A ready-to-use acidic, brushite-forming calcium phosphate cement

Compositional Variations in Calcium Phosphate Cement and Poly(Lactic-Co-Glycolic-Acid) Porogens Do Not Affect the Orthotopic Performance of Calcium Phosphate Cement/Poly(Lactic-Co-Glycolic-Acid) Cements

Calcium phosphate cement (CPC) has evolved as an appealing bone substitute material, especially since CPCs were combined with poly(lactic-co-glycolic acid) (PLGA) porogens to render the resulting CPC/PLGA composite degradable. In view of the multiple variables of CPC and PLGA used previously, the effect of CPC composition and PLGA porogen morphology (i.e., microspheres versus microparticles) on the biological performance of CPC/PLGA has not yet been investigated. Consequently, we here aimed to evaluate comparatively various CPC/PLGA formulations varying in CPC composition and PLGA porogen morphology on their performance in a rabbit femoral condyle bone defect model. CPCs with a composition of 85 wt% α-TCP, 15 wt% dicalcium phosphate anhydrate (DCPA) and 5 wt% precipitated hydroxyapatite (pHA), or 100 wt% α-TCP were combined with spherical or irregularly shaped PLGA porogens (CPC/PLGA ratio of 60:40 wt% for all formulations). All CPC/PLGA formulations were applied via injection in bone defects, as created in the femoral condyle of rabbits, and retrieved for histological evaluation after 6 and 12 weeks of implantation. Descriptive histology and quantitative histomorphometry (i.e., material degradation and new bone formation) were used for analyses. Descriptively, all CPC/PLGA formulations showed material degradation at the periphery of the cement within 6 weeks of implantation. After 12 weeks, bone formation was observed extending into the defect core, replacing the degraded CPC/PLGA material. Quantitatively, similar material degradation (up to 87%) and new bone formation (up to 28%) values were observed, irrespective of compositional variations of CPC/PLGA formulations. These data prove that neither the CPC compositions nor the PLGA porogen morphologies as used in this work affect the biological performance of CPC/PLGA formulations in a rabbit femoral condyle bone defect model.

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.

Effects of Superfine Tricalcium Silicate Powder on the Physicochemical and Mechanical Properties of Its Premixed Cement as a Root Canal Filling Material

Calcium silicate-based cement is a promising material for filling root canals. However, it has several drawbacks to its clinical application, including difficult operation and low curing strength. In this study, we successfully prepared an ultrafine tricalcium silicate powder and investigated the effects of this ultrafine powder on the performance of the premixed tricalcium silicate cement, including the curing process, setting time, hydration products, microstructure, injectivity, fluidity, and compressive strength. The results demonstrate that the addition of ultrafine tricalcium silicate powder alters the hydration product content and product morphology of the premixed cement. By increasing the content of the ultrafine powder, the injectable property of the cement can be increased to more than 95%, the fluidity can be increased from 18 mm to 35 mm, and the curing time can be shortened from 13 h to 11 h. Notably, the addition of the ultrafine powder greatly enhances the compressive strength of the hardened cement, which increases from 20.6 MPa to 51.0 MPa. These results indicate that altering the particle size distribution of the powder is an effective method for enhancing the physicochemical and mechanical properties of tricalcium silicate cement as a root canal filling material.

Preparation and Characterization of Mono- and Biphasic Ca1-xAgxHPO4·nH2O Compounds for Biomedical Applications

This study aimed to explore the effects of the full-scale replacement (up to 100%) of Ca2+ ions with Ag1+ ions in the structure of brushite (CaHPO4·2H2O). This substitution has potential benefits for producing monophasic and biphasic Ca1-xAgxHPO4·nH2O compounds. To prepare the starting solutions, (NH4)2HPO4, Ca(NO3)2·4H2O, and AgNO3 at different concentrations were used. The results showed that when the Ag/Ca molar ratio was below 0.25, partial substitution of Ca with Ag reduced the size of the unit cell of brushite. As the Ag/Ca molar ratio increased to 4, a compound with both monoclinic CaHPO4·2H2O and cubic nanostructured Ag3PO4 phases formed. There was a nearly linear relationship between the Ag ion ratio in the starting solutions and the wt% precipitation of the Ag3PO4 phase in the resulting compound. Moreover, when the Ag/Ca molar ratio exceeded 4, a single-phase Ag3PO4 compound formed. Hence, adjusting the Ag/Ca ratio in the starting solution allows the production of biomaterials with customized properties. In summary, this study introduces a novel synthesis method for the mono- and biphasic Ca1-xAgxHPO4·nH2O compounds brushite and silver phosphate. The preparation of these phases in a one-pot synthesis with controlled phase composition resulted in the enhancement of existing bone cement formulations by allowing better mixing of the starting ingredients.

Ready-To-Use and Rapidly Biodegradable Magnesium Phosphate Bone Cement: In Vivo Evaluation in Sheep

In clinical practice, hydroxyapatite (HA) cements for bone defect treatment are frequently prepared by mixing a powder component and a liquid component shortly before implantation in the operation theater, which is time-consuming and error-prone. In addition, HA cements are only slightly resorbed, that is, cement residues can still be found in the bone years after implantation. Here, these challenges are addressed by a prefabricated magnesium phosphate cement paste based on glycerol, which is ready-to-use and can be directly applied during surgery. By using a trimodal particle size distribution (PSD), the paste is readily injectable and exhibits a compressive strength of 9-14 MPa after setting. Struvite (MgNH4 PO4 ·6H2 O), dittmarite (MgNH4 PO4 ·H2 O), farringtonite (Mg3 (PO4 )2 ), and newberyite (MgHPO4 ·3H2 O) are the mineral phases present in the set cement. The paste developed here features a promising degradation of 37% after four months in an ovine implantation model, with 25% of the implant area being newly formed bone. It is concluded that the novel prefabricated paste improves application during surgery, has a suitable degradation rate, and supports bone regeneration.

The Effect of Full-Scale Exchange of Ca2+ with Zn2+ Ions on the Crystal Structure of Brushite and Its Phase Composition

This study was carried out to investigate the effect of a complete exchange of Ca2+ with Zn2+ ions on the structure of brushite (CaHPO4·2H2O), which might be advantageous in the production process of CaxZn1-xHPO4·nH2O. To acquire the starting solutions needed for the current study, (NH4)2HPO4, Ca(NO3)2·4H2O, and Zn(NO3)2·6H2O were utilized in several molar concentrations. The findings indicate that Ca is partly substituted by Zn when the Zn/Ca molar ratio is below 0.25 and that Zn doping hinders the crystallization of brushite. A continued increase in the Zn/Ca molar ratio to 1 (at which point the supersaturation of the Zn solution rises) led to a biphasic compound of monoclinic brushite and parascholzite precipitate. Elevating the Zn/Ca molar ratio to 1.5 resulted in a precipitate of a parascholzite-like mineral. Finally, increasing the Zn/Ca molar ratio to 4 and above resulted in the formation of the hopeite mineral. Future biomaterial production with specific and bespoke characteristics can be achieved by adjusting the Zn/Ca ratio in the starting solution. It Rhas been established that the Zn/Ca ratio in the starting solution can be adjusted to obtain minerals with specific compositions. Thus, new synthesis methods for parascholzite and hopeite were introduced for the first time in this manuscript.

In Vitro and In Vivo Evaluation of Injectable Strontium-Modified Calcium Phosphate Cement for Bone Defect Repair in Rats

Calcium phosphate cement (CPC) has been widely studied, but its lack of osteoinductivity and inadequate mechanical properties limit its application, while strontium is able to promote bone formation and inhibit bone resorption. In this study, different proportions of tristrontium silicate were introduced to create a novel strontium-modified calcium phosphate cement (SMPC). The physicochemical properties of SMPC and CPC were compared, and the microstructures of the bone cements were characterized with scanning electron microscopy assays. Then, the effect of SMPC on cell proliferation and differentiation was examined. Furthermore, local inflammatory response and osteogenesis after SMPC implantation were also confirmed in the study. Finally, a rat model of isolated vertebral defects was used to test the biomechanical properties of the cements. The results showed that SMPC has better injectability and a shorter setting time than CPC. Meanwhile, the addition of tristrontium silicate promoted the mechanical strength of calcium phosphate cement, and the compressive strength of 5% SMPC increased to 6.00 ± 0.74 MPa. However, this promotion effect gradually diminished with an increase in tristrontium silicate, which was also found in the rat model of isolated vertebral defects. Furthermore, SMPC showed a more preferential role in promoting cell proliferation and differentiation compared to CPC. Neither SMPC nor CPC showed significant inflammatory responses in vivo. Histological staining suggested that SMPCs were significantly better than CPC in promoting new bone regeneration. Importantly, this osteogenesis effect of SMPC was positively correlated with the ratio of tristrontium silicate. In conclusion, 5% SMPC is a promising substitute material for bone repair with excellent physicochemical properties and biological activity.

Preparation and characterizations of an injectable and biodegradable high-strength iron-bearing brushite cement for bone repair and vertebral augmentation applications

Brushite cements have good osteoconductive and resorbable properties, but the low mechanical strength and poor injectability limit their clinical applications in load-bearing conditions and minimally invasive surgery. In this study, an injectable brushite cement that contains monocalcium phosphate monohydrate (MCPM) and β-tricalcium phosphate (β-TCP) as its solid phase and ammonium ferric citrate (AFC) solution as the aqueous medium was designed to have high mechanical strength. The optimized formulation achieved a compressive strength of 62.8 ± 7.2 MPa, which is above the previously reported values of hand-mixing brushite cements. The incorporation of AFC prolonged the setting times and greatly enhanced the injectability and degradation properties of the cements. In vitro and in vivo experiments demonstrated that the brushite cements exhibited good biocompatibility and bone regeneration capacity. The novel brushite cement is promising for bone healing in load-bearing applications.

The Impact of Full-Scale Substitution of Ca2+ with Ni2+ Ions on Brushite’s Crystal Structure and Phase Composition

Because the impact of the full-scale substitution of Ca2+ in brushite (CaHPO4·2H2O) with Ni2+ ions has never been systematically explored, it is the focus of this investigation, as it holds potential for use in CaxNi1−xHPO4·nH2O production. These biomaterials have many beneficial characteristics that can be modified to suit diverse applications, including bone tissue regeneration and pharmaceutics. For the present study, NaH2PO4·2H2O, Ca(NO3)2·4H2O, and Ni(NO3)2·6H2O were used in various molar concentrations to obtain the required starting solutions. Previous studies have shown that adding Ni ions in the initial solution below 20% results in the precipitation of monophasic brushite with slight changes in the crystal structure. However, this study confirms that when the Ni ions substitution increases to 20%, a mixture of phases from both brushite and hexaaquanickel(II) hydrogenphosphate monohydrate HNiP (Ni(H2O)6·HPO4·H2O) is formed. The results confirm that the full replacement (100%) of Ca ions by Ni ions results in a monophasic compound solely comprising orthorhombic HNiP nanocrystals. Therefore, a novel technique of HNiP synthesis using the precipitation method is introduced in this research work. These materials are subsequently analyzed utilizing powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The obtained results confirm that the material microstructure is controlled by the Ni/Ca ratio in the starting solution and can be modified to obtain the desired characteristics of phases and crystals.

Functional Macromolecular Adhesives for Bone Fracture Healing

Compared with traditional internal fixation devices, bone adhesives are expected to exhibit remarkable advantages, such as improved fixation of comminuted fractures and maintained spatial location of fractured scattered bone pieces in treating bone injuries. In this review, different bone adhesives are summarized from the aspects of bone tissue engineering, and the applications of bone adhesives are emphasized. The concepts of "liquid scaffold" and "liquid plate" are proposed to summarize two different research directions of bone adhesives. Furthermore, significant advances of bone adhesives in recent years in mechanical strength, osseointegration, osteoconductivity, and osteoinductivity are discussed. We conclude this topic by providing perspectives on the state-of-the-art research progress and future development trends of bone adhesives. We hope this review will provide a comprehensive summary of bone adhesives and inspire more extensive and in-depth research on this subject.

Silk fibroin hydrogels induced and reinforced by acidic calcium phosphate - A simple way of producing bioactive and drug-loadable composites for biomedical applications

Silk fibroin (SF) hydrogels have attracted extensive interest in biomedical applications due to their biocompatibility and wide availability. However, their generally poor mechanical properties limit their utility. Here, injectable, ready-to-use SF-based composites, simultaneously induced and reinforced by acidic calcium phosphates, were prepared via a dual-paste system requiring no complex chemical/physical treatment. The composite was formed by mixing a monocalcium phosphate monohydrate paste with a β-tricalcium phosphate/SF paste. The conformational transition of SF in an acidic environment forms continuous networks, and the acidic calcium phosphate, brushite and monetite, formed simultaneously in the networks during mixing. The composites displayed a partly elastomeric compression behavior, with mechanical properties increasing with an increasing calcium phosphate and β-sheet content at the lower calcium phosphate contents evaluated (22.2-36.4 wt%). While the stiffness was still relatively low, the materials presented a high elasticity and ductility, and no failure at stresses in the range of failure stresses of trabecular bone. Furthermore, the calcium phosphate confers bioactivity to the material, and the composites with a promising in vitro cell response also showed potential as drug vehicles, using vancomycin as a model drug. These dual-paste systems exhibit potential utility in biomedical applications, such as bone void fillers and drug vehicles.

Effect of Ca2+ Replacement with Cu2+ Ions in Brushite on the Phase Composition and Crystal Structure

The gradual replacement of Ca2+ with Cu2+ ions in brushite (CaHPO4·2H2O) has been extensively studied and discussed. The approach adopted in this work has not been systematically explored in previous studies. This novel approach may prove beneficial for the production of Ca1−xCuxHPO4·nH2O materials with desired properties suitable for medical applications. Solutions of sodium dihydrogen orthophosphate dihydrate, NaH2PO4·2H2O, calcium nitrate tetrahydrate, Ca(NO3)2·4H2O, copper nitrate trihydrate, Cu(NO3)2·3H2O, ammonium hydroxide solution, and diluted HCl were used for the preparation of these materials. At low Cu/Ca molar ratios (up to 0.25) in the starting solution, biphasic phosphate minerals were formed: brushite and sampleite. When the Cu/Ca molar ratio increases gradually from 0.67 to 1.5, sampleite-like mineral precipitates. Powdered XRD (X-ray diffraction), thermogravimetric (TG) analysis, and SEM (scanning electron microscopy) techniques were employed for the study of the microstructure of the produced materials for different degrees of Ca replacement with Mg. It is found that the Cu/Ca ratio in the starting solution can be adjusted to obtain materials with tailored composition. Thus, a new method of sampleite-like synthesis as a rare mineral is introduced in this study. Both phosphate minerals brushite and sampleite-like minerals are attractive as precursors of bioceramics and biocements. The search for such products that may decrease the possibility of post prosthetic or implant infection can be crucial in preventing devastating post-surgical complications.

Hyaluronic-Acid-Based Organic-Inorganic Composites for Biomedical Applications

Applications of natural hyaluronic acid (HYH) for the fabrication of organic-inorganic composites for biomedical applications are described. Such composites combine unique functional properties of HYH with functional properties of hydroxyapatite, various bioceramics, bioglass, biocements, metal nanoparticles, and quantum dots. Functional properties of advanced composite gels, scaffold materials, cements, particles, films, and coatings are described. Benefiting from the synergy of properties of HYH and inorganic components, advanced composites provide a platform for the development of new drug delivery materials. Many advanced properties of composites are attributed to the ability of HYH to promote biomineralization. Properties of HYH are a key factor for the development of colloidal and electrochemical methods for the fabrication of films and protective coatings for surface modification of biomedical implants and the development of advanced biosensors. Overcoming limitations of traditional materials, HYH is used as a biocompatible capping, dispersing, and structure-directing agent for the synthesis of functional inorganic materials and composites. Gel-forming properties of HYH enable a facile and straightforward approach to the fabrication of antimicrobial materials in different forms. Of particular interest are applications of HYH for the fabrication of biosensors. This review summarizes manufacturing strategies and mechanisms and outlines future trends in the development of functional biocomposites.

Monetite, an important calcium phosphate compound-Its synthesis, properties and applications in orthopedics

This review recognizes a unique calcium phosphate (CaP) phase known as monetite or dicalcium phosphate anhydrous (DCPA, CaHPO₄), and presents an overview of its properties, processing, and applications in orthopedics. The motivation for the present effort is to highlight the state-of-the-art research and development of monetite and propel the research community to explore more of its potentials in orthopedics. After a brief introduction of monetite, we provide a summary of its various synthesis routes like dehydration, solvent-based, energy-assisted processes and also discuss the formation of different crystal structures with respect to the synthesis conditions. Subsequently, we discuss the material's noteworthy physico-chemical properties including the crystal structure, vibrational spectra, solubility, thermal decomposition, and conversion to other phases. Of note, we focus on the biological (in vitro and in vivo) properties of monetite, given its ever-increasing popularity as a biomaterial for medical implants. Appropriately, we discuss various orthopedic applications of monetite as bone cement, implant coatings, granules for defect fillers, and scaffolds. Many in vitro and in vivo studies confirmed the favorable osteointegration and osteoconduction properties of monetite products, along with a better balance between implant resorption and new bone formation as compared to other CaP phases. The review ends with translational aspects of monetite and presents thoughts about its possible future research directions. Further research may explore but not limited to improvements in mechanical strength of monetite-based scaffolds, using monetite particles as a therapeutic agent delivery, and tissue engineering strategies where monetite serves as the biomaterial. STATEMENT OF SIGNIFICANCE: This is the first review that focusses on the favorable potential of monetite for hard tissue repair and regeneration. The article accurately covers the "Synthesis-Structure-Property-Applications" correlations elaborating on monetite's diverse material properties. Special focus is put on the in vitro and in vivo properties of the material highlighting monetite as an orthopedic material-of-choice. The synthesis techniques are discussed which provide important information about the different fabrication routes for monetite. Most importantly, the review provides comprehensive knowledge about the diverse biomedical applications of monetite as granules, defect--specific scaffolds, bone cements and implant coatings. This review will help to highlight monetite's potential as an effective regenerative medicine and catalyze the continuing translation of this bioceramic from the laboratory to clinics.

Effect of the Addition of Alginate and/or Tetracycline on Brushite Cement Properties

Calcium phosphate cements have the advantage that they can be prepared as a paste that sets in a few minutes and can be easily adapted to the shape of the bone defect, which facilitates its clinical application. In this research, six formulations of brushite (dicalcium phosphate dihydrated) cement were obtained and the effect of the addition of sodium alginate was analyzed, such as its capacity as a tetracycline release system. The samples that contain sodium alginate set in 4 or 5 min and showed a high percentage of injectability (93%). The cements exhibit compression resistance values between 1.6 and 2.6 MPa. The drug was released in a range between 12.6 and 13.2% after 7 days. The antimicrobial activity of all the cements containing antibiotics was proven. All samples reached values of cell viability above 70 percent. We also observed that the addition of the sodium alginate and tetracycline improved the cell viability.

Recent Trends in the Development of Bone Regenerative Biomaterials

The goal of a biomaterial is to support the bone tissue regeneration process at the defect site and eventually degrade in situ and get replaced with the newly generated bone tissue. Biomaterials that enhance bone regeneration have a wealth of potential clinical applications from the treatment of non-union fractures to spinal fusion. The use of bone regenerative biomaterials from bioceramics and polymeric components to support bone cell and tissue growth is a longstanding area of interest. Recently, various forms of bone repair materials such as hydrogel, nanofiber scaffolds, and 3D printing composite scaffolds are emerging. Current challenges include the engineering of biomaterials that can match both the mechanical and biological context of bone tissue matrix and support the vascularization of large tissue constructs. Biomaterials with new levels of biofunctionality that attempt to recreate nanoscale topographical, biofactor, and gene delivery cues from the extracellular environment are emerging as interesting candidate bone regenerative biomaterials. This review has been sculptured around a case-by-case basis of current research that is being undertaken in the field of bone regeneration engineering. We will highlight the current progress in the development of physicochemical properties and applications of bone defect repair materials and their perspectives in bone regeneration.

Gradual Replacement of Ca2+ with Mg2+ Ions in Brushite for the Production of Ca1−xMgxHPO4·nH2O Materials

The present study investigates the gradual replacement of Ca2+ with Mg2+ ions in brushite (CaHPO4·2H2O). To date, this approach has not been systematically explored and may prove beneficial for the production of Ca1−xMgxHPO4·nH2O materials with tailored properties which are suitable for environmental and medical applications. For their production, solutions of sodium dihydrogen orthophosphate dehydrate, NaH2PO4·2H2O, calcium nitrate tetrahydrate, Ca(NO3)2·4H2O, magnesium nitrate hexahydrate, Mg(NO3)2·6H2O and ammonium hydroxide solution, NH4OH, were used. At low Mg/Ca molar ratios (up to 0.25) in the starting solution, partial replacement of Ca with Mg takes place (Mg doping) but no struvite is produced as discrete phase. When the Mg/Ca molar ratio increases gradually to 1.5, in addition to Mg-doped brushite, struvite, NH4MgPO4·6H2O, precipitates. The microstructure of the materials produced for different degrees of Ca replacement with Mg has been analyzed in depth with the use of powdered XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy), thermogravimetric (TG) analysis and SEM (scanning electron microscopy). The results of this study prove that the Mg/Ca ratio in the starting solution can be monitored in such a way that materials with tailored composition are obtained.

Biomechanical Evaluation of an Injectable Alginate / Dicalcium Phosphate Cement Composites for Bone Tissue Engineering

Biocompatible dicalcium phosphate (DCP) cements are widely used as bone repair materials. In this study, we aimed to investigate the impact of different amounts of sodium alginate (SA) on the microstructural, mechanical, and biological properties of DCP cements. Beta-tricalcium phosphate (β-TCP) was prepared using a microwave-assisted wet precipitation system. Lattice parameters of the obtained particles determined from X-ray diffraction (XRD), were in good match with a standard phase of β-TCP. Scanning electron microscopy (SEM) examination revealed that the particles were in globular shape. Furthermore, all functional groups of β-TCP were also detected using Fourier-transform infrared spectroscopy (FTIR) spectra. DCP cement (pure phase) was synthesized using monocalcium phosphate monohydrate (MCPM)/β-TCP powder mixture blended with 1.0 mL of water. SA/DCP cement composites were synthesized by dissolving different amounts of SA into water (1.0 mL) to obtain different final concentrations (0.5%, 1%, 2% and 3%). The prepared cements were characterized with XRD, SEM, FTIR and Thermogravimetric analysis (TGA). XRD results showed that pure DCP and SA/DCP cements were in a good match with Monetite phase. SEM results confirmed that addition of SA inhibited the growth of DCP particles. Setting time and injectability behaviour were significantly improved upon increasing the SA amount into DCP cements. In vitro biodegradation was evaluated using Simulated body fluid (SBF) over 21 days at 37 °C. The highest cumulative weight loss (%) in SBF was observed for 2.0% SA/DCP (about 26.52%) after 21 days of incubation. Amount of Ca²⁺ ions released in SBF increased with the addition of SA. DCP and SA/DCP cements showed the highest mechanical strength after 3 days of incubation in SBF and declined with prolonged immersion periods. In vitro cell culture experiments were conducted using Dental pulp stem cells (DPSCs). Viability and morphology of cells incubated in extract media of DCP and SA/DCP discs after 24 h incubation was studied with MTT assay and fluorescence microscopy imaging, respectively. All cements were cytocompatible and viability of cells incubated in extracts of cements was higher than observed in the control group. Based on the outcomes, SA/DCP bone cements have a promising future to be utilized as bone filler.

Multifunctional Calcium-Deficient Hydroxyl Apatite-Alginate Core-Shell-Structured Bone Substitutes as Cell and Drug Delivery Vehicles for Bone Tissue Regeneration

In this work, we fabricated unique coiled-structured bioceramics contained in hydrogel beads for simultaneous drug and cell delivery using a combination of bone cement chemistry and bioprinting and characterized them. The core of the calcium-deficient hydroxyl apatite (CDHA) contains quercetin, which is a representative phytoestrogen isolated from onions and apples, to control the metabolism of bone tissue regeneration through sustained release over a long period of time. The shell consists of an alginate hydrogel that includes preosteoblast MC3T3-E1 cells. Ceramic paste and hydrogel were simultaneously extruded to fabricate core-shell beads through the inner and outer nozzles, respectively, of a concentric nozzle system based on a material-extruding-based three-dimensional (3D) printing system. The formation of beads and the coiled ceramic core is related to both alginate concentration and printing conditions. The size of the microbeads and the thickness of the coiled structure could be controlled by adjusting the nozzle conditions. The whole process was carried out at physiological conditions (37 °C) to be gentle on the cells. The alginate shell undergoes solidification by cross-linking in CaCl₂ or monocalcium phosphate monohydrate (MCPM) solution, while the hardening and cementation of the α-tricalcium phosphate (α-TCP) core to CDHA are subsequently initiated by immersion in phosphate-buffered saline solution. This process replaces the typical sintering of ceramic processing to prevent damage to the hydrogel, cells, and drugs in the beads. The cell-loaded beads were then cultured in cell culture media where the cells could maintain good viability during the entire testing period, which was over 50 days. Cell growth and elongation were observed even in the alginate along the CDHA coiled structure over time. Sustained release of quercetin without any initial burst was also confirmed during a test period of 120 days. These novel structured microbeads with multibiofunctionality can be used as new bone substitutes for hard tissue regeneration in indeterminate defect sites.

Di-tert-butylphosphate Derived Thermolabile Calcium Organophosphates: Precursors for Ca(H2PO4)2, Ca(HPO4), α-/β-Ca(PO3)2, and Nanocrystalline Ca10(PO4)6(OH)2

Thermally and hydrolytically unstable di-tert-butyl phosphate (dtbp-H) has been used as synthon to prepare discrete and polymeric calcium phosphates that are convenient single-source precursors for a range of calcium phosphate ceramic biomaterials. The reactivity of dtbp-H toward two different calcium sources has been found to vary significantly, e.g., the reaction of Ca(OMe)₂ with dtbp-H in a 1:6 molar ratio in petroleum ether forms a mononuclear calcium hexa-phosphate complex [Ca(dtbp)₂(dtbp-H)₄] (1), whereas the change of calcium source to CaH₂, in a 1:2 molar ratio under otherwise similar reaction conditions, yields the calcium phosphate polymer, [Ca(μ-dtbp)₂(H₂O)₂·H₂O]_n(2). Compounds 1 and 2 have been extensively characterized by various spectroscopic and analytical techniques. The solid-state structures of both 1 and 2 have been determined by single-crystal X-ray diffraction studies. In discrete molecule 1, the central calcium ion is surrounded by two anionic dtbp and four neutral dtbp-H ligands in an octahedral coordination environment. Compound 2 is a one-dimensional polymer in which adjacent calcium ions are connected through double dtbp bridges. Solid-state thermolysis of bulk 1 in air leads to the exclusive formation of calcium metaphosphate β-Ca(PO₃)₂ in the entire temperature range of 400-800 °C. Thermal decomposition of polymer 2, however, can be fine-tuned to produce either α-Ca(PO₃)₂ or β-Ca(PO₃)₂ depending on the thermolysis conditions employed. Although the sample sintered at 600 °C produces exclusively α-form of Ca(PO₃)₂, the sample annealed at 800 °C or above produces β-form. Both α- and β-forms can also be successively formed one after other by a slow heating of a freshly prepared 2 on the powder diffractometer sample holder. Additional forms of ceramic phosphates have been prepared by solvothermal conditions because of the highly labile nature of the tert-butoxy groups of dtbp in 1 and 2. Solution decomposition of either 1 or 2 in boiling toluene at 140 °C in a sealed tube produces calcium dihydrogen phosphate [Ca(H₂PO₄)₂·H₂O] as the only product in the form of single crystals. Solution thermolysis of 2 in protic solvents such as water and methanol can be biased to produce other calcium phosphate biomaterials such as hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂]and calcium monohydrogen phosphate [Ca(HPO₄)] in the presence of additional calcium precursors such as CaO and Ca(OMe)₂, respectively.

Role of Iron on Physical and Mechanical Properties of Brushite Cements, and Interaction with Human Dental Pulp Stem Cells

Improving the physical, mechanical and biological properties of brushite cements (BrC) is of a great interest for using them in bone and dental tissue engineering applications. The objective of this study was to incorporate iron (Fe) at different concentrations (0.25, 0.50, and 1.00 wt.%) to BrC and study the role of Fe on phase composition, setting time, compressive strength, and interaction with human dental pulp stem cells (hDPSCs). Results showed that increase in Fe concentration increases the β-tricalcium phosphate (β-TCP)/ dicalcium phosphate dihydrate (DCPD) ratio and prolongs the initial and final setting time due to effective role of Fe on stabilizing the β-TCP crystal structure and retarding its dissolution kinetic, in a dose dependent manner where the highest setting time was recorded for 1.00 wt.% Fe-BrC sample. Addition of low concentrations of Fe (0.25 and 0.50 wt.%) did not have adverse effect on compressive strength and strength was in the range of 5.7-7.05 (±~1.4) MPa; however, presence of 1.00 wt.% Fe decreases the strength of BrC from 7.05 ± 1.57 MPa to 3.12 ± 1.06 MPa. Interaction between the BrCs and hDPSCs was evaluated by cell proliferation assay, scanning electron microscopy, and live/dead staining. Low concentrations of 0.25, and 0.50 wt.% of Fe did not have any adverse effect on cell attachment and proliferation; while significant decrease in cellular activity was evident in BrC samples doped with 1.00 wt. %. Together, these data show that low concentrations of Fe (equal or less than 0.50 wt. %) can be safely added to BrC without any adverse effect on physical, mechanical and biological properties in presence of hDPSCs.

Effect of Baghdadite Substitution on the Physicochemical Properties of Brushite Cements

Brushite cements have been clinically used for irregular bone defect filling applications, and various strategies have been previously reported to modify and improve their physicochemical properties such as strength and injectability. However, strategies to address other limitations of brushite cements such as low radiopacity or acidity without negatively impacting mechanical strength have not yet been reported. In this study, we report the effect of substituting the beta-tricalcium phosphate reactant in brushite cement with baghdadite (Ca₃ZrSi₂O₉), a bioactive zirconium-doped calcium silicate ceramic, at various concentrations (0, 5, 10, 20, 30, 50, and 100 wt%) on the properties of the final brushite cement product. X-ray diffraction profiles indicate the dissolution of baghdadite during the cement reaction, without affecting the crystal structure of the precipitated brushite. EDX analysis shows that calcium is homogeneously distributed within the cement matrix, while zirconium and silicon form cluster-like aggregates with sizes ranging from few microns to more than 50 µm. X-ray images and µ-CT analysis indicate enhanced radiopacity with increased incorporation of baghdadite into brushite cement, with nearly a doubling of the aluminium equivalent thickness at 50 wt% baghdadite substitution. At the same time, compressive strength of brushite cement increased from 12.9 ± 3.1 MPa to 21.1 ± 4.1 MPa with 10 wt% baghdadite substitution. Culture medium conditioned with powdered brushite cement approached closer to physiological pH values when the cement is incorporated with increasing amounts of baghdadite (pH = 6.47 for pure brushite, pH = 7.02 for brushite with 20 wt% baghdadite substitution). Baghdadite substitution also influenced the ionic content in the culture medium, and subsequently affected the proliferative activity of primary human osteoblasts in vitro. This study indicates that baghdadite is a beneficial additive to enhance the radiopacity, mechanical performance and cytocompatibility of brushite cements.