Hui-Jiuan Chen

Microchannel Wetting for Controllable Patterning and Alignment of Silver Nanowire with High Resolution.

Patterning and alignment of conductive nanowires are essential for good electrical isolation and high conductivity in various applications. Herein a facile bottom-up, additive technique is developed to pattern and align silver nanowires (AgNWs) by manipulating wetting of dispersions in microchannels. By forming hydrophobic/hydrophilic micropatterns down to 8 μm with fluoropolymer (Cytop) and SiO2, the aqueous AgNW dispersions with the optimized surface tension and viscosity self-assemble into microdroplets and then dry to form anisotropic AgNW networks. The alignment degree characterized by the full width at half-maximum (FWHM) can be well-controlled from 39.8° to 84.1° by changing the width of microchannels. A mechanism is proposed and validated by statistical analysis on AgNW alignment, and a static model is proposed to guide the patterning of general NWs. The alignment reduced well the electrical resistivity of AgNW networks by a factor of 5 because of the formation of efficient percolation path for carrier conduction.

Physical activation of innate immunity by spiky particles

Microbial biochemicals have been indicated as the primary stimulators of innate immunity, the first line of the body’s defence against infections. However, the influence of topological features on a microbe’s surface on immune responses remains largely unknown. Here we demonstrate the ability of TiO2 microparticles decorated with nanospikes (spiky particles) to activate and amplify the immune response in vitro and in vivo. The nanospikes exert mechanical stress on the cells, which results in potassium efflux and inflammasome activation in macrophages and dendritic cells during phagocytosis. The spiky particles augment antigen-specific humoral and cellular immune responses in the presence of monophosphoryl lipid A and elicit protective immunity against tumour growth and influenza viral infection. The study offers insights into how surface physical cues can tune the activation of innate immunity and provides a basis for engineering particles with increased immunogenicity and adjuvanticity.Spikes on the surface of TiO2 microparticles, mimicking the nanotopological structures found on pathogens, boost the immune response in animal models and can be used to enhance the immunogenic effect of vaccines and adjuvants.

Multiscale nanowire-microfluidic hybrid strain sensors with high sensitivity and stretchability

Nanomaterials with low-dimensional morphology have been explored for enhancing the performance of strain sensors, but it remains difficult to achieve high stretchability and sensitivity simultaneously. In this work, a composite structure strain sensor based on nanomaterials and conductive liquid is designed, demonstrated, and engineered. The nanowire-microfluidic hybrid (NMH) strain sensor responds to multiscale strains from 4% to over 400%, with a high sensitivity and durability under small strain. Metal nanowires and carbon nanotubes are used to fabricate the NMH strain sensors, which simultaneously exhibit record-high average gauge factors and stretchability, far better than the conventional nanowire devices. Quantitative modeling of the electrical characteristics reveals that the effective conductivity percolation through the hybrid structures is the key to achieving high gauge factors for multiscale sensing. The sensors can operate at low voltages and are capable of responding to various mechanical deformations. When fixed on human skin, the sensors can monitor large-scale deformations (skeleton motion) and small-scale deformations (facial expressions and pulses). The sensors are also employed in multichannel, interactive electronic system for wireless control of robotics. Such demonstrations indicate the potential of the sensors as wearable detectors for human motion or as bionic ligaments in soft robotics.Nanowire-microfluidic strain sensors: a stretchable multi-scale sensing solutionBy combining metal nanowires and conductive polymers, high-performance stretchable nanowire-microfluidic strain sensors are realized. A team lead by Chuan Liu from the School of Electronics and Information Technology at Sun Yat-Sen University developed a hybrid strain sensor consisting of brittle metal nanowires and conductive polymers. These robust nanowire-microfluidic strain sensors are sensitive to multiscale strains––from 4% to over 400%––and show record-high gauge factor, a figure-of-merit that quantifies the level of sensitivity. The hybrid strain sensor’s high performance is made possible by the electric percolation pathways formed between the parallel nanowire network and the microfluidic channels. The combination of high stretchability and high sensitivity over a large strain range enables the device to be suitable for multiscale sensing. Liu and coworkers demonstrate the applicability of their nanowire-microfluidic strain sensors to human motion detection and human–machine interactive systems.

Nanospikes-mediated Anomalous Dispersities of Hydropobic Micro-objects and their Application for Oil Emulsion Cleaning

Many fields of applications require dispersion of hydrophobic particles in water, which is traditionally achieved by using surfactants or amphiphilic molecules to modify particle surfaces. However, surfactants or amphiphilic molecules may disturb the native solution or particles’ surface hydrophobicity, limiting extended applications such as oil emulsion cleaning. Recently one example of 2 μm-size polystyrene microparticles covered with ZnO nanospikes has been shown to exhibit excellent dispersity in water in spite of surface hydrophobicity. Whether this anomalous dispersion phenomenon was applicable to other hydrophobic microparticle systems was still unclear and its application scope was limited. Here the anomalous dispersities of different hydrophobic spiky micro-objects were systematically explored. The results show that the anomalous dispersion phenomenon was universally observed on different hydrophobic spiky micro-objects including different hydrophobic coating, particle sizes, material compositions and core particle morphologies. In addition, the spiky micro-objects displayed anomalous dispersity in water without compromising surface hydrophobicity, and their applications for oil spills absorption and oil emulsion cleaning were demonstrated. This work offers unique insight on the nanospikes-mediated anomalous dispersion phenomenon of hydrophobic micro-object and potentially extends its applicability and application scopes.

Nanospikes functionalization as a universal strategy to disperse hydrophilic particles in non-polar media

Dispersion of hydrophilic particles in non-polar media has many important applications yet remains difficult. Surfactant or amphiphilic functionalization was conventionally applied to disperse particles but is highly dependent on the particle/solvent system and may induce unfavorable effects and impact particle hydrophilic nature. Recently 2 μm size polystyrene microbeads coated with ZnO nanospikes have been reported to display anomalous dispersity in phobic media without using surfactant or amphiphilic functionalization. However, due to the lack of understanding whether this phenomenon was applicable to a wider range of conditions, little application has been derived from it. Here the anomalous dispersity phenomenons of hydrophilic microparticles covered with nanospikes were systematically assessed at various conditions including different particle sizes, material compositions, particle morphologies, solvent hydrophobicities, and surface polar groups. Microparticles were functionalized with nanospikes through hydrothermal route, followed by dispersity test in hydrophobic media. The results suggest nanospikes consistently prevent particle aggregation in various particle or solvent conditions, indicating the universal applicability of the anomalous dispersion phenomenons. This work provides insight on the anomalous dispersity of hydrophilic particles in various systems and offers potential application to use this method for surfactant-free dispersions.

Hollow Nanoneedle-Electroporation System To Extract Intracellular Protein Repetitively and Nondestructively

Techniques used to understand the dynamic expression of intracellular proteins are critical in both fundamental biological research and biomedical engineering. Various methods for analyzing proteins have been developed, but these methods require the extraction of intracellular proteins from the cells resulting in cell lysis and subsequent protein purifications from the lysate, which limits the potential of repetitive extraction from the same set of viable cells to track dynamic intracellular protein expression. Therefore, it is crucial to develop novel methods that enable nondestructive and repeated extraction of intracellular proteins. This work reports a hollow nanoneedle-electroporation system for the repeated extraction of intracellular proteins from living cells. Hollow nanoneedles with ∼450 nm diameter were fabricated by a material deposition and etching process, followed by integration with a microfluidic device. Long-lasting electrical pulses were coupled with the nanoneedles to permeate the cell membrane, allowing intracellular contents to diffuse into the microfluidic channels located below the cells via hollow nanoneedles. Using lactate dehydrogenase B (LDHB) as the model intracellular protein, the nanoneedle-electroporation system effectively and repeatedly extracted LDHB from the same set of cells at different time points, followed by quantitative analysis of LDHB via standard enzyme-linked immunosorbent assay. Our work demonstrated an efficient method to nondestructively probe intracellular protein levels and monitor the dynamic protein expression, with great potential to help understanding cell behaviors and functions.

TiO2 nanowire-templated hierarchical nanowire network as water-repelling coating

Extraordinary water-repelling properties of superhydrophobic surfaces make them novel candidates for a great variety of potential applications. A general approach to achieve superhydrophobicity requires low-energy coating on the surface and roughness on nano- and micrometre scale. However, typical construction of superhydrophobic surfaces with micro-nano structure through top-down fabrication is restricted by sophisticated fabrication techniques and limited choices of substrate materials. Micro-nanoscale topographies templated by conventional microparticles through surface coating may produce large variations in roughness and uncontrollable defects, resulting in poorly controlled surface morphology and wettability. In this work, micro-nanoscale hierarchical nanowire network was fabricated to construct self-cleaning coating using one-dimensional TiO2 nanowires as microscale templates. Hierarchical structure with homogeneous morphology was achieved by branching ZnO nanowires on the TiO2 nanowire backbones through hydrothermal reaction. The hierarchical nanowire network displayed homogeneous micro/nano-topography, in contrast to hierarchical structure templated by traditional microparticles. This hierarchical nanowire network film exhibited high repellency to both water and cell culture medium after functionalization with fluorinated organic molecules. The hierarchical structure templated by TiO2 nanowire coating significantly increased the surface superhydrophobicity compared to vertical ZnO nanowires with nanotopography alone. Our results demonstrated a promising strategy of using nanowires as microscale templates for the rational design of hierarchical coatings with desired superhydrophobicity that can also be applied to various substrate materials.

Enhancement of polar phases in PVDF by forming PVDF/SiC nanowire composite

Different contents of silicon carbide (SiC) nanowires were mixed with Poly(vinylidene fluoride) (PVDF) to facilitate the polar phase crystallization. It was shown that the annealing temperature and SiC content affected on the phase and crystalline structures of PVDF/SiC samples. Furthermore, the addition of SiC nanowire enhanced the transformation of non-polar α phase to polar phases and increased the relative fraction of β phase in PVDF. Due to the nucleating agent mechanism of SiC nanowires, the ion-dipole interaction between the negatively charged surface of SiC nanowires and the positive CH2 groups in PVDF facilitated the formation of polar phases in PVDF.