A study of bioactive glass-ceramic's mechanical properties, apatite formation, and medical applications.

Apparently, bioactive glass-ceramics are made by doing a number of steps, such as creating a microstructure from dispersed crystals within the residual glass, which provides high bending strength, and apatite crystallizes on surfaces of glass-ceramics when calcium ions are present in the blood. Apatite crystals grow on the glass and ceramic surfaces due to the hydrated silica. These materials are biocompatible with living bone in a matter of weeks, don't weaken mechanically or histologically, and exhibit good osteointegration as well as mechanical properties that are therapeutically relevant, such as fracture toughness and flexural strength. As part of this study, we examined mechanical properties, process mechanisms involved in apatite formation, and potential applications for bioactive glass-ceramic in orthopedic surgery, including load-bearing devices.

Angiogenesis, Osseointegration, and Antibacterial Applications of Polyelectrolyte Multilayer Coatings Incorporated With Silver/Strontium Containing Mesoporous Bioactive Glass on 316L Stainless Steel.

The main causes for failure in implant surgery are prolonged exposure of implants or wound and tissue ischemia. Bacterial infection caused by the surrounding medical environment and equipment is also a major risk factor. The medical risk would be greatly reduced if we could develop an implant coating to guide tissue growth and promote antibacterial activity. Mesoporous bioactive glasses are mainly silicates with good osteoinductivity and have been used in medical dentistry and orthopedics for several decades. Strontium ions and silver ions could plausibly be incorporated into bioactive glass to achieve the required function. Strontium ions are trace elements in human bone that have been proposed to promote osseointegration and angiogenesis. Silver ions can cause bacterial apoptosis through surface charge imbalance after bonding to the cell membrane. In this study, functional polyelectrolyte multilayer (PEM) coatings were adhered to 316L stainless steel (SS) by spin coating. The multilayer film was composed of biocompatible and biodegradable collagen as a positively charged layer, γ-polyglutamic acid (γ-PGA) as a negatively charged layer. Chitosan was incorporated to the 11th positively charged layer as a stabilizing barrier. Spray pyrolysis prepared mesoporous bioactive glass incorporated with silver and strontium (AgSrMBG) was added to each negatively charged layer. The PEM/AgSrMBG coating was well hydrophilic with a contact angle of 37.09°, hardness of 0.29 ± 0.09 GPa, Young's modulus of 5.35 ± 1.55 GPa, and roughness of 374.78 ± 22.27 nm, as observed through nano-indention and white light interferometry. The coating's antibacterial activity was sustained for 1 month through the inhibition zone test, and was biocompatible with rat bone marrow mesenchymal stem cells (rBMSCs) and human umbilical vein endothelial cells (HUVECs), as observed in the MTT assay. There was more hydroxyapatite precipitation on the PEM/AgSrMBG surface after being soaked in simulated body fluid (SBF), as observed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). In both in vitro and in vivo tests, the PEM/AgSrMBG coating promoted angiogenesis, osseointegration, and antibacterial activity due to the sustained release of silver and strontium ions.

Investigation of Bone Growth in Additive-Manufactured Pedicle Screw Implant by Using Ti-6Al-4V and Bioactive Glass Powder Composite.

In this study, we optimized the geometry and composition of additive-manufactured pedicle screws. Metal powders of titanium-aluminum-vanadium (Ti-6Al-4V) were mixed with reactive glass-ceramic biomaterials of bioactive glass (BG) powders. To optimize the geometry of pedicle screws, we applied a novel numerical approach to proposing the optimal shape of the healing chamber to promote biological healing. We examined the geometry and composition effects of pedicle screw implants on the interfacial autologous bone attachment and bone graft incorporation through in vivo studies. The addition of an optimal amount of BG to Ti-6Al-4V leads to a lower elastic modulus of the ceramic-metal composite material, effectively reducing the stress-shielding effects. Pedicle screw implants with optimal shape design and made of the composite material of Ti-6Al-4V doped with BG fabricated through additive manufacturing exhibit greater osseointegration and a more rapid bone volume fraction during the fracture healing process 120 days after implantation, per in vivo studies.

Deformations of Ti-6Al-4V additive-manufacturing-induced isotropic and anisotropic columnar structures: Insitu measurements and underlying mechanisms.

The deformations of isotropic and anisotropic Ti-6Al-4V columnar structures fabricated by additive manufacturing were extensively examined. The distinct texture and microstructure distributions were characterised. In situ X-ray diffraction measurements show different lattice activities resulting from the different microstructure distributions. Spatially resolved mapping revealed manufacturing-induced crystallite-orientation distributions that determine the deformation mechanisms. We propose a self-consistent model to correlate the multi-scale characteristics, from the anisotropic-texture-distribution microstructure to the bulk mechanical properties. We determined that basal and pyramidal slip activities were activated by tension deformation. The underlying additive-manufacturing-induced crystal plasticity plays a major role. We find that the texture development of the columnar structures and the distribution of crystallite orientation achieved by different processing conditions during additive manufacturing have important effects on the mechanical properties. The dominant deformation mode for the anisotropic Ti-6Al-4V columnar structure is basal slip, and that for the isotropic Ti-6Al-4V columnar structure is pyramidal slip. The difference may be important for determining the fatigue behaviour.

Correlation of Morphology and In-Vitro Degradation Behavior of Spray Pyrolyzed Bioactive Glasses.

Bioactive glass (BG) is considered to be one of the most remarkable materials in the field of bone tissue regeneration due to its superior bioactivity. In this study, both un-treated and polyethylene glycols (PEG)-treated BG particles were prepared using a spray pyrolysis process to study the correlation between particle morphology and degradation behavior. The phase compositions, surface morphologies, inner structures, and specific surface areas of all BG specimens were examined by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption/desorption, respectively. Simulated body fluid (SBF) immersion evaluated the assessments of bioactivity and degradation behavior. The results demonstrate three particle morphologies of solid, porous, and hollow factors. The correlation between porosity, bioactivity, and degradation behavior was discussed.

Manipulation of the degradation behavior of calcium sulfate by the addition of bioglass.

A bioactive calcium sulfate/glass composite was prepared using a sintering technique, and Ca-P-Si glass particles were prepared by spray pyrolysis. The glass exhibited bioactivity in terms of its ability to form apatite in a simulated body fluid. The glass was transformed into two crystallized phases, i.e., calcium phosphate and calcium silicate, respectively, during the heating stage. The presence of the crystallized phases retarded the densification of calcium sulfate. A high sintering temperature of 1200 °C was needed to prepare the composite. The increased addition of glass enhanced the strength and decreases the degradation rate of calcium sulfate. The new composite is not only degradable but also bioactive.

Control of Dopant Distribution in Yttrium-Doped Bioactive Glass for Selective Internal Radiotherapy Applications Using Spray Pyrolysis.

In this study, we demonstrate the fabrication of Y-doped bioactive glass (BG), which is proposed as a potential material for selective internal radiotherapy applications. Owing to its superior bioactivity and biodegradability, it overcomes the problem of yttrium aluminosilicate spheres that remain in the host body for a long duration after treatment. The preparation of Y-doped BG powders were carried out using a spray pyrolysis method. By using two different yttrium sources, we examine the change of the local distribution of yttrium concentration. In addition, characterizations of phase information, particle morphologies, surface areas, and bioactivity were also performed. The results show that both Y-doped BG powders are bioactive and the local Y distribution can be controlled.

Effect of Acetic Acid Concentration on Pore Structure for Mesoporous Bioactive Glass during Spray Pyrolysis.

Mesoporous bioactive glass (MBG) is considered as one of the most important materials in the field of bone implants and drug carriers, owing to its superior bioactivity. In previous studies, tri-block surfactants (e.g., F127 and P123) were commonly used as pore-forming agents. However, the use of surfactants may cause serious problems such as micelle aggregation and carbon contamination and thus decrease bioactivity. Therefore, in this study, we demonstrated the synthesis of MBG using acetic acid (HAc) as a pore-forming agent to overcome the disadvantages caused by surfactants. Both untreated and HAc-treated BG powders were synthesized using spray pyrolysis and various characterizations were carried out. The results show that a mesoporous structure was successfully formed and the highest specific surface area of ~230 m²/g with improved bioactivity was reported.

Morphology Control of Eu-Doped Amorphous Gehlenite Phosphors Prepared by Spray Pyrolysis.

Eu-doped amorphous gehlenite phosphors with various morphologies were synthesized using spray pyrolysis. Along with un-treated precursor, two commonly used pore-forming agents, polyethylene glycol and hydrogen peroxide, were applied to achieve porous and hollow particle structures. The phase compositions, surface morphologies, inner structures and photoluminescence properties of the resulting phosphors were examined by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and fluorescence spectrometry. The results showed that the morphologies of the particles were well-controlled, and a correlation between morphology and photoluminescence properties was established.

Composite Polyelectrolyte Multilayer and Mesoporous Bioactive Glass Nanoparticle Coating on 316L Stainless Steel for Controlled Antibiotic Release and Biocompatibility.

Bacterial infection in wounds or implants can cause osteomyelitis, eventually leading to orthopedic implant failure. In this study, polyelectrolyte multilayer (PEM) coating comprising collagen as the cationic layer, chitosan as the barrier layer and γ-poly-glutamic acid as the anionic layer were fabricated onto a 316L stainless steel substrate by spin coating technique. Tetracycline-loaded 57S mesoporous bioactive glass nanoparticles (57S MBG, SiO2:CaO:P2O5 = 57:33:10 by wt%) were introduced into the γ-poly-glutamic acid layers. Herein, 57S MBG nanoparticles were successfully incorporated into the PEMs with a total thickness of ∼53 µm on 316L stainless steel (SS-PEMs-57S), which exhibited good hydrophilicity with a contact angle of 18.71°. The hardness of SS-PEMs-57S was 0.66 GPa while the Young's modulus was 11.5 GPa; these values are similar to those for the cortical bone. The surface roughness of MBG nanoparticle-incorporated PEMs increased from 231 to 384 nm. Controlled release of tetracycline loaded in MBG nanoparticles resulted in sustained antibacterial effect for up to 7 days, with higher release efficacy at low pH, which may be induced by inflammation or infection. Tetracycline loaded in SS-PEMs-57S showed good bacterial inhibition and maintained good cell viability in rat bone marrow mesenchymal stem cells (BMSCs) in the MTT assay. Moreover, SS-PEMs-57S also promoted mineralization of BMSCs. Therefore, this surface modification technology has great potential for endowing orthopedic implants with antibacterial and osteoconductive properties.

The Correlation of Pore Size and Bioactivity of Spray-Pyrolyzed Mesoporous Bioactive Glasses.

SiO2-CaO-P2O5-based mesoporous bioactive glasses (MBGs) were synthesized by spray pyrolysis in this study. Three commonly used non-ionic tri-block copolymers (L121, P123, and F127) with various lengths of hydrophilic chains were applied as structural templates to achieve different pore sizes. A mesoporous structure was observed in each as-prepared specimen, and the results showed that the L121-treated MBG had the largest pore size. The results of bioactivity tests indicated that the growth of hydroxyapatite is related to the pore size of the materials.

The Correlation of Surfactant Concentrations on the Properties of Mesoporous Bioactive Glass.

Bioactive glass (BG), a potential biomaterial, has received increasing attention since the discovery of its superior bioactivity. One of the main research objectives is to improve the bioactive property of BGs; therefore, surfactant-derived mesoporous bioactive glasses (MBGs) were developed to provide a high specific surface area for achieving higher bioactivity. In this study, various concentrations of typical triblock F127 surfactant were used to manipulate the morphology, specific surface area, and bioactivity of MBG particles. Two typical morphologies of smooth (Type I) and wrinkled (Type II) spheres were observed, and the population of Type II particles increased with an increase in the surfactant concentration. A direct correlation between specific surface area and bioactivity was observed by comparing the data obtained using the nitrogen adsorption-desorption method and in vitro bioactive tests. Furthermore, the optimal surfactant concentration corresponding to the highest bioactivity revealed that the surfactant aggregated to form Type II particles when the surface concentration was higher than the critical micelle concentration, and the high population of Type II particles may reduce the specific surface area because of the loss of bioactivity. Moreover, the formation mechanism of SP-derived MBG particles is discussed.

Monodispersity of magnetic immuno-nanoprobes enhances the detection sensitivity of low abundance biomarkers in one drop of serum.

To enhance the detection sensitivity of target clinical protein biomarkers, a simple and rapid nanoprobe-based immuno-affinity mass spectrometry assay employing biocompatible monodisperse magnetic nanoparticles (MNPs) is reported herein. The MNPs were synthesized via a streamlined protocol that includes (a) fabrication of core MNPs using the thermal decomposition method to minimize aggregation, (b) surface protection by gold coating (MNP@Au) and surfactant coating using MNP@IGEPAL to improve hydrophilicity, and lastly, (c) oriented functionalization of antibodies to maximize immuno-affinity. The enrichment performances of the monodisperse MNPs for the C-reactive protein (CRP) serum biomarker were then evaluated and compared with aggregated magnetic nanoparticles synthesized from the conventional co-precipitation method (MNP(CP)). The detection sensitivity for CRP at an extremely low amount of serum sample (1 µL) was enhanced ∼19- and ∼15-fold when monodisperse MNP@Au and MNP@IGEPAL, respectively, were used. Furthermore, the detection sensitivity of CRP by this approach (1 ng mL(-1), S/N = 3) provided a 1000-fold sensitivity enhancement to the clinical cut-off (1 µg mL(-1)) of CRP. We supposed that these observed improvements are due to the enhanced nanoparticle dispersibility and size uniformity which eliminated completely other non-specific binding of high-abundance serum proteins. Most interestingly, the enrichment efficiency correlates more closely with the MNP dispersibility than the ligand density. Our investigation revealed the critical role of MNP dispersibility, as well as provided mechanistic insight into its impact on immunoaffinity enrichment and detection of CRP in one drop of serum sample. This strategy offers an essential advantage over the other methods by providing a simple and facile biofunctionalization protocol while maintaining excellent solvent dispersibility of MNPs.

The Influence of Phase Separation on Bioactivity of Spray Pyrolyzed Bioactive Glass.

In this study, bioactive glass (BG) particles were synthesized directly using spray pyrolysis (SP). Since the bioactivity of glass particles is well correlated with their chemical composition, how to obtain homogenous bioactive glass becomes an important issue. For SP, the main reason for chemical inhomogeneity was considered to be caused by the difference in the precipitation speed of each precursor. So, two Si-containing precursors of BG, namely tetraethyl orthosilicate (TEOS) and silicon acetate (SiA), have been applied to prepare BG particles. The bioglasses were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy to examine their phase composition, and surface structures, inner morphologies and chemical compositions. It was observed that, under the calcination temperature of 700 degrees C, TEOS-derived powder contained Si-rich nanoparticles and Si-deficit submicron particles as inhomogeneity, whereas the SiA-derived powder was homogenous. The reason of inhomogeneity is that TEOS dissolves in "volatile" ethanol more readily than in water via the SP mechanism of "gas-to-particle-conversion" to form Si-rich nanoparticles. The presence of Si-rich nanoparticles causes Si-deficit "wollastonite submicron particles" to form, which impairs the bioactivity. Finally, BG particle formation mechanisms from different precursors have been proposed.

Control of Ag nanoparticle distribution influencing bioactive and antibacterial properties of Ag-doped mesoporous bioactive glass particles prepared by spray pyrolysis.

Mesoporous bioactive glasses (MBGs) have become important bone implant materials because of their high specific surface area resulting in high bioactivity. Doping MBGs with Ag removes one of the remaining challenges to their applications, namely their lack of intrinsic antibacterial properties. In present work we demonstrate that Ag-doped MBGs can be prepared in one-step spray pyrolysis (SP) process. The SP preparation method offers the advantages of short processing times and continuous production over the sol-gel method previously used to prepare MBGs. Using scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction we demonstrate that the synthesized MBG particles have amorphous structure with nanocrystalline Ag inclusions. The scanning transmission electron microscopy-X-ray energy dispersive spectrometry of cross-sectional samples shows that the distribution of the Ag dopant nanoparticles within MBGs can be controlled by using the appropriate formulation of the precursors. The distribution of the Ag dopant nanoparticles within the MBG particles was found to affect their surface areas, bioactivities and antibacterial properties. Based on the observations, we propose a mechanism describing MBG particle formation and controlling dopant distribution.

Manipulation of dopant distribution in yttrium-doped ceria particles.

Yttrium is one of the most widely used dopants (e.g., in yttrium-doped ceria (YDC) and yttria-stabilized zirconia) for improving performance of solid electrolytes utilized in solid oxide fuel cells. Oxygen ion conductivity is known to be a function of yttrium concentration in the electrolytes and thus it is important to further understand the factors that influence such concentration distribution. In this study, we examine the change in the distribution of yttrium concentration after annealing in YDC particles. The geometry and morphology of YDC particles, synthesized by spray pyrolysis, were characterized using transmission electron microscopy, and the distribution of yttrium was investigated by X-ray energy-dispersive spectroscopy (XEDS) considering electron interaction volume and geometry of the particle in the XEDS profile analysis. In addition, relative concentrations of Ce(lll) ions, which are thought to be proportional to the concentrations of the oxygen vacancies in the YDC particles, were examined using X-ray photoelectron spectroscopy to correlate with yttrium concentration distributions. It was found that in the as-prepared hollow spherical particles the concentration of yttrium increases linearly from the inner surface towards the outer surface. After annealing the distribution of yttrium becomes non-linear and the dopant is found to migrate to the inner and outer surfaces of the particle. The decrease of the concentration of Ce(lll) ions upon annealing followed by the formation of the dopant concentration gradient is likely due to the increase of the size of the crystallites in the particles.

Characterization of mesoporosity in ceria particles using electron microscopy.

The geometry and three-dimensional (3D) morphology of the ceria particles synthesized by spray pyrolysis (SP) from two different precursors--cerium acetate hydrate and cerium nitrate hydrate (CeA and CeN ceria particles)--were characterized by transmission electron microscopy and electron tomography. Results were compared with surface area measurements, confirming that the surface area of CeA ceria particles is twice as large as that of CeN ceria particles. This result was supported by 3D microstructural observations, which have revealed that CeA ceria particles contain open pores (connected to surfaces) and closed pores (embedded in particles), while CeN ceria particles only contained closed pores. This experimental result suggests that the type of porosity is controlled by the precursors and could be related to their melting temperature during the heating process in SP.

A new system for synthesis of high quality nonpolar GaN thin films.

High quality nonpolar m-plane GaN films were successfully grown on LiGaO(2) (100) substrates for the first time. This m-plane GaN/LiGaO(2) (100) system opens a new approach for realizing highly-efficient nitride devices.

Study of nano-Ag particles doped TiO2 prepared by photocatalysis.

Nano-silver (Ag) particle doped TiO2 composite photocatalyst was prepared by photocatalytic reaction of anatase TiO2 with AgNO3 solution. Microstructures of these particles were characterized using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDAX) and transmission electron microscopy (TEM). Its photocatalytic behavior was examined by the degradations of two dyes, methyl orange and methylene blue. In contrast to Ag free TiO2 particles, the nano-Ag particle doped TiO2 photocatalyst exhibits much higher catalytic activity. It was also found that 1.0 wt% Ag doped to the TiO2 particles, synthesized through 10 hour ultraviolet (UV) irradiation, offer the best photocatalytic property.

Cross-sectional observation of yttrium and nickel oxide doped ceria powder.

In this paper, microstructures of ceria powder, synthesized using spray pyrolysis method, were characterized by focused ion beam technique and transmission electron microscopy. Dependence of the shape of powder particle on the size was found. It appears a spherical shape with the diameter less than approximately 500 nm and shows cup-like shape when their diameters become larger as a result of concaving. This suggests that the spherical particle has a hollow structure as proved by focused ion beam cross-sectioning. It was also found that both the inner and the outer shells of particles are crystalline but comprised of different phases with the inner shell being NiO and the outer shell CeO2. These results benefit from a transmission electron microscopy sample preparation method to produce a cross-section of the particle. The detail of the method was described in the paper.