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Crack formation is considered one of the significant failure modes of layered oxide cathode materials for Na-ion batteries because particle cracks accelerate electrolyte decomposition, transition metal dissolution, and electrical contact loss. However, the crack formation mechanism of layered sodium transition metal oxides has not been fully understood yet. Herein, the in-plane crack formation mechanism of O3-type Na0.8Mg0.2Fe0.4Mn0.4O2 is demonstrated in terms of oxygen gas evolution due to air-exposure using in situ mass spectrometry and various atomic-scale analyses. When Na0.8Mg0.2Fe0.4Mn0.4O2 is exposed to air, Na+ ions are unevenly deintercalated in a form of stripe pattern along the in-plane direction. The deintercalation of Na+ ions gives rise to phase transition from the layered structure to the disordered structure, including spinel-like and rock salt-like structures, resulting in forming the nanoscale vertical heterostructure of alternating layered and disordered phases along the out-of-plane direction. The formation of the disordered structure is accompanied by oxygen gas evolution. As a result, cracks occur along the in-plane direction of Na0.8Mg0.2Fe0.4Mn0.4O2 because of the internal gas pressure due to oxygen gas evolution. Moreover, air-stable surface-modified Na0.8Mg0.2Fe0.4Mn0.4O2 is introduced to suppress crack formation, leading to excellent electrochemical performance, such as stable capacity retention over 200 cycles.

Dynamic manipulation of supramolecular self-assembled structures is achieved irreversibly or under non-physiological conditions, thereby limiting their biomedical, environmental, and catalysis applicability. In this study, microgels composed of azobenzene derivatives stacked via π-cation and π-π interactions are developed that are electrostatically stabilized with Arg-Gly-Asp (RGD)-bearing anionic polymers. Lateral swelling of RGD-bearing microgels occurs via cis-azobenzene formation mediated by near-infrared-light-upconverted ultraviolet light, which disrupts intermolecular interactions on the visible-light-absorbing upconversion-nanoparticle-coated materials. Real-time imaging and molecular dynamics simulations demonstrate the deswelling of RGD-bearing microgels via visible-light-mediated trans-azobenzene formation. Near-infrared light can induce in situ swelling of RGD-bearing microgels to increase RGD availability and trigger release of loaded interleukin-4, which facilitates the adhesion structure assembly linked with pro-regenerative polarization of host macrophages. In contrast, visible light can induce deswelling of RGD-bearing microgels to decrease RGD availability that suppresses macrophage adhesion that yields pro-inflammatory polarization. These microgels exhibit high stability and non-toxicity. Versatile use of ligands and protein delivery can offer cytocompatible and photoswitchable manipulability of diverse host cells.

The development of a compliant neural probe is necessary to achieve chronic implantation with minimal signal loss. Although fiber-based neural probes fabricated by the thermal drawing process have been proposed as a solution, their long-term effect on the brain has not been thoroughly investigated. Here, we examined the mechanical interaction of thermally drawn fiber implants with neural tissue through computational and histological analyses. Specifically, finite element analysis and immunohistochemistry were conducted to evaluate the biocompatibility of various fiber implants made with different base materials (steel, silica, polycarbonate, and hydrogel). Moreover, the effects of the coefficient of friction and geometric factors including aspect ratio and the shape of the cross-section on the strain were investigated with the finite element model. As a result, we observed that the fiber implants fabricated with extremely softer material such as hydrogel exhibited significantly lower strain distribution and elicited a reduced immune response. In addition, the implants with higher coefficient of friction (COF) and/or circular cross-sections showed a lower strain distribution and smaller critical volume. This work suggests the materials and design factors that need to be carefully considered to develop future fiber-based neural probes to minimize mechanical invasiveness.