Printable hydrogels desired in bioengineering have extremely high demands on biocompatibility and mechanic strength, which can hardly be achieved in conventional hydrogels made with biopolymers. Here, we show that on employment of the strategy of coordination-triggered hierarchical self-assembly of naturally occurring small-molecule folic acid, supramolecular hydrogels with robust mechanical elastic modulus comparable to synthetic double-network polymer gels can be made at concentrations below 1%. A sequence of hierarchical steps are involved in the formation of this extraordinary hydrogel: petrin rings on folate form tetramers through hydrogen bonding, tetramers stack into nanofibers by π-π stacking, and zinc ions cross-link the nanofibers into larger-scale fibrils and further cross-link the fibril network to gel water. These supramolecular qualities endow the hydrogel with shear-thinning and instant healing ability, which makes the robust gel injectable and printable into various three-dimensional structures. Owing to the excellent biocompatibility, the gel can support cells three-dimensionally and can be used as an ideal carrier for imaging agent (Gd), as well as chemodrugs. In combination with its easy formation and abundant sources, this newly discovered metallo-folate supramolecular hydrogel is promising in various bioengineering technological applications.

We report temporal and spectral domain observation of regenerative oscillation in monolithic silicon heterostructured photonic crystals cavities with high quality factor to mode volume ratios (Q/V). The results are interpreted by nonlinear coupled mode theory (CMT) tracking the dynamics of photon, free carrier population and temperature variations. We experimentally demonstrate effective tuning of the radio frequency (RF) tones by laser-cavity detuning and laser power levels, confirmed by the CMT simulations with sensitive input parameters.

Chaos has revolutionized the field of nonlinear science and stimulated foundational studies from neural networks, extreme event statistics, to physics of electron transport. Recent studies in cavity optomechanics provide a new platform to uncover quintessential architectures of chaos generation and the underlying physics. Here, we report the generation of dynamical chaos in silicon-based monolithic optomechanical oscillators, enabled by the strong and coupled nonlinearities of two-photon absorption induced Drude electron–hole plasma. Deterministic chaotic oscillation is achieved, and statistical and entropic characterization quantifies the chaos complexity at 60 fJ intracavity energies. The correlation dimension D2 is determined at 1.67 for the chaotic attractor, along with a maximal Lyapunov exponent rate of about 2.94 times the fundamental optomechanical oscillation for fast adjacent trajectory divergence. Nonlinear dynamical maps demonstrate the subharmonics, bifurcations and stable regimes, along with distinct transitional routes into chaos. This provides a CMOS-compatible and scalable architecture for understanding complex dynamics on the mesoscopic scale.

Plasmonic structures possess rich physics related to the sensitivity of plasmon resonance to the change in the environmental dielectric constant, the enhanced light scattering and optical extinction, and the local field enhancement enabled strong light-matter interactions, which have been applied in refractive-index sensors, optical feedback in various micro-or nano-cavity lasers, surface enhanced Raman scattering spectroscopy, and high-sensitivity molecular detection. However, ultrafast optical response is another important aspect of plasmons, which can be utilized to achieve switching of optical signals in different spectral bands. These optical switching designs are very important for applications in optical logic circuits and optical communication system. In this review, we summarize a series of reports on ultrafast plasmonic optical switches, where we focus our discussions on the structural and device designs, instead of on their physics. By categorizing the designs of optical switches into different groups by their featured performances, we intend to propose the development trend and the commonly interested mechanisms of such ultrafast optical switches. We hope this review will supply helpful concepts and technical approaches for further development and new applications of ultrafast optical switching devices.