Flexible Fabrication Technique Research Articles

Multipatterned Chondrocytes' Scaffolds by FL-MOPL with a BSA-GMA Hydrogel to Regulate Chondrocytes' Morphology.

Repairing articular cartilage damage is challenging due to its low regenerative capacity. In vitro, cartilage regeneration is a potential strategy for the functional reconstruction of cartilage defects. A hydrogel is an advanced material for mimicking the extracellular matrix (ECM) due to its hydrophilicity and biocompatibility, which is known as an ideal scaffold for cartilage regeneration. However, chondrocyte culture in vitro tends to dedifferentiate, leading to fibrosis and reduced mechanical properties of the newly formed cartilage tissue. Therefore, it is necessary to understand the mechanism of modulating the chondrocytes' morphology. In this study, we synthesize photo-cross-linkable bovine serum albumin-glycidyl methacrylate (BSA-GMA) with 65% methacrylation. The scaffolds are found to be suitable for chondrocyte growth, which are fabricated by homemade femtosecond laser maskless optical projection lithography (FL-MOPL). The large-area chondrocyte scaffolds have holes with interior angles of triangle (T), quadrilateral (Q), pentagon (P), hexagonal (H), and round (R). The FL-MOPL polymerization mechanism, swelling, degradation, and biocompatibility of the BSA-GMA hydrogel have been investigated. Furthermore, cytoskeleton and nucleus staining reveals that the R-scaffold with larger interior angle is more effective in maintaining chondrocyte morphology and preventing dedifferentiation. The scaffold's ability to maintain the chondrocytes' morphology improves as its shape matches that of the chondrocytes. These results suggest that the BSA-GMA scaffold is a suitable candidate for preventing chondrocyte differentiation and supporting cartilage tissue repair and regeneration. The proposed method for chondrocyte in vitro culture by developing biocompatible materials and flexible fabrication techniques would broaden the potential application of chondrocyte transplants as a viable treatment for cartilage-related diseases.

Printed Circuit Board Coils of Multitrack Litz Structure for 3.3-kW Inductive Power Transfer System

This paper presents the optimization procedure of an inductive power transmission (IPT) system which utilizes large size spiral printed circuit board (PCB) coils for high-power transfer. Printed circuit boards for coil assembly provides advantages in the manufacturing process through the use of cost-effective flexible fabrication techniques. Furthermore, this kind of construction offers a low profile device, which is of great interest for applications with space constraints. PCB-based IPT system coils can achieve high energy efficiency by applying litz-structure braiding techniques, as investigated in this work, where the objective was to obtain an optimized balance between the conduction losses and proximity losses associated with the number and dimensions of the traces. Considering the geometrical dimensions and manufacturing constraints, we will proceed to obtain the characteristics of the coil to achieve optimal performance. The estimation of coil losses were in part based on finite element simulations, and the results were conveniently processed with the appropriate mathematical methods. Numerical simulation and experimental results were conducted for validation on a prototype suitable to transfer up to 3.3 kW for a transmitter-receiver distance of 10 cm. In the experimental arrangement, a maximum efficiency in the coils of 93% has been measured, and the overall efficiency of 88% has been reached for the entire IPT system.

Sol-Gel Barium Titanate Nanohole Array as a Nonlinear Metasurface and a Photonic Crystal.

The quest of a nonlinear optical material that can be easily nanostructured over a large surface area is still ongoing. Here,wedemonstrate a nanoimprinted nonlinear barium titanate2D nanohole array that shows the optical properties of a 2D photonic crystal and a metasurface, depending on the direction of the optical axis. The challenge of nanostructuring the inert metal-oxide is resolved by direct soft nanoimprint lithography with sol-gel derived barium titanate enabling critical dimensions of 120 nm with aspect ratios of five. The nanohole array exhibits a photonic bandgap in the infrared range when probed along the slab axis, while lattice resonant states are observed in out-of-plane transmission configuration. The enhanced light-matter interaction from the resonant structure enables to increase in the second-harmonic generation in the near-ultraviolet by a factor of 18 illustrating the potential in the flexible fabrication technique for barium titanate photonicdevices.

Bioinspired Synergy Strategies Empower Small‐Scale Robots with Higher Performance

Small‐scale robots need to be agile to perform various tasks in complex environments and the design faces great challenges with limited size and power consumption. However, the advent of advanced functional materials, compliant structures/mechanisms, and flexible fabrication techniques has brought new evolution directions to robotics. These technologies enrich the robots' actuation strategies, improving their performance of small robots while simplifying the complexity of the system and thus making it possible to be applied in diverse scenarios, such as disaster rescue, medical, and environmental exploration. In nature, small organisms have shown numerous efficient survival strategies. They can easily achieve locomotion tasks with low energy consumption. For example, dragonflies complete long flights with the help of wind, and stenus (one kind of rove beetle) uses the surface tension of liquids to dodge prey quickly. Insects are usually considered to be agile, efficient, and intelligent, which is the same requirement as for small robots. Yet the corresponding bioinspired design strategies bring new opportunities and challenges to the development of small‐scale robots. Herein, the development trends of small‐scale robots are analyzed and discussed, and several potential bioinspired synergy strategies are induced, which may be useful for the future design of insect‐level soft robots.

Study on the Inter-Laminar Shear Strength and Contact Angle of Glass Fiber/ABS and Glass Fiber/Carbon Fiber/ABS Hybrid Composites

In recent days, the uses of 3D printing have been successfully implemented in various applications due to their advantages. Besides, the need for sustainable choice has created a demand for the augmented use of thermoplastic composites. Thus, additive manufacturing techniques have become the essence of composite fabrication to achieve an automated and flexible fabrication technique. The present study used fused deposition modelling (FDM) and hot press moulding technique to produce composite samples. The composite laminates were fabricated by using acrylonitrile butadiene styrene (ABS) as polymer and woven glass fiber (GF) and woven carbon fiber (CF) used as reinforcements. Further, the laminates were subjected to inter-laminar shear strength (ILSS) and contact angle. The inter-laminar shear strength and the contact angle of hybrid samples were compared with virgin ABS and pure glass fiber-reinforced composites. The study reported a maximum ILSS of 198.5MPa achieved by GF/CF/ABS hybrid composites, which was higher by 17% and 217% compared with GF/ABS and ABS samples, respectively. The contact angle results showed an increase due to the incorporation of fibers with ABS by 5% and 13% in GF/ABS and GF/CF/ABS, respectively, contributing to the adhesion. The contact angle values achieved were 100.5°, 105.15°, and 113.39° by ABS, GF/ABS and GF/CF/ABS making them hydrophobic in nature. These developed reinforced materials, such as carbon fiber, glass fiber and ABS matrix composites, could be used in automotive, aerospace and wind energy applications.

Bio-Sensor Based on Trapped Mode All-Dielectric Metasurface Coated with Graphene Layer to Enhance Sensitivity

All-dielectric metasurfaces have been widely used in nanophotonics because of their properties, such as negligible Ohmic loss, stable properties, and flexible fabrication techniques. We propose an all-dielectric metasurface consisting of subwavelength particles, which supports a “trapped” mode after the introduction of adequate symmetry-breaking in the silicon meta-atoms. Coating the metasurface with monolayer graphene enables the adsorption of nucleic acids such as DNA and RNA. We compare the resonant states in the transmission spectrum and find that the proposed metasurface is ultra-sensitive to the surrounding environment and exhibits excellent biosensing performance. Our conclusions indicate that all-dielectric metasurfaces can be a promising platform to realize ultra-sensitive bio-sensors.

Hybrid Modeling of Electrohydrodynamic Jet Printing

Additive manufacturing (AM) has grown quickly in popularity as a fast, flexible fabrication technique. However, the physical complexity of most AM processes makes it difficult to produce dynamical models that capture the system evolution from the beginning to the end of the process. This difficulty in model creation inhibits the application of many sophisticated control techniques that may improve process performance and reliability. This work uses a hybrid dynamical system structure and the combination of physics- and data-driven partial process models to address the modeling challenge for a specific AM technology—a microscale resolution technique called electrohydrodynamic jet printing—in which electric field is used to eject droplets from the meniscus at the end of a fluid-filled nozzle. Specifically, modeling of the fluid meniscus as a paraboloidal cap instead of a spherical cap extends the range of meniscus deformation that can be captured by the physics-driven model. In addition, the physics-driven model fidelity is improved by using equilibrium information and two-parameter correction coefficients identified from data to relax assumptions on the electric field and nozzle geometry models. Then, the maximum stable meniscus deformation is leveraged to define the limit of the physics-driven model’s applicability, and for the remaining segment of the process, data-driven time-delayed linear time invariant models are identified. Finally, the complete hybrid model is validated against empirical time series data.

Optical NP problem solver on laser-written waveguide platform.

Cognitive photonic networks are researched to efficiently solve computationally hard problems. Flexible fabrication techniques for the implementation of such networks into compact and scalable chips are desirable for the study of new optical computing schemes and algorithm optimization. Here we demonstrate a femtosecond laser-written optical oracle based on cascaded directional couplers in glass, for the solution of the Hamiltonian path problem. By interrogating the integrated photonic chip with ultrashort laser pulses, we were able to distinguish the different paths traveled by light pulses, and thus infer the existence or the absence of the Hamiltonian path in the network by using an optical correlator. This work proves that graph theory problems may be easily implemented in integrated photonic networks, down scaling the net size and speeding up execution times.

Micro/Meso Roll-to-Plate (R2P) Imprinting Process to Fabricate Micro Channel/Riblet Features

Functional metallic surface micro/meso structures such as micro channels/grooves or micro riblets have been increasingly applied in many fields, such as optics, tribology, fluid-dynamics and heat exchange or mass tranfer. Micro/meso forming has the potential of efficiently and economically fabricating functional microstructures over a large surface area. A mciro/meso roll-to-plate imprinting technique was proposed and the process system was self-developed. The pure copper specimens with various grains were imprinted to investigate the effects of mould cavity dimensions (width, spacing, and fillet) and grain size on the formation of features. It was concluded that the width and grain size had significant effects on the feature formation. Wider groove or larger size grain was helpful to enhance the flowability of materials. Moreover, the technique was validated for high throughput, low cost, low emission, and flexible fabrication technique.

Fabrication techniques for three-dimensional metamaterials in the midinfrared

The authors have developed two versions of a flexible fabrication technique known as membrane projection lithography that can produce nearly arbitrary patterns in “212 D” and fully three-dimensional (3D) structures. The authors have applied this new technique to the fabrication of split ring resonator-based metamaterials in the midinfrared. The technique utilizes electron beam lithography for resolution, pattern design flexibility, and alignment. The resulting structures are nearly three orders of magnitude smaller than equivalent microwave structures that were first used to demonstrate a negative index material. The fully 3D structures are highly isotropic and exhibit both electrically and magnetically excited resonances for incident transverse electromagnetic waves.

Nano/micro structure fabrication of metal surfaces using the combination of nano plastic forming, coating and roller imprinting processes

The fabrication technique using the combination of nano plastic forming, coating and roller imprinting processes to transfer nano/micro patterns onto the surface of metallic materials is developed. In this process, nano plastic forming (NPF) of pure aluminum (Al 99%) using a diamond tool is combined with a coating technique to produce a nickel die. The nickel die is then used for the double plate roller imprinting process to transfer the pattern onto the surface of metallic material. Experimental works with 0.1 N to 1.0 N indentation load variations and 2.5 µm to 7.5 µm pitch variations using a knife edge diamond tool are conducted to study the feasibility of this technique. Comparisons between the master mold, nickel die and rolling result in terms of geometries show good agreement, thus validating the proposed approach for high throughput, low cost, low emission and flexible fabrication technique. The capability of the proposed method is demonstrated in the fabrication of cross, net and brick patterns.

Fabrication of low OH loss holey fibers with varying air hole sizes and their optical properties

We experimentally investigate a flexible fabrication technique for low OH and transmission losses holey fibers with a Ge-doped core and air holes in a silica cladding region. Versatile holey fibers of different size, pitch, and shape of air holes were achieved by controlling the temperature and heating time of the holey fiber preform. In addition, we suppress the OH loss of less than ∼0.323dB/km at 1383nm. After fabricating holey fibers, we measure their optical properties including cut-off wavelength, mode field diameter, splicing loss, dispersion, bending loss, and polarization dependent loss based on the size of air holes. The total transmission loss was measured to be ∼0.226dB/km at 1550nm by improving the fabrication process. After fabricating optical patch cord based on holey fibers, we measured the long-term stability of the fabricated holey fiber by using the temperature cycling technique for 24 and obtained low power fluctuation of 0.2dB. We achieve the high quality holey fiber with a low bending loss of ∼0.04dB/turn under a bending radius of 2.5mm at 1550nm. We also obtain a tunable band rejection filter with a number of bending turns.

Fabrication and tuning of nanoscale metallic ring and split-ring arrays

Metallic structures with dimensions smaller than the wavelength of light demonstrate optical properties which depend strongly on the nanoparticle size, shape, and interparticle spacing. The optical properties are caused by the excitation of localized surface plasmon resonances that lead to strong enhancement and confinement of the optical field and can be exploited for many applications including surface-enhanced Raman spectroscopy, near-field scanning optical microscopy, and negative refractive index materials. In order to fully exploit the properties of these structures, both a highly reproducible and flexible fabrication technique and an in-depth understanding of the optical properties are needed. In this article, the authors demonstrate the fabrication of arrays of gold rings and split rings on glass using electron beam lithography. Electron beam lithography allows not only precise control of the size, shape, and spacing of the arrays but also the scope to design novel shapes at will. We characterize these arrays using polarization dependent spectroscopy. The structures can support multiple plasmon resonances, demonstrating that excellent uniformity across the array is achieved. These resonances are further characterized using a finite difference time domain method to model the electric field distribution around the ring structures.

Optical gain in Er-doped SiO 2–TiO 2 waveguides fabricated by the sol–gel technique

The sol–gel technique is a highly flexible technique for fabrication of oxide glasses, and various researchers have previously reported fluorescence studies of Er-doped sol–gel films and monoliths. Here we report the fabrication of Er-doped strip-loaded sol–gel silicate waveguides, using a silica–titania–alumina host composition, and Er concentrations up to ≈1.1×10 20 Er 3+/cm 3, for possible application in integrated optic waveguide amplifiers. We have obtained high fluorescence lifetimes (>8 ms), propagation loss values of 0.6–0.75 dB/cm at 1330 nm, and favourable fluorescence spectral shape. Relative gain levels up to 1 dB/cm were obtained. These results indicate that about half the Er ions effectively contribute to gain, suggesting segregation of the remaining ions in crystallites or clusters of some kind.

Structural materials by powder HIP for fusion reactors

Tokamak blankets have complex shapes and geometries with double curvature and embedded cooling channels. Usual manufacturing techniques such as forging, bending and welding generate very complex fabrication routes. Hot Isostatic Pressing (HIP) is a versatile and flexible fabrication technique that has a broad range of commercial applications. Powder HIP appears to be one of the most suitable techniques for the manufacturing of such complex shape components as fusion reactor modules. During the HIP cycle, consolidation of the powder is made and porosity in the material disappears. This involves a variation of 30% in volume of the component. These deformations are not isotropic due to temperature gradients in the part and the stiffness of the canister. This paper discusses the following points: (i) Availability of manufacturing process by powder HIP of 316LN stainless steel (ITER modules) and F82H martensitic steel (ITER Test Module and DEMO blanket) with properties equivalent to the forged one. (ii) Availability of powerful modelling techniques to simulate the densification of powder during the HIP cycle, and to control the deformation of components during consolidation by improving the canister design. (iii) Material data base needed for simulation of the HIP process, and the optimisation of canister geometry. (iv) Irradiation behaviour on powder HIP materials from preliminary results.