Self-setting properties of a β-dicalcium silicate reinforced calcium phosphate cement

Synthetic Calcium-Phosphate Materials for Bone Grafting

Synthetic bone grafting materials play a significant role in various medical applications involving bone regeneration and repair. Their ability to mimic the properties of natural bone and promote the healing process has contributed to their growing relevance. While calcium-phosphates and their composites with various polymers and biopolymers are widely used in clinical and experimental research, the diverse range of available polymer-based materials poses challenges in selecting the most suitable grafts for successful bone repair. This review aims to address the fundamental issues of bone biology and regeneration while providing a clear perspective on the principles guiding the development of synthetic materials. In this study, we delve into the basic principles underlying the creation of synthetic bone composites and explore the mechanisms of formation for biologically important complexes and structures associated with the various constituent parts of these materials. Additionally, we offer comprehensive information on the application of biologically active substances to enhance the properties and bioactivity of synthetic bone grafting materials. By presenting these insights, our review enables a deeper understanding of the regeneration processes facilitated by the application of synthetic bone composites.

Role of magnesium and aluminum substitution on the structural properties and bioactivity of bioglasses synthesized from biogenic silica

The objective of this study was to investigate the effect of magnesium (1 wt%) and aluminum (1 wt%) incorporation on the in vitro bioactivity and biodegradation behavior of 45S5 bioactive glasses synthesized from rice husk biogenic silica. The performance of biogenic silica-based samples was compared well with commercial silica-based counterparts. The in vitro biodegradation behavior of bioactive glasses was evaluated by the weight loss of samples and pH variation in the Tris buffer solution. Based on composition, bioglasses possessed different properties before and after simulated body fluid (SBF) immersion. The incorporation of magnesium (Mg) and aluminum (Al) enhanced the Vickers hardness of bioglasses. All the bioglasses showed the hydroxyapatite layer formation after SBF treatment as confirmed by the dissolution, FTIR, SEM and XRD analysis, however it was more prominent in the rice husk silica-based 45S5 bioglass. The biogenic silica seems to be a promising starting material for bioglass systems to be used in bone tissue engineering applications.

Hydrolysis, setting properties and in vitro characterization of wollastonite/newberyite bone cement mixtures

Bone cements based on magnesium phosphates such as newberyite (N; MgHPO₄.3H₂O) have been shown as potential bone substitutes due to their biocompatibility, biodegradability and ability to support osteoblast differentiation and proliferation. Newberyite can hydrolyze to hydrated magnesium phosphate compounds (e.g. bobierite (Mg₃(PO₄)₂.8H₂O)) at alkaline conditions. In this study, 25 and 50 wt% of crystalline β -wollastonite (woll; CaSiO₃) was admixed to newberyite powder in order to both enhance the acid-base hydrolysis of newberyite and to produce a functional bone cement. The setting process of wollastonite/newberyite cement mixtures started with the hydrolysis of the wollastonite with further transformation of newberyite into bobierite and the formation of magnesium silicate phase. The results demonstrated that 25 wollastonite/newberyite and 50 wollastonite/newberyite cement pastes at optimal powder/liquid ratios had final setting times of ∼34 and 25 min and compressive strength values of 18 and 32 MPa after seven days setting, respectively. The tests of cytotoxicity of cement extracts on osteoblastic cells and contact cytotoxicity of the cement substrates showed different results. The osteoblasts cultured in cement extracts readily proliferated which confirmed the non-cytotoxic concentration of ions released from both cements. On the other hand, a strong cytotoxic character of 25 wollastonite/newberyite sample surface in contrary to high (∼80%) proliferation activity of cells on the 50 wollastonite/newberyite cement substrate was observed. The differences in cell proliferation activity was attributed to different surface topographies of cement substrates, where needle-like precipitated microcrystals of magnesium phosphate phase (in 25 wollastonite/newberyite cement) prevented the adhesion and proliferation of osteoblasts contrary to the smoother surface covered by extremely fine nanoparticles in the 50 wollastonite/newberyite cement.

Calcium Phosphate Cement with Antimicrobial Properties and Radiopacity as an Endodontic Material

Calcium phosphate cements (CPCs) have several advantages for use as endodontic materials, and such advantages include ease of use, biocompatibility, potential hydroxyapatite-forming ability, and bond creation between the dentin and appropriate filling materials. However, unlike tricalcium silicate (CS)-based materials, CPCs do not have antibacterial properties. The present study doped a nonwashable CPC with 0.25–1.0 wt % hinokitiol and added 0, 5, and 10 wt % CS. The CPCs with 0.25–0.5 wt % hinokitiol showed appreciable antimicrobial properties without alterations in their working or setting times, mechanical properties, or cytocompatibility. Addition of CS slightly retarded the apatite formation of CPC and the working and setting time was obviously reduced. Moreover, addition of CS dramatically increased the compressive strength of CPC. Doping CS with 5 wt % ZnO provided additional antibacterial effects to the present CPC system. CS and hinokitiol exerted a synergic antibacterial effect, and the CPC with 0.25 wt % hinokitiol and 10 wt % CS (doped with 5 wt % ZnO) had higher antibacterial properties than that of pure CS. The addition of 10 wt % bismuth subgallate doubled the CPC radiopacity. The results demonstrate that hinokitiol and CS can improve the antibacterial properties of CPCs, and they can thus be considered for endodontic applications.

Systematic investigation of β-dicalcium silicate-based bone cements in vitro and in vivo in comparison with clinically applied calcium phosphate cement and Bio-Oss®

Herein we systematically investigated the biological performance of a β-dicalcium silicate (β-C₂S)-based bone cement in comparison with the clinically used calcium phosphate cement (CPC) and Bio-Oss®.

Self-setting calcium orthophosphate formulations

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are bioactive and biodegradable grafting bioceramics in the form of a powder and a liquid. After mixing, both phases form pastes, which set and harden forming either a non-stoichiometric calcium deficient hydroxyapatite or brushite. Since both of them are remarkably biocompartible, bioresorbable and osteoconductive, self-setting calcium orthophosphate formulations appear to be promising bioceramics for bone grafting. Furthermore, such formulations possess excellent molding capabilities, easy manipulation and nearly perfect adaptation to the complex shapes of bone defects, followed by gradual bioresorption and new bone formation. In addition, reinforced formulations have been introduced, which might be described as calcium orthophosphate concretes. The discovery of self-setting properties opened up a new era in the medical application of calcium orthophosphates and many commercial trademarks have been introduced as a result. Currently such formulations are widely used as synthetic bone grafts, with several advantages, such as pourability and injectability. Moreover, their low-temperature setting reactions and intrinsic porosity allow loading by drugs, biomolecules and even cells for tissue engineering purposes. In this review, an insight into the self-setting calcium orthophosphate formulations, as excellent bioceramics suitable for both dental and bone grafting applications, has been provided.

In vitro studies of calcium phosphate silicate bone cements

A novel calcium phosphate silicate bone cement (CPSC) was synthesized in a process, in which nanocomposite forms in situ between calcium silicate hydrate (C-S-H) gel and hydroxyapatite (HAP). The cement powder consists of tricalcium silicate (C(3)S) and calcium phosphate monobasic (CPM). During cement setting, C(3)S hydrates to produce C-S-H and calcium hydroxide (CH); CPM reacts with the CH to precipitate HAP in situ within C-S-H. This process, largely removing CH from the set cement, enhances its biocompatibility and bioactivity. The testing results of cell culture confirmed that the biocompatibility of CPSC was improved as compared to pure C(3)S. The results of XRD and SEM characterizations showed that CPSC paste induced formation of HAP layer after immersion in simulated body fluid for 7 days, suggesting that CPSC was bioactive in vitro. CPSC cement, which has good biocompatibility and low/no cytotoxicity, could be a promising candidate as biomedical cement.

Calcium phosphate-based composites as injectable bone substitute materials

A major weakness of current orthopedic implant materials, for instance sintered hydroxyapatite (HA), is that they exist as a hardened form, requiring the surgeon to fit the surgical site around an implant to the desired shape. This can cause an increase in bone loss, trauma to the surrounding tissue, and longer surgical time. A convenient alternative to harden bone filling materials are injectable bone substitutes (IBS). In this article, recent progress in the development and application of calcium phosphate (CP)-based composites use as IBS is reviewed. CP materials have been used widely for bone replacement because of their similarity to the mineral component of bone. The main limitation of bulk CP materials is their brittle nature and poor mechanical properties. There is significant effort to reinforce or improve the mechanical properties and injectability of calcium phosphate cement (CPC) and this review resumes different alternatives presented in this specialized literature.

Preparation and characterization of a novel strontium-containing calcium phosphate cement with the two-step hydration process

A novel Sr-containing calcium phosphate cement (CPC) with excellent compressive strength, good radiopacity and suitable setting time was developed in this work. The two-step hydration reaction resulted in a high compressive strength, with a maximum of up to 74.9MPa. Sr was doped into the calcium-deficient hydroxyapatite as a hydrated product during the hydration reaction of the CPC. Because of the existence of Sr element and the compact microstructure after hydration, the Sr-containing CPC shows good radiopacity. It is expected to be used in orthopedic and maxillofacial surgery for bone defects repairing.

Novel bioactive composite bone cements based on the beta-tricalcium phosphate-monocalcium phosphate monohydrate composite cement system

Bioactive composite bone cements were obtained by incorporation of tricalcium silicate (Ca3SiO5, C3S) into a brushite bone cement composed of beta-tricalcium phosphate [beta-Ca3(PO4)2, beta-TCP] and monocalcium phosphate monohydrate [Ca(H2PO4)2.H2O, MCPM], and the properties of the new cements were studied and compared with pure brushite cement. The results indicated that the injectability, setting time and short- and long-term mechanical strength of the material are higher than those of pure brushite cement, and the compressive strength of the TCP/MCPM/C3S composite paste increased with increasing aging time. Moreover, the TCP/MCPM/C3S specimens showed significantly improved in vitro bioactivity in simulated body fluid and similar degradability in phosphate-buffered saline as compared with brushite cement. Additionally, the reacted TCP/MCPM/C3S paste possesses the ability to stimulate osteoblast proliferation and promote osteoblastic differentiation of the bone marrow stromal cells. The results indicated that the TCP/MCPM/C3S cements may be used as a bioactive material for bone regeneration, and might have significant clinical advantage over the traditional beta-TCP/MCPM brushite cement.

Calcium-phosphate-silicate composite bone cement: self-setting properties and in vitro bioactivity

In this study, a novel low temperature setting calcium phosphate-silicate cement was obtained by mixing CaHPO(4) x 2H(2)O (DCPD) and Ca(3)SiO(5) (C(3)S) with 0.75 M sodium phosphate buffers (pH = 7.0) as liquid phase. The self-setting properties of the obtained DCPD/C(3)S paste with liquid to powder ratio (L/P) of 0.6 ml/g, such as setting times, injectability, degradability and compressive strength were investigated and compared with that of DCPD/CaO cement system. The results indicated that, with the weight ratio of C(3)S varied from 20% to 40%, the workable DCPD/C(3)S pastes could set within 20 min, and the hydrated cement showed significantly higher compressive strength (around 34.0 MPa after 24 h) than that of the DCPD/CaO cement system (approximately 10.0 MPa). Furthermore, the in vitro pH value of the cements was investigated by soaking in simulated body fluid (SBF) for 12 h, and the result indicated that the DCPD/C(3)S did not induce significant increase or decrease of pH value in SBF. Additionally, the composite cement possesses better ability to support and stimulate cell proliferation than the DCPD/CaO cement. With good hydraulic properties, improved biocompatibility and moderate degradability, the novel DCPD/C(3)S bone cement may be a potential candidate as bone substitute.

Calcium Orthophosphate Cements and Concretes

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are a bioactive and biodegradable grafting material in the form of a powder and a liquid. Both phases form after mixing a viscous paste that after being implanted, sets and hardens within the body as either a non-stoichiometric calcium deficient hydroxyapatite (CDHA) or brushite, sometimes blended with unreacted particles and other phases. As both CDHA and brushite are remarkably biocompartible and bioresorbable (therefore, in vivo they can be replaced with newly forming bone), calcium orthophosphate cements represent a good correction technique for non-weight-bearing bone fractures or defects and appear to be very promising materials for bone grafting applications. Besides, these cements possess an excellent osteoconductivity, molding capabilities and easy manipulation. Furthermore, reinforced cement formulations are available, which in a certain sense might be described as calcium orthophosphate concretes. The concepts established by calcium orthophosphate cement pioneers in the early 1980s were used as a platform to initiate a new generation of bone substitute materials for commercialization. Since then, advances have been made in the composition, performance and manufacturing; several beneficial formulations have already been introduced as a result. Many other compositions are in experimental stages. In this review, an insight into calcium orthophosphate cements and concretes, as excellent biomaterials suitable for both dental and bone grafting application, has been provided.

Improved injectability and in vitro degradation of a calcium phosphate cement containing poly(lactide-co-glycolide) microspheres

An injectable calcium phosphate cement (CPC) containing 30 wt.% poly(lactide-co-glycolide) (PLGA) microspheres was developed in the present study. Sodium citrate solution was used as the cement liquid phase. The effects of sodium citrate concentration on the injectability, rheological properties, mechanical strength and self-setting properties of CPC containing PLGA microspheres were systematically investigated. The in vitro degradation behavior of the composite during immersion in phosphate buffer solution was also studied. With an increase in sodium citrate concentration, the viscosity and yield stress of the paste were reduced, thereby improving the injectability. At a sodium citrate concentration of 15%, the injectability of the paste reached 95%. The compressive strength of the specimen was also enhanced by the addition of sodium citrate. The specimens had a compressive strength of 32.24+/-2.72 MPa at 15% sodium citrate concentration, compared to 22.15+/-3.60 MPa for the specimen without sodium citrate. The in vitro degradation results demonstrate that incorporated PLGA microspheres can provide the required high strength to CPC in the early stage, which would gradually degrade to create macropores for bone ingrowth. In conclusion, an in situ macropore-generable CPC exhibited excellent injectability and high early strength, and should be a promising material for bone repair and bone reconstruction.