Recent advances on akermanite calcium-silicate ceramic for biomedical applications

Owing to great biocompatibility and high capacity of apatite formation, bioceramics, especially calcium silicate-based compounds, were extensively employed in orthopedic and dental uses concerning biomedical applications. Lately, akermanite (AK; Ca₂MgSi₂O₇), as a bioceramic containing Ca-, Mg- and Si, has gained an increased level of attention because of its more tunable mechanical characteristics and degradation rate. All studies indicate that this magnesium incorporating Ca-silicate ceramic has a great capacity to use as a bone graft material to fulfill the necessity of bone reconstruction. Despite the rising interest in using these materials in biomedical fields, there has not yet been an extensive overview of this bioceramic property and its potential benefits. Thus, it has been speculated that this concept and the emergence of akermanite bioactive ceramics might lead to significant upcoming advancements in the field of bone tissue engineering (BTE). Definitely, the approach still requires additional advances to considerably better respond to the vital concerns regarding the clinical application. The review tackles the present research trends on akermanite ceramics for biomedical purposes such as bone scaffold, coating materials, bone cement, and treatment of osteoporotic bone defects, commencing with recent status and shifting to upcoming developments.     

Preparation,Characterization, and In Vitro Bioactivity of Nagelschmidtite Bioceramics

The aim of this study is to prepare Ca, P and Si‐containing ternary oxide nagelschmidtite (NAGEL, Ca₇Si₂P₂O₁₆) bioceramics and explore their in vitro bioactivity for potential bone tissue regeneration. We prepared dense NAGEL ceramics through high‐temperature sintering of NAGEL ceramic powders. The apatite‐mineralization ability, dissolution rate, and human osteoblast response (including cytotoxicity analysis, attachment, morphology, proliferation, and bone‐related gene expression) to NAGEL ceramics have been systematically studied by comparing with conventional β‐tricalcium phosphate (β‐TCP) ceramics. The results showed that NAGEL ceramics possessed more obvious apatite mineralization and dissolution (degradation) and stimulated bone‐related gene expression (OCN and OPN) of osteoblasts than β‐TCP ceramics. NAGEL ceramics also showed no significant cytotoxicity. NAGEL ceramics supported osteoblast attachment, proliferation, and osteogenic gene expression, with a comparable cell proliferation activity with β‐TCP ceramics. These results indicate that novel NAGEL bioceramics with the specific composition of Ca₇Si₂P₂O₁₆, are a promising biomaterial for bone tissue regeneration application.     

In vitro behavior of bioactive phosphate glass–ceramics from the system P2O5–Na2O–CaO containing titania

Soda lime phosphate bioglass–ceramics with incorporation of small additions of TiO₂ were prepared in the metaphosphate and pyrophosphate region, using an appropriate two-step heat treatment of controlled crystallization defined by differential thermal analysis results. Identification and quantification of crystalline phases precipitated from the soda lime phosphate glasses were performed using X-ray diffraction analysis. Calcium pyrophosphate (β-Ca₂P₂O₇), sodium metaphosphate (NaPO₃), calcium metaphosphate (β-Ca(PO₃)₂), sodium pyrophosphate (Na₄P₂O₇), sodium calcium phosphate (Na₄Ca(PO₃)₆) and sodium titanium phosphate (Na₅Ti(PO₄)₃) phases were detected in the prepared glass–ceramics. The degradation of the prepared glass–ceramics was carried out for different periods of time in simulated body fluid at 37 °C using granules in the range 0.300–0.600 mm. The released ions were estimated by atomic absorption spectroscopy and the surface textures were measured by scanning electron microscopy. Investigation of in vitro bioactivity of the prepared glass–ceramics was done by the measurement of the infrared reflection spectra for the samples after immersion in the simulated body fluid for different periods at 37 °C. The result showed that no apatite layer was formed on the surface of the samples and the dominant phase remained on the surface was β-Ca₂P₂O₇, which is known for its bioactivity.     

Enhancement in the osteogenesis and angiogenesis of calcium phosphate cement by incorporating magnesium-containing silicates

Based on the good osteogenic and angiogenic effects of silicon and magnesium elements, three types of micro-nano magnesium-containing silicates (MS), including akermanite (Ake, Ca₂MgSi₂O₇), diopside (Dio, CaMgSi₂O₆) and forsterite (For, Mg₂SiO₄), were incorporated into calcium phosphate cement (CPC) to improve its osteogenic and angiogenic performances for clinical application. In this present work, the physicochemical properties, osteogenesis and angiogenesis of MS/CPCs (Ake/CPCs, Dio/CPCs and For/CPCs) were investigated systematically and comparatively. The results showed that all MS/CPCs had good biomineralization and significantly stimulated the osteogenic differentiation of mBMSCs and angiogenic differentiation of HUVECs, respectively. Besides, the stimulating effects were related to not only the category of MS, but also the content of MS. The For/CPCs had a good angiogenic property but their initial setting times were beyond 60 min. The Dio/CPCs showed the lowest biological performance among the three groups of MS/CPCs due to the lower ion release (Si and Mg). The Ake was the ideal modifier that could provide CPC with appropriate physicochemical properties, better osteogenesis and angiogenesis. Simultaneously, a higher addition (10 wt%) of akermanite resulted in the best potential to bone regeneration. Taken together, this research provides an effective approach to improve the overall performance of CPC, and 10Ake/CPC is of great promising prospect in bone repair.     

Structural,physicomechanical, and in vitro biodegradation studies on Sr-doped bioactive ceramic

This study aimed to investigate the effect of Sr substitution on the structure, mechanical properties, bioactivity, and biodegradation of akermanite (Ca₂MgSi₂O₇). Samples were synthesized through solid-state synthesis followed by heat treatment at 1200 °C and 1250 °C. X-ray diffraction patterns showed that Sr substitution did not change the Ca₂MgSi₂O₇ phase. Fourier transform infrared spectra demonstrated that the silicate structure of Ca₂MgSi₂O₇ also remained unchanged. The field emission scanning electron microscopy revealed that partial Sr substitution enhanced the density of Ca₂MgSi₂O₇ and reduced the grain size. The optimum dopant with the highest mechanical properties was 0.05Sr. However, the mechanical properties decreased beyond 0.05Sr because of the large grain size. The mechanical properties of Sr-substituted samples sintered at 1250 °C were lower due to high liquid phase formation. Sr substitution supported apatite formation and controlled Ca₂MgSi₂O₇ degradation after the samples were soaked in simulated body fluid solution (SBF).     

Non-isothermal crystallization kinetics and microstructure of a silver doped calcium aluminophosphate glass

The role of metallic silver in crystallization behavior of CaO–Al₂O₃–TiO₂–P₂O₅ system glasses was investigated utilizing differential thermal analysis, X-ray diffractometry, atomic force microscope and scanning electron microscopy. Initial glasses were heat treated in hydrogen atmosphere to convert silver ions to the metallic state, prior to crystallization. The presence of metallic silver led to noticeable decreasing of crystallization temperatures as well as effective crystallization of calcium titanium phosphate (CaTi₄(PO₄)₆), calcium metaphosphate (Ca(PO₃)₂) and calcium pyrophosphate (Ca₂P₂O₇) phases. Kinetic of crystallization was also evaluated before and after hydrogen heat treatment under non-isothermal conditions. It was found that activation energy for crystallization was not significantly influenced by the metallic silver. However, the calculated Avrami exponents confirmed the dominant role of metallic silver as an effective nucleating agent in bulk crystallization of the reduced glasses. By leaching of the silver free and silver containing glass–ceramics, calcium pyrophosphate (Ca₂P₂O₇) phase was selectively dissolved out and left porous microstructures with various pore morphologies and dimensions.     

Estimation of ancient firing technique by the characterization of semi-fused Hellenistic potsherds from Harabebezikan/Turkey

This study discusses the availability of different ancient firing techniques for some semi-fused potsherds which were recovered from an archeological excavation carried out for a Hellenistic workshop at Harabebezikan (Turkey). There are different ancient firing techniques such as open or surface firing (bonfire), pit firing and kiln firing. Each firing technique may create different effects on pottery. It sometimes may be possible to distinguish the firing technique used for a pottery if some evidential characteristics of firing could be defined. The potsherds were characterized with different analytical techniques in order to enlighten firing technique used for the production. Wavelength dispersive X-ray fluorescence (WDXRF) and X-ray diffraction (XRD) analysis were performed for chemical and mineralogical/phase contents, respectively. Scanning electron microscopy (SEM) in combination with energy dispersive X-ray spectrometry (EDX) was further performed for microstructural and microchemical characterization. Quartz (SiO₂), calcite (CaCO₃), plagioclase [(Na,Ca)AlSi₃O₈], hematite (α-Fe₂O₃), pyroxenes [Ca(Mg,Al)(Si,Al)₂O₆]/[Ca(Mg,Fe)Si₂O₆], akermanite (Ca₂MgSi₂O₇) and leucite (KAlSi₂O₆) were identified in the samples. Abundance of new mineral formations in the samples, related firing temperatures, microstructural and microchemical investigations suggested that kiln firing was the most probable technique for the production of the investigated potsherds.     

Zirconium modified calcium-silicate-based nanoceramics: An in vivo evaluation in a rabbit tibial defect model

Over the past two decades calcium silicate (Ca–Si) based ceramics have been introduced as bioactive materials for bone tissue engineering applications and repairing bone defects. Recently, it is reported that zirconium modified calcium-silicate-based (Ca₃ZrSi₂O₉, Baghdadite) ceramics stimulate cell proliferation and osteogenic differentiation of osteoblasts. The aim of this work was preparation, characterization, and evaluation of biological properties of Baghdadite in the nanoparticles form. These nanoparticles were synthesized by sol-gel method and were annealed at 1150°C. Fabricated nanoparticles were investigated using XRD, FE-SEM, EDX, and MTT in vitro, then implanted to the rabbit tibia as a bone animal model. The characterization results showed that nanoparticles with expected composition were successfully synthesized using sol-gel method. According to MTT result, these nanoparticles were nontoxic. In addition, the proliferation of bone marrow derived mesenchymal stem cells was increased after 96 hours of culturing in the presence of nanoparticles compared to the control. Histopathological results also demonstrated that the defected bone was completely regenerated when implanted with nanoparticles after 6 weeks. Taking together, according to the results, Ca₃ZrSi₂O₉ nanoparticles as a bioceramic with excellent biological properties can be applied for improvement of bone lesions healing process in the orthopedic and dental application.     

Structural,morphological and mechanical insights from La2O3 doped machinable silicate glass ceramics for biomedical applications

Machinable glass ceramics attracted much attention in recent years due to its improved mechanical and therapeutic performances. La₂O₃ doped SiO₂–Al₂O₃–MgO–K₂CO₃–CaO–MgF₂ glass and glass ceramics (GCs) were synthesized using melt-quenching and solid-state reaction methods. Herein, doping impact of La₂O₃ on physical, optical, morphological, mechanical, and biological properties were studied. XRD reveals the major phase formation of monoclinic cuspidine, Ca₄F₂Si₂O₇ with some minor phases. 3 mol% of La₂O₃ GCs shows a new major crystalline phase of akermanite, Ca₂MgSi₂O₇. FTIR study shows that La₂O₃ acts as a network modifier and non-bridging oxygens presented in the glassy structure tends to be increased. Optical band gap and particle size were lies in the range of 4.18–4.10 eV, and 50–57 nm, respectively. Rod-like morphology and their elemental distributions were confirmed via SEM and EDS techniques. TEM studies suggested that the lattice planes agreed with the XRD results and confirmed a major phase formation of Ca₂MgSi₂O₇. Enhanced mechanical properties were observed using Universal Testing Machine. The cell viability and cell cytotoxicity, were performed by MTT and ALP assay.     

The role of Ca2+ ions in the formation of high optical quality Cr4+,Ca:YAG ceramics

The distribution of Ca²⁺ ions in high optical quality Cr⁴⁺,Ca:YAG ceramics after vacuum sintering followed by air annealing was successfully investigated by HRTEM, STEM, EDX, XPS and optical absorption spectroscopy. The HRTEM microscopy reveals the formation of clear grain boundaries without any impurity phase. A highly-doped thin Ca-rich layer was detected at the grain boundary with Ca²⁺ concentration up to 4.9% RTM, while the concentration of Ca²⁺ ions in the grain volume is less than 0.25%. The layer suppressed grain growth allowing the production of high optical quality ceramics with the average grain size of 1.95 ± 0.27 μm, which is five times smaller than in calcium-free ceramics.The air annealing of Cr⁴⁺,Ca:YAG ceramics results in a 10-fold decrease in Ca²⁺ ion concentration at the grain boundaries, practically removing the Ca-rich layer, moreover, the procedure generates Cr⁴⁺ ions within the grains. Most of the calcium originated from the Ca-rich layer diffuses outside the ceramics or dissolves into Al₂O₃ impurities without interfering with the generation of Cr⁴⁺.     

Effect of MgO addition on the crystallization and in vitro bioactivity of glass ceramics in the CaO–MgO–SiO2–P2O5 system

CaO–MgO–SiO₂–P₂O₅ glass ceramics were successfully prepared by sintering the sol–gel-derived powders. The effects of MgO addition on the samples crystallization and structure were investigated by means of differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition, samples degradation and in vitro bioactivity assays were also evaluated. With more MgO addition, the glass ceramics crystallization kinetics under non-isothermal conditions changed from bulk crystallization to surface crystallization, and new crystal phases of Ca₂MgSi₂O₇ and SiO₂ were induced. In addition, it is observed that with increasing MgO concentration, the glass ceramics degradability gradually decreased and the formation of apatite was delayed.     

Tailoring bioactive and mechanical properties in polycrystalline CaO–SiO2–P2O5 glass-ceramics

Biological functions and mechanical properties are vital factors for artificial bone materials, with great clinic demand for bone injuries and defects. This study highlights mechanical strengths, in vitro and in vivo biological behaviors of the bioactive CaO–SiO₂–P₂O₅ glass-ceramics tailored by the nucleating agent P₂O₅. A high mechanical flexural strength of ～170 MPa and hardness of ～720 HV were achieved, owing to strengthened Si–O bonds in the network. In vitro cell tests demonstrate remarkable viability (using L929 cells) and bioactivity (using bone marrow-derived mesenchymal stromal cells), associated with the release of Ca²⁺ ions in the solution due to weakened Ca–O bonds in the glass-ceramic network. The assay in the simulated body ?uid revealed a formation of the hydroxyapatite-phase layer, which may act as a bridge to facilitate bioactivity on the CaO–SiO₂–P₂O₅ glass-ceramics. In vivo assay shows a significant bone-ingrowth capability on the CaO–SiO₂–P₂O₅ glass-ceramic. This work paves a promising route to utilize P₂O₅–nucleated CaO–SiO₂–P₂O₅ glass-ceramics for load-bearing bone replacement.     

From C–S–H to C–A–S–H: Experimental study and thermodynamic modelling

It has long been known that the stoichiometry of C–S–H varies with the calcium hydroxide concentration in solution. However, this issue is still far from understood. We revisit it in both experimental and modelling aspects. A careful analysis of the solubility confirms the existence of three different C–S–H phases, defined as Ca₄H₄Si₅O₁₆, Ca₂H₂Si₂O₇ and Ca₆(HSi₂O₇)₂(OH)₂, respectively. The variation of the Ca/Si ratio of the three phases has been described by surface reactions: the increase of the Si content is accounted for by silicate bridging, the increase of calcium content and the surface charge are accounted for by reactions involving silanol groups via deprotonation and complexation with calcium. In the presence of Al in solution, the uptake of Al by C–S–H is experimentally observed. The Al content increases with Al concentration. C–A–S–H formation is modelled by the competition between silicate and aluminate tetrahedra for the bridging of the dimeric silicates in C–S–H.     

Effect of Sr and Ca substitution of Ba on the photoluminescence properties of the Eu2+ activated Ba2MgSi2O7 phosphor

The effects of Sr and Ca substitution of Ba on the Ba_1.98-xSr_x(Ca_x)MgSi₂O₇:Eu²⁺ photoluminescence properties have been investigated. The physical mechanisms for the photoluminescence variations are discussed. With Rietveld refinement method, the crystal structure of Ba_1.98MgSi₂O₇:0.02Eu²⁺ and the lattice parameters of Sr and Ca substituted phosphors were refined. The emission band shift, the photoluminescence intensity variation, the phosphor chromaticity evolution, the Eu²⁺ lifetime distribution and the thermal stability elevation were investigated. With Sr and Ca substitution, the cell is shrinks. The cell shrinkage is resulting in the increase of the Eu²⁺ 5d electron crystal field splitting intensity, which is the reason for the emission band shift towards the long wavelength band. The photoluminescence intensity is increased firstly and then decreased. The intensity variation is the competitive result between the increase of the crystal structure rigidity and the rise of the lattice defect. The correlated color temperature can be cut down and the color purity can be adjusted. The photoluminescence life time of Eu²⁺ is raised firstly and then decreased. For Sr and Ca substitution, the thermal stability can be elevated. With the forbidden band gap calculation, the reason for the thermal stability elevation was investigated that for the substituted phosphors the forbidden band gap is enlarged and then limits the Eu²⁺ 5d self-ionization from the splitting levels to the conduction band. This work reveals that the Sr and Ca substitution of Ba can elevate the Ba_1.98-xSr_x(Ca_x)MgSi₂O₇:Eu²⁺ photoluminescence properties and improve the applications for the White Light Emitting Diode.     

Variable range hopping conduction in fully dense calcium cobalt oxide textured ceramics

Fully dense hot-pressed calcium cobalt oxide (Ca₃Co₄O₉) pellet exhibits textures with Lotgering factor of unity and supports the ideally aligned (00?l), l =?2, 3, 4, 5 crystallographic planes associated in the ceramics. The DC electrical conductivity of the Ca₃Co₄O₉ pellets connected to metal/Ca₃Co₄O₉-pellet/metal device structures in vertical and lateral configurations follow Mott's variable range hopping. The exhibition of anisotropic ratio of ~ 10 between the room temperature conductivity values in both the structures, reveal the presence of partially oriented textured grains in the currently developed Ca₃Co₄O₉ ceramics.     

Inorganic-salt coprecipitation synthesis,fluoride-doping,bioactivity and physiological pH buffering evaluations of bredigite

Bredigite (Ca₇MgSi₄O₁₆), with suitable bioactivity, biodegradation, biocompatibility and mechanical properties, is a promising candidate for the repair and regeneration of damaged bone tissues. In this research, for the first time, bredigite was synthesized by a facile and inexpensive coprecipitation method using inorganic salt precursors, followed by calcination at 1200 °C. Additionally, 0.5 mol% fluoride was successfully doped into the structure without the formation of any second phases. X-ray diffraction and Fourier-transform infrared spectroscopy confirmed the formation of single-phase orthorhombic bredigite in the samples and the incorporation of fluoride in the doped sample, respectively. Both the undoped and doped samples exhibited apatite-formation ability in terms of the precipitation of hydroxycarbonate apatite when exposed to a simulated physiochemical medium, with an increase in this characteristic as a result of fluoride doping. The addition of fluoride also lowered and buffered the pH value of the medium, where the enhancement of this parameter is due to the fast bioresorption of bredigite affecting disadvantageously biocompatibility.     

A comparative study on in vitro behavior of calcium silicate ceramics synthesized from biowaste resources

Calcium silicate ceramics have received significant attention for biomedical applications for their excellent bioactivity and osteoconduction properties. Sol-gel process is extensively used for the fabrication of calcium silicates. In sol-gel process, calcium nitrate tetra hydrate (Ca(NO₃)₂·4H₂O) and tetraethylorthosilicate (TEOS) are used as precursors. However, these precursors are expensive. The objective of this work was to compare in vitro behavior of calcium silicate (CaSiO₃) produced using biowaste such as rice husk ash (RHA) and eggshells (coded; NCS) with CaSiO₃ prepared using TEOS and Ca(NO₃)₂·4H₂O (coded; CCS). Thermal investigation results revealed that the crystallization temperature for NCS is relatively lower (772°C) than for CCS (870°C). Bioactivity was studied in vitro using simulated body fluid (SBF) with respect to mineralization rate of hydroxyapatite. Mineralization of a greater hydroxyapatite was observed on NCS ceramics than CCS ceramics after incubation for 3, 7, 14 days in SBF solution, which was confirmed using X-ray diffractometer, Fourier transform infrared spectroscopy, scanning electron microscopy-energy dispersive spectroscopy. Degradation studies were conducted in Tris-HCl solution and the test results revealed that NCS ceramics has lower dissolution rate than CCS ceramics. The antimicrobial assay has shown that NCS samples exhibit significant zone of inhibition against Escherichia coli and Staphylococcus aureus which confirmed that the CaSiO₃ prepared from RHA and eggshell can prevent bacteria from adhering to the surface. In addition cell culture studies revealed that NCS ceramics possess good cytocompatibility with MG-63 cells and significantly promoted cell proliferation.     

Fabrication and properties of CaSiO3/ Sr3(PO4)2 composite scaffold based on extrusion deposition

In recent years, 3D printing technology has been increasingly used to fabricate porous bone scaffolds for treating bone tissue defects. Calcium silicate (CS) is a bioceramic material with broad application prospects, but the characteristics of poor sintering performance and fast degradation have limited its further application. In this paper, porous CS scaffolds with different proportions of strontium phosphate (Sr₃(PO₄)₂) were formed by pneumatic extrusion deposition. Experiments showed that the Sr element replaced the Ca element in CaSiO₃, which altered the crystal structure of CaSiO₃, changed its physical and chemical properties, and improved the sintering property of CS ceramics. At the same time, the substituted Ca element formed Ca₃(PO₄)₂. After mixing Ca₃(PO₄)₂ and CaSiO₃, the grain of CaSiO₃ was refined and the sintering property was improved. Because of this dual role, the Sr element improved the sintering property of CaSiO₃ ceramics and delayed the degradation of CS ceramics. Moreover, cell experiments showed that the addition of the Sr element had a positive effect on cell proliferation and differentiation.     

Effects of Nd Content on Structure and Chemical Durability of Zirconolite–Barium Borosilicate Glass‐Ceramics

The effects of Nd₂O₃ content (0–12 wt %) on crystalline phases, microstructure, and chemical durability of barium borosilicate glass‐ceramics belonging to SiO₂–B₂O₃–Na₂O–BaO–CaO–TiO₂–ZrO₂–Nd₂O₃ system were studied. The results show that the glass‐ceramics with 2–6 wt% of Nd₂O₃ possess mainly zirconolite and titanite phases along with a small amount baddeleyite phase in the bulk. Calcium titanate appears when the Nd₂O₃ content increases to 8 wt%, and the amount of quadrate calcium titanate crystals increases with further increasing content of Nd₂O₃. For the glass‐ceramics with 6 wt% Nd₂O₃ (Nd‐6), Nd elements homogeneously distribute in zirconolite, titanite, and residual glass phases. There is a strong enrichment of Nd in calcium titanate crystals for the sample with 10 wt% Nd₂O₃. The viscosity of Nd‐6 glass is about 49 dPa·s at 1150°C. Moreover, Nd‐6 glass‐ceramics show the lower normalized leaching rates of B (LR_B), Ca (LR_Ca), and Nd (LR_Nd) when compared to that of the sample with 8 wt% Nd₂O₃. After 42 days, LR_B, LR_Ca, and LR_Nd of the Nd‐6 glass‐ceramics are about 6.8 × 10^?3, 1.6 × 10^?3, and 4.4 × 10^?6 g·m^?2·d^?1, respectively.     

Superior hybrid improper ferroelectricity and enhanced ferromagnetism of Ca3(Ti1-xCox)2O7 ceramics through the superexchange interaction

Ca₃(Ti_1-xCo_x)₂O₇ ceramics were prepared by a tartaric acid sol-gel method and sintered in an oxygen atmosphere. The introduction of Co²⁺/Co³⁺ as acceptor dopants leads to the formation of more oxygen vacancies and defect dipoles in Ca₃(Ti_1-xCo_x)₂O₇ ceramics. Oxygen vacancy and defect dipoles lead to the transition of dielectric, leakage, and ferroelectric behaviors of Ca₃(Ti_1-xCo_x)₂O₇ ceramics. The coexistence of hybrid improper ferroelectricity and ferromagnetism at room temperature in Ca₃(Ti_1-xCo_x)₂O₇ ceramics has been successfully realized through the superexchange interaction of Co–O–Co. Ca₃(Ti_1-xCo_x)₂O₇ ceramics exhibit superior ferroelectricity (the remnant polarization is 3.29 μC/cm²) and enhanced ferromagnetism (the remnant magnetization reaches 6.4×10^?3 emu/g). This strategy based on the introduction of transition metal ions with unfilled 3d shells at B sites is an important approach to realize novel room-temperature single-phase multiferroic materials for Ca₃Ti₂O₇-based materials.