Diffusion Bonding of Al2O3 Dispersion-Strengthened 316L Composite by Gleeble 3800.

The aim of this work is to investigate the bonding properties of the ceramic dispersion-strengthened 316L (CDS-316L) composites with the reference 316L stainless steel (REF-316L) using a Gleeble 3800 physical simulator. In previous works, two different composites, REF-316L and 316L, with 1 wt% Al2O3 composite (CDS-316L) have been prepared by spark plasma sintering (SPS). In the present work, these specimens were diffusion-bonded using the following parameters: a temperature range of 950-1000 °C and a uniaxial pressure of 20-30 MPa. It was observed that the deformation of the CDS-316L during the uniaxial bonding process was higher compared to the 316L steel rods. The addition of alumina particles increased the micro-hardness of the 316L steel. The samples were broken in the CDS-316L zones, not at the diffusion-bonded interfaces. No diffusion zones have been observed within the investigated magnification for all composites, where the interfaces between the different specimens were well defined.

Amorphous, Carbonated Calcium Phosphate and Biopolymer-Composite-Coated Si3N4/MWCNTs as Potential Novel Implant Materials.

A biodegradable amorphous carbonated calcium phosphate (caCP)-incorporated polycaprolactone (PCL) composite layer was successfully deposited by a spin coater. In this specific coating, the PCL acts as a bioadhesive, since it provides a better adherence of the coatings to the substrate compared to powder coatings. The caCP-PCL coatings were deposited and formed thin layers on the surface of a Si3N4-3 wt% MWCNT (multiwalled carbon nanotube) substrate, which is an emerging type of implant material in the biomedical field. The composite coatings were examined regarding their morphology, structure and biological performance. The biocompatibility of the samples was tested in vitro with MC3T3-E1 preosteoblast cells. Owing to the caCP-PCL thin layer, the cell viability values were considerably increased compared to the substrate material. The ALP and LDH tests showed numerous living cells on the investrigated coatings. The morphology of the MC3T3-E1 cells was examined by fluorescent staining (calcein and DAPI) and scanning electron microscopy, both of which revealed a well-spread, adhered and confluent monolayer of cells. All performed biocompatibility tests were positive and indicated the applicability of the deposited thin composite layers as possible candidates for orthopaedic implants for an extended period.

Advanced Bioactive Glasses: The Newest Achievements and Breakthroughs in the Area.

Bioactive glasses (BGs) are especially useful materials in soft and bone tissue engineering and even in dentistry. They can be the solution to many medical problems, and they have a huge role in the healing processes of bone fractures. Interestingly, they can also promote skin regeneration and wound healing. Bioactive glasses are able to attach to the bone tissues and form an apatite layer which further initiates the biomineralization process. The formed intermediate apatite layer makes a connection between the hard tissue and the bioactive glass material which results in faster healing without any complications or side effects. This review paper summarizes the most recent advancement in the preparation of diverse types of BGs, such as silicate-, borate- and phosphate-based bioactive glasses. We discuss their physical, chemical, and mechanical properties detailing how they affect their biological performances. In order to get a deeper insight into the state-of-the-art in this area, we also consider their medical applications, such as bone regeneration, wound care, and dental/bone implant coatings.

Biominerals Added Bioresorbable Calcium Phosphate Loaded Biopolymer Composites.

Nanocrystalline calcium phosphate (CP) bioceramic coatings and their combination with biopolymers are innovative types of resorbable coatings for load-bearing implants that can promote the integration of metallic implants into human bodies. The nanocrystalline, amorphous CP particles are an advantageous form of the various calcium phosphate phases since they have a faster dissolution rate than that of crystalline hydroxyapatite. Owing to the biomineral additions (Mg, Zn, Sr) in optimized concentrations, the base CP particles became more similar to the mineral phase in human bones (dCP). The effect of biomineral addition into the CaP phases was thoroughly studied. The results showed that the shape, morphology, and amorphous characteristic slightly changed in the case of biomineral addition in low concentrations. The optimized dCP particles were then incorporated into a chosen polycaprolactone (PCL) biopolymer matrix. Very thin, non-continuous, rough layers were formed on the surface of implant substrates via the spin coating method. The SEM elemental mapping proved the perfect incorporation and distribution of dCP particles into the polymer matrix. The bioresorption rate of thin films was followed by corrosion measurements over a long period of time. The corrosion results indicated a faster dissolution rate for the dCP-PCL composite compared to the dCP and CP powder layers.

Influence of Graphene Type and Content on Friction and Wear of Silicon Carbide/Graphene Nanocomposites in Aqueous Environment.

Two different types of graphene materials were used as functional nanofillers for the mechanical and tribological improvement of silicon carbide/graphene nanocomposites. On the one hand is thermally reduced graphite oxide (TRGO) reduced at three different temperatures, and on the other hand is graphene made of three different organic precursors, which were directly coated on silicon carbide (SiC) platelets (GSiC). Additionally, benchmark materials were also used as carbon fillers. The SiC/graphene nanocomposites with 2 wt% filler content were manufactured by pressureless sintering (PLS). Some composites were produced with higher graphene contents of 4% and 8% and sintered by spark plasma sintering (SPS). Microstructural analyses were conducted using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Underwater lubrication, the SP sintered TRGO and GSiC materials with high graphene content have shown the most promising tribological performance. Furthermore, the reduced size of the homogeneously distributed nanoparticles promotes the formation of surface states, which improve the friction and wear properties.

Investigation of the RF Sputtering Process and the Properties of Deposited Silicon Oxynitride Layers under Varying Reactive Gas Conditions.

In a single process run, an amorphous silicon oxynitride layer was grown, which includes the entire transition from oxide to nitride. The variation of the optical properties and the thickness of the layer was characterized by Spectroscopic Ellipsometry (SE) measurements, while the elemental composition was investigated by Energy Dispersive Spectroscopy (EDS). It was revealed that the refractive index of the layer at 632.8 nm is tunable in the 1.48-1.89 range by varying the oxygen partial pressure in the chamber. From the data of the composition of the layer, the typical physical parameters of the process were determined by applying the Berg model valid for reactive sputtering. In our modelling, a new approach was introduced, where the metallic Si target sputtered with a uniform nitrogen and variable oxygen gas flow was considered as an oxygen gas-sputtered SiN target. The layer growth method used in the present work and the revealed correlations between sputtering parameters, layer composition and refractive index, enable both the achievement of the desired optical properties of silicon oxynitride layers and the production of thin films with gradient refractive index for technology applications.

Comparison of the Morphological and Structural Characteristic of Bioresorbable and Biocompatible Hydroxyapatite-Loaded Biopolymer Composites.

Calcium phosphate (CaP)-based ceramic-biopolymer composites can be regarded as innovative bioresorbable coatings for load-bearing implants that can promote the osseointegration process. The carbonated hydroxyapatite (cHAp) phase is the most suitable CaP form, since it has the highest similarity to the mineral phase in human bones. In this paper, we investigated the effect of wet chemical preparation parameters on the formation of different CaP phases and compared their morphological and structural characteristics. The results revealed that the shape and crystallinity of CaP particles were strongly dependent on the post-treatment methods, such as heat or alkaline treatment of as-precipitated powders. In the next step, the optimised cHAp particles have been embedded into two types of biopolymers, such as polyvinyl pyrrolidone (PVP) and cellulose acetate (CA). The pure polymer fibres and the cHAp-biopolymer composites were produced using a novel electrospinning technique. The SEM images showed the differences between the morphology and network of CA and PVP fibres as well as proved the successful attachment of cHAp particles. In both cases, the fibres were partially covered with cHAp clusters. The SEM measurements on samples after one week of immersion in PBS solution evidenced the biodegradability of the cHAp-biopolymer composites.

Silicon Nitride and Hydrogenated Silicon Nitride Thin Films: A Review of Fabrication Methods and Applications.

Silicon nitride (SiNx) and hydrogenated silicon nitride (SiNx:H) thin films enjoy widespread scientific interest across multiple application fields. Exceptional combination of optical, mechanical, and thermal properties allows for their utilization in several industries, from solar and semiconductor to coated glass production. The wide bandgap (~5.2 eV) of thin films allows for its optoelectronic application, while the SiNx layers could act as passivation antireflective layers or as a host matrix for silicon nano-inclusions (Si-ni) for solar cell devices. In addition, high water-impermeability of SiNx makes it a potential candidate for barrier layers of organic light emission diodes (OLEDs). This work presents a review of the state-of-the-art process techniques and applications of SiNx and SiNx:H thin films. We focus on the trends and latest achievements of various deposition processes of recent years. Historically, different kinds of chemical vapor deposition (CVD), such as plasma enhanced (PE-CVD) or hot wire (HW-CVD), as well as electron cyclotron resonance (ECR), are the most common deposition methods, while physical vapor deposition (PVD), which is primarily sputtering, is also widely used. Besides these fabrication methods, atomic layer deposition (ALD) is an emerging technology due to the fact that it is able to control the deposition at the atomic level and provide extremely thin SiNx layers. The application of these three deposition methods is compared, while special attention is paid to the effect of the fabrication method on the properties of SiNx thin films, particularly the optical, mechanical, and thermal properties.

Processing of Al2O3-AlN Ceramics and Their Structural, Mechanical, and Tribological Characterization.

The aim of this study is to present a novel, lower sintering temperature preparation, processing, structural, mechanical, and tribological testing of the AlN-Al2O3 ceramics. The precursor powder of AlN was subjected to oxidation in ambient environment at 900 °C for 3, 10, and 20 h, respectively. These oxidized powders were characterized by SEM and XRD to reveal their morphology, phase, and crystal structure. The SEM results showed coarse powder particles and the presence of aluminum oxide (Al2O3) phase at the surface of aluminum nitride (AlN). The XRD analysis has shown increasing aluminum-oxy-nitride conversion of aluminum nitride as the holding time of oxidation increased. The highest percentage of conversion of AlN powder to AlN-Al2O3 was observed after 10 h. Simultaneously the powders were compacted and sintered using the hot isostatic pressing (HIP) under inert environment (N2 gas) at 1700 °C, 20 MPa for 5 h. This led to the compaction and increase in density of the final samples. Mechanical tests, such as bending test and tribology tests, were carried out on the samples. The mechanical properties of the samples were observed to improve in the oxidized samples compared to the precursor AlN. Moreover, applying longer oxidation time, the mechanical properties of the sintered samples enhanced significantly. Optimum qualitative (microstructure, oxide percentage) and quantitative (tribology, hardness, and bending tests) properties were observed in samples with 10-h oxidation time.

Microstructure and Fracture Mechanism Investigation of Porous Silicon Nitride-Zirconia-Graphene Composite Using Multi-Scale and In-Situ Microscopy.

Silicon nitride-zirconia-graphene composites with high graphene content (5 wt.% and 30 wt.%) were sintered by gas pressure sintering (GPS). The effect of the multilayer graphene (MLG) content on microstructure and fracture mechanism is investigated by multi-scale and in-situ microscopy. Multi-scale microscopy confirms that the phases disperse evenly in the microstructure without obvious agglomeration. The MLG flakes well dispersed between ceramic matrix grains slow down the phase transformation from α to ß-Si3N4, subsequent needle-like growth of ß-Si3N4 rods and the densification due to the reduction in sintering additives particularly in the case with 30 wt.% MLG. The size distribution of Si3N4 phase shifts towards a larger size range with the increase in graphene content from 5 to 30 wt.%, while a higher graphene content (30 wt.%) hinders the growth of the ZrO2 phase. The composite with 30 wt.% MLG has a porosity of 47%, the one with 5 wt.% exhibits a porosity of approximately 30%. Both Si3N4/MLG composites show potential resistance to contact or indentation damage. Crack initiation and propagation, densification of the porous microstructure, and shift of ceramic phases are observed using in-situ transmission electron microscopy. The crack propagates through the ceramic/MLG interface and through both the ceramic and the non-ceramic components in the composite with low graphene content. However, the crack prefers to bypass ceramic phases in the composite with 30 wt.% MLG.

Morphological, Chemical, and Biological Investigation of Ionic Substituted, Pulse Current Deposited Calcium Phosphate Coatings.

Ionic substituted calcium phosphate coatings (iCP) have been prepared by the electrochemical pulse current deposition technique with an alternate pulse on and off time of 5 ms onto a titanium alloy substrate. The elemental distribution and morphology of the deposited layers have been extensively studied by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and transmission electron microscopy (TEM). The crystallinity and phase structure of iCPs have been investigated by X-ray diffraction (XRD). The corrosion characteristics and biodegradability of coatings have been determined by electrochemical measurements, recording potentiodynamic curves in a physiological solution over a long-term immersion period. The cell viability tests confirmed that the iCP coating was biocompatible, while the corrosion tests proved its biodegradable characteristic. In our paper, we compare the morphological, chemical, and biological characteristics of silver and zinc substituted calcium phosphate layers deposited by the electrochemical method.

Corrosion and biocompatibility examination of multi-element modified calcium phosphate bioceramic layers.

Multi-ions doped bioactive calcium phosphate (dCaP) layers were developed by pulse current deposition onto surgical grade titanium alloy material (Ti6Al4V). The coatings were electrodeposited from base electrolyte containing adequate amounts of calcium nitrate and ammonium dihydrogen phosphate at 70 °C. After electrodeposition, the pure CaP layers were doped with different ions that possess bioactive and antimicrobial properties, such as Zn2+, Mg2+, Sr2+ and Ag+ ions. The morphology and structure of coatings were characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy-dispersive X-ray Spectroscopy (EDX) as well as XRD and FT-IR measurements. The results revealed the pulse current deposited and surface post-treated CaP layer to be mainly in hydroxyapatite phase. The corrosion properties of bioceramic coatings were assessed in conventional simulated body fluid (SBF) in a three electrode open cell by using potentiodynamic polarization measurements over two weeks period. The electrochemical results revealed that the pure calcium phosphate (CaP) coated implant material and the bare implant possess the highest resistivity to corrosion, while the modified calcium phosphate coating showed lower corrosion resistance by at least one order of magnitude. The cell viability measurements showed that the electrochemically deposited CaP layer was biocompatible.

Highly wear-resistant and low-friction Si3N4 composites by addition of graphene nanoplatelets approaching the 2D limit.

Graphene nanoplatelets (GNPs) have emerged as one of the most promising filler materials for improving the tribological performance of ceramic composites due to their outstanding solid lubricant properties as well as mechanical and thermal stability. Yet, the addition of GNPs has so far enabled only a very limited improvement in the tribological properties of ceramics, particularly concerning the reduction of their friction coefficient. This is most likely due to the challenges of achieving a continuous lubricating and protecting tribo-film through a high GNP coverage of the exposed surfaces. Here we demonstrate that this can be achieved by efficiently increasing the exfoliation degree of GNPs down to the few-layer (FL) range. By employing FL-GNPs as filler material, the wear resistance of Si3N4 composites can be increased by more than twenty times, the friction coefficient reduced to nearly its half, while the other mechanical properties are also preserved or improved. Confocal Raman spectroscopy measurements revealed that at the origin of the spectacular improvement of the tribological properties is the formation of a continuous FL- GNP tribo-film, already at 5 wt% FL-GNP content.

Comparative study of hydroxyapatite from eggshells and synthetic hydroxyapatite for bone regeneration.

OBJECTIVES: The objective of this study was to evaluate the physical properties of synthetic hydroxyapatite (sHA) and hydroxyapatite from eggshells (eHA) by Fourier-transform infrared (FT-IR) and x-ray diffraction (XRD) and to compare the regenerative ability of the bone using sHA and eHA in a rabbit calvarial defect model. STUDY DESIGN: FT-IR and XRD were used to compare the physical properties of sHA and eHA. sHA was purchased from Sigma, and eHA was kindly donated from the Hungarian academy of science. Sixteen New Zealand white rabbits were used for the animal study. After the formation of a bilateral parietal bony defect (diameter 8.0 mm), either sHA or eHA was grafted into the defect. The defect in the control was left unfilled. Bone regeneration was evaluated by histomorphometry at 4 and 8 weeks after the operation. RESULTS: The peak broadening of the XRD experiments were in agreement with scanning electron microscope observation; the sHA had a smaller granule size than the eHA. The eHA had impurities phases of CaO (International Center for Diffraction Data (ICDD) 075-0264) and Ca(OH)(2) (ICDD 072-0156). Total new bone was 17.11 ± 10.24% in the control group, 28.81 ± 12.63% in sHA group, and 25.68 ± 10.89% in eHA group at 4 weeks after the operation. The difference was not statistically significant (P > .05). Total new bone at 8 weeks after the operation was 27.50 ± 10.89% in the control group, 38.62 ± 17.42% in sHA group, and 41.99 ± 8.44% in the eHA group. When comparing the sHA group to the control group, the difference was not statistically significant (P > .05). However, the eHA group was significantly different from the control group (P = .038). When comparing the eHA group to the sHA group, the difference was not statistically significant (P > .05). CONCLUSIONS: Both types of HA showed higher bone formation than the unfilled control. However, eHA had significantly higher bone formation than the unfilled control at 8 weeks after operation.

Distribution patterns of different carbon nanostructures in silicon nitride composites.

The dispersion properties of single- and multi-walled carbon nanotubes as well as mechanically exfoliated few layer graphene flakes within the silicon nitride ceramic matrix have been investigated. Small angle neutron scattering experiments have been employed to gain information on the dispersion of the nano-scale carbon fillers throughout the entire volume of the samples. The neutron scattering data combined with scanning electron microscopy revealed strikingly different distribution patterns for different types of carbon nanostructures. The scattering intensities for single wall carbon nanotubes (SWCNTs) reveal a decay exponent characteristic to surface fractals, which indicate that the predominant part of nanotubes can be found in loose networks wrapping the grains of the polycrystalline matrix. By contrast, multi wall carbon nanotubes (MWCNTs) were found to be present mainly in the form of bulk aggregate structures, while few-layer graphene (FLG) flakes have been individually dispersed within the host matrix, under the very same preparation and processing conditions.

Development of nano-hydroxyapatite graft with silk fibroin scaffold as a new bone substitute.

PURPOSE: This study involves a comparison between the bone regeneration of nano-hydroxyapatite (nHA), as derived from eggshells either with or without silk fibroin scaffolds, and the unfilled control in the rabbit calvarial bony defect model. MATERIALS AND METHODS: Sixteen 4-month-old New Zealand white rabbits, with a mean weight of 2.8 kg (range, 2.5-3.0 kg), were used in this experiment. After the formation of bilateral parietal bony defects (diameter, 8.0 mm), either an nHA or an nHA+silk fibroin combination (nHA+silk) was grafted. The control was unfilled defect. The bone regeneration was evaluated by micro-computed tomography (µCT) and histomorphometric analyses at 4 and 8 weeks. RESULTS: All measured variables of the µCT analysis were significantly higher in the grafted groups (nHA and nHA+silk) than in the unfilled control groups at both 4 and 8 weeks after operation (P < .05). On histomorphometric analysis, there was no significant difference between the groups at 4 weeks after operation. However, the nHA group exerted significantly higher bone regeneration (40.16% ± 8.27%) compared with the unfilled control group (25.66% ± 10.98%) or the nHA+silk group (16.62% ± 3.05%) (P < .05). CONCLUSION: The nHA from eggshells exerted better bone formation than the unfilled control group on both µCT and histomorphometric analyses. Considering the rapid healing in bony defect and easy availability, the nHA from the eggshells could prove to be a good new bone substitute.