Surface Modification Technology Research Articles

Effect of Pinless Friction Stir Processing on Microstructure and Properties of Surface Modification Layer of 2024 Aluminum Alloy

Abstract Friction stir processing (FSP) is an advanced material surface modification technology that is both green and energy-efficient. This technology plays a crucial role in regulating the surface microstructure of alloys and improving their material surface properties. It achieves this through the synergistic effect of non-equilibrium thermodynamics and surface mechanical deformation. In this work, the surface modification of an aluminum alloy was performed using pin-less FSP. And the modified surface was then analyzed using stress-strain curves, optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical tests to investigate the impact of spindle velocity on the modified layer's properties. Results of the study show after undergoing pin-free FSP modification treatment, the surface of the alloy appears bright and flat. The modified layer displays refined grains and numerous dispersed second-phase particles. Furthermore, the grains in the modified layer exhibit a gradient distribution from the surface to the matrix. Regarding the properties, Compared to the base material (BM), the yield strength (σ0.2) and tensile strength (σb) of the alloy-modified layer were increased by 34.8% and 29.4%, respectively. The maximum elongation (δ) of the modified coating reached 22.3%. The modified layer exhibits a tough-brittle mixed fracture pattern. Additionally, the modified layer's corrosion resistance significantly improves. The performance of the modified coating shows the most significant improvement when the spindle speed reaches 1000 rpm. The study aims to explore the effect of spindle speed on the properties of alloy-modified layers produced by FSP without a stirring pin. This research could be used to create superior metal matrix composites by adding reinforcement particles.

One-step laser interference lithography for large-scale preparation of a superhydrophobic Ti6Al4V surface with improved hardness, friction reduction and corrosion resistance

Metal workpieces are the bedrock of modern industries as aerospace, marine and car manufacturing. As the pursuit for machinery with excellent performance continues to increase, existing metals are unable to fulfill the requirements of machinery, so surface modification technology has emerged. In this paper, a highly efficient and cost-effective surface modification method using laser interference lithography (LIL) is proposed to prepare superhydrophobic surfaces with corrosion resistance over a large area on Ti6Al4V surfaces. Large-area uniform stripe structures were fabricated on the Ti6Al4V surface by controlling the interference process parameters and spot splicing paths, and then modifying FAS to obtain a superhydrophobic surface. The stripe structure provides more air pockets, which lays the foundation for improved superhydrophobicity and friction reduction. Furthermore, the dense recast layer formed by LIL cauterization completely isolates the Ti6Al4V materials from the corrosive medium, further improving corrosion resistance. The experimental results showed that the hardness reached 15.62 Gpa (313.65% improvement), the coefficient of friction (COF) was reduced to 0.144 (66.5% reduction), and the corrosion resistance was improved by two orders of magnitude. As a contactless fabrication technology for periodic structures, LIL has great potential in the field of surface modification.

Effect of shot peening on surface characteristics and high-temperature corrosion behaviour of super 13Cr martensitic stainless steel

Super 13Cr, as an economy stainless steel (SS) for oil country tubular goods, needs stable corrosion resistance in high-pressure and high-temperature (HPHT) downhole medium. Severe plastic deformation (SPD) are the surface modification technology to improve mechanical properties, fatigue behavior and corrosion resistance of metals, and shot peening (SP) has been the most widely used SPD process. However, there are quite limited studies about the microsutructure evolution, residual stress, and high-temperature corrosion behavior of SP treated martensitic SS. In this study, super 13Cr martensitic SS was treated by shot peening with various air pressures and nozzle speeds. The surface characteristics and high-temperature corrosion behaviour in 3.17 mol/L K2HPO4 solution was investigated through finite element model analysis, characterization of residual stress and microstructure, as well as electrochemical and stress corrosion cracking (SCC) tests at 160 °C and 10 MPa. The results showed that SP treated super 13Cr could generate high-level compressive residual stress and SPD microstucture, including nano-sized equiaxed grains, gradient lamellar structure and fragmented carbides. Increasing air pressure contributed to achieve uniform nanocrystalline, but tended to generate high dislocation density and surface defects. The improving effect of SP treatment at low air pressure of 0.15 MPa on passivation ability was limited, and high air pressure adversely impacted corrosion resistance. SP treated specimens showed high SCC susceptibility, due to the introduction of more surface defects, high angle grain boundaries, and dislocations.

Stent coating containing a charged silane coupling agent that regulates protein adsorption to confer antithrombotic and cell-adhesion properties

The evolution of endovascular therapies, particularly in the field of intracranial aneurysm treatment, has been truly remarkable and is characterized by the development of various stents. However, ischemic complications related to thrombosis or downstream emboli pose a challenge for the broader clinical application of such stents. Despite advancements in surface modification technologies, an ideal coating that fulfills all the desired requirements, including anti-thrombogenicity and swift endothelialization, has not been available. To address these issues, we investigated a new coating comprising 3-aminopropyltriethoxysilane (APTES) with both anti-thrombogenic and cell-adhesion properties. We assessed the anti-thrombogenic property of the coating using an in vitro blood loop model by evaluating the platelet count and the level of the thrombin–antithrombin (TAT) complex, and investigating thrombus formation on the surface using scanning electron microscopy (SEM). We then assessed endothelial cell adhesion on the metal surfaces. In vitro blood tests revealed that, compared to a bare stent, the coating significantly inhibited platelet reduction and thrombus formation; more human serum albumin spontaneously adhered to the coated surface to block thrombogenic activation in the blood. Cell adhesion tests also indicated a significant increase in the number of cells adhering to the APTES-coated surfaces compared to the numbers adhering to either the bare stent or the stent coated with an anti-fouling phospholipid polymer. Finally, we performed an in vivo safety test by implanting coated stents into the internal thoracic arteries and ascending pharyngeal arteries of minipigs, and subsequently assessing the health status and vessel patency of the arteries by angiography over the course of 1 week. We found that there were no adverse effects on the pigs and the vascular lumens of their vessels were well maintained in the group with APTES-coated stents. Therefore, our new coating exhibited both high anti-thrombogenicity and cell-adhesion properties, which fulfill the requirements of an implantable stent.

Stent coating containing a charged silane coupling agent that regulates protein adsorption to confer antithrombotic and cell-adhesion properties

The evolution of endovascular therapies, particularly in the field of intracranial aneurysm treatment, has been truly remarkable and is characterized by the development of various stents. However, ischemic complications related to thrombosis or downstream emboli pose a challenge for the broader clinical application of such stents. Despite advancements in surface modification technologies, an ideal coating that fulfills all the desired requirements, including anti-thrombogenicity and swift endothelialization, has not been available. To address these issues, we investigated a new coating comprising 3-aminopropyltriethoxysilane (APTES) with both anti-thrombogenic and cell-adhesion properties. We assessed the anti-thrombogenic property of the coating using an in vitro blood loop model by evaluating the platelet count and the level of the thrombin–antithrombin (TAT) complex, and investigating thrombus formation on the surface using scanning electron microscopy (SEM). We then assessed endothelial cell adhesion on the metal surfaces. In vitro blood tests revealed that, compared to a bare stent, the coating significantly inhibited platelet reduction and thrombus formation; more human serum albumin spontaneously adhered to the coated surface to block thrombogenic activation in the blood. Cell adhesion tests also indicated a significant increase in the number of cells adhering to the APTES-coated surfaces compared to the numbers adhering to either the bare stent or the stent coated with an anti-fouling phospholipid polymer. Finally, we performed an in vivo safety test by implanting coated stents into the internal thoracic arteries and ascending pharyngeal arteries of minipigs, and subsequently assessing the health status and vessel patency of the arteries by angiography over the course of 1 week. We found that there were no adverse effects on the pigs and the vascular lumens of their vessels were well maintained in the group with APTES-coated stents. Therefore, our new coating exhibited both high anti-thrombogenicity and cell-adhesion properties, which fulfill the requirements of an implantable stent.

Synergistic effect of NiCr-Cr3C2 + Y2O3 to enhanced performance of Ti-based composite fabricated by laser cladding

The surface modification technology, which is of great significance in aerospace, energy, and other fields, is based on reinforcement. In this study, a titanium-based composite material system, formed using laser cladding and based on NiCr-Cr3C2 + Y2O3 dual additives, was investigated. TiC reinforcement particles were generated in situ through the reaction between NiCr-Cr3C2 and Ti6Al4V during the cladding process. Additionally, Ni and Cr elements provided solid solution-strengthening effects to the matrix. Meanwhile, Y2O3 particles were introduced ex-situ, effectively eliminating defects in the coating and inhibiting the dendritic growth of TiC particles. This process enhanced the dispersion-strengthening effect of TiC. The titanium-based composite material, incorporating NiCr-Cr3C2 + Y2O3, exhibited excellent tribological performance, displaying a wear rate of approximately 4.22 × 10−4 mm3·N−1·m−1.

Experimental study of nucleate boiling heat transfer of refrigerant-oil mixture on various modified surfaces

As a crucial component of refrigeration and heat pump system, the evaporator performance directly affects system efficiency. Due to the lubricating oil in the compressor circulating into the evaporator, studying the nucleate boiling heat transfer (NBHT) of refrigerant-oil mixture is of greater practical and guiding significance. Surface modification technology has opened up a new avenue for enhancing NBHT of refrigerant-oil mixture. Therefore, experimental study was conducted on NBHT characteristics of R134a-POE mixture and R1234ze(E)-POE mixture on smooth surface, initial laser-ablated surface, stabilized laser-ablated surface, machined surface, and composite processed surface. The effects of oil concentration (ω), surface microstructure and surface wettability on NBHT of refrigerant were discussed and analyzed, and the underlying heat transfer mechanisms were elucidated. The research indicates that for NBHT of refrigerant-oil mixture, surface microstructure has a greater impact than surface wettability. To enhance heat transfer coefficient (HTC), it is crucial to establish a surface pattern comprising alternating regions of high and low nucleation sites to mitigate bubble interaction and coalescence. Once this objective is attained, enhancing surface wettability can be contemplated. The addition of oil promotes foaming and induces tornado-shaped bubble group, which facilitate heat transfer. However, the rise in mixture viscosity and surface tension exerts a more pronounced adverse effect on heat transfer, outweighing the positive impacts of foaming and tornado-shaped bubble group. Consequently, the presence of oil diminishes HTC. And as ω and heat flux increase, HTC further decreases. Additionally, the increase in vaporization nuclei on modified surface leads to a higher local ω, the increase in ω further weakens the enhanced heat transfer effect of modified surface, and thus narrows the difference in HTC among various modified surfaces. The research results aim to uncover the mechanisms by which surface wettability, surface microstructure, and lubricating oil affect NBHT of refrigerant.

Effect of pulse laser nitriding on the superheated steam corrosion behavior of Zr alloy

Zirconium (Zr) alloy fuel cladding is exposed to harsh environments such as high temperature and high pressure for a long time. Surface modification technology can effectively improve its high-temperature oxidation resistance. In this work, pulse laser nitriding technology was used to perform laser nitriding treatment on Zr alloys at different laser energies. The effect of different energy levels of laser nitriding treatments on the superheated steam corrosion resistance of Zr alloys was studied. First-principles was used to reveal the mechanism of how the diffusion layer improves the performance of Zr alloys in resisting superheated steam corrosion after nitriding treatment. Results indicate that the surface of Zr alloys treated with laser nitriding exhibits a molten feature. When the laser energy is 100 mJ, N mainly exists in the form of a diffusion layer in the Zr alloy substrate. As the laser energy rises to 200 mJ and above, the ZrN phase is generated. After 1000 h of superheated steam corrosion, the corrosion weight gain of the 100 mJ sample was reduced by approximately 50 % compared to the Zr alloy. The corrosion weight gain of the 400 mJ sample increased by approximately 12 %. The presence of the ZrN phase accelerates the oxidation degradation rate of Zr alloy. When N atoms exist as a diffusion layer, the transition from tetragonal zirconia to monoclinic zirconia can be suppressed. First-principles calculations showed that when O and N atoms coexist in the Zr alloy substrate, their binding performance with surface O is significantly decreases, thus further improving the 100 mJ sample's resistance to superheated steam corrosion.

Direct electrocatalytic sensing of myoglobin using an annealed Au-implanted electrode

Ion implantation is a versatile and green material surface modification technology that modifies the structure of target-neat surface by bombardment of non-metal or heavy metal ions. A new Au nanoparticle loaded ITO (AuNPs/ITO) electrodes was prepared by ion implantation and thermal annealing method in this work. The obtained nanoparticles were characterized by Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical methods. The direct electrocatalysis of Myoglobin (MB) was reported. It was found that after annealing at 500 °C for 2 h, the damage part of the implanted sample was eliminated. The surface coverage of MB on the MB/AuNPs/ITO electrode and the MB/annealed-AuNPs/ITO electrode was 4.35× 10−11 mol·cm−2 and 1.23 × 10−10 mol·cm−2, respectively. The results show that this composite method can be used to fabricate an electrocatalytic biosensor.

Recent Advances in Metal Oxide Electron Transport Layers for Enhancing the Performance of Perovskite Solar Cells.

Perovskite solar cells (PSCs) have attracted considerable interest owing to their low processing costs and high efficiency. A crucial component of these devices is the electron transport layer (ETL), which plays a key role in extracting and transmitting light-induced electrons, modifying interfaces, and adjusting surface energy levels. This minimizes charge recombination in PSCs, a critical factor in their performance. Among the various ETL materials, titanium dioxide (TiO2) and tin dioxide (SnO2) stand out due to their excellent electron mobility, suitable band alignment, high transparency, and stability. TiO2 is widely used because of its appropriate conduction band position, easy fabrication, and favorable charge extraction properties. SnO2, on the other hand, offers higher electron mobility, better stability under UV illumination, and lower processing temperatures, making it a promising alternative. This paper summarizes the latest advancements in the research of electron transport materials, including material selection and a discussion of electron collection. Additionally, it examines doping techniques that enhance electron mobility and surface modification technologies that improve interface quality and reduce recombination. The impact of these parameters on the performance and passivation behavior of PSCs is also examined. Technological advancements in the ETL, especially those involving TiO2 and SnO2, are currently a prominent research direction for achieving high-efficiency PSCs. This review covers the current state and future directions in ETL research for PSCs, highlighting the crucial role of TiO2 and SnO2 in enhancing device performance.

Tailoring Surface Engineering with Expanded Precursor Libraries via Rapid Mussel-Inspired Chemistry.

Mussel-inspired coating is a substrate-independent surface modification technology. However, its application is limited by time-consuming, tailoring specific functions require tedious secondary reaction. To overcome those drawbacks, a strategy for the rapid fabrication of diverse coatings by expanding the library of precursors using oxidation coupled with polyamine was proposed. Based on DFT simulations of the reaction pathways, a method was developed to achieve rapid deposition of coatings by coupling oxidation and polyamines, which simultaneously accelerated the oxidation of precursors and polymer chain growth. The feasibility and generalizability of the strategy was validated by the rapid coating of 10 catechol derivatives and polyamines on various substrates. The surface properties of the substrates such as functional group densities, Zeta potential and contact angles can be easily tuned. The tailored surface engineering application of the strategy was demonstrated by the heavy metal adsorbents and superwetting materials prepared through the delicate combination of different building blocks. Our strategy was flexible in terms of diverse surface engineering design which greatly enriched the connotation of mussel-inspired technique.

Surface modification of biomedical titanium alloy for hard tissue repair and reconstruction

In biomedical applications, various materials are used, including metals and their alloys, polymers and ceramics. Among them, titanium (Ti) and titanium alloys are widely utilised in implant materials due to their excellent corrosion resistance and high mechanical strength. However, despite these advantages, titanium is biologically inert and does not integrate well with human cells. Therefore, surface modification of titanium implants plays a crucial role in determining the rate of osseointegration and the overall success of the implants. The primary objective of this review is to provide a detailed introduction to surface modification technologies for titanium alloy implants. The aim is to enhance the biological activity, wear resistance, corrosion resistance and antibacterial properties and reduce the release of ions from the implants. By modifying the surface of titanium implants, it is possible to create a more favourable environment for cell adhesion, proliferation and differentiation. Various techniques, such as physical methods (e.g. sandblasting, acid etching) and chemical methods (e.g. surface oxidation, plasma treatment) can be employed to modify the surface properties of titanium implants. These surface modification techniques can enhance the interaction between the implant and the surrounding biological environment, promoting osseointegration and improving the long-term stability of the implant. Additionally, surface modifications can help reduce the release of potentially harmful ions from the implant, minimise bacterial adhesion and improve the overall biocompatibility of the implant. In conclusion, surface modification of titanium alloy implants is a critical aspect of biomedical engineering. By improving the biocompatibility of titanium implants, these modifications contribute to the success and longevity of implants used in hard tissue repair and reconstruction.

Bionanocomposites preparation by design: Planning based on the modification of ceria nanoparticles by polydopamine interleaved with the chitosan biopolymer

Herein, the marine source polymer, chitosan (CS), was utilized to fabricate bionanocomposites by mussel-inspired sonochemical assisted method. The surface modified nanofillers as active ingredients were provided by assembling biomimetic polydopamine (PDA) onto the CeO2 nanoparticles through redox polymerization as a surface modification technology. Standard spectroscopic methods were used to characterize the resulting cerium oxide PDA-treated nanoparticles (NPs). CeO2/PDA/CS nanocomposites (NC)s were manufactured using a sonochemical process by inserting nanostructured fillers into the CS polymer matrix. The morphological features and structural characteristics of NCs were considered using field emission scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and thermogravimetric analysis techniques. It was found that based on the biomimetic PDA layer the hydrogen bond interactions between CS biopolymer functional units with PDA functional units have occurred. Therefore, a pleasant distribution of surface adapted NPs in macromolecular matrix in the form of nanostructured composites was observed.

Grain refinement and Laves phase dispersion by high-intensity ultrasonic vibration in laser cladding of Inconel 718

Laser cladding is a promising surface modification and repair technology for fabricating Inconel 718 parts. However, laser cladding may produce coarse grains and brittle Laves phase, leading to a significant decrease in performance. The application of high-intensity ultrasonic vibration in laser cladding is able to refine grain and reduce Laves phase. This study investigates the distribution characteristics and the evolution mechanism of the grains and Laves phase in laser cladding with high-intensity ultrasonic vibration. The effects of high-intensity ultrasonic vibration on alteration of grain characteristics and the reduction of Laves phase were analyzed and discussed through ultrasonic vibration-assisted laser cladding experiments. Results indicate that high-intensity ultrasonic vibration promoted a columnar-to-equiaxed transition, and reduced the grain size from 75.6 μm to 48.8 μm. Furthermore, the Laves phase had a decrease of 47.1% in the volume fraction, and transformed from a long-striped shape into a fine granular shape, leading to a more homogeneous distribution of elements in Laves phase. The change in the grains and the Laves phase is attributed to dendrite fragmentation and inhibition of element segregation by nonlinear effects of ultrasound including cavitation and acoustic streaming. The findings of this study confirm the significant benefits of applying high-intensity ultrasonic vibration in laser cladding and provide insight into the underlying evolution mechanisms of high-intensity ultrasonic vibration for grains and Laves phase.

Cellulose acetate filter rods tuned by surface engineering modification for typical smoke components adsorption

Abstract A series of filter rods (FRs) with sodium alginate (SA) modification were prepared by a simple one-pot pre-treatment surface modification method for the retention of typical smoke components. The influences of SA on the physico-chemical properties and adsorption behaviors (or retention characteristics) toward FRs were investigated in detail. Based on the results of XRD, BET, and SEM, it can be inferred that SA modification has no influences on compositions and textural properties of FRs. However, surface modification of FR by SA can greatly improve the hydrophilicity of FR, which is crucial for water retention. In situ diffuse Fourier-transform infrared spectroscopy results demonstrate that FR modified by 2 g·L−1 SA presents superior adsorption character for acetone. The differences in the adsorption or retention of water and acetone are ascribed to surface enriched functional groups tuned by surface engineering modification. By contrast, the modification of SA had no obvious effect on the adsorption of CO at room temperature. By contrast, at high temperature, low modification concentration is conducive to the CO2 and CO adsorption. It presents a good perspective for the rational design of new filter materials to reduce the release of harmful components in cigarette smoke.

Molten salt-modified Ti3C2Tx MXene with tunable oxygen-functionalized surfaces for effective detection of NO2 at room temperature

The abundant tunable functional groups and room-temperature sensing properties of MXenes have garnered increasing interest in the field of gas sensing. However, the majority of research has exclusively focused on the combined impact of external substances with MXenes functional groups, with limited exploration into the modulation of MXenes’ intrinsic functional groups. In this work, we successfully produced molten salt-modified Ti3C2Tx MXene (M-Ti3C2Tx) with tunable oxygen-functionalized surfaces using the molten salt immersion method and employed it as a chemical resistive gas sensor to detect NO2 at room temperature (RT). Using diverse analytical techniques, we propose the O−addition effect on the surface titanium atoms and the O−substitution effect on the edge carbon atoms, refining the existence form of –O functional groups as well as realizing the effective regulation of the intrinsic functional groups. With a high response (∼25.87%−100 ppm NO2, whose response value is five times higher than that of pristine Ti3C2Tx), relatively rapid response speed (∼99 s−25 ppm NO2), high sensitivity (∼0.29 ppm−1), low detection limits (theoretical LoD is 3.3 ppm), good selectivity and long-term stability (maintain stable within 28 days) at RT, the sensor based on M-Ti3C2Tx demonstrates excellent NO2 sensing performance. To understand the sensing mechanism, density functional theory (DFT) calculations were conducted to explore adsorption behaviors. Theoretical analysis validates that M-Ti3C2Tx has a stronger adsorption capacity for NO2 (Ead = −1.149 eV) owing to the formation of covalent bond between the –O functional group and the nitrogen atom of NO2. The application of the molten salt can effectively modulate the intrinsic functional groups of MXenes, expanding the scope of MXenes surface modification engineering and creating new opportunities for enhancing the gas sensing capabilities of MXenes.

In-situ-growth of hard-coating, its impact on mechanical performances in cemented-carbides

This study focuses on preparing two types of cemented carbides: one with Ti elements and the other without, using a stepwise sintering process, primarily evaluating their mechanical properties. The research includes a thorough analysis of microstructure changes and post-wear surface alterations, coupled with assessments of phase composition, element content, relative density, surface hardness, fracture toughness, and wear properties. Results reveal that cemented carbides treated with in-situ surface modification under high-temperature nitrogen atmospheres exhibit exceptional densification. An in-situ hard-phases layer, predominantly TiN or Ti(C, N), is gradually grown on the surface of the WC-Co-Mo-TiNC cemented carbides, enhancing surface hardness and fracture toughness. This technology fortifies the material against indentation, crack expansion, and fracture, significantly improving wear resistance and extending service life. In essence, the in-situ surface modification technology, especially under high-temperature nitrogen atmospheres, emerges as a transformative approach, enhancing mechanical properties and substantially improving wear resistance for prolonged practical applications.

Experimental studies of hydrodynamics of the «plate» type canonical region with a modified surface

The possibility of using biomimetic approaches, in particular, the "lotus leaf" effect, expressed in the superhydrophobicity of streamlined surfaces, is considered. The results are presented of experimental studies of the influence produced by various modifications of the surface of the “plate” type canonical region on its hydraulic characteristics. The plates were streamlined in a hydrodynamic tray of rectangular cross-section. Copper plates with dimensions of 200x300x1 mm were studied. Three plates were considered, identical in geometry, but with different surface conditions — one in its original state; one with surfaces modified based on a surfactant; and one with surfaces treated by laser ablation (laser formation of a multimodal relief) with subsequent modification based on surfactants. In the course of experimental studies, the velocity distribution behind streamlined plates with different surface characteristics was obtained. Based on the nature of the velocity variations of the trail behind the streamlined plates, it is concluded that the amount of hydraulic resistance decreases due to surface modification. The weighted average velocity behind the streamlined plate increased by more than 4% for a plate with a combined modified surface compared to the original one. The process of a copper plate surface modifying using laser ablation, as well as the formation of additional surfactant molecular layers in order to achieve the maximum effect of superhydrophobicity is described. The most effective technological features of the laser ablation process are determined, such as the radiation power and frequency, the most preferred relief of modified surfaces and its geometric parameters. The most characteristic features of the influence of the surface roughness on the wetting angle (θ) are considered. With the OSA 20 complex, the wetting angles were determined for all the prepared plate samples. The research results prove the prospects of this surface modification technology for use in hydraulic machines.

Synergistic Amelioration of Osseointegration and Osteoimmunomodulation with a Microarc Oxidation-Treated Three-Dimensionally Printed Ti-24Nb-4Zr-8Sn Scaffold via Surface Activity and Low Elastic Modulus.

Biomaterial scaffolds, including bone substitutes, have evolved from being primarily a biologically passive structural element to one in which material properties such as surface topography and chemistry actively direct bone regeneration by influencing stem cells and the immune microenvironment. Ti-6Al-4V(Ti6Al4V) implants, with a significantly higher elastic modulus than human bone, may lead to stress shielding, necessitating improved stability at the bone-titanium alloy implant interface. Ti-24Nb-4Zr-8Sn (Ti2448), a low elastic modulus β-type titanium alloy devoid of potentially toxic elements, was utilized in this study. We employed 3D printing technology to fabricate a porous scaffold structure to further decrease the structural stiffness of the implant to approximate that of cancellous bone. Microarc oxidation (MAO) surface modification technology is then employed to create a microporous structure and a hydrophilic oxide ceramic layer on the surface and interior of the scaffold. In vitro studies demonstrated that MAO treatment enhances the proliferation, adhesion, and osteogenesis capabilities on the scaffold surface. The chemical composition of the MAO-Ti2448 oxide layer is found to enhance the transcription and expression of osteogenic genes in bone mesenchymal stem cells (BMSCs), potentially related to the enrichment of Nb2O5 and SnO2 in the oxide layer. The MAO-Ti2448 scaffold, with its synergistic surface activity and low stiffness, significantly activates the anti-inflammatory macrophage phenotype, creating an immune microenvironment that promotes the osteogenic differentiation of BMSCs. In vivo experiments in a rabbit model demonstrated a significant improvement in the quantity and quality of the newly formed bone trabeculae within the scaffold under the contact osteogenesis pattern with a matched elastic modulus. These trabeculae exhibit robust connections to the external structure of the scaffold, accelerating the formation of an interlocking structure between the bone and implant and providing higher implantation stability. These findings suggest that the MAO-Ti2448 scaffold has significant potential as a bone defect repair material by regulating osteoimmunomodulation and osteogenesis to enhance osseointegration. This study demonstrates an optional strategy that combines the mechanism of reducing the elastic modulus with surface modification treatment, thereby extending the application scope of β-type titanium alloy.

Numerical investigation on pool boiling heat transfer with trapezoidal/inverted trapezoidal micro-pillars using LBM

Pool boiling with high-efficient heat transfer process is crucial to chemical engineering, nuclear engineering, electronic cooling, and other energy conversion applications. Surface modification technology has attracted more attention in recent years as a simple and reliable boiling enhancement technique. Most of the studies using surface modification technology have focused on the enhancement effect of rectangular micro-structures, only a few researchers have adequately investigated the enhancement effects on pool boiling heat transfer and mechanisms of other complex micro-structures (like circle, trapezoid, or inverted trapezoid). In the present study, the pool boiling processes on surfaces with trapezoidal/inverted trapezoidal micro-pillars were numerically investigated using lattice Boltzmann method (LBM). The bubble dynamics and heat transfer characteristics during the pool boiling processes on surfaces with different pillar bottom angles (30° ≤ θ ≤ 135°) were compared under different wall-superheat conditions. The orthogonal tests were adopted on micro-pillars to optimize the geometric parameters, including the bottom angle of the micro-pillar, the bottom width of the micro-pillar, the number of the micro-pillar, and the height of the micro-pillar. A new CHF correlation on the mixed wettability surface with trapezoidal/inverted trapezoidal micro-pillars was proposed. It can be found that the main mechanism of nucleate boiling heat transfer on the micro-pillars is the evaporation of the microlayer, and the pillar bottom angle reveals a remarkable effect on the pool boiling performance on the mixed wettability surfaces. The surface of θ = 135° has the minimum wall-superheat at the onset of nucleate boiling (ONB). Within a wide range of wall-superheat conditions, the heat transfer efficiency of pool boiling firstly increases with the increasing of the bottom angle of the micro-pillar and subsequently decreases. The surface of θ = 60° has the highest critical heat flux (CHF). The surface of θ = 90° has the highest heat transfer efficiency in the film boiling process. The results of orthogonal tests suggested that the bottom angle of the micro-pillar is the most significant influential factor, and the optimal geometrical combinations were proposed. The new CHF correlation has acceptable accuracy in predicting the CHF on surfaces with trapezoidal/inverted trapezoidal pillars, which provides guidance for the design and optimization of micro-structured surface modification in various pool boiling applications.