able to create a beak that possesses steep mechanical gradients with stiffness differences of two orders of magnitude occurring over centimeter-length scales. [1,2] Further, the mantis shrimp saddle is spatially organized with a highly mineralized outer layer that imparts stiffness, and a chitin-protein inner layer that confers flexibility. [3,4] In addition to synthesizing static structures, biology is also capable of creating the dynamic material systems that are needed for living systems to reconfigure during complex developmental programs (insect metamorphosis) [5] ; remodel for wound healing [6,7] ; and match properties to disparate functional needs (e.g., the lubricating and shock-absorbing properties of synovial fluid). [8] In many cases, biology creates such dynamic material systems using polymeric networks that are cross-linked through reversible physical interactions that can respond to local stimuli, [9] heal, [10][11][12] and balance the needs for strength and plasticity. [1,2,13,14] For instance, the electrostatic interactions between Ca 2+ and collagen act as sacrificial bonds to prevent brittle fracture in bone, [13,14] while domains in the titin protein that can reversibly unfold may allow muscles to withstand large deformations. [9] This emerging understanding of biological materials is also inspiring the development of high-performance technological materials. For instance, the mussel byssus illustrates the importance of coupling cross-linking mechanisms, as it uses covalent cross-links to confer strength and structural memory (i.e., elasticity) and reversible metal coordination bonds to confer the toughness and self-healing capabilities required to withstand what would seem to be nonrecoverable deformations. [10][11][12] There is growing interest in applying such a dual cross-linking strategy to fabricate high-toughness materials. A common technological approach is to use two interpenetrating polymeric networks that are individually cross-linked through separate mechanisms. [15][16][17][18][19][20][21][22][23] One network is cross-linked through strong (often covalent) bonds that confer elasticity, while the second network is cross-linked through weaker (often physical) interactions that can be broken and reformed in ways that dissipate mechanical energy to confer toughness to the dual polymeric network. [18,24] Alternative technological approaches to introduce energy-dissipating capabilities to materials include the use of nanocomposites [25][26][27] and phase-separated gels, [28] as well as topological gels (e.g., double networks, [16,29] slide-ring gels, [30] Biology uses various cross-linking mechanisms to tailor material properties, and this is inspiring technological efforts to couple independent crosslinking mechanisms to create hydrogels with complex mechanical properties. Here, it is reported that a hydrogel formed from a single polysaccharide can be triggered to reversibly switch cross-linking mechanisms and switch between elastic and viscoelastic properties. Specifically, the pH-resp...

Focusing on the interesting new concept of all-metal electride, centrosymmetric molecules e–+M2+(Ni@Pb12)2–M2++e– (M = Be, Mg, and Ca) with two anionic excess electrons located at the opposite ends of the molecule are obtained theoretically. These novel molecular all-metal electrides can act as infrared (IR) nonlinear optical (NLO) switches. Whereas the external electric field (F) hardly changes the molecular structure of the all-metal electrides, it seriously deforms their excess electron orbitals and average static first hyperpolarizabilities (β0 e(F)). For e–+Ca2+(Ni@Pb12)2–Ca2++e–, a small external electric field F = 8 × 10–4 au (0.04 V/Å) drives a long-range excess electron transfer from one end of the molecule through the middle all-metal anion cage (Ni@Pb12)2– to the other end. This long-range electron transfer is shown by a prominent change of excess electron orbital from double lobes to single lobe, which forms an excess electron lone pair and electronic structure Ca2+(Ni@Pb12)2–Ca2++2e–. Therefore, the small external electric field induces a dramatic β0 e(F) contrast from 0 (off form) to 2.2 × 106 au (on form) in all-metal electride molecule Ca­(Ni@Pb12)­Ca. Obviously, such switching is high sensitive. Interestingly, in the switching process, such long-range excess electron transfer does not alter the valence and chemical bond nature. Then, this switching mechanism is a distinct nonbonding evolution named electronic structure isomerization, which means that such switching has the advantages of being fast and reversible. Besides, these all-metal electride molecules also have a rare IR transparent characteristic (1.5–10 μm) in NLO electride molecules, and hence are commendable molecular IR NLO switches. Therefore, this work opens a new research field of electric field manipulated IR NLO switches of molecular all-metal electrides.

An electride molecule e–···K­(1)+···calix­[4]­pyrrole···K­(2)+···e– as an external electric field (F) manipulated nonlinear optical (NLO) switch is designed theoretically for the first time. As this molecule is an unusual singlet diradical electride molecule with two easily driven excess electrons (by electric field) at two opposite ends of the molecule, a novel switching mechanism of electronic structure isomerization emerges as a distinctive nonbonding evolution in the electride molecule. A small electric field driving leads to a long-range excess electron transfer from one side K(1) through the middle calix[4]­pyrrole to the other side K(2), forms a lone excess electron pair of s-type rather than a single bond, and quenches the singlet diradical. Meanwhile, the molecular electronic structure becomes K(1)+···calix­[4]­pyrrole···K­(2)+···2e–. Therefore, the small electric field driving brings a very high static first hyperpolarizability (β0) contrast from 0 (F = 0, Off form) to 4.060 × 105 au (F = a small nonzero value of 5 × 10–4 au, On form). Notably, under the electric field of 30 × 10–4 au, β0 reaches the largest value of 3.147 × 106 au and the molecule displays the most optimal NLO switching behavior. Furthermore, we consider also that 4H atoms of calix[4]­pyrrole are substituted with 4F and 2Be atoms, respectively; then the 2Be and 4F substitution effects on the NLO switch in electride molecules are exhibited. This work opens a new research field of an electric field manipulated NLO switch of electride molecules.

For the 3D printing of bioscaffolds, the importance of a suitable bioink cannot be overemphasized. With excellent printability and biocompatibility, alginate (Alg) is one of the most used bioinks. However, its bioinert nature and insufficient mechanical stability, due to only crosslinking via cation interactions, hinder the practical application of Alg-based bioinks in the individualized therapy of tissue defects. To overcome these drawbacks, for the first time, an ε-polylysine (ε-PL)-modified Alg-based bioink (Alg/ε-PL) is produced. The introduction of ε-PL improves the printability of the Alg-based bioink due to increasing electrostatic interactions, which enhances the selfsupporting stability of the as-printed scaffolds. The presence of the functional crosslinking -COOH and -NH 2 groups in Alg and ε-PL under mild conditions further enhances the mechanical stability of the scaffolds, far exceeding that of Alg/Ca 2+ scaffolds. The surface charge of the prepared scaffolds is finely tuned by the feed ratio of Alg to ε-PL and postimmobilization of different quantities of additional ε-PL, with a view to enhancing cell adhesion and further biofunctionalization. The results indicate that chondroitin sulfate, an extracellular matrix component, and vascular endothelial growth factor can be successfully applied to biofunctionalize the scaffolds via electrostatic adsorption for enhanced biological activity.