Advanced Fabrication Methods Research Articles

A Review of Advances in Fabrication Methods and Assistive Technologies of Micro-Structured Surfaces

Micro-structured surfaces possess excellent properties of friction, lubrication, drag reduction, antibacterial, and self-cleaning, which have been widely applied in optical, medical, national defense, aerospace fields, etc. Therefore, it is requisite to study the fabrication methods of micro-structures to improve the accuracy and enhance the performance of micro-structures. At present, there are plenty of studies focusing on the preparation of micro-structures; therefore, systematic review of the technologies and developing trend on the fabrication of micro-structures are needed. In present review, the fabrication methods of various micro-structures are compared and summarized. Specially, the characteristics and applications of ultra-precision machining (UPM) technology in the fabrication of micro-structures are mainly discussed. Additionally, the assistive technologies applied into UPM, such as fast tool servo (FTS) technology and slow tool servo (STS) technology to fabricate micro-structures with different characteristics are summarized. Finally, the principal characteristics and applications of fly cutting technology in manufacturing special micro-structures are presented. From the review, it is found that by combining different machining methods to prepare the base layer surface first and then fabricate the sublayer surface, the advantages of different machining technologies can be greatly exerted, which is of great significance for the preparation of multi-layer and multi-scale micro-structures. Furthermore, the combination of ultra-precision fly cutting and FTS/STS possess advantages in realizing complex micro-structures with high aspect ratio and high resolution. However, residual tool marks and material recovery are still the key factors affecting the form accuracy of machined micro-structures. This review provides advances in fabrication methods and assistive technologies of micro-structured surfaces, which serves as the guidance for both fabrication and application of multi-layer and multi-scale micro-structures.

Emerging technologies for cardiac tissue engineering and artificial hearts.

Heart diseases, especially cardiovascular diseases, have brought heavy burden on society for their high morbidity and mortality. In clinical, heart transplantation is recognized as an effective strategy to rescue the lives of patients, while it may suffer from lack of donors and possible immune responses. In view of this, tremendous efforts have been devoted to developing alternative strategies to recover the function and promote the regeneration of cardiac tissues. As an emerging field blending cell biology and material science, tissue engineering technique allows the construction of biomimetic living complexes as organ substitutes for heart repair. In this review, we will present the recent progress in cardiac tissue engineering and artificial hearts. After introducing the critical elements in cardiac tissue engineering, we will present advanced fabrication methods to achieve scaffolds with desired micro/nanostructure design as well as the applications of these bioinspired scaffolds. We will also discuss the current dilemma and possible development direction from a biomedical perspective.

Emerging low-cost, large-scale photonic platforms with soft lithography and self-assembly

Advancements in micro/nanofabrication have enabled the realization of practical micro/nanoscale photonic devices such as absorbers, solar cells, metalenses, and metaholograms. Although the performance of these photonic devices has been improved by enhancing the design flexibility of structural materials through advanced fabrication methods, achieving large-area and high-throughput fabrication of tiny structural materials remains a challenge. In this aspect, various technologies have been investigated for realizing the mass production of practical devices consisting of micro/nanostructural materials. This review describes the recent advancements in soft lithography, colloidal self-assembly, and block copolymer self-assembly, which are promising methods suitable for commercialization of photonic applications. In addition, we introduce low-cost and large-scale techniques realizing micro/nano devices with specific examples such as display technology and sensors. The inferences presented in this review are expected to function as a guide for promising methods of accelerating the mass production of various sub-wavelength-scale photonic devices.

Synthesis of photocatalytic TiO2 nanotubes on additively manufactured Ti-alloy substrates

The pursuit of sustainable and clean energy sources has led to the exploration of green hydrogen as a versatile and eco-friendly energy carrier. This research paper focuses on the application of photocatalytic electrolysis, particularly utilizing titanium dioxide (TiO2) nanotubes, for efficient hydrogen production. The study investigates the synthesis of TiO2 nanotubes on additive manufacturing (AM)-produced substrates and explores the effects of post-synthesis annealing and cleaning techniques. The results demonstrate well-organized and uniform nanotubes, with the morphology depending on the annealing ramp rate. X-ray diffraction analysis reveals a phase transformation to anatase with a grain size of approximately 28 nm upon annealing. The study emphasizes the importance of post-synthesis cleaning in achieving desired nanotube surfaces. Cleaning with ethanol followed by 10 vol% HCl produces well-organized nanotubes of varying sizes. Overall, the research contributes to the understanding of surface modification techniques and nanostructured architectures for optimizing hydrogen photoelectrodes. The study also highlights the potential of AM in advanced fabrication methods for improved photoelectrochemical electrodes and offers valuable insights for future work in this field.

Ag-Decorated Si Microspheres Produced by Laser Ablation in Liquid: All-in-One Temperature-Feedback SERS-Based Platform for Nanosensing.

Combination of dissimilar materials such as noble metals and common semiconductors within unified nanomaterials holds promise for optoelectronics, catalysis and optical sensing. Meanwhile, difficulty of obtaining such hybrid nanomaterials using common lithography-based techniques stimulates an active search for advanced, inexpensive, and straightforward fabrication methods. Here, we report one-pot one-step synthesis of Ag-decorated Si microspheres via nanosecond laser ablation of monocrystalline silicon in isopropanol containing AgNO3. Laser ablation of bulk silicon creates the suspension of the Si microspheres that host further preferential growth of Ag nanoclusters on their surface upon thermal-induced decomposition of AgNO3 species by subsequently incident laser pulses. The amount of the AgNO3 in the working solution controls the density, morphology, and arrangement of the Ag nanoclusters allowing them to achieve strong and uniform decoration of the Si microsphere surface. Such unique morphology makes Ag-decorated Si microspheres promising for molecular identification based on the surface-enhanced Raman scattering (SERS) effect. In particular, the designed single-particles sensing platform was shown to offer temperature-feedback modality as well as SERS signal enhancement up to 106, allowing reliable detection of the adsorbed molecules and tracing their plasmon-driven catalytic transformations. Considering the ability to control the decoration degree of Si microspheres by Ag nanoclusters via amount of the AgNO3, the developed one-pot easy-to-implement PLAL synthesis holds promise for gram-scale production of high-quality hybrid nanomaterial for various nanophotonics and sensing applications.

Multiphysics Simulation of the NASA SIRIUS-CAL Fuel Experiment in the Transient Test Reactor Using Griffin

After approximately 50 years, NASA is restarting efforts to develop nuclear thermal propulsion (NTP) for interplanetary missions. Building upon nuclear engine tests performed from the late 1950s to the early 1970s, the present research and testing focuses on advanced materials and fabrication methods. A number of transient tests have been performed to evaluate materials performance under high-temperature, high-flux conditions, with several more experiments in the pipeline for future testing. The measured data obtained from those tests are being used to validate the Griffin reactor multiphysics code for this particular type of application. Griffin was developed at Idaho National Laboratory (INL) using the MOOSE framework. This article describes the simulation results of the SIRIUS-CAL calibration experiment in the Transient Reactor Test Facility (TREAT). SIRIUS-CAL was the first transient test conducted on NASA fuels, and although the test was performed with a relatively low core peak power, the test specimen survived a temperature exceeding 900 K. Griffin simulations of the experiment successfully matched the reactor’s power transient after calibrating the initial control rod position to match the initial reactor period. The thermal-hydraulics model largely matches the time-dependent response of a thermocouple located within the experiment specimen to within the uncertainty estimate. However, the uncertainty range is significant and must be reduced in the future.

Current and Future Trends for Polymer Micro/Nanoprocessing in Industrial Applications.

Polymers are widely used in optical devices, electronic devices, energy-harvesting/storage devices, and sensors, owing to their low weight, excellent flexibility, and simple fabrication process. With advancements in micro/nanoprocessing techniques and more demanding application requirements, it is becoming necessary to realize high-resolution fabrication of polymers to prepare miniaturized devices. This is particularly because conventional processing technologies suffer from high thermal stress and strong adhesion/friction, which can irreversibly damage the micro/nanostructures of miniaturized devices. In addition, although the use of advanced fabrication methods to prepare high-resolution micro/nanostructures is explored, these methods are limited to laboratory research or small-batch production. This review focuses on the micro/nanoprocessing of polymeric materials and devices with high spatial precision and replication accuracy for industrial applications. Specifically, the current state-of-the-art techniques and future trends for micro/nanomolding, high-energy beam processing, and micro/nanomachining are discussed. Moreover, an overview of the fabrication and applications of various polymer-based elements and devices such as microlenses, biosensors, and transistors is provided. These techniques are expected to be widely applied for multiscale and multimaterial processing as well as for multifunction integration in next-generation integrated devices, such as photoelectric, smart, and biodegradable devices.

Creating three-dimensional magnetic functional microdevices via molding-integrated direct laser writing

Magnetically driven wireless miniature devices have become promising recently in healthcare, information technology, and many other fields. However, they lack advanced fabrication methods to go down to micrometer length scales with heterogeneous functional materials, complex three-dimensional (3D) geometries, and 3D programmable magnetization profiles. To fill this gap, we propose a molding-integrated direct laser writing-based microfabrication approach in this study and showcase its advanced enabling capabilities with various proof-of-concept functional microdevice prototypes. Unique motions and functionalities, such as metachronal coordinated motion, fluid mixing, function reprogramming, geometrical reconfiguring, multiple degrees-of-freedom rotation, and wireless stiffness tuning are exemplary demonstrations of the versatility of this fabrication method. Such facile fabrication strategy can be applied toward building next-generation smart microsystems in healthcare, robotics, metamaterials, microfluidics, and programmable matter.

Enhanced thermally conductive TPU/graphene filaments for 3D printing produced by melt compounding

AbstractConducting polymers are a potential solution to the issue of wide‐range manufacture of flexible electronics, since many polymers are suitable to advanced fabrication methods, such as fused deposition modeling (FDM) 3D printing. Therefore, it is proposed in this work a ductile thermoplastic polyurethane (TPU)/graphene nanocomposite with enhanced thermal conductivity that would be suitable for additive manufacturing processes. The nanocomposites were produced by melt compounding technique, which does not require the use of toxic solvents and is characteristic of being used by the thermoplastic industry. The filaments were then analyzed in terms of graphene dispersion, microstructural changes, mechanical behavior, and thermal conductivity. It was verified that graphene does not have a good interaction with the TPU matrix, presenting voids at the interface and forming agglomerates at higher contents. However, it was able to affect the TPU's hard segments organization, leading to a more ordered structure up to 1.0 wt%. Consequently, the thermal conductivity was enhanced up to the graphene concentration by about 14% in relation to neat TPU. Additionally, even though the system presented a poor interface, no mechanical properties were lost, that is, the composite remained ductile even after graphene insertion, which is extremely interesting for additive manufacturing processes.

Carbon dots based photocatalysis for environmental applications

Carbon quantum dots (CQDs) have attracted intensive interest in the scientific community attributed to their quantum effect, non-toxicity, fluorescence, photoluminescence, and up-conversion properties, and have been extensively applied in sensing, biomedical, optoelectronic and catalysis fields. Especially, CQDs can act as photocatalysts and be used in energy and environmental areas, such as wastewater remediation and solar energy conversion to fuels and green chemicals. This review will briefly introduce the unique physicochemical properties of CQDs, such as light absorption, photoluminescence, and up-conversion luminescence. The advanced fabrication methods and modification strategies of CQDs will also be summarized. Finally, we will show the broad applications of CQDs in photocatalytic pollutant removal and hydrogen/hydrogen-peroxide production, discussing the structure-activity relationship of CQDs and their complexes in the field of catalysis. Lastly, the key issues and perspectives for future energy and environmental applications are presented. This comprehensive review will provide new insight and inspiration in the synthesis, improvement, and photocatalytic application of CQDs.

Three-Dimensional Printing Strategies for Irregularly Shaped Cartilage Tissue Engineering: Current State and Challenges.

Although there have been remarkable advances in cartilage tissue engineering, construction of irregularly shaped cartilage, including auricular, nasal, tracheal, and meniscus cartilages, remains challenging because of the difficulty in reproducing its precise structure and specific function. Among the advanced fabrication methods, three-dimensional (3D) printing technology offers great potential for achieving shape imitation and bionic performance in cartilage tissue engineering. This review discusses requirements for 3D printing of various irregularly shaped cartilage tissues, as well as selection of appropriate printing materials and seed cells. Current advances in 3D printing of irregularly shaped cartilage are also highlighted. Finally, developments in various types of cartilage tissue are described. This review is intended to provide guidance for future research in tissue engineering of irregularly shaped cartilage.

Metallurgical Failure Investigation of Combustion Chamber Leakage in a Heavy-duty Gas Turbine Engine

Abstract In this contribution, a case study is presented describing the failure of a combustion chamber assembly in a non-OEM (Original Equipment Manufacturer) gas turbine engine used for power generation. It showed how even advanced fabrication methods, such as Electron Beam (EB) welding, could trigger fatigue fracture, even if there are no material defects, no weld imperfections, no fabrication flaws, and even if everything is within specified limits. As is so often the case in component failures, the fact that failures occur anyway, despite the absence of out-of-spec material properties, and even though there were no fabrication flaws, is attributable to the design; which is often not sturdy enough to withstand unexpected dynamic loading.

Investigating Time-Dependent Active Motion of Janus Micromotors using Dynamic Light Scattering.

Advances in fabrication methods have positioned Janus micromotors (JMs) as candidates for use as autonomous devices in applications across diverse fields, spanning drug delivery to environmental remediation. While the design of most micromotors is straightforward, the non-steady state active motion exhibited by these systems is complex and difficult to characterize. Traditionally, JM active motion is characterized using optical microscopy single particle tracking for systems confined in 2D. Dynamic light scattering (DLS) offers an alternative high-throughput method for characterizing the 3Dactive motion in bulk JM dispersions with additional capabilities to quantify time-dependent behavior for a broader range of JM sizes. Here, the active motion of spherical JMs is examined by DLS and it is demonstrated that the method enables decoupling of the translational and rotational diffusion. Systematic studies quantifying the time-dependent diffusive properties as a function of fuel concentration, JM concentration, and time after fuel addition are presented. The analyses presented in this work position DLS to facilitate future advances of JM systems by serving as a fast-screening characterization method for active motion.

Evaluation of advanced methods and materials for construction of scintillation detector light guides

New techniques for fabrication of optically clear structures (3D printing and casting) can be applied to fabrication of light guides, especially complex -shaped ones, for scintillation detectors. In this investigation, we explored the spectral transmissivity of sample light guides created with different fabrication methods and materials. A spectrophotometer was used to measure the transmissivity of the samples to determine their compatibility with a number of commonly used inorganic scintillators (NaI(Tl), BGO, LaBr3, LaCr3, CSI(Tl) and LYSO). These measurements showed that stereolithography with a Stratasys 3D printer using Somos WaterClear Ultra 10122® produced the most compatible light guide with common organic scintillators, especially LYSO (peak emission λ=420 nm) (a scintillator commonly used in positron emission tomography (PET) imaging). Additionally, Polytek Poly-Optic® 1730 clear urethane produced a cast light guide that was the most optically compatible with these scintillators. To demonstrate the ability to create a unique shaped scintillation detector using 3D-printing and casting methods, a small arc-shaped piece of LYSO was coupled to a 4 × 4 array of 4 mm2 silicon photomultipliers (SiPM) using light guides made from these materials. For comparative purposes, a light guide was also fabricated using standard acrylic, a material often used in current light guides. All detectors produced similar event position maps. The energy resolution for 18F (511 keV photopeak) was 13% for the acrylic light-guide-based detector, while it was 18% for the printed light-guide-based detector and 20% for the cast light-guide-based detector. Results from this study demonstrate that advanced fabrication methods have the potential to facilitate creation of light guides for scintillation detectors. Continued advancements in materials and methods will likely result in improved optical performance for 3D-printed structures.

Vascular Tissue Engineering: Challenges and Requirements for an Ideal Large Scale Blood Vessel.

Since the emergence of regenerative medicine and tissue engineering more than half a century ago, one obstacle has persisted: the in vitro creation of large-scale vascular tissue (>1 cm3) to meet the clinical needs of viable tissue grafts but also for biological research applications. Considerable advancements in biofabrication have been made since Weinberg and Bell, in 1986, created the first blood vessel from collagen, endothelial cells, smooth muscle cells and fibroblasts. The synergistic combination of advances in fabrication methods, availability of cell source, biomaterials formulation and vascular tissue development, promises new strategies for the creation of autologous blood vessels, recapitulating biological functions, structural functions, but also the mechanical functions of a native blood vessel. In this review, the main technological advancements in bio-fabrication are discussed with a particular highlights on 3D bioprinting technologies. The choice of the main biomaterials and cell sources, the use of dynamic maturation systems such as bioreactors and the associated clinical trials will be detailed. The remaining challenges in this complex engineering field will finally be discussed.

Rat Calvarial Bone Regeneration by 3D-Printed β-Tricalcium Phosphate Incorporating MicroRNA-200c.

Advanced fabrication methods for bone grafts designed to match defect sites that combine biodegradable, osteoconductive materials with potent, osteoinductive biologics would significantly impact the clinical treatment of large bone defects. In this study, we engineered synthetic bone grafts using a hybrid approach that combined three-dimensional (3D-)printed biodegradable, osteoconductive β-tricalcium phosphate (β-TCP) with osteoinductive microRNA(miR)-200c. 3D-printed β-TCP scaffolds were fabricated utilizing a suspension-enclosing projection-stereolithography (SEPS) process to produce constructs with reproducible microarchitectures that enhanced the osteoconductive properties of β-TCP. Collagen coating on 3D-printed β-TCP scaffolds slowed the release of plasmid DNA encoding miR-200c compared to noncoated constructs. 3D-printed β-TCP scaffolds coated with miR-200c-incorporated collagen increased the transfection efficiency of miR-200c of both rat and human BMSCs and additionally increased osteogenic differentiation of hBMSCs in vitro. Furthermore, miR-200c-incorporated scaffolds significantly enhanced bone regeneration in critical-sized rat calvarial defects. These results strongly indicate that bone grafts combining SEPS 3D-printed osteoconductive biomaterial-based scaffolds with osteoinductive miR-200c can be used as superior bone substitutes for the clinical treatment of large bone defects.

Charge Carrier Mobility Improvement in Diketopyrrolopyrrole Block-Copolymers by Shear Coating.

Shear coating is a promising deposition method for upscaling device fabrication and enabling high throughput, and is furthermore suitable for translating to roll-to-roll processing. Although common polymer semiconductors (PSCs) are solution processible, they are still prone to mechanical failure upon stretching, limiting applications in e.g., electronic skin and health monitoring. Progress made towards mechanically compliant PSCs, e.g., the incorporation of soft segments into the polymer backbone, could not only allow such applications, but also benefit advanced fabrication methods, like roll-to-roll printing on flexible substrates, to produce the targeted devices. Tri-block copolymers (TBCs), consisting of an inner rigid semiconducting poly-diketo-pyrrolopyrrole-thienothiophene (PDPP-TT) block flanked by two soft elastomeric poly(dimethylsiloxane) (PDMS) chains, maintain good charge transport properties, while being mechanically soft and flexible. Potentially aiming at the fabrication of TBC-based wearable electronics by means of cost-efficient and scalable deposition methods (e.g., blade-coating), a tolerance of the electrical performance of the TBCs to the shear speed was investigated. Herein, we demonstrate that such TBCs can be deposited at high shear speeds (film formation up to a speed of 10 mm s−1). While such high speeds result in increased film thickness, no degradation of the electrical performance was observed, as was frequently reported for polymer−based OFETs. Instead, high shear speeds even led to a small improvement in the electrical performance: mobility increased from 0.06 cm2 V−1 s−1 at 0.5 mm s−1 to 0.16 cm2 V−1 s−1 at 7 mm s−1 for the TBC with 24 wt% PDMS, and for the TBC containing 37 wt% PDMS from 0.05 cm2 V−1 s−1 at 0.5 mm s−1 to 0.13 cm2 V−1 s−1 at 7 mm s−1. Interestingly, the improvement of mobility is not accompanied by any significant changes in morphology.

Increasing the packing density of assays in paper-based microfluidic devices.

Paper-based devices have a wide range of applications in point-of-care diagnostics, environmental analysis, and food monitoring. Paper-based devices can be deployed to resource-limited countries and remote settings in developed countries. Paper-based point-of-care devices can provide access to diagnostic assays without significant user training to perform the tests accurately and timely. The market penetration of paper-based assays requires decreased device fabrication costs, including larger packing density of assays (i.e., closely packed features) and minimization of assay reagents. In this review, we discuss fabrication methods that allow for increasing packing density and generating closely packed features in paper-based devices. To ensure that the paper-based device is low-cost, advanced fabrication methods have been developed for the mass production of closely packed assays. These emerging methods will enable minimizing the volume of required samples (e.g., liquid biopsies) and reagents in paper-based microfluidic devices.

Wearable fiber-based thermoelectrics from materials to applications

Thermoelectrics, enabling direct converting between heat and electricity, have become one of the most promising techniques for the realization of energy-saving and environmental protection. As a key member of the thermoelectric family, fiber-based thermoelectrics possess significant potential in the area of charging wearable electronics, owing to their high performance, high flexibility, and high stability features. Based on the fast development of fiber-based thermoelectrics, this review aims to comprehensively summarize the state-of-the-art fiber-based thermoelectric materials and devices, including their unique designs, chemical engineering, advanced fabrication methods, outstanding thermoelectric properties, and wide applications. In the end, we point out the challenge and outlook for further improving thermoelectric performance, flexibility, and stability of fiber-based thermoelectrics.

Rat Calvarial Bone Regeneration by 3D-Printed Beta-Tricalcium Phosphate Incorporating MicroRNA-200c

Advanced fabrication methods of bone grafts designed to match defect sites that combine biodegradable, osteoconductive materials with potent, osteoinductive biologics would significantly impact the clinical treatment of large bone defects. In this study, we engineered synthetic bone grafts using a hybrid material approach that combined 3D-printed biodegradable, osteoconductive β-tricalcium phosphate (β-TCP) with osteoinductive microRNA(miR)-200c. 3D-printed β-TCP scaffolds were fabricated utilizing suspension-enclosing projection-stereolithography (SEPS) process to produce constructs with reproducible microarchitectures that enhanced the osteoconductive properties of β-TCP. 3D-printed β-TCP scaffolds coated with miR-200c incorporated collagen increased the transfection efficiency of miR-200c and osteogenic differentiation of hBMSCs in vitro. Furthermore, these hybrid material, miR-incorporated scaffolds significantly enhanced bone regeneration in critical-sized rat calvarial defects. These results strongly indicate that through use of SEPS 3D-printing technology, hybrid scaffolds combined by osteoconductive biomaterials and osteoinductive biologics can be used as superior bone substitutes for the clinical treatment of large bone defects.