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Cranial dura mater is a dense interwoven vascularized connective tissue that helps regulate neurocranial remodeling by responding to strains from the growing brain. Previous ex vivo experimentation has failed to account for the role of prestretch in the mechanical behavior of the dura. Here we aim to estimate the prestretch in mouse cranial dura mater and determine its dependency on direction and age. We performed transverse and longitudinal incisions in parietal dura excised from newborn (day ∼ 4) and mature (12 weeks) mice and calculated the ex vivo normalized incision opening (measured width over length). Then, similar incisions were simulated under isotropic stretching within Abaqus/Standard. Finally, prestretch was estimated by comparing the ex vivo and in silico normalized openings. There were no significant differences between the neonatal and adult mice when comparing cuts in the same direction, but adult mice were found to have significantly greater stretch in the anterior–posterior direction than in the medial–lateral direction, while neonatal dura was essentially isotropic. Additionally, our simulations show that increasing curvature impacts the incision opening, indicating that flat in silico models may overestimate prestretch. [ABSTRACT FROM AUTHOR]

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Conductive polymer hydrogels are vital in strain sensors, yet achieving high resilience and toughness is a challenge. This study employs a prestretch method to engineer a tough conductive polymer hydrogel with sufficient resilience. Initially, a blend film of polyvinylalcohol (PVA) and ethylene‐vinyl alcohol copolymer (EVOH) is prepared through solution casting, followed by a swelling process to form a PVA‐EVOH hydrogel. This hydrogel, with PVA crystallites as crosslinking points, exhibits high toughness. The hydrogel is then immersed in pyrrole and ferric chloride solutions for in‐situ polymerization of polypyrrole (PPy), creating a conductive PPy/PVA‐EVOH hydrogel. Finally, a 200% prestretch is applied, breaking short chains within the network, eliminating energy dissipation at low strains. This results in a hydrogel with a 100% elastic deformation range, while maintaining high fracture toughness (1700 J m‐2). The prestretched PPy/PVA‐EVOH hydrogel functions as a strain sensor with low hysteresis, providing consistent strain measurements during loading and unloading. This outperforms the non‐prestretched sample, which shows inconsistent responses between stretching and releasing. [ABSTRACT FROM AUTHOR]

A new class of thin flexible structures is introduced that morph from flat into prescribed 3D shapes through strain mismatch between layers of a composite plate. To achieve control over the target shape, two different concepts are coupled. First, motivated by biological growth, strain mismatch is applied between the flat composite layers to transform it into a 3D shape. Depending on the amount of the applied strain mismatch, the transformation involves buckling into one of the available finite number of deformation modes. Second, inspired by kirigami, portions of the material are removed from one of the layers according to a specific pattern. This dramatically increases the number of possible 3D shapes and allows us to attain specific topologies. An experimental apparatus that allows precise control of the strain mismatch is devised. An inverse problem is posed, where starting from a given target shape, the physical parameters that make these shapes possible are determined. To show how the concept works, it focuses on circular composite plates and designs a kirigami pattern that yields a hemispherical structure. The analysis combines a theoretical approach with numerical simulations and physical experiments to understand and predict the shape transition from 2D to 3D. The tools developed here can be extended to attain arbitrary 3D shapes. The initially flat shape suggests that conventional additive manufacturing techniques can be used to functionalize the soft kirigami composite to fabricate, for example, deployable 3D structures, smart skins, and soft electromagnetic metasurfaces. [ABSTRACT FROM AUTHOR]