Effect of Baghdadite Substitution on the Physicochemical Properties of Brushite Cements

Evaluation of baghdadite (Ca3ZrSi2O9) cements for the application as novel endodontic filling materials

OBJECTIVES

Baghdadite (Ca3ZrSi2O9) cements of various composition have been investigated in this study regarding an application as endodontic filling materials.

METHODS

Cements were either obtained by mixing mechanically activated baghdadite powder with water (maBag) or by subsequently substituting the ß-tricalcium phosphate (ß-TCP) component in a brushite forming calcium phosphate cement. The cements were analyzed for their mechanical performance, injectability, radiopacity, phase composition and antimicrobial properties.

RESULTS

The cements demonstrated sufficient mechanical performance with a compressive strength of ∼1 MPa (maBag) and 2.3 - 17.4 MPa (substituted calcium phosphate cement), good injectability > 80 % depending on the powder to liquid ratio and an intrinsic radiopacity of 1.13 - 2.05 mm aluminum equivalent. Immersion in artificial saliva proved their bioactivity by the formation of calcium phosphate and calcium silicate precipitates on the cement surface. The bacterial activity of Staphylococcus aureus cultured on the surface of the cements was found to be similar compared to clinical standard ProRoot MTA cement or even reduced by a factor of 3 for Streptococcus mutans.

SIGNIFICANCE

In combination with their antibacterial properties, baghdadite cements are thought to have the potential to fulfil the clinical requirements for endodontic filling materials.

Biological and Mechanical Performance of Dual-Setting Brushite-Silica Gel Cements

Bone defects resulting from trauma, diseases, or surgical procedures pose significant challenges in the field of oral and maxillofacial surgery. The development of effective bone substitute materials that promote bone healing and regeneration is crucial for successful clinical outcomes. Calcium phosphate cements (CPCs) have emerged as promising candidates for bone replacement due to their biocompatibility, bioactivity, and ability to integrate with host tissues. However, there is a continuous demand for further improvements in the mechanical properties, biodegradability, and bioactivity of these materials. Dual setting of cements is one way to improve the performance of CPCs. Therefore, silicate matrices can be incorporated in these cements. Silicate-based materials have shown great potential in various biomedical applications, including tissue engineering and drug delivery systems. In the context of bone regeneration, silicate matrices offer unique advantages such as improved mechanical stability, controlled release of bioactive ions, and enhanced cellular responses. Comprehensive assessments of both the material properties and biological responses of our samples were conducted. Cytocompatibility was assessed through in vitro testing using osteoblastic (MG-63) and osteoclastic (RAW 264.7) cell lines. Cell activity on the surfaces was quantified, and scanning electron microscopy (SEM) was employed to capture images of the RAW cells. In our study, incorporation of tetraethyl orthosilicate (TEOS) in dual-curing cements significantly enhanced physical properties, attributed to increased crosslinking density and reduced pore size. Higher alkoxysilyl group concentration improved biocompatibility by facilitating greater crosslinking. Additionally, our findings suggest citrate's potential as an alternative retarder due to its positive interaction with the silicate matrix, offering insights for future dental material research. This paper aims to provide an overview of the importance of silicate matrices as modifiers for calcium phosphate cements, focusing on their impact on the mechanical properties, setting behaviour, and biocompatibility of the resulting composites.

Baghdadite: A Novel and Promising Calcium Silicate in Regenerative Dentistry and Medicine

For several years, ceramic biomaterials have been extensively utilized to rebuild and substitute for body tissues. Calcium silicates have been proven to exhibit excellent bioactivity due to apatite formation and cell proliferation stimulation, in addition to degradability at levels adequate for hard tissue formation. These ceramics' excellent biological characteristics have attracted researchers. Baghdadite is a calcium silicate incorporating zirconium ions that enhances human osteoblast multiplication and development, increasing mineralization, and ossification. It has currently received much interest in academic institutions and has been extensively explored in the form of permeable frameworks, varnishes, bone adhesive and gap fillings, microparticles, and nanospheres, particularly in a wide range of biomedical applications. This review article aims to summarize and analyze the most recent research on baghdadite's mechanical characteristics, apatite-forming capability, dissolution pattern, and physiochemical qualities as a scaffold for dentofacial tissuè regeneration purposes.

Recent advances on bioactive baghdadite ceramic for bone tissue engineering applications: 20 years of research and innovation (a review)

Various artificial bone graft substitutes based on ceramics have been developed over the last 20 years. Among them, calcium-silicate-based ceramics, which are osteoconductive and can attach directly to biological organs, have received great attention for bone tissue engineering applications. However, the degradation rate of calcium-silicate and bone formation is often out of balance, resulting in stress shielding (osteopenia). A new strategy to improve the drawbacks of these ceramics is incorporating trace elements such as Zn, Mg, and Zr into their lattice structures, enhancing their physical and biological properties. Recently, baghdadite (Ca₃ZrSi₂O₉) ceramic, one of the most appealing calcium-silicate-based ceramics, has demonstrated high bioactivity, biocompatibility, biodegradability, and cell interaction. Because of its physical, mechanical, and biological properties and ability to be shaped using various fabrication techniques, baghdadite has found high potential in various biomedical applications such as coatings, fillers, cement, scaffolds, and drug delivery systems. Undoubtedly, there is a high potential for this newly developed ceramic to contribute significantly to therapies to provide a tremendous clinical outcome. This review paper aims to summarize and discuss the most relevant studies performed on baghdadite-based ceramics and composites by focusing on their behavior in vivo and in vitro.

Development of a bioactive and radiopaque bismuth doped baghdadite ceramic for bone tissue engineering

Baghdadite (Ca₃ZrSi₂O₉, BAG), is a Zr-doped calcium silicate that has outstanding bioactivity both in vitro and in vivo. Bioceramic scaffolds should be sufficiently radiopaque to be distinguishable in vivo from surrounding bone structures. To enhance the radiopacity of BAG, this study investigated the effect of incorporating bismuth ions into its crystalline structure (Bi_xCa_3-xZrSi₂O₉, x = 0, 0.1, 0.2, 0.5; BAG, Bi0.1-BAG, Bi0.2-BAG, Bi0.5-BAG, respectively). Monophasic baghdadite was retained after bismuth ion incorporation up to x = 0.2 at calcination temperatures of 1350 °C. When pressed and sintered, energy dispersive x-ray spectroscopy showed that BAG and Bi0.1-BAG retained crystalline homogeneity, but Bi0.2-BAG formed zirconium-rich crystalline regions. BAG, Bi0.1-BAG and Bi0.2-BAG exhibited non-degradation after 56 days of immersion in culture medium. Bi0.1-BAG exhibited the lowest change in culture medium pH (+0.0), compared to BAG (+0.7) and Bi0.2-BAG (+0.2) after 56 days of culture media immersion. Bi0.1-BAG exhibited similar strength and modulus to BAG (σ: 200-290 MPa; E: 4-5 GPa), and significantly higher compressive strength and modulus versus Bi0.2-BAG (σ: 150-200 MPa; E: 3.5-4 GPa) across 56 days of aqueous immersion. In vitro studies using primary human bone derived cells (HOBs) demonstrated a significant increase in HOBs proliferation when cultured on Bi0.1-BAG for seven days compared to BAG and Bi0.2-BAG. Importantly, Bi0.1-BAG showed increased radiopacity by ~33%, when compared to BAG, and by ~115% when compared to biphasic calcium phosphate. The properties of Bi0.1-BAG show promise for its use as a bioactive ceramic with sufficient radiopacity for treatment of bone defects.

Rapid Fabrication of MgNH4PO4·H2O/SrHPO4 Porous Composite Scaffolds with Improved Radiopacity via 3D Printing Process

Although bone repair scaffolds are required to possess high radiopacity to be distinguished from natural bone tissues in clinical applications, the intrinsic radiopacity of them is usually insufficient. For improving the radiopacity, combining X-ray contrast agents with bone repair scaffolds is an effective method. In the present research, MgNH₄PO₄·H₂O/SrHPO₄ 3D porous composite scaffolds with improved radiopacity were fabricated via the 3D printing technique. Here, SrHPO₄ was firstly used as a radiopaque agent to improve the radiopacity of magnesium phosphate scaffolds. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) were used to characterize the phases, morphologies, and element compositions of the 3D porous composite scaffolds. The radiography image showed that greater SrHPO₄ contents corresponded to higher radiopacity. When the SrHPO₄ content reached 9.34%, the radiopacity of the composite scaffolds was equal to that of a 6.8 mm Al ladder. The porosity and in vitro degradation of the porous composite scaffolds were studied in detail. The results show that magnesium phosphate scaffolds with various Sr contents could sustainably degrade and release the Mg, Sr, and P elements during the experiment period of 28 days. In addition, the cytotoxicity on MC3T3-E1 osteoblast precursor cells was evaluated, and the results show that the porous composite scaffolds with a SrHPO₄ content of 9.34% possessed superior cytocompatibility compared to that of the pure MgNH₄PO₄·H₂O scaffolds when the extract concentration was 0.1 g/mL. Cell adhesion experiments showed that all of the scaffolds could support MC3T3-E1 cellular attachment well. This research indicates that MgNH₄PO₄·H₂O/SrHPO₄ porous composite scaffolds have potential applications in the bone repair fields.

Bioactive Calcium Phosphate-Based Composites for Bone Regeneration

Calcium phosphates (CaPs) are widely accepted biomaterials able to promote the regeneration of bone tissue. However, the regeneration of critical-sized bone defects has been considered challenging, and the development of bioceramics exhibiting enhanced bioactivity, bioresorbability and mechanical performance is highly demanded. In this respect, the tuning of their chemical composition, crystal size and morphology have been the matter of intense research in the last decades, including the preparation of composites. The development of effective bioceramic composite scaffolds relies on effective manufacturing techniques able to control the final multi-scale porosity of the devices, relevant to ensure osteointegration and bio-competent mechanical performance. In this context, the present work provides an overview about the reported strategies to develop and optimize bioceramics, while also highlighting future perspectives in the development of bioactive ceramic composites for bone tissue regeneration.

Baghdadite coating formed by hybrid water-stabilized plasma spray for bioceramic applications: Mechanical and biological evaluations

This work studies the mechanical and biological properties of Baghdadite (BAG, Ca₃ZrSi₂O₉) coating manufactured on Ti6Al4V substrates by hybrid water-stabilized plasma spray (WSP-H). Hydroxyapatite (HAp, Ca₁₀(PO₄)₆(OH)₂) coating was produced by gas-stabilized atmospheric plasma spray and used as a reference material. Upon spraying, the BAG coating exhibited lower crystallinity than the HAp coating. Mechanical testing demonstrated superior properties of the BAG coating: its higher hardness, elastic modulus as well as a better resistance to scratch and wear. In the cell viability study, the BAG coating presented better human osteoblast attachment and proliferation on the coating surface after three days and seven days compared to the HAp counterpart. Furthermore, the gene expression study of human osteoblasts indicated that the BAG coating surface showed higher expression levels of osteogenic genes than those on the HAp coating. Overall, this study indicates that enhanced mechanical and bioactive properties can be achieved for the BAG coating compared to the benchmark HAp coating. It is therefore concluded here that the BAG coating is a potential candidate for coating orthopedic implants.

Setting Characteristics and High Compressive Strength of an Anti-washout, Injectable Calcium Phosphate Cement Combined with Thermosensitive Hydrogel

In this work, a thermosensitive poly(D,L-lactide-co-glycolide)-poly(ethylene glycol)-poly(D,L-lactide-co-glycolide) (PLGA-PEG-PLGA) hydrogel was introduced into calcium phosphate cement (CPC) to enhance the anti-washout property of CPC. The effects of the hydrogel on the setting time, injectability, anti-washout property and compressive strength of CPC were thoroughly investigated. The results showed that the hydrogel significantly increased the injectability and anti-washout property of CPC, meanwhile maintained the setting time with an acceptable range. Moreover, the hydrogel improved the initial compressive strength of CPC. The composite cement with 20% v/v hydrogel in the liquid phase showed fine crystals of hydration product, a more compact microstructure and lower porosity compared with control CPC. The analysis of X-ray diffraction (XRD), infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) indicated that suitable volume ratio of hydrogel (20% v/v) in the setting liquid of CPC could promote the formation of hydroxyapatite in the early hydration period. The degradation behavior of the cement was characterized by immersion tests in simulated body fluid. The hydrogel had no adverse effect on the degradation rate of CPC over the immersion period of 23 days. This study indicated that incorporating PLGA-PEG-PLGA hydrogel could be a promising strategy to reinforce the handing properties and initial compressive strength of calcium phosphate cement.

Baghdadite Ceramics Prevent Senescence in Human Osteoblasts and Promote Bone Regeneration in Aged Rats

Bone fractures and critical-sized bone defects present significant health threats for the elderly who have limited capacity for regeneration due to the presence of functionally compromised senescent cells. A wide range of synthetic materials has been developed to promote the regeneration of critical-sized bone defects, but it is largely unknown if a synthetic biomaterial (scaffold) can modulate cellular senescence and improve bone regeneration in aged scenarios. The current study investigates the interaction of Baghdadite (Ca₃ZrSi₂O₉) ceramic scaffolds with senescent human primary osteoblast-like cells (HOBs) and its bone regeneration capacity in aged rats. A senescent HOB model was established by repeatedly passaging HOBs till passage 7 (P7). Compared to the clinically used hydroxyapatite/tricalcium phosphate (HA/TCP), Baghdadite prevented senescence induction in P7 HOBs and markedly negated the paracrine effect of P7 HOB secretomes that mediated the up-regulations of cellular senescence-associated gene expression levels in P2 HOBs. We further demonstrated that conditioned media extracted from Baghdadite corrected the dysfunctional mitochondria in P7 HOBs. In vivo, the bone regeneration capacity was enhanced when 3D printed Baghdadite scaffolds were implanted in a calvaria critical-sized bone defect model in both young and aged rats compared to HA/TCP scaffolds, but a better effect was observed in aged rats than in young rats. This study suggests that Baghdadite ceramic represents a novel and promising biomaterial approach to promote bone regeneration capacity in the elderly by providing an anti-senescent microenvironment.