Transplantable stem cell nanobridge scaffolds for accelerating articular cartilage regeneration.

Microfracture technique for treating articular cartilage defects usually has poor clinical outcomes due to critical heterogeneity and extremely limited in quality. To improve the effects of current surgical technique (i.e., microfracture technique), we propose the transplantable stem cell nanobridge scaffold, acting as a protective bridge between host tissue and defected cartilage as well as microfracture-derived cells. Nanobridge scaffolds have a sophisticated nanoaligned structure with freestanding and flexible shapes for imposing direct structural guidance to cells including transplanted stem cells and host cells, and it can induce not only chondrocyte migration but also stem cell differentiation, maturation, and growth factor secretion. The transplantable stem cell nanobridge scaffold is capable of reconstructing the defected cartilage with homogeneous architecture and highly enhanced adhesive stress similar with native cartilage tissue by the synergistic effects of stem cells-based chondro-induction and nanotopography-based chondro-conduction. Our findings demonstrate a significant advancement in the traditional treatment technique by using a nanoengineered tool for achieving successful cartilage regeneration.

Geometric Scaling of the Current-Phase Relation of Niobium Nanobridge Junctions.

The nanobridge junction (NBJ) is a type of Josephson junction that is advantageous for the miniaturization of superconducting circuits. However, the current-phase relation (CPR) of the NBJ usually deviates from a sinusoidal function, which has been explained by a simplified model with correlation only to its effective length. Here, we investigated both measured and calculated CPRs of niobium NBJs of a cuboidal shape with a three-dimensional bank structure. From a sine-wave to a sawtooth-like form, we showed that deviated CPRs of NBJs can be described quantitatively by its skewness Δθ. Furthermore, the measured dependence of Δθ on the critical current I0 from 108 NBJs turned out to be consistent with the calculated dependence derived from the change in geometric dimensions. This suggested that the CPRs of NBJs can be tuned by their geometric dimensions. In addition, the calculated scaling behavior of Δθ versus I0 in 3D space was provided for the future design of superconducting circuits of a high integration level by using niobium NBJs.

Gate-Tunable Critical Current of the Three-Dimensional Niobium Nanobridge Josephson Junction.

Recent studies have shown that the critical currents of several metallic superconducting nanowires and Dayem bridges can be locally tuned by using a gate voltage (Vg). Here, we report a gate-tunable Josephson junction structure constructed from a three-dimensional (3D) niobium nanobridge junction (NBJ) with a voltage gate on top. Measurements up to 6 K showed that the critical current of this structure can be tuned to zero by increasing Vg. The critical gate voltage was reduced to 16 V and may possibly be reduced further by reducing the thickness of the insulation layer between the gate and the NBJ. Furthermore, the flux modulation generated by Josephson interference of two parallel 3D NBJs can also be tuned by using Vg in a similar manner. Therefore, we believe that this gate-tunable Josephson junction structure is promising for superconducting circuit fabrication at high integration levels.

Limitations of the Current-Phase Relation Measurements by an Asymmetric dc-SQUID.

Exotic quantum transport phenomena established in Josephson junctions (JJs) are reflected by a nonsinusoidal current-phase relation (CPR). The solidified approach to measuring the CPR is via an asymmetric dc-SQUID with a reference JJ that has a high critical current. We probed this method by measuring CPRs of hybrid JJs based on the 3D topological insulator (TI) Bi2Te2Se with a nanobridge acting as a reference JJ. We captured both highly skewed and sinusoidal critical current oscillations within single devices which contradict the uniqueness of the CPR. This implies that the widely used method provides inaccurate CPR measurement and leads to misinterpretation. It was shown that the accuracy of the CPR measurement is mediated by the asymmetry in derivatives of the CPRs but not in critical currents, as was previously thought. Finally, we provided considerations for an accurate CPR measurement via the most commonly used reference JJs.

Titanium Nitride as a New Prospective Material for NanoSQUIDs and Superconducting Nanobridge Electronics.

Nanobridge Josephson junctions and nanometer-scale superconducting quantum interference devices (nanoSQUIDs) based on titanium nitride (TiN) thin films are described. The TiN films have a room temperature resistivity of ~15 µΩ·cm, a superconducting transition temperature Tc of up to 5.3 K and a coherence length ξ(4.2 K) of ~105 nm. They were deposited using pulsed DC magnetron sputtering from a stoichiometric TiN target onto Si (100) substrates that were heated to 800 °C. Electron beam lithography and highly selective reactive ion etching were used to fabricate nanoSQUIDs with 20-nm-wide nanobridge Josephson junctions of variable thickness. X-ray and high-resolution electron microscopy studies were performed. Non-hysteretic I(V) characteristics of the nanobridges and nanoSQUIDs, as well as peak-to-peak modulations of up to 17 µV in the V(B) characteristics of the nanoSQUIDs, were measured at 4.2 K. The technology offers prospects for superconducting electronics based on nanobridge Josephson junctions operating within the framework of the Ginzburg-Landau theory at 4.2 K.

Primary and Secondary Mesoscopic Hybrid Materials of Au Nanoparticles@Silk Fibroin and Applications.

In this work, we demonstrate the principle of mesoscopic construction of silk fibroin (SF) hybrid materials, which endows the materials with new performance. In implementing this strategy, mediating molecules, wool keratin (WK) molecules, were adopted to in-line synthesize Au nanoparticles (WK@AuNPs), which further create the stable linkage of AuNPs with SF nanofibril networks via templated ß-crystallization. Fourier transform infrared spectroscopy, X-ray diffraction, and atomic force microscopy demonstrate that the mesoscopic hybrid network structure of the hybrid materials is different from neat SF materials, which gives rise to various new performances, that is, long-stable fluorescence emission. As the fluorescence emission can be characteristically annealed by Cu ions, therefore be adopted as the highly selective ion probes. Moreover, as WK@AuNPs are homogeneously connected to SF nanofibril networks, the carbonization of the materials leads to secondary hybrid materials of carbon-Au, where nano-sized Au particles are well distributed in carbonized mesoscopic conductive carbon networks. Such hybrid materials of carbon-Au can be further fabricated into electrochemical (i.e., dopamine) sensors, which are demonstrated to have excellent sensing performance.

In Situ Liquid Cell TEM Reveals Bridge-Induced Contact and Fusion of Au Nanocrystals in Aqueous Solution.

During nanoparticle coalescence in aqueous solution, dehydration and initial contact of particles are critically important but poorly understood processes. In this work, we used in situ liquid-cell transmission electron microscopy to directly visualize the coalescence process of Au nanocrystals. It is found that the Au atomic nanobridge forms between adjacent nanocrystals that are separated by a ∼0.5 nm hydration layer. The nanobridge structure first induces initial contact of Au nanocrystals over their hydration layers and then surface diffusion and grain boundary migration to rearrange into a single nanocrystal. Classical density functional theory calculations and ab initio molecular dynamics simulations suggest that the formation of the nanobridge can be attributed to the accumulation of auric ions and a higher local supersaturation in the gap, which can promote dehydration, contact, and fusion of Au nanocrystals. The discovery of this multistep process advances our understanding of the nanoparticle coalescence mechanism in aqueous solutions.

Approaching Gas Phase Electrodeposition: Process and Optimization to Enable the Self-Aligned Growth of 3D Nanobridge-Based Interconnects.

A nanowire bonding process referred to as gas-phase electrodeposition is reported to form nanobridge-based interconnects. The process is able to grow free-standing point-to-point electrical connections using metallic wires. As a demonstration, programmable interconnects and an interdigitated electrode array are shown. The process is more material efficient when compared with conventional vapor deposition since the material is directed to the point of use.