Fabrication Method Research Articles

Silk Fibroin Nanofibers: Advancements in Bioactive Dressings through Electrospinning Technology for Diabetic Wound Healing

Background: Non-healing diabetic wounds represent a significant clinical challenge globally, necessitating innovative approaches in drug delivery to enhance wound healing. Understanding the pathogenesis of these wounds is crucial for developing effective treatments. Bioactive dressings and polymeric nanofibers have emerged as promising modalities, with silk biomaterials gaining attention for their unique properties in diabetic wound healing. Purpose of Review: The purpose of this review is to examine the challenges and innovations in treating non-healing diabetic wounds, emphasizing the global burden and the need for effective solutions. This review explores the complex mechanisms of wound healing in diabetes and evaluates the therapeutic potential of bioactive dressings and polymeric nanofibers. Special focus is given to the application of silk biomaterials, particularly silk fibroin, for wound healing, detailing their properties, mechanisms, and clinical translation. This review also describes various nanofiber fabrication methods, especially electrospinning technology, and presents existing evidence on the effectiveness of electrospun silk fibroin formulations. Recent Findings: Recent advancements highlight the potential of silk biomaterials in diabetic wound healing, owing to their biocompatibility, mechanical strength, and controlled drug release properties. Electrospun silk fibroin-based formulations have shown promising results in preclinical and clinical studies, demonstrating accelerated wound closure and tissue regeneration. Summary: Non-healing diabetic wounds present a significant healthcare burden globally, necessitating innovative therapeutic strategies. Bioactive dressings and polymeric nanofibers, particularly silk-based formulations fabricated through electrospinning, offer promising avenues for enhancing diabetic wound healing. Further research is warranted to optimize formulation parameters and validate efficacy in larger clinical trials.

A fabrication strategy for millimeter-scale, self-sensing soft-rigid hybrid robots.

Soft robots typically involve manual assembly of core hardware components like actuators, sensors, and controllers. This increases fabrication time and reduces consistency, especially in small-scale soft robots. We present a scalable monolithic fabrication method for millimeter-scale soft-rigid hybrid robots, simplifying the integration of core hardware components. Actuation is provided by soft-foldable polytetrafluoroethylene film-based actuators powered by ionic fluid injection. The desired motion is encoded by integrating a mechanical controller, comprised of rigid-flexible materials. The robot's motion can be self-sensed using an ionic resistive sensor by detecting electrical resistance changes across its body. Our approach is demonstrated by fabricating three distinct soft-rigid hybrid robotic modules, each with unique degrees of freedom: translational, bending, and roto-translational motions. These modules connect to form a soft-rigid hybrid continuum robot with real-time shape-sensing capabilities. We showcase the robot's capabilities by performing object pick-and-place, needle steering and tissue puncturing, and optical fiber steering tasks.

Fabrication of mRNA encapsulated lipid nanoparticles using state of the art SMART-MaGIC technology and transfection in vitro

The messenger ribose nucleic acid (mRNA) in the form of Corona virus of 2019 (COVID-19) vaccines were effectively delivered through lipid nanoparticles (LNP) proving its use as effective carriers in clinical applications. In the present work, mRNA (erythropoietin (EPO)) encapsulated LNPs were prepared using a next generation state-of-the-art patented, Sprayed Multi Absorbed-droplet Reposing Technology (SMART) coupled with Multi-channeled and Guided Inner-Controlling printheads (MaGIC) technologies. The LNP-mRNA were synthesized at different N/P ratios and the particles were characterized for particle size and zeta potential (Zetasizer), encapsulation or complexation (gel retardation assay) and transfection (Fluorescence microscopy and ELISA) in MG63 sarcoma cells in vitro. The results showed a narrow distribution of mRNA-lipid particles of 200 nm when fabricated with SMART alone and then the size was reduced to approximately 50 nm with the combination of SMART-MaGIC technologies. The gel retardation assay showed that the N/P > 1 exhibited strong encapsulation of mRNA with lipid. The in vitro results showed the toxicity profile of the lipids where N/P ratio of 5 was optimized with > 50% cell viability. It can be concluded that the functional LNP-mRNA prepared and analyzed with SMART-MaGIC technologies, could be a potential new fabrication method of mRNA loaded LNPs for point-of-service or distributed manufacturing.

Fabrication Method of High-Porous Ceramic Shellular

Fabrication Method of High-Porous Ceramic Shellular

Effect of Al precursor’s properties on interactions with self-assembled monolayers for area selective deposition

Area selective deposition (ASD) is a high-precision atomic-level manufacturing technology that enables the development of bottom-up manufacturing methods in the future semiconductor field. The area selective deposition behavior of Al precursors on 1-octadecylthiol (ODT) passivated Cu/SiO2 surfaces was studied through experimental and theoretical analysis. The relationship between precursor steric hindrance, symmetry, penetration depth in ODT, and adsorption energy was elucidated. The loss of selectivity caused by different penetration depths of the precursor in ODT can be post-treated with acids or H2 plasma to remove the physisorption of precursor molecules between ODT chains, thereby improving the selectivity. Reliable ASD technology has been successfully applied to Cu/SiO2 patterns. Dimethylaluminum isopropoxide can selectively deposit about 10 nm of Al2O3 on SiO2 without detectable defects on the Cu area. This provides important insights into the choice of precursors in the ASD process and can extend its application to a wider range of device manufacturing schemes.

Investigation on in-situ tensile behaviors of 6061 aluminum alloy fabricated by wire additive friction stir deposition

Rod based additive friction stir deposition (R-AFSD) offers unique advantages for the integrated manufacturing of aluminum alloy near-net-shape large parts. However, the deposition process often faces issues like thick ends of raw material rods and difficulties in continuous feeding. In this study, wire based additive friction stir deposition (W-AFSD) was used for the solid state deposition of 3 mm diameter 6061 aluminum alloy wire. The microstructure evolution and mechanical properties of the deposit along the build direction were systematically characterized, clarifying the recrystallization mechanism and isotropy of the mechanical properties. In-situ scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) were used to study the deformation behavior of the deposit during in situ tensile testing, revealing a cooperative deformation mechanism involving grain rotation and intragranular slip. Results show that during in-situ tensile testing, the average rotation angle of five selected grains is 6.90°. Additionally, deposits with numerous grain boundaries due to recrystallization can hinder dislocation movement and pin the slip system within the grains during tensile testing. Due to the synergy of these mechanisms, the yield strengths of the longitudinal and transverse samples of the deposit are 183 MPa and 190 MPa, respectively, much higher than previously reported values. This article introduces a new solid state additive manufacturing method, offering new insights for efficient, high-strength continuous additive manufacturing of aluminum alloys and their deformation mechanisms.

Microstructure and strength of a 3D-printed Ti–6Al–4V alloy subjected to high-pressure torsion

Currently, one of the effective 3D printing methods is wire-feed electron-beam additive manufacturing (EBAM), which allows producing large-sized commercial billets from Ti–6Al–4V titanium alloy. However, Ti–6Al–4V alloy produced by this method demonstrates reduced strength properties. It is known that it is possible to increase the strength properties of metallic materials by refining their grain structure by high-pressure torsion (HPT). This work is aimed at studying the influence of high-pressure torsion on the microstructure, and mechanical strength of a structural Ti–6Al–4V titanium alloy produced by the wire-feed electron-beam additive manufacturing method. The microstructure of a 3D-printed Ti–6Al–4V alloy in the initial state, and after high-pressure torsion, was studied using optical, scanning and transmission electron microscopy. An EBSD analysis of the material in its original state was carried out. The microhardness of the material in the initial and deformed states was measured. Using the dependence of the yield strength on microhardness, the estimated mechanical strength of the material after processing by the high-pressure torsion method was determined. The microstructural features of the 3D-printed Ti–6Al–4V alloy after high-pressure torsion, which provide increased strength of this material, are discussed. The research results demonstrate that 3D printing, using the electron-beam additive manufacturing method, allows producing a Ti–6Al–4V titanium alloy with a microstructure unusual for this material, which consists of columnar primary β-grains with a transverse size of 1–2mm, inside of which martensitic α'-Ti needles are located. Thin β-Ti layers with a thickness of about 200nm are observed between the α'-Ti needles. Further deformation treatment of the alloy, using the high-pressure torsion method, allowed forming an ultrafine-grained structure in its volume, presumably consisting of α-grains with an average size of (25±10)nm. High-pressure torsion of the 3D-printed alloy allowed achieving rather high microhardness values of (448±5)НV0.1, which, according to the HV=2.8–3σy ratio, corresponds to the estimated yield strength of approximately 1460MPa.

Sound‐Based Assembly of Magnetically Actuated Soft Robots Toward Enhanced Release of Extracellular Vesicles

Magnetic soft robots have emerged as promising tools in biomedicine due to their wireless actuation, rapid response, and compatibility with biological systems. Despite the various innovative strategies proposed for their fabrication, they suffer from complex processes and limited cellular compatibility. Therefore, there is an urgent need to explore alternative approaches that are fast, mild, and highly tunable. Herein, a novel fabrication strategy for contactless assembly of soft‐robots is introduced for the first time. This technology exploits hydrodynamic instabilities at the free surface of a fluid layer, thus enabling the fabrication of centimeter‐scale robots featuring diverse structural properties. These features show a wide range of deformation modes in response to magnetic fields, including folding, bending, and expanding. Furthermore, the design and assembly of novel actuators with customized shapes as fish‐ and butterfly‐like structures is shown. The fabricated patterns exhibit different modes of motion under the influence of uniform magnetic fields. As a proof of concept, an innovative application of this technology combined with the proposed soft robots is represented by the enhanced release of extracellular vesicles. Altogether, this novel fabrication method along with the newly developed magnetic soft robots enables the manufacturing of high‐performance, multifunctional, and cytocompatible intelligent systems.

Comparing Low-Dose Carvedilol Continuous Manufacturing by Solid and Liquid Feeding in Self-Emulsifying Delivery Systems via Hot Melt EXtrusion (SEDEX)

Background/Objectives: This study compared two pilot scale continuous manufacturing methods of solid self-emulsifying drug delivery systems (SEDDSs) via hot melt extrusion (HME). Methods: A model poorly water-soluble drug carvedilol in low dose (0.5–1.0% w/w) was processed in HME either in a conventional powder form or pre-dissolved in the liquid SEDDS. Results: HME yielded a processable final product with up to 20% w/w SEDDS. Addition of carvedilol powder resulted in a non-homogeneous drug distribution in the extrudates, whereas a homogeneous drug distribution was observed in pre-dissolved carvedilol. SEDDSs were shown to have a plasticizing effect, reducing the HME process torque up to 50%. Compatibility between excipients and carvedilol in the studied ratios after HME was confirmed via DSC and WAXS, demonstrating their amorphous form. Solid SEDDSs with Kollidon® VA64 self-emulsified in aqueous medium within 15 min with mean droplet sizes 150–200 nm and were independent of the medium temperature, whereas reconstitution of Soluplus® took over 60 min and mean droplet size increased 2-fold from 70 nm to 150 nm after temperature increased from 25 °C to 37 °C, indicating emulsion phase inversion at cloud point. Conclusions: In conclusion, using Kollidon® VA64 and pre-dissolved carvedilol in SEDDS has shown to yield a stabile HME process with a homogenous carvedilol content in the extrudate.

Investigation of the Impact of Manufacturing Methods on Protein-Based Long-Acting Injectable Formulations: A Comparative Assessment for Microfluidics vs. Conventional Methods.

Therefore, rhCCL22-loaded poly(lactic-co-glycolic) acid (PLGA) microparticles were prepared by conventional homogenization and microfluidics methods. The resulting microparticles were analyzed comparatively, focusing on critical quality attributes such as microparticle size, size distribution, morphology, drug encapsulation efficiency, release kinetics, and batch-to-batch variations in relation to the manufacturing method. Our results demonstrated that the conventional method resulted in microparticles with denser surface porosity and wider size distribution as opposed to microparticles prepared by the microfluidics method, which could contribute to a significant difference in the drug-release kinetics. Additionally, our findings indicated minimal variation within batches for the microparticles prepared by the microfluidics method. Overall, this study highlights the comparative assessment of several critical quality attributes and batch variations associated with the manufacturing methods of protein-loaded microparticles which is crucial for ensuring consistency in efficacy, regulatory compliance, and quality control in the drug formulation manufacturing process.

Magnetic alginate microrobots with dual-motion patterns through centrifugally driven flow control

Mobile microrobots have gained increasing attention in biomedical applications because they can be precisely actuated to targeted positions in a tiny space. However, their use in biomedical applications is hindered by the costly and complicated fabrication method. Herein, a facile fabrication method is proposed to produce magnetic alginate microrobots with adjustable dimensions, including teardrop and tadpole shapes, via tunable centrifugally-driven flows. The formation of these microrobots is interpreted by finite element analysis, revealing that the transition between the dripping and jetting regimes of the flow alters the microrobot's shape. The dimensions of the microrobots are quantitatively analyzed based on the flow's extrusion velocity, controlled by nozzle diameters and revolution speeds. Incorporating magnetic nanoparticles into the alginate-based hydrogel enables the microrobots to exhibit distinct motion patterns under a magnetic field. The teardrop-like microrobot can reach a maximum rolling velocity of approximately 2.7 body length s−1 at 2 Hz, while the maximum stick-slip velocity of the tadpole-like microrobot reaches about 0.42 body length s−1 at 5 Hz, comparable to the existing bioinspired magnetic microrobots. These two motion patterns allow the microrobot to overcome obstacles and navigate in vertically constrained environments, respectively. Last, an ultrasound imaging system is deployed to monitor the locomotion and degradation of the microrobots, showing their potential for targeted drug delivery applications.

Laser-Induced Graphene for Advanced Sensing: Comprehensive Review of Applications.

Laser-induced graphene (LIG) and Laser-scribed graphene (LSG) are both advanced materials with significant potential in various applications, particularly in the field of sustainable sensors. The practical uses of LIG (LSG), which include gas detection, biological process monitoring, strain assessment, and environmental variable tracking, are thoroughly examined in this review paper. Its tunable characteristics distinguish LIG (LSG), which is developed from accurate laser beam modulation on polymeric substrates, and they are essential in advancing sensing technologies in many applications. The recent advances in LIG (LSG) applications include energy storage, biosensing, and electronics by steadily advancing efficiency and versatility. The remarkable flexibility of LIG (LSG) and its transformative potential in regard to sensor manufacturing and utilization are highlighted in this manuscript. Moreover, it thoroughly examines the various fabrication methods used in LIG (LSG) production, highlighting precision and adaptability. This review navigates the difficulties that are encountered in regard to implementing LIG sensors and looks ahead to future developments that will propel the industry forward. This paper provides a comprehensive summary of the latest research in LIG (LSG) and elucidates this innovative material's advanced and sustainable elements.

Transparent MXene Microelectrode Arrays for Multimodal Mapping of Neural Dynamics.

Transparent microelectrode arrays have proven useful in neural sensing, offering a clear interface for monitoring brain activity without compromising high spatial and temporal resolution. The current landscape of transparent electrode technology faces challenges in developing durable, highly transparent electrodes while maintaining low interface impedance and prioritizing scalable processing and fabrication methods. To address these limitations, we introduce artifact-resistant transparent MXene microelectrode arrays optimized for high spatiotemporal resolution recording of neural activity. With 60% transmittance at 550 nm, these arrays enable simultaneous imaging and electrophysiology for multimodal neural mapping. Electrochemical characterization shows low impedance of 563 ± 99 kΩ at 1 kHz and a charge storage capacity of 58 mC cm⁻² without chemical doping. In vivo experiments in rodent models demonstrate the transparent arrays' functionality and performance. In a rodent model of chemically-induced epileptiform activity, we tracked ictal wavefronts via calcium imaging while simultaneously recording seizure onset. In the rat barrel cortex, we recorded multi-unit activity across cortical depths, showing the feasibility of recording high-frequency electrophysiological activity. The transparency and optical absorption properties of Ti₃C₂Tx MXene microelectrodes enable high-quality recordings and simultaneous light-based stimulation and imaging without contamination from light-induced artifacts.

Recent Advances in Structure Design and Application of Metal Halide Perovskite-Based Gas Sensor.

Metal halide perovskites (MHPs) are emerging gas-sensing materials and have attracted considerable attention in gas sensors due to their unique bandgap structure and tunable optoelectronic properties. The past decade has witnessed significant developments in the gas-sensing field; however, their intrinsic structural instability and ambiguous gas-sensing mechanisms hamper their practical applications. Herein, we summarize the recent advances in MHP-based gas sensors. The physicochemical properties of MHPs are discussed at first. The structure design, including dimension design and engineering design, is overviewed as well as their fabrication methods, and we put forward our insights into the gas-sensing mechanism of MHPs. It is believed that enhanced understanding of gas-sensing mechanisms of MHPs are helpful for their application as gas-sensing materials, and structure design can enhance their stability, sensing sensitivity, and selectivity to target gases as gas sensors. Subsequently, the latest developments in MHP-based gas sensors are summarized according to their different application scenarios. Finally, we conclude with the current status and challenges in this field and propose future perspectives.

UV-assisted fluctuation-enhanced gas sensing by ink-printed MoS2 devices

In this work, MoS2 flakes were printed on ceramic substrates and investigated toward 1–10 ppm of nitrogen dioxide (NO2), 2–12 ppm of ammonia (NH3), and 2–12 ppm acetone (C3H6O) under UV light (275 nm). The structure of overlapping MoS2 flakes and UV light assistance affected high responsivity to NO2 when DC resistance was monitored, and superior sensitivity to NH3 was obtained from the low-frequency noise spectra. MoS2 exhibited response and recovery times in hundreds of seconds and stability throughout the experiments conducted within a few months. MoS2 sensor exhibited a resistance drift during the detection of a specific relaxation time. Subtracting the baseline burden with exponential drift exposed the direction of changes induced by oxidizing and reducing gases and reduced DL to 80 ppb, 130 ppb, and 360 ppb for NO2, NH3, and C3H6O, respectively. The fluctuation-enhanced sensing (FES) revealed that the adsorption of NO2 on MoS2 decreases the noise intensity, whereas adsorbed NH3 increases the fluctuations of current flowing through the sensor, and these changes are proportional to the concentration of gases. The noise responses for NO2 and NH3 were opposite and higher than DC resistance responses with subtracted baseline (an increase of 50% for 10 ppm of NO2 and an increase of more than 600% for 12 ppm of NH3), showing that FES is a highly sensitive tool to detect and distinguish between these two gases. This way, we introduce a simple and low-cost method of gas sensor fabrication using ink-printed MoS2 and the possibility of enhancing its sensitivity through data processing and the FES method.

(Invited) Epitaxial Process Development and Challenges for Advanced SiGe BiCMOS

The performance of an HBT is primarily influenced by 1D dopant profile obtained by CVD epitaxy. Typically, three epitaxial layers are required to construct an HBT: the collector, the intrinsic base, and the emitter. Collector layer can be grown by either NSEG or selective epitaxy. While the NSEG process is cost effective, it results in autodoping. Switching to selective epitaxy can mitigate autodoping but must be controlled to minimize faceting. The intrinsic base is critical to device performance, with boron positioning being a key factor. Incorporating substitutional carbon atoms into the SiGe lattice significantly reduces boron diffusion. By switching from SiH4 to Si2H6, three times more substitutional carbon incorporation in SiGe without interstitial C atoms at 550 °C is achieved. Below 600 °C, the co-flow approach is ineffective, necessitating a cyclic deposition-etch (CDE) approach to maintain selectivity. Comparisons between CDE and single deposition-etch (DE) approaches show that CDE degrades the monocrystalline SiGeC:B layer, resulting in high RMS roughness and degraded morphology. In contrast, the DE approach shows promising results with lower RMS roughness and no significant morphological degradation. The last epitaxial layer discussed is the emitter. Current fabrication methods involve non-selective Si:As deposition at growth temperatures above 600 °C, resulting in polycrystalline Si:As deposition on dielectrics and monocrystalline Si:As growth on silicon. A novel process developed at 550 °C using Si2H6 as silicon precursor yields monocrystalline emitter by amorphous deposition on dielectrics followed by solid phase epitaxial regrowth. However, this process exhibits TED of arsenic, making it currently not viable.

Characterizing sliding wear behavior of A1100/AlFe (p) composites produced via repeated fold-forging and annealing

Abstract Aluminum matrix/aluminum-iron intermetallic composite materials pose challenges in plastic processing due to the susceptibility of hard intermetallic compound particles to fracture. This study introduces a novel fabrication method involving pure iron mesh, hot-dip aluminum plating, and solidification. Through ten consecutive folding, forging, and intermediate annealing cycles, aluminum matrix and iron undergo diffusion, leading to the formation of Fe2Al5 and FeAl3 interface reaction layers, as confirmed by X-ray diffraction analysis. Subsequent forging cycles cause the breakage or detachment of Fe2Al5 and FeAl3 particles from the interface, resulting in the formation of large-sized Fe2Al5 and small-sized Fe2Al5 intermetallic particles. FeAl3 intermetallic particles are observed via microscopic examination. These particles can be uniformly dispersed within the aluminum matrix through plastic flow, enabling the successful fabrication of A1100/Fe2Al5 and AlFe3 composite sheets. Furthermore, the study investigates the impact of intermetallic compound content, sliding speed, and forward load on the dry sliding wear of A1100/FeAl composites. It is found that Fe2Al5 and AlFe3 intermetallic compound particles effectively mitigate adhesive wear, plowing, and oxidative wear of the composites. With an AlFe intermetallic compound content of 4.3 wt.%, the volume wear rate remains low under conditions corresponding to PV = 56.652 (equivalent to a normal load of 19.6 kPa and a sliding speed of 2.87 m s−1).

Microstructural refinement of an Al-Ce-Mg alloy via Shear Assisted Processing and Extrusion

Al-Ce alloys have attracted recent interest because of their high thermal stability due to the low solubility of Ce in the Al matrix. The Al11Ce3 eutectic phase gives excellent strain hardening behavior and moderate high-temperature strength in the as-cast state. However, its strengthening effect is limited by its coarse as-cast structure. Therefore, alternative manufacturing methods such as additive manufacturing or equal channel angular pressing have been applied to refine the Al11Ce3 phase to good effect. However, these techniques are both expensive and time-consuming. Therefore, this study aims to use Shear Assisted Processing and Extrusion (ShAPE), an emerging solid phase processing technique that is more easily scalable than the previously mentioned methods. ShAPE can produce useful cross-sections of an Al-8Ce-4Mg alloy while refining the Al11Ce3 phase to produce a higher strength material. It was found that a low temperature ShAPE process can improve the room temperature yield strength by ∼60 % compared to a binary Al-4Mg alloy. Additionally, the high-temperature yield strength of the Al-Ce alloys increased by 20 %, with a simultaneous 15 % improvement in ductility compared to the binary Al-Mg alloy. These results highlight the potential for ShAPE as a processing technique for Al-Ce alloys.

Design and performance analysis of a composite flexure hinge based on micro-ultrasonic powder molding

This paper presents a new type of flexure hinge and its fabrication method based on micro-ultrasonic powder molding (micro-UPM). A right-circular notch-type flexure hinge (RFR-RC hinge) comprising an aluminum alloy 7075 (Al 7075) rigid structure and a polypropylene (PP) flexible structure was designed and fabricated. This composite RFR-RC hinge was experimentally studied, and the results helped confirm that the hinge could be considered a complete single structure; the flexible structure had a good forming quality, and the interlocking performance met normal use requirements. The RFR-RC hinge was evaluated in terms of its motion range, stiffness, and stiffness ratio through finite element analysis (FEA) and then compared with a single-material right-circular flexure hinge (RC hinge). The RFR-RC hinge provided a significantly wider operation range with a lower actuation force than the Al 7075-RC hinge and a higher motion pureness and accuracy than the PP-RC hinge. The motion stiffness obtained from the FEA was in agreement with the bending test results, thus validating the FEA results to some extent. From the bending tests, the elastic and total motion ranges of the RFR-RC hinge were found to be 0.068 rad and 0.202 rad, respectively. Finally, the fabrication of a 3-RRR compliant parallel mechanism and four typical applications were taken as examples to demonstrate that the RFR-RC hinge and its fabrication method have a wide range of applications.

A Review of Non-Powder-Bed Metal Additive Manufacturing: Techniques and Challenges.

Metal additive manufacturing has significantly evolved since the 1990s, achieving a market valuation of USD 6.36 billion in 2022, with an anticipated compound annual growth rate of 24.2% from 2023 to 2030. While powder-bed-based methods like powder bed fusion and binder jetting dominate the market due to their high accuracy and resolution, they face challenges such as lengthy build times, excessive costs, and safety concerns. Non-powder-bed-based techniques, including direct energy deposition, material extrusion, and sheet lamination, offer advantages such as larger build sizes and lower energy consumption but also encounter issues like residual stress and poor surface finish. The existing reviews of non-powder-bed-based metal additive manufacturing are restricted to one technical branch or one specific material. This survey investigates and analyzes each non-powder-bed-based technique in terms of its manufacturing method, materials, product quality, and summary for easy understanding and comparison. Innovative designs and research status are included.