a phase separation technique in stretched, elastic solids to controllably nucleate and grow small cavities by several orders of magnitude. The ability to make stable cavities of different sizes, as well as the huge range of accessible strains, allows us to systematically study the early stages of cavity expansion. Cavities grow in a scale-free manner, accompanied by irreversible bond breakage that is distributed around the growing cavity rather than being localized to a crack tip. Furthermore, cavities appear to grow at constant driving pressure. This has strong analogies with the plasticity that occurs surrounding a growing void in ductile metals. In particular, we find that, although elastomers are normally considered as brittle materials, small-scale cavity expansion is more like a ductile process. Our results have broad implications for understanding and controlling failure in soft solids., Science Advances, 6 (13), ISSN:2375-2548