This study demonstrates the feasibility of utilizing an allograft material derived from human cadaver cortical bone as a source for Digital Light Processing-based additive manufacturing. The calcined allograft medical product is milled and transformed into a photopolymerizable feedstock for 3D printing of samples intended for property measurement and scaffold-like designs. All printed samples undergo sintering at 1300 degrees C for 1 h. Comprehensive analyses, including X-ray diffraction spectroscopy, energy-dispersive spectroscopy, biodegradation testing, and MTT cell viability assays, are conducted on the calcined material both before and after the additive manufacturing process. The sintered material exhibits mechanical properties comparable to synthetic hydroxyapatite, with a relative density of 81.5 %, compressive strength of 75.8 MPa, tensile strength of 12 MPa, Young's modulus of 3.08 GPa, and Vickers hardness of 0.55 GPa. No significant changes in phase or chemical composition are detected as a result of material sintering. The measured average calcium-to-phosphorus (Ca/P) ratio of 1.65 confirms the calcium-deficient nature of bone mineral. The sintered samples demonstrate promising degradation potential in a TRIS-HCl buffer solution (pH 7.4) and exhibit an average cell viability of 87.7 % (with a maximum of 97.7 %) in the MTT cell viability assay. These findings position the allograft material as an excellent candidate for the fabrication of complex bone implants and provide valuable baseline data, derived from human bone mineral, for enhancing synthetic calcium-phosphate ceramics.

The increasing use of medical implants in various areas of medicine, particularly in orthopedic surgery, oncology, cardiology and dentistry, displayed the limitations in long-term integration of available biomaterials. The effective functioning and successful integration of implants requires not only technical excellence of materials but also consideration of the dynamics of biomaterial interaction with the immune system throughout the entire duration of implant use. The acute as well as long-term decisions about the efficiency of implant integration are done by local resident tissue macrophages and monocyte-derived macrophages that start to be recruited during tissue damage, when implant is installed, and are continuously recruited during the healing phase. Our review summarized the knowledge about the currently used macrophages-based in vitro cells system that include murine and human cells lines and primary ex vivo differentiated macrophages. We provided the information about most frequently examined biomarkers for acute inflammation, chronic inflammation, foreign body response and fibrosis, indicating the benefits and limitations of the model systems. Particular attention is given to the scavenging function of macrophages that controls dynamic composition of peri-implant microenvironment and ensures timely clearance of microorganisms, cytokines, metabolites, extracellular matrix components, dying cells as well as implant debris. We outline the perspective for the application of 3D systems for modelling implant interaction with the immune system in human tissue-specific microenvironment avoiding animal experimentation.

The diffusion stability of a single cavitation bubble in a spherical liquid cell surrounded by an infinite elastic solid is considered. The time-periodic pressure in the solid far away from the liquid cell is used as an external driving, which initiates bubble oscillations along with the gas diffusion process in the bubble-in-cell system. The work is based on the engineering approximation according to which the bubble growth/reduction is considered on average, assuming that during the period of the external driving the mass of gas in the bubble does not noticeably change. This theory predicts the existence of stably oscillating bubbles in confined liquid undergoing an external driving force. Three possible diffusion regimes are revealed: 1) total bubble dissolution, 2) partial bubble dissolution, and 3) partial bubble growth, where the last two regimes provide the diffusion stability in the bubble-in-cell system. The parametric study of the influence of the gas concentration dissolved in the liquid on the resulting stable bubble size is conducted. The obtained results are compared with the results for the case of the stable bubble oscillations in the pressure sound field in a bulk (infinite) liquid. The theoretical findings of the present study can be used for improvement of the modern applications of ultrasound technology.

Laser powder bed fusion provides freedom for producing complex shapes from a variety of alloys. Moreover, it also gives the possibility to manipulate the chemical composition of material during the printing process to improve its properties. The widely use 316L stainless steel exhibits the good corrosion resistance, high ductility, but comparably low strength characteristics. Various approaches can be applied to relax this limitation. Herein we use boron-containing additives to the feedstock powder for improving the microhardness of 316L stainless steel. Boron was found to reduce the porosity of the printed materials and increases the microhardness from 210 to 350 HV. The ultimate tensile strength doubled to 1045 MPa. Such findings allow using the modified 316L steel for tool printing.

Permeability measurements of engineering textiles exhibit large variability as no standardization method currently exists; numerical permeability prediction is thus an attractive alternative. It has all advantages of virtual material characterization, including the possibility to study the impact of material variability and small-scale parameters. This paper presents the results of an international virtual permeability benchmark, which is a first contribution to permeability predictions for fibrous reinforcements based on real images. In this first stage, the focus was on the microscale computation of fiber bundle permeability. In total 16 participants provided 50 results using different numerical methods, boundary conditions, permeability identification techniques. The scatter of the predicted axial permeability after the elimination of inconsistent results was found to be smaller (14%) than that of the transverse permeability (∼24%). Dominant effects on the permeability were found to be the boundary conditions in tangential direction, number of sub-domains used in the renormalization approach, and the permeability identification technique.

Abstract: The centrepiece of this analytical review is the metabolism of hydroxyapatite in its natural, bone, and synthetic forms, where the mitochondria-mediated mechanism may serve as the leading mechanism. The possibility that osteoblast mitochondria play an important role in the initial stages of bone mineralisation is discussed. Furthermore, the paper highlights the key role of mitochondria in the metabolism of synthetic hydroxyapatite.Differences between the results of in vivo and in vitro studies using synthetic hydroxyapatite of different morphologies are also detailed. It is noted that long-term infiltration with immune cells and in vivo studies are necessary to adequately evaluate hydroxyapatite as a bone-plastic material.Particular attention is given to the interaction of hydroxyapatite with immune cells and its ability to affect the ribosomes and mitochondria of cells. Due to its mechanical properties, scalability and potential use for the treatment of extensive bone defects of tumor origin, hydroxyapatite is a promising material.This study also highlights the importance of further development of in vitro research methods in the context of their biomimeticity. Overall, this work offers a theoretical direction for future studies of hydroxyapatite as a bone grafting material and emphasises the value of in vivo studies.

The choice of a manufacturing process, raw materials, and process parameters affects the quality of produced pre-consolidated tapes used in thermoplastic pultrusion. In this study, we used two types of pre-consolidated GF/PP tapes-commercially available (ApATeCh-Tape Company, Moscow, Russia) and inhouse-made tapes produced from commingled yarns (Jushi Holdings Inc., Boca Raton, FL, USA)-to produce pultruded thermoplastic Ø 6 mm bars and 75 mm × 3.5 mm flat laminates. Flat laminates produced from inhouse-made pre-consolidated tapes demonstrated higher flexural, tensile, and apparent interlaminar shear strength compared to laminates produced from commercial pre-consolidated tapes by as much as 106%, 6.4%, and 27.6%, respectively. Differences in pre-consolidated tape manufacturing methods determine the differences in glass fiber impregnation and, thus, differences in the mechanical properties of corresponding pultruded composites. The use of commingled yarns (consisting of matrix and glass fibers properly intermingled over the whole length of prepreg material) makes it possible to achieve a more uniform impregnation of inhouse-made pre-consolidated tapes and to prevent formation of un-impregnated regions and matrix cracks within the center portion of the fiber bundles, which were observed in the case of commercial pre-consolidated tapes. The proposed method of producing pre-consolidated tapes made it possible to obtain pultruded composite laminates with larger cross sections than their counterparts described in the literature, featuring better mechanical properties compared to those produced from commercial pre-consolidated tapes.

The printability of artificial defects inside the additively manufactured laser powder bed fusion (LPBF) 316L stainless steel is investigated. The printing parameters of the LPBF process are optimized to produce artificial defects with reproducible sizes at desired positions while minimizing redundant porosity. The smallest obtained artificial defect is 90 μm in diameter. The accuracy of the geometry of the printed defect depends on both the height and the diameter in the input model. The effect of artificial defects on the very‐high‐cycle fatigue (VHCF) behavior of LPBF 316L stainless steel is also studied. The specimens printed with artificial defects in the center are tested under VHCF using an ultrasonic machine. Crack initiation is accompanied by the formation of a fine granular area (FGA), typical of VHCF. Despite the presence of relatively large artificial defects, FGA formation is observed around accidental natural printing defects closer to the surface, which can still be considered as internal. The causes for this occurrence are discussed.

The mass transport problem for a single cavitation bubble in a spherical liquid cell surrounded by an in-finite elastic solid is considered. To study the rectified diffusion phenomenon, the time-periodic pressure in the solid far away from the bubble is used as an external driving. The work is based on engineer-ing approximation following the assumption by (Fyrillas and Szeri, 1994) that the bubble oscillations are fast and the growth/reduction of the mean bubble size is slow. According to this engineering approxi-mation the problem is splitted into two problems. In the first problem, the effect of the mass transport in the system on the fast bubble oscillations is neglected, whereas in the second problem the bubble growth/reduction is considered at average, assuming that during the period of the external driving the mass of gas in the bubble does not noticeably change. The equations for the dynamics of the soluble bubble in confined liquid are derived, and the discussion of the dependence of the solution on the initial gas concentration in the liquid is reported. Three possible regimes of the bubble dynamics are revealed: 1) total bubble dissolution, when the gas concentration in the liquid is not enough to compensate the mass fluxes in and out of the bubble; 2) partial bubble dissolution, when the small gas concentration in the liquid is enough to compensate the mass fluxes in and out of the bubble, which shrinks to a result-ing stable bubble size; 3) bubble growth, when the concentration of dissolved gas is enough to provide a resulting stable bubble with a larger size than the initial one. The influence of the gas diffusion in the bubble-in-cell system on the cavitation threshold is considered. The parametric study of the impact of the gas concentration in the liquid on the resulting stable bubble size is conducted for different initial bubble radii, liquid cell sizes, pressure amplitudes, and frequencies of the external driving.(c) 2022 Elsevier Ltd. All rights reserved.

View Video Presentation: https://doi.org/10.2514/6.2022-0501.vid For aerospace vehicles, where weight reduction is important, studies have been performed on composites to include different functionalities besides their primary structural function. Some of these functionalities include energy savings, self-health monitoring, ice protection system, and self-curing sensing capabilities, and have been demonstrated individually in carbon fiber reinforced polymer composites. Nano-engineering techniques enable integrating these functionalities in composite systems to add multifunctionalities with insignificant changes in dimension or weight of the composite system, while ensuring that the mechanical properties such as strength are maintained or enhanced. Here, glass fiber reinforced polymer composites are nanoengineered to add multiple multifunctionalities concurrently via hierarchical assemblies of vertically aligned carbon nanotubes. In this preliminary study, the nanoengineering of the composite suggests life-cycle enhancements via an increase in interlaminar shear strength.

The performance of aircraft anti-icing fluids reduces unusually on aviation composites. It is unclear whether this is due to low substrate thermal conductivity or hydrophobicity. Therefore, we considered experimentally the performance of Newtonian and non-Newtonian aircraft anti-icing fluids on substrates with thermal conductivities from 0.17 to 252 W/m.K. It was found that the decrease of substrate thermal conductivity promotes the freezing of Newtonian and low viscous Non-Newtonian fluids compared to the thicker Non-Newtonian one. The thermal conductivity effect can be explained by the competition of two heat transfer processes: heat accumulation and the transfer of latent heat. Thus, Newtonian and low viscous Non-Newtonian aircraft anti-icing fluids must be defined on aviation composites together with substrate thermal conductivity, wettability, and roughness.

Lunar regolith is the most critical material for the in-situ resource utilization in the crewed Moon exploration missions. This natural material can be utilized for the additive manufacturing of concrete or ceramic parts on the Moon's surface to support permanent human presence on the surface of Earth's natural satellite. Due to the scarcity of regolith on Earth, its simulants are used in lab research to prepare the technology for Moon missions. The present study is devoted to the characterization of lunar regolith simulant material, recently developed by the University of Central Florida, that is considered as a suitable material for regolith-focused additive manufacturing technologies. This paper describes the characterization of the LHS-1 and LMS-1 simulants using XRF, XRD, SEM, EDX, DTA, TGA, UV/Vis/NIR spectroscopy, and Laser diffractometry methods to provide data on their mineral, chemical, and fractional composition, as well as, on their morphology and optical properties. The results were compared to the data of the previously developed simulants and the original lunar samples delivered by Apollo and Luna missions. It was found that LHS-1 and LMS-1 simulants well mimic the primary properties of the original lunar regolith and can be potentially used for ISRU research tasks.

In this paper, we will present an approach to compute the signed distance or level set function from the Standard Triangle Language (STL) file format. Then the level set is used to represent the surface of a given object inside the computational domain. The continuity and Navier-Stokes equations are solved numerically to study the fluid flows over the solid body. The finite-volume method (FVM) is applied to approximate all terms in the governing equations to conserve mass and momentum. The cut-cell method is employed to avoid recomputing the mesh points when the body moves around. The transport equation for the level set function is solved accordingly to update the position of the object.

Additive manufacturing (AM) allows printing parts of complex geometries that cannot be produced by standard technologies. Besides, AM provides the possibility to create gradient materials with different structural and physical properties. We, for the first time, printed gradient soft magnetic materials from paramagnetic powders (316L steel and Cu-12Al-2Fe (in wt.%) aluminium bronze)). The magnetic properties can be adjusted during the in-situ printing process. The saturated magnetization value of alloys reaches 49 emu g^{-1}. The changes in the magnetic properties have been attributed to the formation of the BCC phase after mixing two FCC-dominated powders. Moreover, the phase composition of the obtained gradient materials can be predicted with reasonable accuracy by the CALPHAD approach, thus providing efficient optimization of the performance. The obtained results provide new prospects for printing gradient magnetic alloys.

Lunar regolith is the most abundant natural resource on Moon's surface. It is the intensively studied prime candidate for in-situ fabrication and repair (ISFR) technologies for future crewed exploration and resource harvesting missions on the Moon. Additive manufacturing with lunar regolith is a promising ISFR method that can be used for sustainable local production of engineering tools and components. This method requires little quantities of extra materials delivered from Earth, but, like many other prospective ISFR technologies, is sensible to the quality of the pre-processed regolith powders that are used as the primary source materials. The evolution of properties of highland and mare lunar regolith simulants concerning grinding-based pre-processing was studied in this work. The effect of regolith grinding was studied for the processes, relevant to stereolithography-based additive manufacturing. Particle size distribution, mean particle size, UV–Vis, XRD and XRF spectra were acquainted from the samples, ground in a ball mill at various grinding times (to different fraction sizes). The photopolymerization efficiency was assessed for lunar simulant-infilled resins prepared from lunar regolith simulants ground with different parameters. It was found that the grinding time of lunar regolith simulants strongly influences their optical properties – the light absorption in the far UV increased by 5.5 times. Based on the measured photo-polymerization depth, the optimal grinding procedure for mare and highland lunar regolith simulants was determined.

An optimal combination of power and energy characteristics is beneficial for the further progress of supercapacitors-based technologies. We develop a nanoscale dynamic electrolyte model, which describes both static capacitance and the time-dependent charging process, including the initial square-root dependency and two subsequent exponential trends. The observed charging time corresponds to one of the relaxation times of the exponential regimes and significantly depends on the pore size. Additionally, we find analytical expressions providing relations of the time scales to the electrode’s parameters, applied potential, and the final state of the confined electrolyte. Our numerical results for the charging regimes agree with published computer simulations, and estimations of the charging times coincide with the experimental values.

Pre-consolidated tapes in thermoplastic pultrusion solve the problem of impregnating a reinforcement with high -viscosity thermoplastic resins. Thermoplastic glass fiber/polypropylene flat laminates (75 mm x 3.5 mm) were fabricated using pre-consolidated tapes from different manufacturers: pre-consolidated tapes by the ApATeCh-Tape Company (Russia) and pre-consolidated sheets by the Zhongji Company (China). In spite of the equal reinforcement volume fraction (38%), the laminates fabricated from the pre-consolidated sheets exhibited higher compressive, tensile, and flexural strengths than those made from the pre-consolidated tapes, differing by 27.1%, 27.3%, and 19.8%, respectively. The observed difference between the strength characteristics of the studied flat laminates was explained by the presence of unimpregnated regions in the fiber bundles and by matrix cracks in the pre-consolidated tapes, absent in the pre-consolidated sheets, as revealed by the scanning electron micro-scopy analysis. Such defects cannot be corrected during the pultrusion process, resulting in the formation of matrix cracks and debonding, impairing the mechanical performance of the produced pultruded laminates. Pre -consolidated sheets enable pultrusion flat laminates with larger cross-sections, exhibiting better mechanical performance and surface roughness, compared with thermoplastic pultruded composites fabricated from pre -consolidated tapes described in the literature.

This paper presents an investigation into the use of newly pultruded glass-fibre reinforced polypropylene (GFRPP) bars as reinforcement in concrete structures for marine applications. This study conducted a comparative evaluation of the durability of GFRPP bars in distilled water (DW) and alkaline solutions (AS) and in simulated marine concrete environments by investigating their interlaminar shear strength (ILSS). It focused on evaluating the water absorption, mechanical, and microstructural properties of GFRPP bars subjected to hygrothermal environments. Thermogravimetric analysis (TGA) tests obtained the fiber, volume content of the GFRPP bars. GFRPP bars were immersed solutions at different conditions. Scanning Electron Microscopy (SEM) and Fourier Transform Infrared spectroscopy (FTIR) were performed to study the changes of the microstructural and in the chemical composition of the polypropylene (PP) matrix of the GFRPP bars. Based on Arrhenius acceleration theory, the prediction models of ILSS of GFRPP bars in five preset service regions and DW and AS service environments were established to obtain the service time when they completely degraded in each service region and environment. The results show that the water absorptions of the GFRPP bars immersed in water and alkaline solution were described by Fick's equation. Moreover, after 120-day immersion at 60 degrees C, the retention of the ILSS was 67.0 and 67.5 % in DW and AS, respectively. The hygrothermal environments accelerates the development of micro-voids and cracks generated during the pultrusion of GFRPP bars, which is the main reason for the degradation of the long-term mechanical properties, as well as fiber-resin debonding. Finally, the predicted service life in AS solutions is shorter than in DW, owing to the catastrophic effect of glass fiber etching and stripping on the mechanical properties of GFRPP bars.

Droplet impact may rupture a liquid film on a non-wettable surface. The formation of a stable dry spot has only been studied in the inviscid case. Here, we examine the break-up of viscous films, and demonstrate the importance and role of the viscous dissipation in both film and droplet. A new model was therefore proposed to predict the necessary droplet energy to create a dry spot. It also showed that the dissipation contribution in film dominates when the ratio of the thicknesses to drop diameter is larger than 7/4.

The paper describes digital twins for an electrically conductive isotropic CNT-polymer nanocomposite, using representative volume element with boundary conditions being periodic geometrically and electrically. During the CNT generation, the torsion and curvature of CNTs are controlled. The percolation threshold is analysed with scaling towards the infinite RVE. The digital twin sensitivity to model parameters is found as follows: (1) restrictions on the curvature/torsion ensure the independence of the homogenised conductivity on the CNTs discretisation; (2) the conductivity of the nanocomposite increases (for the same CNT volume fraction) with the increase of the CNT length and maximum torsion and decrease of the maximum curvature; (3) the percolation threshold, is in the range of 0.3-0.7% for different CNT parameters; it reduces in half with doubling the CNT length; the curvature and torsion have lesser influence. The critical percolation index is 1.2-1.7, which corresponds to the theoretical values for 3D networks.