Surface patterning nanoparticle-based arrays

In this study, focused ion beam lithography is used to pattern different size and shape island arrays on silicon wafers. Cavity arrays of inverse shapes are then made on silicone mold surfaces by polymerization. After that, Al₂O₃ nanoparticle-based island arrays are created by a surface feature transfer and freeze casting process using an Al₂O₃ colloidal suspension. The effects of silicone mold surface wettability and freezing rate on the Al₂O₃ nanoparticle pattern quality are investigated. The results show that coating the silicone mold surface with a 10 nm thick Au–Pt layer makes the Al₂O₃ nanoparticle suspension more wetting on the mold surface and also likely reduces the dry Al₂O₃ nanoparticle adhesion to the mold surface. Freezing rate should be lower than 1 °C/min to avoid cracks or loose Al₂O₃ nanoparticle packing in the freeze cast features. When these factors are properly controlled, the reported patterning process allows reproduction of micron-size feature arrays from Al₂O₃ nanoparticle suspensions. The studied approach should be applicable to most nanoparticle-based materials and open numerous opportunities for direct-device fabrication.     

Template-assisted electrohydrodynamic atomization of polycaprolactone for orthopedic patterning applications

This paper presents the development of the novel deposition of biodegradable polycaprolactone (PCL) polymer patterns on a metallic substrate using a jet spraying technique, template-assisted electrohydrodynamic atomization (TAEA), at ambient temperature. The structure of patterns was controlled by systematically varying the polymer concentration (2–15 wt.%) and the flow rate (1–25 μl min^? 1). Polymer deposition was carried out in the stable cone-jet mode to precisely control the surface structure and morphology. The patterns were studied by optical microscopy, scanning electron microscopy and profilometry, and a high degree of control over the pattern geometry and thickness was achieved by varying the spraying time. The hardness and the effective elastic modulus of the polymer patterns were estimated using nanoindentation. The effect of load, loading rate and the holding time on the hardness and effective elastic modulus was derived. Optimal results were obtained with 5 wt.% PCL in DMAC solution sprayed within the stable cone-jet mode operating window at a flow rate of 15 μl min^? 1 for 300 s at 11.1 kV with a working distance of 60 mm. Hexagonal patterns were well-defined and repeatable with thickness of ~ 34 μm. The hardness is 1.6 MPa at a loading rate of 0.1 μN/s and nearly halved when the load rate was increased to 1 μN/s. The effective elastic modulus of ~ 12 MPa is obtained for a load rate of 0.1 μN/s.     

Ink-jet printing of ceramic pillar arrays

A high performance 500 nozzle in-line piezoelectric drop-on-demand print-head mounted on a linear table with z-axis control was used to prepare arrays of fine ceramic pillars. Such structures may find applications in miniature heat exchangers, catalyst supports, for cell up-regulation in prosthetics or in polymer-ceramic piezoelectric 1–3 composites. The ink conveyed 14 vol% fine zirconia and deposited a wax-based suspension in an octane-alcohol mixture. The dried ink contained 63 vol% zirconia.     

Novel patterning of nano-bioceramics: template-assisted electrohydrodynamic atomization spraying.

The ability to create patterns of bioactive nanomaterials particularly on metallic and other types of implant surfaces is a crucial feature in influencing cell response, adhesion and growth. In this report, we uncover and elucidate a novel method that allows the easy deposition of a wide variety of predetermined topographical geometries of nanoparticles of a bioactive material on both metallic and non-metallic surfaces. Using different mesh sizes and geometries of a gold template, hydroxyapatite nanoparticles suspended in ethanol have been electrohydrodynamically sprayed on titanium and glass substrates under carefully designed electric field conditions. Thus, different topographies, e.g. hexagonal, line and square, from hydroxyapatite nanoparticles were created on these substrates. The thickness of the topography can be controlled by varying the spraying time.     

Direct-patterning of porphyrin dot arrays and lines using electrohydrodynamic jet printing

In this research, we have fabricated micron-sized patterns of porphyrins on silicon substrates using an electrohydrodynamic (EHD) jet printing technique. Optical and fluorescence microscopies have been used to examine the shape and fluorescence property of porphyrin patterns. The morphology of the porphyrin patterns printed with variously formulated porphyrin inks and the effects of applied voltage, working distance, and substrate properties on the morphology of patterns were investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). We have also demonstrated the acid-vapor sensing capability of the porphyrins by exposing the porphyrin patterns on Si substrates to nitric acid vapor.     

Simple, large-scale patterning of hydrophobic ZnO nanorod arrays

Here we describe a simple, versatile technique to produce large-scale arrays of highly ordered ZnO nanorods. Patterning of three distinct ZnO crystal morphologies is demonstrated through use of different ZnO seed layers. Array formation is accomplished through a simple variation on nanosphere lithography that imprints a thickness variation across a PMMA mask layer. The area of exposed seed layer is controlled through etching time in an oxygen plasma. Subsequent hydrothermal growth from the patterned seed layer produces high-quality ZnO crystals in uniform arrays. The high uniformity of the patterned array is shown to induce a high contact angle hydrophobic state even without the need for chemical modification of the ZnO surface. This technique provides a straightforward way to integrate the optical and electrical properties of high-quality ZnO nanorods with the tunable fluidic properties at the surface of well-ordered arrays.     

High-density regular arrays of nanometer-scale rods formed on silicon surfaces via femtosecond laser irradiation in water

We report on the formation of high-density regular arrays of nanometer-scale rods using femtosecond laser irradiation of a silicon surface immersed in water. The resulting surface exhibits both micrometer-scale and nanometer-scale structures. The micrometer-scale structure consists of spikes of 5-10 mum width, which are entirely covered by nanometer-scale rods that are roughly 50 nm wide and normal to the surface of the micrometer-scale spikes. The formation of the nanometer-scale rods involves several processes: refraction of laser light in highly excited silicon, interference of scattered and refracted light, rapid cooling in water, roughness-enhanced optical absorptance, and capillary instabilities.     

3D printing vertically: Direct ink writing free-standing pillar arrays

Over the last three decades, a variety of additive manufacturing techniques have gradually gained maturity and will potentially play an important role in future manufacturing industries. Among them, direct ink writing has attracted significant attention from both material and tissue engineering areas, where the colloidal ink is extruded and dispensed according to a pre-designed path, usually in the X-Y plane with suitable increments in the Z direction. Undoubtedly, this way of disassembling geometries, simple or complex, can facilitate most of the printing process. However, for one extreme case, i.e. pillar arrays, the size resolution can deviate from both nozzle and design if the common way of slicing and additive manufacturing is used. Therefore, a different printing path is required – directly depositing pillars in a converse gravitational direction. This paper gives multiple examples of printing viscoelastic colloidal ceramic and metal inks uniaxially and periodically into free-standing and height-adjustable pillar arrays. It is expected to inspire the additive manufacturing community that more versatile degrees of freedom and complex printing paths, not confined within only complex shapes, can be achieved by ink-based 3D printing.     

Negative Poisson's ratio polymeric and metallic foams

Foam materials based on metal and several polymers were transformed so that their cellular architecture became re-entrant, i.e. with inwardly protruding cell ribs. Foams with re-entrant structures exhibited negative Poisson's ratios as well as greater resilience than conventional foams. Foams with negative Poisson's ratios were prepared using different techniques and materials and their mechanical behaviour and structure evaluated.     

Electrodeposition of CdSe on nanopatterned pillar arrays for photonic and photovoltaic applications

This work investigates the electrodeposition of CdSe photonic nanostructures into two dimensional (2D) resist templates generated by X-ray lithography. This templated electrolytic infiltration process is particularly interesting for photonic and photovoltaic applications. Both current and voltage controlled electrochemical depositions have been performed to infiltrate CdSe onto the 2D templates. Followed by the removal of the template, triangular arrays of CdSe pillars or networks with more than 1 μm in height were obtained. The detailed studies of deposition parameters such as applied voltage, current density, deposition time, concentrations of electrolytes and temperatures were carried out to determine the optimum conditions to obtain high quality 2D CdSe photonic crystals (PhCs). The full optical and structural characterization of the CdSe nanostructures showed that the CdSe films prepared have a cubic structure with nanometer grain size. Optical absorption studies reveal a bandgap of 2.1 eV for the thin film grown CdSe, blue-shifted from the characteristic 1.7 eV of bulk CdSe, resulting from size quantization effect. Preliminary optical characterization by a micro-reflectance technique is performed in order to assess the performance of the fabricated samples as 2D PhCs.     

Bacterial DNA sample preparation from whole blood using surface-modified Si pillar arrays

A novel bacterial DNA sample preparation device for molecular diagnostics has been developed. On the basis of optimized conditions for bacterial adhesion, surface-modified silicon pillar arrays for bacterial cell capture were fabricated, and their ability to capture bacterial cells was demonstrated. The capture efficiency for bacterial cells such as Escherichia coli, Staphylococcus epidermidis, and Streptococcus mutans in buffer solution was over 75% with a flow rate of 400 microL/min. Moreover, the proposed method captured E. coli cells present in 50% whole blood effectively. The captured cells from whole blood were then in- situ lyzed on the surface of the microchip, and the eluted DNA was successfully amplified by qPCR. These results demonstrate that the full process of pathogen capture to DNA isolation from whole blood could be automated in a single microchip.     

Ordered nanoparticle arrays formed on engineered chaperonin protein templates

Traditional methods for fabricating nanoscale arrays are usually based on lithographic techniques. Alternative new approaches rely on the use of nanoscale templates made of synthetic or biological materials. Some proteins, for example, have been used to form ordered two-dimensional arrays. Here, we fabricated nanoscale ordered arrays of metal and semiconductor quantum dots by binding preformed nanoparticles onto crystalline protein templates made from genetically engineered hollow double-ring structures called chaperonins. Using structural information as a guide, a thermostable recombinant chaperonin subunit was modified to assemble into chaperonins with either 3 nm or 9 nm apical pores surrounded by chemically reactive thiols. These engineered chaperonins were crystallized into two-dimensional templates up to 20 microm in diameter. The periodic solvent-exposed thiols within these crystalline templates were used to size-selectively bind and organize either gold (1.4, 5 or 10nm) or CdSe-ZnS semiconductor (4.5 nm) quantum dots into arrays. The order within the arrays was defined by the lattice of the underlying protein crystal. By combining the self-assembling properties of chaperonins with mutations guided by structural modelling, we demonstrate that quantum dots can be manipulated using modified chaperonins and organized into arrays for use in next-generation electronic and photonic devices.     

Recent progress in nano-biotechnology: compartmentalized micro- and nanoparticles via electrohydrodynamic co-jetting

Compartmentalized particles enable co-presentation of dissimilar sets of properties, thereby offering a broad design space for multifunctional particles. Electrohydrodynamic co-jetting is a simple, yet versatile fabrication technique that can be used to prepare such multicompartmental particles and fibers. Processing conditions are summarized for co-jetting of aqueous and organic polymer solutions as well as nanoparticle suspensions. Because particles can comprise distinct polymers in different compartments, selective surface modification becomes possible. The latter can result in unidirectional interactions with cells or may pave new routes towards targeted drug delivery.     

Fabrication of stacked-ring netted tubular constructs via 3D template electrohydrodynamic printing

Electrohydrodynamic (EHD) printing is an emerging additive manufacturing process which provides several opportunities for advanced fiber patterning and alignment. In this study, stacked-ring netted tubular constructs were printed using controlled EHD fiber deposition. To achieve this, a modified EHD system was developed which integrated air and heating moduli, in addition to a 3D cylindrical collector. The impact of additional peripheral components was evident through enhanced solidification of as-formed polycaprolactone (PCL) polymer fiber prints, which further enabled fabrication of stacked PCL fiber rings. Subsequently, stacked-ring netted tubular constructs (via x-axis deposition manipulation) were fabricated. Electric field simulations were used to elucidate construct formation mechanism. The modified printing system provides much needed control on fiber deposition and solidification, enabling integration of essential bio-interface features and morphologies (e.g., tissue structure and surface mimicry) for advanced 3D biomaterial engineering.     

A method for filling complex polymeric microfluidic devices and arrays

This paper describes an improved method for filling microfluidic structures with aqueous solutions. The method, channel outgas technique (COT), is based on a filling procedure carried out at reduced pressures. This procedure is compared with previously reported methods in which microfluidic channels are filled either by using capillary forces or by applying a pressure gradient at one or more empty reservoirs. The technique has proven to be > 90% effective in eliminating the formation of bubbles within microfluidic networks. It can be applied to many devices, including those containing PDMS-terminated channel features, a single channel inlet, and three-dimensional arrays.     

Micropatterned polymeric gratings as chemoresponsive volatile organic compound sensors: implications for analyte detection and identification via diffraction-based sensor arrays

Micropatterned polymeric diffraction gratings have been fabricated and evaluated as volatile organic chemical sensors. When operated under nonresonant conditions, sensor elements were found to respond in a rapid (response time 5-15 s) and reproducible fashion to each analyte investigated. Relative response magnitudes were found to be in qualitative agreement with those obtained via surface acoustic wave techniques. Preliminary limits of detection as determined by investigations with micropatterned polyepichlorohydrin, polyisobutylene, and polybutadiene gratings, respectively, were found to be 8, 11, and 7 ppm for toluene, 25, 258; and 72 ppm for methyl ethyl ketone; 41, 102, and 34 ppm for chloroform; and 460, 60, and 59 ppm for hexane. While generally less than 1 order of magnitude higher than those observed for identical polymer/analyte combinations in SAW studies, the observed limits of detection were at or below governmental standards (OSHA-PEL and NIOSH-REL) for each analyte evaluated. These diffraction-based sensors show promise for integration into an array-based sensor system, providing simultaneous identification and quantification of unknown analytes and simple analyte mixtures.     

Growth of high-aspect ratio horizontally-aligned ZnO nanowire arrays

A method of fabricating horizontally-aligned zinc-oxide (ZnO) nanowire (NW) arrays with full control over the width and length is demonstrated. SEM images reveal the hexagonal structure typical of zinc oxide NWs. Arrays of high-aspect ratio horizontal ZnO NWs are fabricated by making use of the lateral overgrowth from dot patterns created by electron beam lithography (EBL). An array of patterned wires are lifted off and transferred to a flexible PDMS substrate with possible applications in several key nanotechnology areas.