Microribbons composed of directionally self-assembled nanoflakes as highly stretchable ionic neural electrodes.

Many natural materials possess built-in structural variation, endowing them with superior performance. However, it is challenging to realize programmable structural variation in self-assembled synthetic materials since self-assembly processes usually generate uniform and ordered structures. Here, we report the formation of asymmetric microribbons composed of directionally self-assembled two-dimensional nanoflakes in a polymeric matrix during three-dimensional direct-ink printing. The printed ribbons with embedded structural variations show site-specific variance in their mechanical properties. Remarkably, the ribbons can spontaneously transform into ultrastretchable springs with controllable helical architecture upon stimulation. Such springs also exhibit superior nanoscale transport behavior as nanofluidic ionic conductors under even ultralarge tensile strains (>1,000%). Furthermore, to show possible real-world uses of such materials, we demonstrate in vivo neural recording and stimulation using such springs in a bullfrog animal model. Thus, such springs can be used as neural electrodes compatible with soft and dynamic biological tissues.

Injectable and Crosslinkable PLGA-Based Microribbons as 3D Macroporous Stem Cell Niche.

Poly(lactide-co-glycolide) (PLGA) has been widely used as a tissue engineering scaffold. However, conventional PLGA scaffolds are not injectable, and do not support direct cell encapsulation, leading to poor cell distribution in 3D. Here, a method for fabricating injectable and intercrosslinkable PLGA microribbon-based macroporous scaffolds as 3D stem cell niche is reported. PLGA is first fabricated into microribbon-shape building blocks with tunable width using microcontact printing, then coated with fibrinogen to enhance solubility and injectability using aqueous solution. Upon mixing with thrombin, firbornogen-coated PLGA microribbons can intercrosslink into 3D scaffolds. When subject to cyclic compression, PLGA microribbon scaffolds exhibit great shock-absorbing capacity and return to their original shape, while conventional PLGA scaffolds exhibit permanent deformation after one cycle. Using human mesenchymal stem cells (hMSCs) as a model cell type, it is demonstrated that PLGA µRB scaffolds support homogeneous cell encapsulation, and robust cell spreading and proliferation in 3D. After 28 days of culture in osteogenic medium, hMSC-seeded PLGA µRB scaffolds exhibit an increase in compressive modulus and robust bone formation as shown by staining of alkaline phosphatase, mineralization, and collagen. Together, the results validate PLGA µRBs as a promising injectable, macroporous, non-hydrogel-based scaffold for cell delivery and tissue regeneration applications.

Light-Driven Continuous Twist Movements of Microribbons.

Despite many advances in the development of artificial systems with helical twist motions or deformations, obtaining materials that can undergo continuous twist movements upon an energy input remains a great challenge. In this work, a continuous twist movement of microribbons driven by scanning laser irradiation, a process that a twist generates initially at one end of the microribbon and is continuously transmitted to the other end and then kept twisting, is reported. Key factors to the achievement of this movement are the fabrication of elastic microribbons that possess relatively low elastic modulus and diagonal photoinduced π-stacking distortion relative to the microribbon long axis. Furthermore, the scanning laser irradiation is required to drive the π-stacking distortion with the spatiotemporal coordination for the continuous twist movement of microribbons. These findings may be extended to the achievement of other sophisticated continuous movements of microscale systems.

Vascular smooth muscle cells can be circumferentially aligned inside a channel using tunable gelatin microribbons.

The gold standard to measure arterial health is vasodilation in response to nitric oxide (NO). Vasodilation is generally measured via pressure myography of arteries isolated from animal models. However, animal arteries can be difficult to obtain and may have limited relevance to human physiology. It is, therefore, critical to engineer human cell-based arterial models capable of contraction. Vascular smooth muscle cells (SMCs) must be circumferentially aligned around the vessel lumen to contract the vessel, which is challenging to achieve in a soft blood vessel model. In this study, we used gelatin microribbons to circumferentially align SMCs inside a hydrogel channel. To accomplish this, we created tunable gelatin microribbons of varying stiffnesses and thicknesses and assessed how SMCs aligned along them. We then wrapped soft, thick microribbons around a needle and encapsulated them in a gelatin methacryloyl hydrogel, forming a microribbon-lined channel. Finally, we seeded SMCs inside the channel and showed that they adhered best to fibronectin and circumferentially aligned in response to the microribbons. Together, these data show that tunable gelatin microribbons can be used to circumferentially align SMCs inside a channel. This technique can be used to create a human artery-on-a-chip to assess vasodilation via pressure myography, as well as to align other cell types for 3D in vitro models.

Super-Ballistic Width Dependence of Thermal Conductivity in Graphite Nanoribbons and Microribbons.

The super-ballistic temperature dependence of thermal conductivity, facilitated by collective phonons, has been widely studied. It has been claimed to be unambiguous evidence for hydrodynamic phonon transport in solids. Alternatively, hydrodynamic thermal conduction is predicted to be as strongly dependent on the width of the structure as is fluid flow, while its direct demonstration remains an unexplored challenge. In this work, we experimentally measured thermal conductivity in several graphite ribbon structures with different widths, from 300 nm to 1.2 µm, and studied its width dependence in a wide temperature range of 10-300 K. We observed enhanced width dependence of the thermal conductivity in the hydrodynamic window of 75 K compared to that in the ballistic limit, which provides indispensable evidence for phonon hydrodynamic transport from the perspective of peculiar width dependence. This will help to find the missing piece to complete the puzzle of phonon hydrodynamics, and guide future attempts at efficient heat dissipation in advanced electronic devices.

Sub-ppb-Level Detection of Nitrogen Dioxide Based on High-Quality Black Phosphorus.

The development of gas sensors based on two-dimensional (2D) layered materials has received lots of focus attributing to their excellent gas sensitivity. Here, a black phosphorus (BP) gas sensor device is fabricated based on high-quality few-layered BP microribbons using a facile route. Although BP is well known to oxidize in ambient conditions, energy dispersive spectroscopy (EDS) mapping manifests that the few-layered BP microribbons undergo slight oxidation and contamination during the grinding process. It is interesting that the surface and side of BP microribbons have nanoscale thin films and step-like nanoscale thin films, respectively, owing to the in-plane slip of the few-layered BP microribbons in the process of grinding, which are different from the conventional BP bulk crystals. The layered BP microribbon gas sensor demonstrated a high response to low-concentration NO2 and a very low limit of detection (LOD) of 0.4 ppb of NO2 under N2 and air conditions, which is the lowest LOD for NO2 detection reported so far. The mechanisms for excellently sensitive detection of NO2 for the BP microribbons have been investigated by first-principles calculations combined with experiment results, revealing that the sensitization mechanisms of the BP microribbon sensor are abundant nanoscale thin films, an optimum bandgap range with optimal carrier concentration, a hierarchical homojunction structure, and strong adsorption energy to NO2. In addition, the BP microribbon sensor demonstrated high selectivity to NO2, a low LOD under a high relative humidity, and good repeatability. The reported results of the BP sensor may provide great promise for improving the performance of other 2D material-based gas sensors and may expand sensing applications.

Microribbon-hydrogel composite scaffold accelerates cartilage regeneration in vivo with enhanced mechanical properties using mixed stem cells and chondrocytes.

Juvenile chondrocytes are robust in regenerating articular cartilage, but their clinical application is hindered by donor scarcity. Stem cells offer an abundant autologous cell source but are limited by slow cartilage deposition with poor mechanical properties. Using 3D co-culture models, mixing stem cells and chondrocytes can induce synergistic cartilage regeneration. However, the resulting cartilage tissue still suffers from poor mechanical properties after prolonged culture. Here we report a microribbon/hydrogel composite scaffold that supports synergistic interactions using co-culture of adipose-derived stem cells (ADSCs) and neonatal chondrocytes (NChons). The composite scaffold is comprised of a macroporous, gelatin microribbon (µRB) scaffolds filled with degradable nanoporous chondroitin sulfate (CS) hydrogel. We identified an optimal CS concentration (6%) that best supported co-culture synergy in vitro. Furthermore, 7 days of TGF-ß3 exposure was sufficient to induce catalyzed cartilage formation. When implanted in vivo, µRB/CS composite scaffold supported over a 40-fold increase in compressive moduli of cartilage produced by mixed ADSCs/NChons to ~330 kPa, which surpassed even the quality of cartilage produced by 100% NChons. Together, these results validate µRB/CS composite as a promising scaffold for cartilage regeneration using mixed populations of stem cells and chondrocytes.

Low-Voltage, High-Performance Flexible Organic Field-Effect Transistors Based on Ultrathin Single-Crystal Microribbons.

Organic field-effect transistors (OFETs) have acquired increasing attention because of their wide range of potential applications in electronics; nevertheless, high operating voltage and low carrier mobility are considered as major bottlenecks in their commercialization. In this work, we demonstrate low-voltage, flexible OFETs based on ultrathin single-crystal microribbons. Flexible OFETs fabricated with 2,7-dioctylbenzothieno[3,2-b]benzothiophene (C8-BTBT) based solution-processed ultrathin single-crystal microribbon as the semiconductor layer and high-k polymer, polysiloxane-poly(vinyl alcohol) composite as an insulator layer manifest a significantly low operating voltage of -4 V, and several devices showed a high mobility of >30 cm2 V-1 s-1. Besides, the carrier mobility of the fabricated devices exhibits a slight degradation in static bending condition, which can be retained by 83.3% compared with its original value under a bending radius of 9 mm. As compared to the bulk C8-BTBT single-crystal-based OFET, which showed a large crack only after 50 dynamic bending cycles, our ultrathin single-crystal-based counterpart demonstrates a much better dynamic force stability. Moreover, under a 20 mm bending radius, the mobility of the device decreased by only 11.7% even after 500 bending cycles and no further decrease was observed until 1000 bending cycles. Our findings reveal that ultrathin C8-BTBT single-crystal-based flexible OFETs are promising candidates for various high-performance flexible electronic devices.

Freestanding Laser-Assisted Reduced Graphene Oxide Microribbon Textile Electrode Fabricated on a Liquid Surface for Supercapacitors and Breath Sensors.

Graphene microribbons (rGO-MRs) are highly desired for their high electrical conductivities and specific surface areas, which contribute to multiple applications in thin, flexible, textile supercapacitors, sensors, and actuators. Herein, we demonstrate a facile method for creating reduced graphene oxide microribbons with microscale architecture utilizing a simple blue-violet diode laser under ambient conditions. This method takes advantage of the photochemical reduction mechanism of self-assembled graphene oxide liquid crystals (GO-LC), allowing rGO-MR patterns to be directly printed on the solution surface. The rGO-MR films demonstrated tunable diameters and can be tailored into any geometries. A maximum intrinsic electrical conductivity for rGO-MR reaching 325.8 S/m was observed. The rGO-MR textile electrodes can be assembled into microsupercapacitors with a high areal specific capacitance of 14.4 mF/cm2, a low charge-transfer impedance, and an exceptional cycling performance with a retained 96.8% capacitance after 10 000 cycles. The rGO-MR films also experience changes in resistance in response to the moisture adsorption from human breaths and therefore can also be employed as a breathing sensor for health monitoring. The presented facile method for creating multilayered rGO-MR films directly on liquid surfaces can further expand the potential for three-dimensional printing graphitic materials for various multifunctional applications.

Organic Single-Crystalline Ribbons of a Rigid "H"-type Anthracene Derivative and High-Performance, Short-Channel Field-Effect Transistors of Individual Micro/Nanometer-Sized Ribbons Fabricated by an "Organic Ribbon Mask" Technique.

The synthesis of a rigid, planar H-type anthracene derivative is described. Single-crystalline ribbons at micro- and nanometer sizes can be controllably produced and transistors based on an individual ribbon can be fabricated in situ through a newly developed "organic ribbon mask" method, in which the channel length of the transistors can be easily scaled down to sub-micrometer level.

Polypyrrole Actuator Based on Electrospun Microribbons.

The development of soft actuators by using inexpensive raw materials and straightforward fabrication techniques, aiming at creating and developing muscle like micromanipulators, represents an important challenge nowadays. Providing such devices with biomimetic qualities, for example, sensing different external stimuli, adds even more complexity to the task. We developed electroactive polymer-coated microribbons that undergo conformational changes in response to external physical and chemical parameters. These were prepared following three simple steps. During the first step nylon-6/6 microribbons were fabricated by electrospinning. In a second step the microribbons were one side coated with a metallic layer. Finally, a conducting layer of polypyrrole was added by means of electrochemical deposition. Strips of polypyrrole-coated aligned microribbon meshes were tested as actuators responding to current, pH, and temperature. The electrochemical activity of the microstructured actuators was investigated by recording cyclic voltammograms. Chronopontentiograms for specific current, pH, and temperature values were obtained in electrolytes with different compositions. It was shown that, upon variation of the external stimulus, the actuator undergoes conformational changes due to the reduction processes of the polypyrrole layer. The ability of the actuator to hold and release thin wires, and to collect polystyrene microspheres from the bottom of the electrochemical cell, was also investigated.

Uniaxially Stretched Flexible Surface Plasmon Resonance Film for Versatile Surface Enhanced Raman Scattering Diagnostics.

Surface-enhanced Raman scattering (SERS) spectroscopy affords a rapid, highly sensitive, and nondestructive approach for label-free and fingerprint diagnosis of a wide range of chemicals. It is of great significance to develop large-area, uniform, and environmentally friendly SERS substrates for in situ identification of analytes on complex topological surfaces. In this work, we demonstrate a biodegradable flexible SERS film via irreversibly and longitudinally stretching metal deposited biocompatible poly(ε-caprolactone) film. This composite film after stretching shows surprising phenomena: three-dimensional and periodic wave-shaped microribbons array embedded with a high density of nanogaps functioning as hot-spots at an average gap size of 20 nm and nanogrooves array along the stretching direction. The stretched polymer surface plasmon resonance film gives rise to more than 10 times signal enhancement in comparison with that of the unstretched composite film. Furthermore, the SERS signals with high uniformity exhibit good temperature stability. The polymer SPR film with excellent flexibility and transparency can be conformally attached onto arbitrary nonplanar surfaces for in situ detection of various chemicals. Our results pave a new way for next-generation flexible SERS detection means, as well as enabling its huge potentials toward green wearable devices for point-of-care diagnostics.

Direction-Controlled Light-Driven Movement of Microribbons.

Novel direction-controlled movements of microribbons self-assembled from perylene diimide molecules are reported on various hydrophobic surfaces under scanning laser irradiation. A "dynamic exciton charge model" is developed to elucidate the underlying mechanism. The findings provide an innovative strategy for the design of microscale systems capable of continuous and directional movement driven by light.

Giant morphological change in layered microribbons featuring reversible sliding of stacking layers.

A light-induced giant lateral or longitudinal morphological change in layered microribbons is reported. This morphological change originates from the directional sliding of the stacking layers with respect to one another between their polar surfaces, into which the photoexcited intermolecular non-bonded distortion is translated. Upon exposure to an electron beam, the laterally displaced layers slide back to their original positions.

Photo-crosslinkable PEG-based microribbons for forming 3D macroporous scaffolds with decoupled niche properties.

PEG-based microribbons are designed and fabricated as building blocks for constructing a 3D cell niche with independently tunable biochemical, mechanical, and topographical cues. This platform supports direct cell encapsulation, allows spatial patterning of biochemical cues, and may provide a valuable tool for facilitating the analyses of how interactive niche signaling regulates cell fate in three dimensions.

From nanospheres to microribbons: Self-assembled Eosin Y doped PMMA nanoparticles as photonic crystals.

A modified emulsion synthesis of poly(methylmethacrylate) (PMMA) with the Eosin Y (EY), commercial chromophore, yields dye doped polymeric nanoparticles (PMMA@EY). A systematic investigation on the experimental parameters (monomer and initiator concentration, reaction time and MMA/EY molar ratio) has been explored to modulate physico-chemical properties of the dye doped polymeric colloids. Spherical shaped particles, doped with EY (0.5-3.0 wt%; loading efficiency η = 11-15%), with controlled diameters in the range 240-510 nm, low dispersity and ζ-potential values in the range between -42 mV and -59 mV, have been synthesized and characterized by means of UV-Vis spectrometry, Dynamic Light Scattering (DLS), laser Doppler electrophoresis and Scanning Electron Microscopy (SEM). Microribbons based on PMMA@EY nanoparticles have been fabricated by room temperature self-assembly of aqueous colloidal suspension on highly wettable glass substrates. Surface chemical treatment assisted the formation of long (up to few centimeters) regular ribbons with rectangular section. Lateral size and height of the structures have been controlled by changing the suspension concentration and/or the deposition volume: the higher suspension concentration produces larger and thicker ribbons and the higher deposited volume produces thicker ribbons (up to 23 µm with 198 µL of a 3 wt% suspension). Moreover, a transition from a film-like to a ribbon-like growth has been observed with increasing nanoparticles concentration. Short range ordering and photonic crystal features have been maintained in the fluorescent ribbon microarchitecture, resulting in a self-assembled material with excellent potential for the development of mirror-less and random lasers.