This paper introduces a class of ferromagnetic, folded, soft composite material for skin-interfaced electrodes with releasable interfaces to stretchable, wireless electronic measurement systems. These electrodes establish intimate, adhesive contacts to the skin, in dimensionally stable formats compatible with multiple days of continuous operation, with several key advantages over conventional hydrogel based alternatives. The reported studies focus on aspects ranging from ferromagnetic and mechanical behavior of the materials systems, to electrical properties associated with their skin interface, to system-level integration for advanced electrophysiological monitoring applications. The work combines experimental measurement and theoretical modeling to establish the key design considerations. These concepts have potential uses across a diverse set of skin-integrated electronic technologies.

Materials chemistries for hydrogel scaffolds that are capable of programming temporal (4D) attributes of cellular decision‐making in supported 3D microcultures are described. The scaffolds are fabricated using direct‐ink writing (DIW)—a 3D‐printing technique using extrusion to pattern scaffolds at biologically relevant diameters (≤ 100 µm). Herein, DIW is exploited to variously incorporate a rheological nanoclay, Laponite XLG (LAP), into 2‐hydroxyethyl methacrylate (HEMA)‐based hydrogels—printing the LAP–HEMA (LH) composites as functional modifiers within otherwise unmodified 2D and 3D HEMA microstructures. The nanoclay‐modified domains, when tested as thin films, require no activating (e.g., protein) treatments to promote robust growth compliances that direct the spatial attachment of fibroblast (3T3) and preosteoblast (E1) cells, fostering for the latter a capacity to direct long‐term osteodifferentiation. Cell‐to‐gel interfacial morphologies and cellular motility are analyzed with spatial light interference microscopy (SLIM). Through combination of HEMA and LH gels, high‐resolution DIW of a nanocomposite ink (UniH) that translates organizationally dynamic attributes seen with 2D gels into dentition‐mimetic 3D scaffolds is demonstrated. These analyses confirm that the underlying materials chemistry and geometry of hydrogel nanocomposites are capable of directing cellular attachment and temporal development within 3D microcultures—a useful material system for the 4D patterning of hydrogel scaffolds.

We perform a combined experimental-theoretical study of the Fe-oxychalcogenides (FeOCh) series La2O2Fe2OM 2 (M =S, Se), which are among the latest Fe-based materials with the potential to show unconventional high-Tc superconductivity (HTSC). A combination of incoherent Hubbard features in X-ray absorption (XAS) and resonant inelastic X-ray scattering (RIXS) spectra, as well as resitivity data, reveal that the parent FeOCh are correlation-driven insulators. To uncover microscopics underlying these findings, we perform local density approximation-plus-dynamical mean field theory (LDA+DMFT) calculations that reveal a novel Mott-Kondo insulating state. Based upon good agreement between theory and a range of data, we propose that FeOCh may constitute a new, ideal testing ground to explore HTSC arising from a strange metal proximate to a novel selective-Mott quantum criticality.

We present the results of structural and magnetic phase comparisons of the iron oxychalcogenides La 2 O 2 Fe 2 OM 2 (M = S, Se). Elastic neutron scattering reveals that M = S and Se have similar nuclear structures at room and low temperatures. We find that both materials obtain antiferromagnetic ordering at a Neel temperature T N 90.1 ± 0.16 K and 107.2 ± 0.06 K for M = Se and S, respectively. The magnetic arrangements of M = S, Se are obtained through Rietveld refinement.We find the order parameter exponent β to be 0.129 ± 0.006 for M = Se and 0.133 ± 0.007 for M = S. Each of these values is near the Ising symmetry value of 1/8. This suggests that although lattice and electronic structural modifications result from chalcogen exchange, the nature of the magnetic interactions is similar in these materials.

In article number https://doi.org/10.1002/adhm.201800788, Ralph G. Nuzzo and co‐workers show micro‐scaffold hydrogels that are fabricated using the additive manufacturing technique of direct‐ink writing (DIW). The hydrogel compositions are optimized for multilayer printing and are used to tune growth compliance by directing the temporal dynamics and spatial distribution of cell attachment without the use of surface‐modifying treatments. Image courtesy of Joselle M. McCracken.