Graphene-Alumina Nanocomposites with Improved Mechanical Properties for Biomedical Applications

Enhancing the Properties of Yttria-Stabilized Zirconia Composites with Zeolitic Imidazolate Framework-Derived Nanocarbons

Ceramic matrix composites (CMCs) reinforced with nanocarbon have attracted significant interest due to their potential to enhance mechanical, thermal, and electrical properties. Although the investigation of carbon-based materials such as graphene and carbon nanotubes as additives for advanced ceramics has been widespread, the utilization of metal-organic framework (MOF)-derived nanocarbons in CMCs remains largely unexplored. We extended our previous proof-of-concept investigations by demonstrating the effectiveness of a different type of MOF-derived carbon as a reinforcing phase in an alternative ceramic matrix. We employed spark plasma sintering (SPS) to consolidate yttria-stabilized zirconia (YSZ) and zeolitic imidazolate framework (ZIF-67) powder blends at 1300 °C and a uniaxial pressure of 50 MPa. YSZ serves as the ceramic matrix, whereas ZIF-67 serves as the nanocarbon source. The composite exhibits a highly significant improvement in fracture toughness with an increase of up to 13% compared to that of the YSZ monolith. The formation of ZIF-derived nanocarbon interlayers is responsible for the observed enhancement in ductility, which can be attributed to their ability to facilitate energy dissipation during crack propagation and inhibit grain growth. Furthermore, the room-temperature electrical conductivity of the sintered samples demonstrates a substantial improvement, primarily due to the in situ formation of nanocarbon-based fillers, reaching an impressive 27 S/m with 10 wt % ZIF-67 content. Based on the results, it can be inferred that the incorporation of in situ MOF-derived nanocarbons into CMCs leads to a substantial improvement in both the mechanical and electrical properties.

Comprehensive Review on Biomaterials and Their Inherent Behaviors for Hip Repair Applications

Developing biomaterials for hip prostheses is challenging and requires dedicated attention from researchers. Hip replacement is an inevitable and remarkable orthopedic therapy for enhancing the quality of patient life for those who have arthritis as well as trauma. Generally, five types of hip replacement procedures are successfully performed in the current medical market: total hip replacements, hip resurfacing, hemiarthroplasty, bipolar, and dual mobility systems. The average life span of artificial hip joints is about 15 years, and several studies have been conducted over the last 60 years to improve the performance and thereby increase the lifespan of artificial hip joints. Present-day prosthetic hip joints are linked to the wide availability of biomaterials. Metals, ceramics, and polymers are some of the most promising types of biomaterials; nevertheless, each biomaterial has advantages and disadvantages. Metals and ceramics fail in most applications owing to stress shielding and the emission of wear debris; ongoing research is being carried out to find a remedy to these unfavorable responses. Recent research found that polymers and composites based on polymers are significant alternative materials for artificial joints. With growing research and several biomaterials, recent reviews lag in effectively addressing hip implant materials' individual mechanical, tribological, and physiological behaviors. This Review comprehensively investigates the historical evolution of artificial hip replacement procedures and related biomaterials' mechanical, tribological, and biological characteristics. In addition, the most recent advances are also discussed to stimulate and guide future researchers as they seek more effective methods and synthesis of innovative biomaterials for hip arthroplasty application.

Sustainable Microfabrication Enhancement of Graphene Nanoplatelet-Reinforced Biomedical Alumina Ceramic Matrix Nanocomposites

Studies about adding graphene reinforcement to improve the microfabrication performance of alumina (Al₂O₃) ceramic materials are still too rare and incomplete to satisfy sustainable manufacturing requirements. Therefore, this study aims to develop a detailed understanding of the effect of graphene reinforcement to enhance the laser micromachining performance of Al₂O₃-based nanocomposites. To achieve this, high-density Al₂O₃ nanocomposite specimens were fabricated with 0 wt.%, 0.5 wt.%, 1 wt.%, 1.5 wt.%, and 2.5 wt.% graphene nanoplatelets (GNPs) using a high-frequency induction heating process. The specimens were subjected to laser micromachining. Afterward, the effects of the GNP contents on the ablation depth/width, surface morphology, surface roughness, and material removal rate were studied. The results indicate that the micro-fabrication performance of the nanocomposites was significantly affected by the GNP content. All nanocomposites exhibited improvement in the ablation depth and material removal rate compared to the base Al₂O₃ (0 wt.% GNP). For instance, at a higher scanning speed, the ablation depth was increased by a factor of 10 times for the GNP-reinforced specimens compared to the base Al₂O₃ nanocomposites. In addition, the MRRs were increased by 2134%, 2391%, 2915%, and 2427% for the 0.5 wt.%, 1 wt.%, 1.5 wt.%, and 2.5 wt.% GNP/Al₂O₃ nanocomposites, respectively, compared to the base Al₂O₃ specimens. Likewise, the surface roughness and surface morphology were considerably improved for all GNP/Al₂O₃ nanocomposite specimens compared to the base Al₂O₃. This is because the GNP reinforcement reduced the ablation threshold and increased the material removal efficiency by increasing the optical absorbance and thermal conductivity and reducing the grain size of the Al₂O₃ nanocomposites. Among the GNP/Al₂O₃ nanocomposites, the 0.5 wt.% and 1 wt.% GNP specimens showed superior performance with minimum defects in most laser micromachining conditions. Overall, the results show that the GNP-reinforced Al₂O₃ nanocomposites can be machined with high quality and a high production rate using a basic fiber laser system (20 Watts) with very low power consumption. This study shows huge potential for adding graphene to alumina ceramic-based materials to improve their machinability.

Ni@CNTs/Al2O3 Ceramic Composites with Interfacial Solder Strengthen the Segregated Network for High Toughness and Excellent Electromagnetic Interference Shielding

Ingenious microstructure design and appropriate multicomponent strategies are still challenging for advanced electromagnetic interference (EMI) shielding materials with excellent shielding effectiveness (SE) and reliable mechanical properties in harsh environments and low filling levels. In this study, nickel@multiwalled carbon nanotubes/alumina (Ni@CNTs/Al₂O₃) ceramic composites with segregated structures and electric/magnetic-coupling networks anchored by CNTs and magnetic Ni nanofillers were prepared by hot-press sintering. CNTs/Al₂O₃ ceramic composites exhibit a percolation threshold of only about 0.32013 vol %, which is lower than those of other reported CNTs/Al₂O₃ composites with segregated or uniformly dispersed structures. The electrical conductivity and EMI SE of 9CNTs/Al₂O₃ ceramic composites with 9 vol % (4.76 wt %) CNT content were 103.1 S/m and 33.6 dB, respectively. In addition, EMI SE and toughness were both enhanced by the synergistic effect of Ni nanoparticles and CNTs. In the unit of a segregated structure, a three-dimensional (3D) electric/magnetic-coupling network effectively captures and attenuates electromagnetic wave energy by electrical conduction, dielectric loss, and magnetic loss. On the other hand, the pull-out of CNTs and deflection of cracks distributed along the segregated structures synergistically enhance the fracture toughness of Ni@CNTs/Al₂O₃ ceramic composites. High-performance 3Ni@5CNTs/Al₂O₃ ceramic composites with 5 vol % (2.64 wt %) and 3 vol % (0.76 wt %) CNT contents have been achieved, whose EMI SE is 41.8 dB, density is 90.99%, flexural strength is 197.83 ± 18.62 MPa, and fracture toughness is 6.03 ± 0.23 MPa·m^1/2. This efficient method provides a promising way to fabricate EMI shielding ceramic composites with high mechanical properties.

Optical-Thermally Excited Graphene Resonant Mass Detection: A Molecular Dynamics Analysis

In consideration of the presented optical-thermally excited resonant mass detection scheme, molecular dynamics calculations are performed to investigate the thermal actuation and resonant mass sensing mechanism. The simulation results indicate that an extremely high temperature exists in a 6% central area of the graphene sheet exposed to the exciting laser. Therefore, constraining the laser driving power and enlarging the laser spot radius are essential to weaken the overheating in the middle of the graphene sheet, thus avoiding being burned through. Moreover, molecular dynamics calculations demonstrate a mass sensitivity of 214 kHz/zg for the graphene resonator with a pre-stress of 1 GPa. However, the adsorbed mass would degrade the resonant quality factor from 236 to 193. In comparison, the sensitivity and quality factor could rise by 1.3 and 4 times, respectively, for the graphene sheet with a pre-stress of 5 GPa, thus revealing the availability of enlarging pre-stress for better mass sensing performance.

The Effect of Edge Mode on Mass Sensing for Strained Graphene Resonators

Edge mode could disturb the ultra-subtle mass detection for graphene resonators. Herein, classical molecular dynamics simulations are performed to investigate the effect of edge mode on mass sensing for a doubly clamped strained graphene resonator. Compared with the fundamental mode, the localized vibration of edge mode shows a lower frequency with a constant frequency gap of 32.6 GHz, despite the mutable inner stress ranging from 10 to 50 GPa. Furthermore, the resonant frequency of edge mode is found to be insensitive to centrally located adsorbed mass, while the frequency of the fundamental mode decreases linearly with increasing adsorbates. Thus, a mass determination method using the difference of these two modes is proposed to reduce interferences for robust mass measurement. Moreover, molecular dynamics simulations demonstrate that a stronger prestress or a higher width–length ratio of about 0.8 could increase the low-quality factor induced by edge mode, thus improving the performance in mass sensing for graphene resonators.

Effect of the Pressure of Reaction Gases on the Growth of Single-Crystal Graphene on the Inner Surfaces of Copper Pockets

Single-crystal graphene has attracted much attention due to its excellent electrical properties in recent years, and many growth methods have been proposed, including the copper pockets method. In the copper pockets method, a piece of copper foil is folded into a pocket and put into a chemical vapor deposition (CVD) system for the growth of graphene. The dynamic balance of evaporation and deposition of copper on the inner surfaces of the copper pockets avoids high surface roughness caused by the evaporation of copper in open space, such as the outer surfaces of copper pockets. Much lower partial pressure of methane in the copper pockets and lower surface roughness reduce the nucleation density of graphene and increase the size of single-crystal graphene. It is found that the growth pressure is closely related to the size of single-crystal graphene prepared by the copper pockets method; the higher the growth pressure, the larger the size of single-crystal graphene. It is also found that the growth pressure has an effect on the inner surface roughness of the copper pockets, but the effect is not significant. The main factor affecting the size of the single-crystal graphene is the change in the volume of the copper pockets caused by the change in the growth pressure, and the volume of the copper pockets determines the content of methane in the copper pockets. According to the above law, the size of single-crystal graphene prepared by the copper pockets method can be enlarged by increasing the growth pressure. The size of single-crystal graphene can be enlarged in a wide range as the growth pressure can be increased in a wide range. In our experiments, when the growth pressure reached 450 Pa, single-crystal graphene with a diameter of 450 μm was prepared.

Intercalation: Constructing Nanolaminated Reduced Graphene Oxide/Silica Ceramics for Lightweight and Mechanically Reliable Electromagnetic Interference Shielding Applications

There is a critical need to develop lightweight and mechanically reliable materials for electromagnetic interference (EMI) shielding applications in the harsh environment. In this study, we propose a low-density (∼2.2 g/cm³) reduced graphene oxide (rGO)/silica ceramic with multilayer rGO sheets parallelly aligned inside the silica matrix through a new intercalation strategy. The parallel rGO sheets lead to outstanding EMI shielding effectiveness values of 29-33 dB in the X-band, owing to the interlayer multiple reflections of the electromagnetic wave. Meanwhile, the parallel rGO sheets elevate the flexural strength by 110-130% and improve the fracture toughness by 100-130% compared with the monolithic silica by capturing and deflecting the propagating cracks. The nanolaminated structure constructed by the intercalation approach can effectively break the trade-off between mechanical properties and EMI shielding performances in the graphene/ceramic composites, thus opening up new opportunities in the lightweight and mechanically reliable EMI applications.

Embedding two-dimensional graphene array in ceramic matrix

Dispersing two-dimensional (2D) graphene sheets in 3D material matrix becomes a promising route to access the exceptional mechanical and electrical properties of individual graphene sheets in bulk quantities for macroscopic applications. However, this is highly restricted by the uncontrolled distribution and orientation of the graphene sheets in 3D structures as well as the weak graphene-matrix bonding and poor load transfer. Here, we propose a previously unreported avenue to embed ordered 2D graphene array into ceramics matrix, where the catastrophic fracture failure mode of brittle ceramics was transformed into stable crack propagation behavior with 250 to 500% improvement in the mechanical toughness. An unprecedentedly low dry sliding friction coefficient of 0.06 in bulk ceramics was obtained mainly due to the inhibition of the microcrack propagation by the ordered 2D graphene array. These unique and low-cost 2D graphene array/ceramic composites may find applications in severe environments with superior structural and functional properties.

Graphene platelet reinforced copper composites for improved tribological and thermal properties

In this work, investigations were conducted to evaluate a type of graphene platelet–reinforced copper (GPL/Cu) composite for enhanced tribological and thermal properties. The pin-on-disc (steel) results show that the wear loss and the friction coefficient of the composites decrease by nearly 80% and 70%, respectively, in comparison with those of pure Cu. Thermal conductivity of the composites initially improves substantially by approximately 30% with a slight loading of 0.25 vol% GPLs and decreases gradually with a higher content of GPLs. Microstructural analysis reveals that the enhancement in the tribological property is attributed to both the self-lubricating property of GPLs and grain refinement while the improvement in the thermal property is closely associated with the uniform dispersion of GPLs.

The uniform dispersion and self-lubricating property of GPLs enhance both the tribological and thermal performances.

Recent Advances and Future Prospects in Spark Plasma Sintered Alumina Hybrid Nanocomposites

Although ceramics have many advantages when compared to metals in specific applications, they could be more widely applied if their low properties (fracture toughness, strength, and electrical and thermal conductivities) are improved. Reinforcing ceramics by two nano-phases that have different morphologies and/or properties, called the hybrid microstructure design, has been implemented to develop hybrid ceramic nanocomposites with tailored nanostructures, improved mechanical properties, and enhanced functionalities. The use of the novel spark plasma sintering (SPS) process allowed for the sintering of hybrid ceramic nanocomposite materials to maintain high relative density while also preserving the small grain size of the matrix. As a result, hybrid nanocomposite materials that have better mechanical and functional properties than those of either conventional composites or nanocomposites were produced. The development of hybrid ceramic nanocomposites is in its early stage and it is expected to continue attracting the interest of the scientific community. In the present paper, the progress made in the development of alumina hybrid nanocomposites, using spark plasma sintering, and their properties are reviewed. In addition, the current challenges and potential applications are highlighted. Finally, future prospects for developing alumina hybrid nanocomposites that have better performance are set.

Carbon Nanotubes and Graphene as Nanoreinforcements in Metallic Biomaterials: a Review

Current challenges in existing metallic biomaterials encourage undertaking research in the development of novel materials for biomedical applications. This paper critically reviews the potential of carbon nanotubes (CNT) and graphene as nanoreinforcements in metallic biomaterials for bone tissue engineering. Unique and remarkable mechanical, electrical, and biological properties of these carbon nanomaterials allow their use as secondary-phase reinforcements in monolithic biomaterials. The nanoscale dimensions and extraordinarily large surface areas of CNT and graphene make them suitable materials for purposeful reaction with living organisms. However, the cytocompatibility of CNT and graphene is still a controversial issue that impedes advances in utilizing these promising materials in clinical orthopedic applications. The interaction of CNT and graphene with biological systems including proteins, nucleic acids, and human cells is critically reviewed to assess their cytocompatibity in vitro and in vivo. It is revealed that composites reinforced with CNT and graphene show enhanced adhesion of osteoblast cells, which subsequently promotes bone tissue formation in vivo. This potential is expected to pave the way for developing ground-breaking technologies in regenerative medicine and bone tissue engineering. In addition, current progress and future research directions are highlighted for the development of CNT and graphene reinforced implants for bone tissue engineering.

Carbon nanostructures in biology and medicine

Carbon nanostructures have unique physical, chemical, and electrical properties, which have attracted great interest from scientists. Carbon dots, carbon nanotubes, graphene and other carbon nanomaterials are being successfully implemented in electrochemical sensing, biomedical and biological imaging.

Stainless steel with tailored porosity using canister-free hot isostatic pressing for improved osseointegration implants

Porous biomedical implants hold great potential in preventing stress shielding while improving bone osseointegration and regeneration.

Comprehensive Review on the Use of Graphene-Based Substrates for Regenerative Medicine and Biomedical Devices

Recent research suggests that graphene holds great potential in the biomedical field because of its extraordinary properties. Whereas initial attempts focused on the use of suspended graphene for drug delivery and bioimaging, more recent work has demonstrated its advantages for preparing substrates for tissue engineering and biomedical devices and products. Cells are known to interact with and respond to nanoparticles differently when presented in the form of a substrate than in the form of a suspension. In tissue engineering, a stable and supportive substrate or scaffold is needed to provide mechanical support, chemical stimuli, and biological signals to cells. This review compiles recent advances of the impact of both graphene and graphene-derived particles to prepare supporting substrates for tissue regeneration and devices as well as the associated cell response to multifunctional graphene substrates. We discuss the interaction of cells with pristine graphene, graphene oxide, functionalized graphene, and hybrid graphene particles in the form of coatings and composites. Such materials show excellent biological outcomes in vitro, in particular, for orthopedic and neural tissue engineering applications. Preliminary evaluation of these graphene-based materials in vivo reinforces their promise for tissue regeneration and implants. Although the reported findings of studies on graphene-based substrates are promising, several questions and concerns associated with their in vivo use persist. Possible strategies to examine these issues are presented.

Towards large scale preparation of graphene in molten salts and its use in the fabrication of highly toughened alumina ceramics

Highly crystalline graphene nanosheets were reproducibly generated by the electrochemical exfoliation of graphite electrodes in molten LiCl containing protons. The graphene product has been successfully applied in several applications. This paper discusses the effect of molten salt produced graphene on the microstructures and mechanical properties of alumina articles produced by slip casting and pressureless sintering, which is one of the most convenient methods for the commercial production of alumina ceramics. In addition to graphene, graphite powder and multi-walled carbon nanotubes (CNTs) were also used to prepare alumina articles for comparative purposes. A graphene strengthening effect was realized through microstructural refinement and by influencing the formation of alumina nanorods during the sintering of α-Al₂O₃ articles. The fracture toughness of the sintered alumina articles increased to an impressive value of 6.98 MPa m^1/2 by adding 0.5 wt% graphene nanosheets. This was attributed to the unique microstructure obtained, comprised of micrometer sized alumina grains separated by alumina nanorods.