In vitro studies of hydrogen peroxide treated titanium for biomedical applications

Pure titanium substrate was subjected to chemical treatment with different concentrations of hydrogen peroxide and subsequently heat treated to produce a titania gel layer with anatase nature. The surface modified substrates were then immersed in simulated body fluid for the formation of calcium phosphate layer over the surface. Titanium treated with 15 wt.% of hydrogen peroxide produced a uniform porous layer, which was found to induce the calcium phosphate formation more easily. However, titanium treated with 5 wt.% and 25 wt.% of hydrogen peroxide exhibited inhomogeneous surface for the growth of calcium phosphate layer. Further, the corrosion behaviour of the untreated and hydrogen peroxide treated specimens in simulated body fluid was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy. The results have shown that the surface modified titanium using 15 wt.% of hydrogen peroxide exhibited higher corrosion resistance compared to specimens treated with other concentrations of hydrogen peroxide.     

Spark plasma sintering,mechanical and in-vitro behavior of a novel Sr- and Mg-containing bioactive glass for biomedical applications

The so-called BGMS10, a bioactive glass containing 10 mol.% SrO and 10 mol.% MgO, displays a low inclination to crystallize, as confirmed by its high activation energy (538.9 kJ/mol). Such peculiar aspect and the beneficial use of SPS allow for the obtainment of 99.7 % dense and fully amorphous products at 750 °C. The incipient crystallization in the glass is observed when temperature is increased to 850 °C, while 95 wt. % crystallized ceramics are produced at 950 °C. Main crystalline phases are α- and β-CaSiO₃, with grain size of 89 and 97 nm, respectively. Glass crystallization is accompanied by Young’s modulus increase from 90.92 to 98.38 GPa. On the other hand, partially crystallized samples (850 °C) exhibit higher Vickers hardness (718.8) compared to fully crystallized ones (619.8), which show lower density (98.6 %). In-vitro tests in SBF indicate that the silica-gel film preceding apatite nucleation is mostly formed on the amorphous substrate region.     

Morphological,mechanical, and biological evolution of pure hydroxyapatite and its composites with titanium carbide for biomedical applications

Pure hydroxyapatite (HAp) was synthesized successfully via a wet chemical precipitation method. To study the influence of TiC (weight % of 5, 10, 15) substitution on the mechanical behavior of pure HAp, its composites with TiC were synthesized using a solid-state reaction method. Herein, detailed investigations of pure HAp and its composites using X-ray powder diffraction (XRD), FTIR spectroscopy, Raman spectroscopy, UV-VIS spectroscopy, SEM followed by EDAX and particle size analysis were carried out. XRD study reveals the phase stability of the prepared HAp and composite samples. However, FTIR and Raman spectroscopic studies revealed the bond formation among the various constituents. Mechanical behavior of HAp, and its composites with TiC were studied using numerous parameters like density, Young's modulus, fracture toughness, and load absorption capability. Based on these studies, it was revealed that the addition of 5 wt % substitution of TiC sintered at 1200 °C significantly enhanced the mechanical properties of pure HAp. Hence, 5 wt % of TiC composite 95HAp-5TiC showed the best mechanical characteristics such as density (2.3060 g/cm³), Young's modulus (14.53 MPa), fracture toughness (19.82 MPa m^1/2), maximum compressive strength (186 MPa) respectively. Cytotoxicity and osteogenic activities of the synthesized pure HAp and its composite, 95HAp-5TiC were performed using osteoblast cells (mouse calvarial) at different concentrations of the samples (0.01 μg, - 100 μg). From the above studies, the cell viability and ALP activities of the composite, 95HAp-5TiC found to be excellent than that of pure HAp. Hence, this composite sample may be utilized for bone implant applications.     

Boron-based bioactive glasses: Properties,processing, characterization and applications

The performance of many biological processes is thought to be affected by boron, and a deficiency is linked to delayed bone growth. Boron is therefore a bioactive element that is advantageous to both people and animals. Another well-known benefit of boron is that it promotes bone growth and wound healing. Glass structure, glass processing properties, biodegradability, biocompatibility, bioactivity, and cytotoxicity are all significantly impacted by the introduction of boron to bioactive glasses in a range of concentrations. According to research so far, boron based bioactive glasses (BBGs) frequently surpass silicate glasses in terms of bioactivity and potential for bone healing. Additionally, they could be employed as medication delivery systems for the treatment of infections and conditions like osteoporosis. By adding modifying ions, BBGs capacity to heal wounds or repair bone can be increased. Boron based bioactive glasses are typically synthesized via melt-quenching, although a more recent, more promising technique sol-gel processing is starting to attract interest. This review analyses the available literature to offer an in-depth overview of BBG properties, their real-world applications, challenges, and suggestions for future study.     

Structural behavior and in vitro bioactivity evaluation of hydroxyapatite-like bioactive glass based on the SiO2-CaO-P2O5 system

Silicate bioglass is of great importance in bone engineering because of its excellent bioactivity and osteogenic effects. In this study, hydroxyapatite-like bioactive glass based on the xSiO₂-CaO-P₂O₅ (x = 30, 45, 60 and 90 mol.%, Ca/P = 1.67) system was synthesized by the sol-gel method, and the corresponding structural evolution, apatite-forming ability and cytotoxicity were systematically investigated. The results suggest that both a higher heat treatment temperature and a lower SiO₂ content increase the crystallinity tendency of the bioglass, and the samples become obviously compact as the SiO₂ amount increases from 30 to 90 mol.%. Compared with the samples with higher SiO₂ content, the 30Si sample shows more remarkable internal connected mesoporous structures, with a higher specific surface area up to 129.12 m²/g, exhibiting excellent hydroxyapatite formation in simulated body fluid. Moreover, no obvious inhibitory effect was presented on human periodontal ligament cells (hPDLCs) for any of the silicate glass samples.     

Influence of Cu on the mechanical and tribological properties of Ti3SiC2

Ti₃SiC₂/Cu composites with different contents of Cu were fabricated by mechanical alloying and spark plasma sintering method. The phase composition and structure of the composites were analyzed by X-ray diffractometry and scanning electron microscopy equipped with energy dispersive spectroscopy. The mechanical and tribological properties of Ti₃SiC₂/Cu composites were tested and analyzed compared with monolithic Ti₃SiC₂ in details. The results show that the Cu leads to the decomposition of Ti₃SiC₂ to produce TiC_x, Ti₅Si₃C_y, Cu₃Si, and TiSi₂C_z. The friction coefficient and wear rate of the composites are lower than that of monolithic Ti₃SiC₂, which is ascribed to the fixing effect of hard TiC_x, Ti₅Si₃C_y, and Cu₃Si to inhibit the abrasive friction and wear. However, at elevated temperatures (ranging from room temperature to 600 °C) the friction and wear of the composites are higher than those at room temperature. Plastic flowing and tribo-oxidation wear accompanied by material transference contribute to the increased friction and wear at elevated temperatures.     

Biocompatibility,physico-chemical and mechanical properties of hydroxyapatite-based silicon dioxide nanocomposites for biomedical applications

High-energy ball milling was employed to prepare carbonated hydroxyapatite/silicon dioxide (CHA/SiO₂) nanocomposites. Then, these nanocomposite powders were sintered at 900 and 1300 °C. XRD technique, FTIR spectroscopy and SEM were employed to examine the structure, molecular structure and microstructure of the sintered nanocomposites samples, respectively. Moreover, their mechanical properties were also measured. Furthermore, in vitro bioactivity and cytotoxicity of these nanocomposites were evaluated. The results indicated that the successive increases in SiO₂ contents led to remarkable enhancement for densification behavior, mechanical properties and in vitro bioactivity of nanocomposites sintered at 900 °C. However, further increase in the sintering temperature to 1300 °C caused dramatic decreases in density and mechanical properties of nanocomposites. On the contrary, better bioactivity behavior was achieved. Amazingly, the obtained results revealed that the sample having the highest content of SiO₂ and sintered at 900 °C had no toxic effects on bone-like cells while, that sintered at 1300 °C exhibited mild cytotoxicity. Based on the variations in the abovementioned properties, these nanocomposites can be used in different biomedical applications.     

Investigation of in vitro mineralization of silicate-based 45S5 and 13-93 bioactive glasses in artificial saliva for dental applications

Bioactive glasses are important class of materials that have a wide range of applications in tissue engineering and dentistry. In dental tissue engineering, nanofibrous structures exhibit interesting features, such as high surface area, surface functionalization and porosity. In this study, silicate-based 45S5 and 13-93 bioactive glass fibers were fabricated using electrospinning technique and their in vitro mineralization behavior was investigated in two different artificial saliva solutions for various time intervals. Results revealed that both 45S5 and 13-93 bioactive glass fibers show high mineralization behavior in artificial saliva solutions. However different hydroxyapatite (HA) formation rates were observed depending on the glass type and the artificial saliva composition. HA formation initiated earlier in 45S5 glass fibers treated in artificial saliva compared to 13-93 glass. On the other hand, after 30 days of treatment, the surface of 13-93 glass fibers converted to pure crystalline HA, whereas, 45S5 glass surface contained some additional crystalline phases such as aragonite and calcite. Treatment in SAGF medium resulted with better HA conversion ability compared to Carter-Brugirard saliva for both types of glass fibers. In conclusion, the use of electrospun nanofibrous 45S5 and 13-93 bioactive glass scaffolds could be one approach suitable to dental applications.     

Electrophoretic deposition of bioactive glass nanopowders on magnesium based alloy for biomedical applications

To slow down the initial biodegradation rate of magnesium (Mg) alloy, crystalline nano-sized bioactive glass coating was used to deposit on micro-arc oxidized AZ91 samples via electrophoretic deposition (EPD). Zeta potential and conductivity of the bioactive glass suspension were characterized at various pH values to identify the most stable dispersion conditions. The bone-bonding properties of bioactive glass coated samples were evaluated in terms of apatite-forming ability during the immersion in simulated body fluid (SBF) solution. Results revealed that the ability to form a bioactive glass coating via EPD was influenced by the degree of its crystalline phase composition. Moreover, the potentiodynamic polarization tests recorded significant drops in corrosion current density and corrosion rate of the coated samples which implies a good level of corrosion protective behavior. These preliminary results show that this process will enable the development of Mg implants in the later stage of bone healing.     

Development by robocasting and mechanical characterization of hybrid HA/PCL coaxial scaffolds for biomedical applications

Porous structures consisting of a tetragonal three-dimensional mesh of interpenetrating coaxial tubes were fabricated by robocasting from hydroxyapatite (HA) inks. After sintering the structures, polycaprolactone (PCL) was infiltrated within the tubes core by injection of a polymer solution. The addition of the polymer enhanced the mechanical performance in terms of toughness over dense- and hollow-strut all-ceramic scaffolds, specially under bending stresses. PCL impregnation improved also the compressive strength over hollow-strut scaffolds —although dense-strut structures remained stronger especially in compression. Thus, this coaxial core-shell strut configuration combines the best features of each material: the necessary stiffness and excellent osteoconductivity of the bioceramic, with the high toughness and ductility of the biopolymer; and allows the fabrication of hybrid scaffolds with the interconnected macroporosity necessary for cell ingrowth. Hence, this work successfully provides a proof-of-concept of this novel strategy for the mechanical enhancement of bioceramic-based scaffolds while preserving their osteoconductive properties.     

Mechanical properties of porous MgO substrates for membrane applications

Advanced design concepts for the application of oxygen transport ceramic membranes are based on thin layers supported by porous substrates. One suitable support material in this respect is porous MgO. However, a careful consideration of the mechanical stability is required to warrant long term performance and reliability under application relevant thermo-mechanical loads. The current work summarizes the effect of the sintering conditions on porosity and mechanical properties and gives elastic modulus and fracture stress as a function of temperature. An enhancement of the strength by the addition of boehmite to MgO was tested. Elastic moduli are determined and compared as obtained by indentation and bending tests. With respect to fracture, specimens in planar geometry are investigated using ring-on-ring bending tests; tubes are tested using an O-ring set-up. Fracture stresses are statistically analyzed. The obtained mechanical parameters are compared to that of other potential porous substrate materials.     

Innovative hydroxyapatite/bioactive glass composites processed by spark plasma sintering for bone tissue repair

Hydroxyapatite-based composites (HA-C) with bioglass as second phase are usually produced by hot-pressing or pressureless sintering. However, such methods require thermal levels which exceed the crystallization temperature of the glass, with possible negative effects on the bioactivity of the final system. Spark plasma sintering (SPS) is a powerful consolidation technique in terms of both processing time and temperature. In this work SPS has been employed, for the first time, to obtain HA-C with an innovative bioglass as second phase. Such glass was designed to be used whenever a thermal treatment is required, thanks to its low tendency to crystallize. A systematic study is conducted to identify the optimal sintering conditions for preparing highly dense composites and, at the same time, to minimize the crystallization of the glassy phase. The obtained samples are highly bioactive and display higher compactness and hardness with respect to the counterparts produced by conventional sintering methods.     

Optimized structural and mechanical properties of borophosphate glass

A series of phosphate glasses composed of (65-x)P₂O₅–15BaO–5Al₂O₃–5ZnO–10Na₂O-xB₂O₃ (x = 0, 2, 4, 6, and 8 mol%) were successfully prepared using the melt-quenching method. The effects of the addition of boron trioxide (B₂O₃) on the physical, structural, and mechanical properties of the glasses were investigated. As the added content of B₂O₃ increased from 0 to 6 mol%, the glass exhibited increased density and transition temperature, and decreased molar volume, indicating optimization of the glass stability. Raman spectroscopy revealed that the introduction of B₂O₃ transformed the glass from a chain structure to a three-dimensional network structure, which enhanced the chemical stability of the glass by the cross-linking of long phosphate chains with boron ions. Regarding the mechanical properties, when the boron content was 6 mol%, the flexural strength of the glass was 41% higher than that of the undoped boron, while the Vickers hardness and Knoop hardness values increased by 20.58% and 7.05%, respectively, and the fracture toughness was slightly decreased. In general, improving the mechanical properties of phosphate glass is of great significance for increasing the applications of this glass.     

Preparation and Properties of Bioactive Composite Based on Bioactive Glass and Poly-L-Lactide

Bioactive and bioresorbable composite was fabricated based on poly-L-lactide (PLLA) and bioactive glass (average particle size: 4.24 µm) by the combination of solvent evaporation technique and hot pressing. Bioactive glass granules are distributed homogeneously in the composite. With the increasing of the amount of bioactive glass, the bending strength and shearing strength of composite decrease while the bending modulus increases. PLLA/bioactive glass composites present a typical morphology of brittle failure with a smooth fracture surface. The biocompatibility test shows that the bioactive glass existing in the composite facilitates both adhesion and proliferation of rat fibroblast on the PLLA/bioactive glass composite film.     

Effect of boron oxide on mechanical and thermal properties of bioactive glass coatings for biomedical applications

Bioactive glass coatings can improve the osteo integration of metallic implants with the host tissue, thereby increasing their lifespan and overall success rate. However, complex composition-structure-property relations in phosphosilicate-based bioactive glasses make experimental determination of these relations and related composition design of bioactive coatings challenging. By applying molecular dynamics (MD)-based atomistic simulations with recently developed effective potentials, this work addresses the challenge by using a material genome approach to obtain the composition and structure effects on various key properties for bioactive coating applications. A series of potential bioactive glass compositions were studied and the composition effects on the mechanical and thermal properties that are critical to these bioactive glasses as a coating to metallic implants were calculated. Particularly, by varying the level of B₂O₃ to SiO₂ substitutions, the effect of composition on various key properties was elucidated. It was found that by using cation in a 1 to 1 ratio (BO_3/2 to SiO₂) instead of the commonly used substitutions (B₂O₃ to SiO₂), the composition effect can be more clearly expressed and, hence, recommended in future composition designs. Together with careful structural analysis, the origin of property changes can be elucidated. The atomistic computer simulation-based approach is, thus, an effective way to guide future bioactive glass designs for bioactive coatings and other applications.     

Thermo-mechanical studies on Er3+-doped fluorophosphate glasses for near infrared lasers

Thermal, mechanical and thermo-mechanical properties of Mg(PO₃)₂-BaF₂-CaF₂-ErF₃ fluorophosphate (FP) glasses with varying Mg(PO₃)₂ and ErF₃ molar ratios have been investigated. The simultaneous thermal analysis revealed that the T_g, T_x, T_p and ΔT increased constantly with increasing Mg(PO₃)₂ and ErF₃ content and that favorable large values of ΔT (>100 °C) were obtained at higher Mg(PO₃)₂ and ErF₃ content. The thermo-mechanical analysis showed that the T_g and T_s increased constantly and coefficient of thermal expansion decreased from 16.5×10⁻⁶ K⁻¹ to 11.2^×10⁻⁶ K⁻¹ with an increase in Mg(PO₃)₂ and ErF₃ content. The Knoop hardness (H_K) increased constantly from 381 kgf/mm² to 480 kgf/mm² with increased Mg(PO₃)₂ and ErF₃ content, which indicates strengthening of the glass network with increased –PO bonds. The H_K measurement at different applied loads and indentation times was carried out and from this study, it was found that an appropriate incorporation of cations into the FP glasses and the optimum rare earth concentration could considerably increase the thermal and mechanical strength of the glass. The studied glass compositions showed beneficial thermal properties and outstanding mechanical strength and can be applied for fiber drawing.     

Review: Elaboration,structure, and mechanical properties of oxynitride glasses

Oxynitride glasses are glasses where threefold coordinated nitrogen atoms substitute for twofold oxygen ones, hence resulting in a larger interatomic cross-linking degree. Such glasses were first observed at the grain boundary in silicon nitride ceramics, where they govern the high-temperature behavior. Later, they were prepared as bulk materials and motivated numerous researches, thanks to their large viscosity, glass transition range, elastic moduli, hardness, and fracture toughness among inorganic and non-metallic glasses. In different chemical systems that were investigated, the synthesis routes and the sources for these exceptional mechanical properties are reviewed. Oxynitride glasses are not easy to process and suffer from the loss of transparency as nitrogen is incorporated over some critical content. Nevertheless, they are attractive “specialty” glasses in various niche areas, thanks to their large refractive index and dielectric constant, improved chemical durability, high softening point, etc., and majorly to their exceptional mechanical properties.     

Zirconia ceramics with additions of Alumina for advanced tribological and biomedical applications

The results of an investigation on slip cast and sintered Y₂O₃ (3 wt%)- stabilized ZrO₂ with additions of 5, 10, 15 wt% Al₂O₃ are reported. The surface roughness, porosity and density of the samples were measured. The hardness HRc and Hv, fracture toughness K_1C, and friction coefficients were also measured using standard methods. The structural properties of the samples were observed by Scanning Electron Microscopy (SEM). The surface topography was evaluated by means of Chromatic White Light Interferometry using MicroSpy® Topo of FRT Rauheit Kontur before and after tribological tests. The phase and chemical composition were analyzed by X-Ray Diffractometry (XRD), Energy Dispersive X-ray (EDX) spectroscopy, and Raman spectroscopy. Results show that the addition of Al₂O₃ into YSZ ceramics in the range of 5–10% allows the mechanical and tribological characteristics of the material that can be applied in different mechanical machines for different metallurgical processes to be improved, as well as in chemical engineering or medicine.     

Effect of fluoride additive on the mechanical properties of hydroxyapatite/alumina composites

The effect of fluoride additives on the mechanical properties of hydroxyapatite/alumina composites was investigated. When MgF₂ (5 vol%) was added to hydroxyapatite/alumina composites, the decomposition of hydroxyapatite was suppressed due to the substitution of F⁻ for OH⁻ in the crystal structure. Comparing two additives, such as MgF₂ and CaF₂, MgF₂ showed much more effective for the suppression of phase decomposition in the hydroxyapatite/alumina composites due to the enhanced substitution of F⁻ for OH⁻. In the case of MgF₂ addition, a relatively high-mechanical properties (flexural strength: ∼170 MPa; Vickers hardness: ∼7 GPa) was obtained compared to MgF₂-free composites.     

Vinyl carbonate photopolymers with improved mechanical properties for biomedical applications

Recently, vinyl carbonates have been demonstrated to be a versatile alternative to acrylates and methacrylates in biomedical applications as they exhibit photoreactivity and mechanical properties on a level or even above (meth)acrylates. Furthermore, much lower cytotoxicity as well as degradation via a surface erosion mechanism qualify them for medical use. However, it is highly desirable to improve the mechanical properties of vinyl carbonates to reach the performance of PLA. Thus, the main focus of this study lies on designing vinyl carbonates with suitable functional groups that are capable of augmenting mechanical properties of vinyl carbonates, e.g. cyclic structures or urethane groups, and implementing them into the vinyl carbonate structures. Resulting monomers were tested regarding their photoreactivity and cytotoxicity. Furthermore, cured specimens were investigated concerning their mechanical properties. In addition, the thiol-ene reaction was utilized to further improve photoreactivity. The new vinyl carbonates exhibit excellent biocompatibility and photoreactivity that can be significantly enhanced through the addition of thiols onto the level of highly photoreactive acrylates. Most importantly, results showed that the mechanical properties could be improved onto the level of PLA and above.