Search Results (66)

Additively manufactured implants may be vulnerable to localized corrosion within narrow gaps, yet the critical crevice geometry and the effectiveness of multilayer coatings under such conditions remain insufficiently understood. This study compares the crevice-corrosion behavior of direct metal laser sintering (DMLS) and conventionally wrought mill-annealed Ti-6Al-4V alloys and evaluates a hierarchical coating comprising a plasma electrolytic oxidation (PEO) layer, a polycaprolactone (PCL) seal, and a porous polylactic acid (PLA) breath-figure topcoat. Electrochemical testing was conducted in simulated body fluid (SBF, pH 7.4, 37 °C) using a tapered crevice cell, followed by microscopic, compositional, and topographical analyses. Both uncoated alloys exhibited passive film breakdown; however, the wrought alloy subsequently repassivated, whereas the DMLS alloy underwent sustained localized attack within the critical crevice gap of ~11.4 µm. The transpassive potentials for DMLS and wrought Ti-6Al-4V with PEO/PCL/PLA coating system were 1.32 V and 1.45 V, respectively. Despite the intrinsic porosity and interfacial gaps of the coating, no crevice-type damage was detected in DMLS Ti-6Al-4V. PCL/PLA hierarchy increased the PEO pore resistance to ~3.5 kΩ cm², reduced the passive current density by ~2 times, and increased the PEO barrier layer resistance to 10⁷ Ω cm². Full article

This research focuses on the development of a robotic cell test bench for manufacturing variable-geometry tubular parts with minimal manual intervention. The system integrates dual-arm manipulation with cutting and laser-welding stations and was evaluated in collaboration with an industrial partner with strict requirements on joint strength and sealing performance. The experimental investigation characterized the influence of key welding process parameters, particularly the robot end-effector travel speed (mm/s) and laser power (W), on the mechanical performance of the welded joints. These parameters were subsequently used to manufacture representative three-dimensional duct geometries. In addition, preliminary sealing evaluations were used to assess the ability of the welded components to withstand internal pressures. These results highlight the influence of mechanical components, geometries, and material behavior, as well as the need for advanced digital tools. A preliminary automated path-generation methodology is introduced to support adaptable robot trajectories. Overall, the results support the feasibility of the integrated robotic manufacturing concept while identifying the additional developments required before fully automated production can be achieved. Full article

Waste-to-hydrogen technology requires the involvement of new material development and performance evaluation for additive manufacturing (AM). Metal 3D printing is a very good possible alternative and is delivering results visible in the circular-economy environment. By using the AM technique, complex operations are avoided when combining the individual components, which is a typical disadvantage in obtaining composite materials; such samples are prepared with only one operation from the starting melt, which is chemically defined. Pyrolysis rotary kiln sealing rings are to be upgraded with several different microstructure coatings in order to improve the surface performance. The surface topology is aimed to be fine, dense and smooth. Also, the target characteristics are a low friction coefficient and a high hardness value, suggesting enhanced wear resistance. For elevated temperatures, 900 °C is selected for cobalt-based superalloy Stellite types with particle reinforcement. Two possibilities for advanced materials production are proposed with the Directed Energy Deposition Plasma Arc (DED-arc) and Laser Directed Energy Deposition (DED-LB). The shell of the rotary kiln sealing ring is made of stainless steel as the base, with the coating overlaid. Selected mixtures in powder form with defined composition are applied. For the DED-arc, commercially available Stellite 6 (Deloro Stellite^® 6) and 20 vol% WC particles with a grain size of 63–150 µm were employed. For the DED-LB, we employed TRIBALOY^® T-800 (Kennametal Stellite^TM) with 25 vol% TiC and a mesh size of −100/+325 (particle diameter between 45 and 150 µm). After the representative samples were metallurgically bonded with the base stainless steel, the relevant properties were obtained. Manufactured samples are compared in terms of microstructures and mechanical properties. Analysis of structure: Intermetallic carbides that formed on the cobalt basis make the composite harder and increase the plasticity in a defined direction. The hypoeutectic structures of Stellite 6 + 20% WC consist of dendrite and interdendrite eutectic. It is observed that with an increase in WC volume fraction, the size of the dendrites becomes finer, and the amount of eutectic structure is increased. For the TRIBALOY^® T-800 with TiC, we obtained relatively smaller grain sizes. The roughness values for the tested samples with WC were initially Ra = 0.8 µm, increasing up to Ra = 3.44 µm after the wear test, whereas for the TiC, they were slightly lower. Microhardness testing revealed increased values compared to the base stainless steels. Advanced sensor analysis with acoustic emission (AE) and electrical contact resistance (ECR) also showed the properties of the new materials. Customizable coatings with tailored properties were deposited by DED-arc and DED-LB. From the tests performed, a new technological procedure for the production of novel pyrolysis rotary kiln sealing rings is proposed. The microhardness, roughness, microstructure and abrasive wear-resistant response of the metallic composite material were examined in order to characterize the stable multiphase system. Full article

Auxetic polymers offer a route to deformation-activated sealing by transforming axial deformation into lateral expansion, enabling controlled conformity and retention within perforated structures. This paper presents the design-space-guided optimisation of a multi-material polymeric auxetic plug for mechanically activated sealing of circular perforation surrogates relevant to military ground-vehicle structures using a controlled thin-wall surrogate validation framework. The sealing combines an SLA-printed Elastic 50A photopolymer auxetic body with TPU 95A load-transfer and priming components. A parameterised re-entrant unit cell was optimised using response-surface design of experiments coupled with nonlinear finite-element analysis. The optimised geometry, with a height of 6 mm, length of 5 mm, strut thickness of 1.25 mm, and re-entrant angle of 31°, achieved a predicted negative Poisson’s ratio of −2.66 under 20% axial strain. Experimental validation using additively manufactured unit cells confirmed the intended auxetic deformation response. The optimised structure was then integrated into a multi-material plug and tested against a solid polymer benchmark, achieving sealing to approximately 22 kPa with improved anchoring across the tested 22–25 mm perforation range. The results establish a mechanism-driven pathway from polymer auxetic unit-cell optimisation to plug-level pressure-sealing performance, demonstrating the potential of multi-material auxetic architectures as deformation-activated sealing systems for temporary repair of perforated military ground-vehicle structures. Full article

This review provides an overview of the latest advances in bionic vascular self-healing cement, focusing on vascular design, fabrication, selection of healing agents, transport and curing mechanisms, and performance evaluation methods. Compared to systems based on microcapsules and microorganisms, vascular networks enable directed and efficient transport of healing agents and repeated healing; however, the presence of hollow channels results in an inevitable loss of mechanical properties. Additive manufacturing, in situ printing based on Pickering emulsions, and direct printing of cement-based or multi-material systems have enhanced geometric flexibility and scalability. However, issues such as channel quality, polymer-cement interface stability, and on-site quality control remain unclear. Regarding the selection of healing agents, epoxy resin systems are generally more suitable for structural healing, polyurethanes are suitable for rapid sealing and wide or irregular cracks, while silicate healing agents are suitable for healing where cement compatibility and durability are prioritized. The most critical research gap lies in the lack of standardized, full-scale, multi-cycle, and long-term environmental validation, which limits the practical engineering application of vascular self-healing technology. Future research should prioritize the integrated design of various performance metrics, the long-term durability of polymers, standardized benchmark testing, and validation based on actual service conditions. Full article

Fused filament fabrication (FFF) is one of the most widely adopted additive manufacturing methods for thermoplastic polyurethane (TPU)-based soft pneumatic actuators, enabling low-cost fabrication, geometric customization, embedded pneumatic architectures, and rapid prototyping for soft robotic systems. However, despite these advantages, achieving reliable airtightness remains a major challenge due to process-induced anisotropy, interlayer voids, incomplete filament fusion, residual porosity, seam discontinuities, material permeability, and interface-related leakage. These defects can significantly reduce pressure retention, actuation efficiency, deformation repeatability, and long-term pneumatic reliability. This review systematically examines the dominant leakage mechanisms affecting FFF-printed soft pneumatic actuators and comparatively analyzes fabrication approaches, TPU material systems, geometric design factors, post-processing methods, sealing strategies, and leakage characterization techniques. Representative experimental observations, including pressure-decay testing, submerged-bubble visualization, microscopy, and localized thermal surface treatment, are also discussed to connect the findings reported in the literature with experimentally observed leakage behavior. Emerging analytical leakage models, sensing technologies, AI-assisted predictive monitoring, and digital-twin-enabled manufacturing frameworks are reviewed as promising approaches for developing leakage-aware soft robotic systems. The review highlights current limitations related to standardized leakage testing, cyclic durability evaluation, scalable sealing strategies, and intelligent manufacturing integration. Overall, airtightness is identified as a coupled material-process-geometry challenge that must be systematically addressed to improve the reliability, scalability, and long-term operational stability of next-generation TPU-based soft pneumatic actuators. The review was conducted following the PRISMA-ScR framework and includes 248 studies published between 2017 and 2026. Full article

This research assessed the impact of probiotic culture incorporation and the sous vide manufacturing method on the physicochemical, textural, colorimetric, and microbiological characteristics of yoghurts during the storage duration. The trials used conventional and sous vide manufacturing techniques using probiotic and classical starting cultures, and the products were analyzed throughout the storage period. The findings indicate that the use of probiotic cultures significantly enhances organic acid synthesis. This rise resulted in a lower pH (≈4.54) and increased titratable acidity (≈1.60%). Furthermore, it has been shown that the total organic acid concentration, mostly lactic acid, rose (≈24,045 mg/kg), while concurrently, the yeast-mold load decreased (≈2.69 log CFU/g). Throughout the storage duration, a reduction in pH and an elevation in acidity and microbial activity were seen in all samples (p < 0.05). The sous vide manufacturing method, due to regulated heat processing and a sealed system design, has decreased syneresis (≈5.65%) and an enhanced dry matter content (≈13.09%). This circumstance has resulted in the development of a more uniform gel structure, thereby enhancing the textural attributes. Color investigations indicated that the integration of probiotics and sous vide decreased the ΔE values, and in samples with ΔE < 3, the color change was imperceptible to the human eye. In conclusion, the simultaneous application of probiotic culture addition and the sous vide production technique has exhibited a synergistic effect on acidity development, microbial stability, textural properties, and color stability, indicating its efficacy in producing higher-quality functional yoghurt. Full article

Effective thermal insulation of cryogenic liquid hydrogen (LH₂) storage tanks remains a critical engineering challenge, as conventional vacuum-based or monolithic systems are constrained by manufacturing complexity, mechanical vulnerability, and poor geometric adaptability. This study presents the design and numerical verification of a four-layer octagonal composite thermal shield fabricated via additive manufacturing: an AA5083 structural layer (5 mm), a boron nitride-doped ceramic plate (1 mm), up to 290 stacked graphene sheets in a sealed compartment, and an outer Fe₃S₄-TiO₂ nanocomposite layer (~30 µm). Steady-state and transient FEA in ANSYS evaluated three convective boundary conditions (h = 10, 15, and 20 W/m²·K), with the inner wall fixed at 20 K. Temperature distributions remained essentially invariant across all cases (20 K inner, ~20.12 K outer), confirming that thermal performance is governed by the multilayer architecture rather than convective intensity. The shield achieved a mean heat flux of 1684 W/m², R_total ≈ 0.163 m²K/W, and a boil-off rate of 13.9 g/hour. Comparative FEA against NASA US9617069 (q = 193.35 W/m²) and JP2018-119634A (q = 37.975 W/m²) highlights the compactness advantage of the proposed 6 mm shield; the coupled thermo-structural assessment yielded a safety factor of 64,182, confirming elastic-regime operation at 20 K. Full article

Photopolymer-based additive manufacturing processes such as stereolithography (SLA) offer high precision and surface quality but generate cured thermoset waste that is typically non-recyclable. In microgravity environments, conventional recycling approaches—based on gravitational settling, open solvent handling, and buoyancy-driven degassing—are ineffective, motivating the development of fully contained, gravity-independent material recovery systems for on-orbit manufacturing. This work presents a conceptual, design-stage closed-loop system architecture for recycling photopolymer resins in microgravity. The system integrates eight subassemblies enabling mechanical fragmentation, solvent-assisted dissolution, filtration, low-pressure degassing, pressurized storage, injection molding, and ultraviolet curing. A hermetically sealed dual-screw shredder produces resin fragments of 1–3 mm, suitable for dissolution. Gas removal is achieved through low-vacuum degassing at approximately 0.1–0.3 bar, with characteristic residence times of 5–10 min, ensuring stable processing prior to injection. Material transport is governed by mechanical conveyance and controlled pressure, eliminating reliance on gravity. The architecture maintains full containment of solids, liquids, and vapors throughout the process. Supported by engineering design considerations, the system establishes a microgravity-compatible pathway for closed-loop recycling of SLA materials. Experimental validation is planned in future work. Full article

Polyether Ether Ketone (PEEK) is a high-performance polymer increasingly utilized in additive manufacturing due to its exceptional thermal, chemical, and mechanical properties. Thus, they are used to produce aerospace brackets, fuel system parts, seals, compressor valve plates, etc. This study investigates the mechanical performance of both neat PEEK and glass fiber-reinforced PEEK (PEEK + GF) composites fabricated via fused deposition modeling (FDM). The effects of print speed, print orientation, and post-heat treatment were systematically evaluated. Among the tested orientations, the 0° print direction with post-heat treatment at 250 °C yielded highest tensile strength of ~80 MPa, outperforming the 45° and 90° orientations. Print speeds ranging from 5 to 20 mm/s and annealing temperatures between 250 °C and 300 °C significantly influenced material properties. For neat PEEK, both tensile strength and microhardness improved with increasing print speed and post-heat treatment, peaking at 20 mm/s and 250 °C. However, annealing at 300 °C led to performance degradation, attributing to gas-induced porosity within the material. The PEEK + GF composites achieved a maximum ultimate tensile strength (UTS) of approximately 83 MPa under the same optimal conditions (20 mm/s print speed and 250 °C post-treatment). This enhancement is attributed to improved fiber alignment along the print path, increased crystallinity, and superior interfacial bonding. Notably, the composites did not exhibit the microstructural damage observed in neat PEEK at the higher annealing temperature. Full article

Background/Objectives: Lithium disilicate (LD) veneers are widely used for minimally invasive anterior rehabilitation because of their favorable optical and mechanical properties. Fully digital workflows have been proposed as alternatives to conventional milling. These approaches combine computer-aided design and manufacturing (CAD/CAM) with 3D-printed burn-out patterns and subsequent heat pressing of LD ingots. However, clinical documentation of multi-unit anterior cases fabricated exclusively through this additive-plus-pressing route remains scarce. This case report aims to describe a fully digital additive-plus-pressing workflow for four maxillary anterior LD veneers and to report 48-month clinical outcomes. Case Presentation: A 52-year-old female presented with esthetic concerns involving the maxillary central and lateral incisors (teeth 11, 12, 21, and 22). After clinical and radiographic evaluation, a minimally invasive veneer-based rehabilitation was planned. Preparations were performed under magnification, and immediate dentin sealing was applied. Digital impressions were obtained with an intraoral scanner, and veneers were designed using CAD software(Exocad DentalDB 3.0 Galway (Exocad GmbH, Darmstadt, Germany). Castable resin patterns were 3D-printed, invested, and heat-pressed using LD ingots, followed by finishing and glazing. Adhesive cementation was performed under rubber dam isolation after hydrofluoric acid etching and silanization of the intaglio surfaces and conditioning of the tooth substrates according to the adhesive protocol, using a dual-cure resin cement. At the 48-month follow-up, all veneers remained intact, with clinically acceptable marginal adaptation, stable color and surface gloss, and no signs of secondary caries or marginal discoloration. The patient reported sustained esthetic satisfaction and comfortable function without postoperative sensitivity. Conclusions: This single-patient report suggests that a fully digital additive-plus-pressing workflow may be clinically viable for high-demand anterior LD veneers, providing favorable medium-term esthetics and patient-centered outcomes with no technical or biological complications. The reproducible protocol described may facilitate the integration of 3D printing and heat pressing into digital veneer rehabilitation and supports further controlled clinical investigations. Full article

This paper investigates the feasibility of manufacturing hydraulic fittings using additive manufacturing (AM) technologies, specifically Fused Deposition Modeling (FDM) and Stereolithography (SLA). The study addresses the environmental challenge of material waste in conventional fitting production by exploring 3D printing as an alternative manufacturing method. Hydraulic fittings were designed using CAD software: SolidWorks 2022 and fabricated using FDM with PETG (Polyethene Terephthalate Glycol) material and SLA with UV-sensitive photopolymer resin. In present studies, on-destructive leak testing was conducted in accordance with PN-EN 1254-4 and PN-EN 1254, at pressures ranging from 0.1 to 1.0 bar. Dimensional accuracy analysis revealed shrinkage of approximately 1% for SLA-printed parts and 2% for FDM-printed parts. Microscopic examination at 50× and 80× magnification showed superior thread quality in SLA samples compared to FDM, which exhibited visible layer separation and material porosity. Leak testing demonstrated that while the brass reference fitting maintained complete seal integrity, both 3D-printed variants failed to achieve leak tightness under operational pressures, with structural failure occurring at 1.0 bar during tightening. The study showed that FDM with PETG material and SLA with UV-sensitive photopolymer resin, despite achieving acceptable dimensional tolerances (±1–2%), do not meet hydraulic leak tightness requirements at pressures exceeding 0.5 bar in their raw state after printing. The results suggest that alternative material formulations (e.g., carbon fiber-reinforced PEEK for FDM or epoxy engineering resins for SLA) warrant further investigation. Potential avenues for improvement include advanced surface treatment, optimization of printing parameters, and modifications to thread geometry to reduce interthread gaps. Full article

Biopolymer adhesives are moving toward frontline use in medicine and manufacturing as the limitations in some petrochemical systems, including cytotoxicity, challenges in wet adhesion for specific families of synthetic resins and formaldehyde emissions associated with amino-formaldehyde materials are becoming increasingly difficult to accept. This review integrates mechanisms, material classes and quantitative performance across biopolymer-based adhesives. We focus on architectures that combine permanent covalent anchoring with reversible, energy-dissipating bonds and on how functional group density, crosslink density, microstructure and additives act as design knobs for wet performance, durability and degradation. Across biomedical applications, chitosan, alginate, gelatin and related hydrogels achieve wet lap-shear strengths on the order of tens of kilopascals, cut liver-bleeding times by roughly half, provide strong antibacterial activity and close diabetic wounds by about 92 percent by day 14. Thermoresponsive alginate–gelatin sealants exceed clinically relevant burst pressures and microneedle patches withstand more than 120 mmHg while sealing arteries in under a minute. In industrial settings, dialdehyde-based starch resins deliver 0.83 to 1.05 MPa dry shear and maintain strength after water immersion while meeting stringent emission classes, and silane-modified nanocellulose in urea–formaldehyde markedly reduces free formaldehyde without sacrificing the internal bond. We conclude by identifying priorities for standardized wet testing, and lifetime matching of strength and degradation that can support large-scale clinical and industrial translation. Full article

Surface roughness is a quality-critical attribute in industrial zinc phosphating, directly affecting sealing performance, coating uniformity, dimensional tolerances, and first-pass production yield in automotive pretreatment lines. While the chemical mechanisms of phosphate coating formation are well understood, the translation of this knowledge into statistically defensible, production-scale prioritization of bath chemistry control levers under real manufacturing constraints remains limited, particularly with respect to surface roughness stability and its environmental implications. This study investigates surface roughness control in a fully operational industrial zinc phosphating line by systematically evaluating the effects of pickling acid chemistry (H₂SO₄ versus H₃PO₄), dissolved ferrous iron (Fe²⁺) levels in pickling and phosphating baths, and nitrate accelerator dosage. A Taguchi L16 (2⁴) experimental design was implemented under real manufacturing constraints. Surface roughness (Rz) was measured in accordance with ISO 4287 and analyzed using a general linear model supported by partial effect size estimation (ηp²) and bootstrap confidence intervals. This approach enables statistically robust ranking of dominant and secondary control parameters, rather than qualitative trend confirmation alone. The robustness of statistically identified trends was independently verified using paired measurements from 25 production components, while scanning electron microscopy provided qualitative mechanistic support. The results demonstrate that pickling acid chemistry and nitrate accelerator dosage are the dominant control parameters governing surface roughness stability, whereas Fe²⁺ concentration does not act as a primary independent driver within the defined Fe²⁺ concentration ranges investigated in this study, but contributes through interaction-dependent mechanisms. Phosphoric acid pickling combined with nitrate acceleration consistently yields lower and more stable roughness values. In addition, roughness-related nonconformities were translated into product carbon footprint outcomes using an ISO 14067–aligned, gate-to-gate framework with Monte Carlo uncertainty analysis, explicitly quantifying the carbon footprint penalties associated with quality-driven rework and external return logistics under industrial production conditions. Full article

The invention concerns a screw-driven shredder for solid photopolymer resin, designed for both terrestrial use and prospective deployment in microgravity environments. The system addresses the need for efficient recycling of cured photopolymer waste generated by stereolithography (SLA) 3D printing—a process not yet implemented in orbit, but envisioned as part of future closed-loop additive manufacturing systems aboard space stations or lunar habitats. The proposed device is a compact, hermetically sealed mechanical unit composed of ten subassemblies, featuring two counter-rotating screw shafts equipped with carbide milling inserts arranged helically to achieve uniform and controlled fragmentation of solid SLA residues. The shredding process is supported by a pressurized inert fluid circuit, utilizing carbon dioxide (CO₂) as a cryogenic working medium to enhance cutting efficiency, reduce heat accumulation, and ensure particle evacuation under microgravity conditions. Studies indicate that CO₂-assisted cooling can reduce tool-tip temperature by 10–30 °C, cutting forces by 5–15%, and electrical power consumption by 5–12% while extending tool life by up to 50%. This invention thus provides a key component for a future in situ photopolymer recycling loop in space while also offering a high-efficiency shredding solution for Earth-based photopolymer waste management in additive manufacturing. Full article