Osteotransductive bone cements

Enhancing Calcium Phosphate Cements: A review of Bacterial Cellulose (BC) and other Biopolymer Reinforcements for Biomedical Applications

Calcium phosphate cements (CPCs) are renowned for their biocompatibility and osteoconductivity, making them ideal for bone tissue engineering. However, their brittleness and low tensile strength limit their use in load-bearing applications. Bacterial cellulose (BC) has emerged as a promising reinforcement material due to its high tensile strength, biocompatibility, and biodegradability. The incorporation of 2 wt% BC into CPCs increased compressive strength from 5 MPa to 12 MPa, representing a 2.4-fold enhancement, while also improving toughness and promoting cellular interactions through its nanofibrillar structure. Additionally, hybrid composites combining BC with collagen, chitosan, or polycaprolactone (PCL) exhibit synergistic effects, further enhancing mechanical properties and biodegradability. These advancements highlight the potential of BC-reinforced CPCs for clinical applications in bone repair and regeneration. Despite these improvements, limited research addresses tensile and flexural properties, which are critical for load-bearing applications, as well as the effects of BC on injectability and setting time for minimally invasive procedures. Emerging innovations, such as electroactive BC-reinforced CPCs for stimulating bone healing, hold significant potential but remain underexplored. Future research should focus on optimising mechanical properties, validating clinical performance, and developing hybrid formulations to expand their use in load-bearing bone repairs.

Injectable bioactive scaffold able to stimulate oral bone regeneration on demand

Bone regeneration in oral surgery remains a challenge, due to the features of the oral environment, characterized by the presence of saliva and extensive interaction with external pathogens. Recent advances in this field highlighted that biomimetic apatites in which Ca2+ is replaced by Fe2+/Fe3+ ions are promising candidates to guide bone regeneration with on demand activation control. In this study the Fe-doped apatite nanoparticles (FeHA) were developed and compared with magnetite nanoparticles, as new magnetic bio-activator, to be embedded in apatitic injectable paste/cement. Upon self-hardening, the new injectable cement generates a mechanically competent 3D superparamagnetic scaffold, endowed with remote activation by using static magnetic fields. We investigated the alkaline phosphatase expression and activity, as well as the behaviour of cells, when seeded onto the scaffold. The results show the ability of the cement to stimulate cell colonization and differentiation and how, when magnetized, they can further boost such phenomena. The proposed devices, in association with a magnetic aligner, can represent a new approach in oral surgery, able to tune the bone remodelling on demand, when the regenerative potential is impaired by physiological conditions such as aging or chronic diseases.

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.

Calcium Phosphate Cements Combined with Blood as a Promising Tool for the Treatment of Bone Marrow Lesions

The solid phase of a commercial calcium phosphate (Graftys^® HBS) was combined with ovine or human blood stabilized either with sodium citrate or sodium heparin. The presence of blood delayed the setting reaction of the cement by ca. 7-15 h, depending on the nature of the blood and blood stabilizer. This phenomenon was found to be directly related to the particle size of the HBS solid phase, since prolonged grinding of the latter resulted in a shortened setting time (10-30 min). Even though ca. 10 h were necessary for the HBS blood composite to harden, its cohesion right after injection was improved when compared to the HBS reference as well as its injectability. A fibrin-based material was gradually formed in the HBS blood composite to end-up, after ca. 100 h, with a dense 3D organic network present in the intergranular space, thus affecting the microstructure of the composite. Indeed, SEM analyses of polished cross-sections showed areas of low mineral density (over 10-20 µm) spread in the whole volume of the HBS blood composite. Most importantly, when the two cement formulations were injected in the tibial subchondral cancellous bone in a bone marrow lesion ovine model, quantitative SEM analyses showed a highly significant difference between the HBS reference versus its analogue combined with blood. After a 4-month implantation, histological analyses clearly showed that the HBS blood composite underwent high resorption (remaining cement: ca. 13.1 ± 7.3%) and new bone formation (newly formed bone: 41.8 ± 14.7%). This was in sharp contrast with the case of the HBS reference for which a low resorption rate was observed (remaining cement: 79.0 ± 6.9%; newly formed bone: 8.6 ± 4.8%). This study suggested that the particular microstructure, induced by the use of blood as the HBS liquid phase, favored quicker colonization of the implant and acceleration of its replacement by newly formed bone. For this reason, the HBS blood composite might be worth considering as a potentially suitable material for subchondroplasty.

Strontium-doped apatitic bone cements with tunable antibacterial and antibiofilm ability

Injectable calcium phosphate cements (CPCs) represent promising candidates for the regeneration of complex-shape bone defects, thanks to self-hardening ability, bioactive composition and nanostructure offering high specific surface area for cell attachment and conduction. Such features make CPCs also interesting for functionalization with various biomolecules, towards the generation of multifunctional devices with enhanced therapeutic ability. In particular, strontium-doped CPCs have been studied in the last years due to the intrinsic antiosteoporotic character of strontium. In this work, a SrCPC previously reported as osteointegrative and capable to modulate the fate of bone cells was enriched with hydroxyapatite nanoparticles (HA-NPs) functionalized with tetracycline (TC) to provide antibacterial activity. We found that HA-NPs functionalized with TC (NP-TC) can act as modulator of the drug release profile when embedded in SrCPCs, thus providing a sustained and tunable TC release. In vitro microbiological tests on Escherichia coli and Staphylococcus aureus strains proved effective bacteriostatic and bactericidal properties, especially for the NP-TC loaded SrCPC formulations. Overall, our results indicate that the addition of NP-TC on CPC acted as effective modulator towards a tunable drug release control in the treatment of bone infections or cancers.

Evaluation of Enamel Acid Resistance and Whitening Effect of the CAP System

This study aimed to compare the effectiveness of a novel professional tooth-strengthening system and a conventional caries-prevention method that involved the use of high fluoride concentrations, to determine whether the system has a whitening effect. Bovine tooth-enamel samples were treated with fluoride gel (conventional APF method) or a mixture of citric acid gel, calcium phosphate (α-TCP), and fluoride gel, referred to as the CAP system; these treatments were performed to generate an acid-resistant layer on the enamel surface. For the evaluation of the acid resistance, a cyclic experiment, involving a 1-h remineralization and a 24-h acid treatment, was conducted thrice after the treatments. The height profiles were observed using a 3D-measuring laser microscope and the hardness was evaluated by Vickers hardness test. The morphological changes in the surface and cross-section of the enamel were observed by scanning electron microscopy. To evaluate the whitening effect, the enamel was ground until the color of the underlying dentin was recognizable; the CAP system was applied once, and the color change was measured using a color difference meter. As a result, it was confirmed that an acid-resistant layer was formed on the tooth surfaces treated with the CAP system, and a whitening effect was obtained.

Influence of Different Nanometals Implemented in PMMA Bone Cement on Biological and Mechanical Properties

Cemented arthroplasty is a common process to fix prostheses when a patient becomes older and his/her bone quality deteriorates. The applied cements are biocompatible, can transfer loads, and dampen vibrations, but do not provide antibacterial protection. The present work is aimed at the development of cement with antibacterial effectivity achieved with the implementation of nanoparticles of different metals. The powders of Ag, Cu with particles size in a range of 10–30 nm (Cu10) and 70–100 nm (Cu70), AgCu, and Ni were added to PMMA cement. Their influence on compression strength, wettability, and antibacterial properties of cement was assessed. The surface topography of samples was examined with biological and scanning electron microscopy. The mechanical properties were determined by compression tests. A contact angle was observed with a goniometer. The biological tests included an assessment of cytotoxicity (XTT test on human cells Saos-2 line) and bacteria viability exposure (6 months). The cements with Ag and Cu nanopowders were free of bacteria. For AgCu and Ni nanoparticles, the bacterial solution became denser over time and, after 6 months, the bacteria clustered into conglomerates, creating a biofilm. All metal powders in their native form in direct contact reduce the number of eukaryotic cells. Cell viability is the least limited by Ag and Cu particles of smaller size. All samples demonstrated hydrophobic nature in the wettability test. The mechanical strength was not significantly affected by the additions of metal powders. The nanometal particles incorporated in PMMA-based bone cement can introduce long-term resistance against bacteria, not resulting in any serious deterioration of compression strength.

Coaxial micro-extrusion of a calcium phosphate ink with aqueous solvents improves printing stability, structure fidelity and mechanical properties

Micro-extrusion-based 3D printing of complex geometrical and porous calcium phosphate (CaP) can improve treatment of bone defects through the production of personalized bone substitutes. However, achieving printing and post-printing shape stabilities for the efficient fabrication and application of rapid hardening protocol are still challenging. In this work, the coaxial printing of a self-setting CaP cement with water and ethanol mixtures aiming to increase the ink yield stress upon extrusion and the stability of fabricated structures was explored. Printing height of overhang structure was doubled when aqueous solvents were used and a 2 log increase of the stiffness was achieved post-printing. A standard and fast steam sterilization protocol applied as hardening step on the coaxial printed CaP cement (CPC) ink resulted in constructs with 4 to 5 times higher compressive moduli in comparison to extrusion process in the absence of solvent. This improved mechanical performance is likely due to rapid CPC setting, preventing cracks formation during hardening process. Thus, coaxial micro-extrusion-based 3D printing of a CPC ink with aqueous solvent enhances printability and allows the use of the widespread steam sterilization cycle as a standalone post-processing technique for production of 3D printed personalized CaP bone substitutes. STATEMENT OF SIGNIFICANCE: Coaxial micro-extrusion-based 3D printing of a self-setting CaP cement with water:ethanol mixtures increased the ink yield stress upon extrusion and the stability of fabricated structures. Printing height of overhang structure was doubled when aqueous solvents were used, and a 2 orders of magnitude log increase of the stiffness was achieved post-printing. A fast hardening step consisting of a standard steam sterilization was applied. Four to 5 times higher compressive moduli was obtained for hardened coaxially printed constructs. This improved mechanical performance is likely due to rapid CPC setting in the coaxial printing, preventing cracks formation during hardening process.

Nanostructured Strontium-Doped Calcium Phosphate Cements: A Multifactorial Design

Calcium phosphate cements (CPCs) have been extensively studied in last decades as nanostructured biomaterials for the regeneration of bone defects, both for dental and orthopedic applications. However, the precise control of their handling properties (setting time, viscosity, and injectability) still represents a remarkable challenge because a complicated adjustment of multiple correlated processing parameters is requested, including powder particle size and the chemical composition of solid and liquid components. This study proposes, for the first time, a multifactorial investigation about the effects of powder and liquid variation on the final performance of Sr-doped apatitic CPCs, based on the Design of Experiment approach. In addition, the effects of two mixing techniques, hand spatula (low-energy) and planetary shear mixing (high-energy), on viscosity and extrusion force were compared. This work aims to shed light on the various steps involved in the processing of CPCs, thus enabling a more precise and tailored design of the device, based on the clinical need.

Strontium-calcium phosphate hybrid cement with enhanced osteogenic and angiogenic properties for vascularised bone regeneration

Vascularized bone tissue engineering is regarded as one of the optimal treatment options for large bone defects. The lack of angiogenic properties and unsatisfactory physicochemical performance restricts calcium phosphate cement (CPC) from application in vascularized bone tissue engineering. Our previous studies have developed a starch and BaSO4 incorporated calcium phosphate hybrid cement (CPHC) with improved mechanical strength and handling properties. However, the bioactivity-especially the angiogenic ability-is still absent and requires further improvement. Herein, based on the reported CPHC and the osteogenic and angiogenic properties of strontium (Sr) ions, a strontium-enhanced calcium phosphate hybrid cement (Sr-CPHC) was developed to improve both biological and physicochemical properties of CPC. Compared to CPC, the initial setting time of Sr-CPHC was prolonged from 2.2 min to 20.7 min. The compressive strength of Sr-CPHC improved from 11.21 MPa to 45.52 MPa compared with CPC as well. Sr-CPHC was biocompatible and showed promotion of alkaline phosphatase (ALP) activity, calcium nodule formation and osteogenic relative gene expression, suggesting high osteogenic-inductivity. Sr-CPHC also facilitated the migration and tube formation of human umbilical vein endothelial cells (HUVECs) in vitro and up-regulated the expression of the vascular endothelial growth factor (VEGF) and Angiopoietin-1 (Ang-1). In vivo evaluation showed marked new bone formation in a rat calvarial defect model with Sr-CPHC implanted. Sr-CPHC also exhibited enhancement of neovascularization in subcutaneous connective tissue in a rat subcutaneous implantation model. Thus, the Sr-CPHC with the dual effects of osteogenesis and angiogenesis shows great potential for clinical applications such as the repair of ischemic osteonecrosis and critical-size bone defects.

Strontium substitution of gelatin modified calcium hydrogen phosphates as porous hard tissue substitutes

Aiming at the generation of a high strontium-containing degradable bone substitute, the exchange of calcium with strontium in gelatin-modified brushite was investigated. The ion substitution showed two mineral groups, the high-calcium containing minerals with a maximum measured molar Ca/Sr ratio of 80%/20% (mass ratio 63%/37%) and the high-strontium containing ones with a maximum measured molar Ca/Sr ratio of 21%/79% (mass ratio 10%/90%). In contrast to the high-strontium mineral phases, a high mass loss was observed for the calcium-based minerals during incubation in cell culture medium (alpha-MEM), but also an increase in strength owing to dissolution and re-precipitation. This resulted for the former in a decrease of cation concentration (Ca + Sr) in the medium, while the pH value decreased and the phosphate ion concentration rose significantly. The latter group of materials, the high-strontium containing ones, showed only a moderate change in mass and a decrease in strength, but the Ca + Sr concentration remained permanently above the initial calcium concentration in the medium. This might be advantageous for a future planned application by supporting bone regeneration on the cellular level.

Reconstruction of Large Osteochondral Defects Using a Hemicondylar Aragonite-Based Implant in a Caprine Model

PURPOSE

To investigate the safety and regenerative potential of a hemicondylar aragonite-based scaffold in the reconstruction of large osteochondral lesions occupying an extensive portion of the medial femoral condyle in a goat model.

METHODS

Eight Saanen goats were treated by the implantation of an aragonite-based scaffold (size: 19 × 8 × 8 mm) on a previously prepared hemicondylar osteochondral defect located in the right medial femoral condyle of the knee. Goats were euthanized after 12 months and the specimens underwent X-ray imaging, macroscopic, micro-computed tomography, histology, and immunohistochemistry evaluations to assess subchondral bone and cartilage regeneration.

RESULTS

In all 8 goats, no adverse event or persistent inflammation was observed. The evaluations performed showed integration of the scaffold, which almost completely resorbed at 12 months. In all animals, no signs of osteoarthritis progression were seen. Concurrent regeneration of the osteochondral unit was observed, with trabecular bone tissue replacing the implant and restoring the subchondral layer, and the formation of an overlying hyaline cartilage surface, well integrated within the surrounding native tissue, also was observed.

CONCLUSIONS

The use of the hemicondylar biphasic aragonite-based implant in the treatment of osteochondral defects in the goat model proved to be technically feasible and safe. The scaffold degraded and was replaced by regenerated tissue within the 12-month study period, restoring the osteochondral unit both at the level of the cartilaginous layer and the subchondral bone.

CLINICAL RELEVANCE

The present animal study describes a scaffold-based procedure for the treatment of large condylar defects, which often require massive allograft or unicompartmental replacement. The aragonite-based implant promoted a regeneration of both cartilage and subchondral bone, and its use as a "biologic" unicondylar prosthesis might be feasible also in the clinical setting.

Mineral-Doped Poly(L-lactide) Acid Scaffolds Enriched with Exosomes Improve Osteogenic Commitment of Human Adipose-Derived Mesenchymal Stem Cells

Exosomes derived from mesenchymal stem cells are extracellular vesicles released to facilitate cell communication and function. Recently, polylactic acid (PLA), calcium silicates (CaSi), and dicalcium phosphate dihydrate (DCPD) have been used to produce bioresorbable functional mineral-doped porous scaffolds-through thermally induced phase separation technique, as materials for bone regeneration. The aim of this study was to investigate the effect of mineral-doped PLA-based porous scaffolds enriched with exosome vesicles (EVs) on osteogenic commitment of human adipose mesenchymal stem cells (hAD-MSCs). Two different mineral-doped scaffolds were produced: PLA-10CaSi-10DCPD and PLA-5CaSi-5DCPD. Scaffolds surface micromorphology was investigated by ESEM-EDX before and after 28 days immersion in simulated body fluid (HBSS). Exosomes were deposited on the surface of the scaffolds and the effect of exosome-enriched scaffolds on osteogenic commitment of hAD-MSCs cultured in proximity of the scaffolds has been evaluated by real time PCR. In addition, the biocompatibility was evaluated by direct-contact seeding hAD-MSCs on scaffolds surface-using MTT viability test. In both formulations, ESEM showed pores similar in shape (circular and elliptic) and size (from 10-30 µm diameter). The porosity of the scaffolds decreased after 28 days immersion in simulated body fluid. Mineral-doped scaffolds showed a dynamic surface and created a suitable bone-forming microenvironment. The presence of the mineral fillers increased the osteogenic commitment of hAD-MSCs. Exosomes were easily entrapped on the surface of the scaffolds and their presence improved gene expression of major markers of osteogenesis such as collagen type I, osteopontin, osteonectin, osteocalcin. The experimental scaffolds enriched with exosomes, in particular PLA-10CaSi-10DCPD, increased the osteogenic commitment of MSCs. In conclusion, the enrichment of bioresorbable functional scaffolds with exosomes is confirmed as a potential strategy to improve bone regeneration procedures.

First successful stabilization of consolidated amorphous calcium phosphate (ACP) by cold sintering: toward highly-resorbable reactive bioceramics

An adequate tuning of amorphous calcium phosphates ionic composition and cold sintering conditions allowed the first successful stabilization of these bioactive compounds. These results show promise for the setup of highly-resorbable bone substitutes.

Osteogenic differentiation of human bone marrow-derived mesenchymal stem cells is enhanced by an aragonite scaffold

Bone graft substitutes and bone void fillers are predominantly used to treat bone defects and bone fusion in orthopaedic surgery. Some aragonite-based scaffolds of coralline exoskeleton origin exhibit osteoconductive properties and are described as useful bone repair scaffolds. The purpose of this study was to evaluate the in vitro osteogenic potential of the bone phase of a novel aragonite-based bi-phasic osteochondral scaffold (Agili-C™, CartiHeal Ltd.) using adult human bone marrow-derived mesenchymal stem cells (MSCs). Analyses were performed at several time intervals: 3, 7, 14, 21, 28 and 42 days post-seeding. Osteogenic differentiation was assessed by morphological characterisation using light microscopy after Alizarin red and von Kossa staining, and scanning electron microscopy. The transcript levels of alkaline phosphatase (ALP), runt-related transcription factor 2 (RUNX2), bone gamma-carboxyglutamate (BGLAP), osteonectin (SPARC) and osteopontin (SPP1) were determined by quantitative PCR. Proliferation was assessed by a thymidine incorporation assay and proliferating cell nuclear antigen (PCNA) immunocytochemistry. Our results demonstrate that the bone phase of the bi-phasic aragonite-based scaffold supports osteogenic differentiation and enhanced proliferation of bone marrow-derived MSCs at both the molecular and histological levels. The scaffold was colonized by differentiating MSCs, suggesting its suitability for incorporation into bone voids to accelerate bone healing, remodelling and regeneration. The mechanism of osteogenic differentiation involves scaffold surface modification with de novo production of calcium phosphate deposits, as revealed by energy dispersive spectroscopy (EDS) analyses. This novel coral-based scaffold may promote the rapid formation of high quality bone during the repair of osteochondral lesions.

The Effect of the Thermosensitive Biodegradable PLGA⁻PEG⁻PLGA Copolymer on the Rheological, Structural and Mechanical Properties of Thixotropic Self-Hardening Tricalcium Phosphate Cement

The current limitations of calcium phosphate cements (CPCs) used in the field of bone regeneration consist of their brittleness, low injectability, disintegration in body fluids and low biodegradability. Moreover, no method is currently available to measure the setting time of CPCs in correlation with the evolution of the setting reaction. The study proposes that it is possible to improve and tune the properties of CPCs via the addition of a thermosensitive, biodegradable, thixotropic copolymer based on poly(lactic acid), poly(glycolic acid) and poly(ethylene glycol) (PLGA⁻PEG⁻PLGA) which undergoes gelation under physiological conditions. The setting times of alpha-tricalcium phosphate (α-TCP) mixed with aqueous solutions of PLGA⁻PEG⁻PLGA determined by means of time-sweep curves revealed a lag phase during the dissolution of the α-TCP particles. The magnitude of the storage modulus at lag phase depends on the liquid to powder ratio, the copolymer concentration and temperature. A sharp increase in the storage modulus was observed at the time of the precipitation of calcium deficient hydroxyapatite (CDHA) crystals, representing the loss of paste workability. The PLGA⁻PEG⁻PLGA copolymer demonstrates the desired pseudoplastic rheological behaviour with a small decrease in shear stress and the rapid recovery of the viscous state once the shear is removed, thus preventing CPC phase separation and providing good cohesion. Preliminary cytocompatibility tests performed on human mesenchymal stem cells proved the suitability of the novel copolymer/α-TCP for the purposes of mini-invasive surgery.

In vivo efficiency of antimicrobial inorganic bone grafts in osteomyelitis treatments

The purpose of the present work was to evaluate in vivo different antimicrobial therapies to eradicate osteomyelitis created in the femoral head of New Zealand rabbits. Five phosphate-based cements were evaluated: calcium phosphate cements (CPC) and calcium phosphate foams (CPF), both in their pristine form and loaded with doxycycline hyclate, and an intrinsic antimicrobial magnesium phosphate cement (MPC; not loaded with an antibiotic). The cements were implanted in a bone previously infected with Staphylococcus aureus to discern the effects of the type of antibiotic administration (systemic vs. local), porosity (microporosity, i.e. <5 μm vs. macroporosity, i.e. >5 μm) and type of antimicrobial mechanism (release of antibiotic vs. intrinsic antimicrobial activity) on the improvement of the health state of the infected animals. A new method was developed, with a more comprehensive composite score that integrates 5 parameters of bone infection, 4 parameters of bone structural integrity and 4 parameters of bone regeneration. This method was used to evaluate the health state of the infected animals, both before and after osteomyelitis treatment. The results showed that the composite score allows to discern statistically significant differences between treatments that individual evaluations were not able to identify. Despite none of the therapies completely eradicated the infection, it was observed that macroporous materials (CPF and CPFd, the latter loaded with doxycycline hyclate) and intrinsic antimicrobial MPC allowed a better containment of the osteomyelitis. This study provides novel insights to understand the effect of different antimicrobial therapies in vivo, and a promising comprehensive methodology to evaluate the health state of the animals was developed. We expect that the implementation of such methodology could improve the criteria to select a proper antimicrobial therapy.

Calcium phosphate bone cement/mesoporous bioactive glass composites for controlled growth factor delivery

Calcium phosphate (CaP) bone cements are widely used for the treatment of bone defects and have been proposed to serve as a delivery platform for therapeutic drugs, proteins and growth factors into the defect region. However, they lack sufficient porosity to allow immediate bone ingrowth and thus foster rapid integration into the bone tissue. In this study we investigated a composite prepared from a hydroxyapatite forming bone cement and mesoporous bioactive glass (MBG) granules as a potential carrier for biologically active proteins. The mechanical properties of the composite were not compromised by up to 10 wt% MBG granule addition, which can be attributed to the strong interface between the cement matrix and MBG particles, however this modification induced a significant increase in porosity within 3 weeks ageing in an aqueous liquid. The release profiles of two proteins, lysozyme and the vascular endothelial growth factor (VEGF), could be controlled when they were loaded onto MBG granules that were subsequently embedded into the cement when compared to direct loading into the cement precursor. Both proteins were also demonstrated to maintain their biologic activity during embedding and release from the composite. These findings suggest the CaP bone cement/MBG composite developed in this study as a potential delivery platform for growth factors or other bioactive substances.

Strontium-modified premixed calcium phosphate cements for the therapy of osteoporotic bone defects

In this study a premixed strontium-containing calcium phosphate bone cement for the application in osteoporotic bone defects has been developed and characterised regarding its material and in vitro properties as well as minimally invasive applicability in balloon kyphoplasty. Strontium was introduced into the cement by substitution of one precursor component, CaCO₃, with its strontium analogue, SrCO₃. Using a biocompatible oil phase as carrier liquid, a cement paste that only set upon contact with aqueous environment was obtained. Strontium modification resulted in an increased strength of set cements and radiographic contrast; and the cements released biologically relevant doses of Sr²⁺-ions that were shown to enhance osteoprogenitor cell proliferation and osteogenic differentiation. Finally, applicability of strontium-containing cement pastes in balloon kyphoplasty was demonstrated in a human cadaver spine procedure. The cement developed in this study may therefore be well suited for minimally invasive, osteoporosis-related bone defect treatment.

STATEMENT OF SIGNIFICANCE

Strontium-releasing calcium phosphate bone cements are promising materials for the clinical regeneration of osteoporosis-related bone defects since they have been shown to stimulate bone formation and at the same time limit osteoclastic bone resorption. Today clinical practice favours minimally invasive surgical techniques, e.g. for vertebral fracture treatment, posing special demands on such cements. We have therefore developed a premixed, strontium-releasing bone cement with enhanced mechanical properties and high radiographic visibility that releases biologically relevant strontium concentrations and thus stimulates cells of the osteogenic lineage. In a pilot experiment we also exemplify its excellent suitability for minimally invasive balloon kyphoplasty procedures.

Calcium Phosphate Bioceramics: A Review of Their History, Structure, Properties, Coating Technologies and Biomedical Applications

Calcium phosphate (CaP) bioceramics are widely used in the field of bone regeneration, both in orthopedics and in dentistry, due to their good biocompatibility, osseointegration and osteoconduction. The aim of this article is to review the history, structure, properties and clinical applications of these materials, whether they are in the form of bone cements, paste, scaffolds, or coatings. Major analytical techniques for characterization of CaPs, in vitro and in vivo tests, and the requirements of the US Food and Drug Administration (FDA) and international standards from CaP coatings on orthopedic and dental endosseous implants, are also summarized, along with the possible effect of sterilization on these materials. CaP coating technologies are summarized, with a focus on electrochemical processes. Theories on the formation of transient precursor phases in biomineralization, the dissolution and reprecipitation as bone of CaPs are discussed. A wide variety of CaPs are presented, from the individual phases to nano-CaP, biphasic and triphasic CaP formulations, composite CaP coatings and cements, functionally graded materials (FGMs), and antibacterial CaPs. We conclude by foreseeing the future of CaPs.

3D plotting of growth factor loaded calcium phosphate cement scaffolds

Additive manufacturing allows to widely control the geometrical features of implants. Recently, we described the fabrication of calcium phosphate cement (CPC) scaffolds by 3D plotting of a storable CPC paste based on water-immiscible carrier liquid. Plotting and hardening is conducted under mild conditions allowing the (precise and local) integration of biological components. In this study, we have developed a procedure for efficient loading of growth factors in the CPC scaffolds during plotting and demonstrated the feasibility of this approach. Bovine serum albumin (BSA) or vascular endothelial growth factor (VEGF), used as model proteins, were encapsulated in chitosan/dextran sulphate microparticles which could be easily mixed into the CPC paste in freeze-dried state. In order to prevent leaching of the proteins during cement setting, usually carried out by immersion in aqueous solutions, the plotted scaffolds were aged in water-saturated atmosphere (humidity). Setting in humidity avoided early loss of loaded proteins but provided sufficient amount of water to allow cement setting, as indicated by XRD analysis and mechanical testing in comparison to scaffolds set in water. Moreover, humidity-set scaffolds were characterised by altered, even improved properties: no swelling or crack formation was observed and accordingly, surface topography, total porosity and compressive modulus of the humidity-set scaffolds differed from those of the water-set counterparts. Direct cultivation of mesenchymal stem cells on the humidity-set scaffolds over 21days revealed their cytocompatibility. Maintenance of the bioactivity of VEGF during the fabrication procedure was proven in indirect and direct culture experiments with endothelial cells.

STATEMENT OF SIGNIFICANCE

Additive manufacturing techniques allow the fabrication of implants with defined architecture (inner pore structure and outer shape). Especially printing technologies conducted under mild conditions allow additionally the (spatially controlled) integration of biological components such as drugs or growth factors. That enables the generation of individualized implants which can better meet the requirements of a patient and of tissue engineering constructs. To our knowledge, simultaneous printing of biological components was up to now only described for hydrogel/biopolymer-based materials which suffer from poor mechanical properties. In contrast, we have developed a procedure (based on 3D plotting of a calcium phosphate cement paste) for the fabrication of designed and growth factor loaded calcium-phosphate-based scaffolds applicable for bone regeneration.

Osteochondral regeneration with a novel aragonite-hyaluronate biphasic scaffold: up to 12-month follow-up study in a goat model

BACKGROUND

The regeneration of articular hyaline cartilage remains an elusive goal despite years of research. Recently, an aragonite-hyaluronate (Ar-HA) biphasic scaffold has been described capable of cartilage regeneration over a 6-month follow-up period. This study was conducted in order to assess the fate of the regenerated osteochondral tissue in a 12-month-long validated caprine model.

HYPOTHESIS/PURPOSE

The hypothesis was that the implantation of the Ar-HA implant leads to tissue regeneration and maturation.

STUDY DESIGN

A two-arm caprine model of a critical osteochondral defect compares the fate of acute osteochondral defects (group A) to Ar-HA implanted defects (group B).

METHODS

Critical 6 mm in diameter and 10-mm in depth osteochondral defects were created in the load-bearing medial femoral condyle of 20 mature goats and randomized into two groups. In group A (n = 6), a blood clot spontaneously filled the defect; in group B (n = 14), a single Ar-HA implant reconstructed the defect. The animals were sacrificed after either 6 or 12 months. Parameters assessed included clinical evaluation, x-rays, micro-CT, ultrasound and histology at both time points, and specimen high-field magnetic resonance imaging with T2 mapping at the 12-month time point.

RESULTS

In most group A animals, the defects were not reconstructed (1/3 at 6 months, and 0/3 at 12 months). Defects in group B were mostly reconstructed (5/7 at 6 months and 6/7 at 12 months). Group A defects were either empty or contained fibrous repair tissue; while group B filling was compatible with hyaline cartilage and normal bone.

CONCLUSION

Ar-HA scaffolds implanted in critical osteochondral defects result in hyaline cartilage formation and subchondral bone regeneration. The results improved at the 12-month time point compared to the 6-month time point, indicating a continuous maturation process without deterioration of the repair tissue.

CLINICAL RELEVANCE

Osteochondral defects are common in humans; the results of the current study suggest that an acellular Ar-HA scaffold might induce cartilage and subchondral bone regeneration.

Dendritic Glycopolymer as Drug Delivery System for Proteasome Inhibitor Bortezomib in a Calcium Phosphate Bone Cement: First Steps Toward a Local Therapy of Osteolytic Bone Lesions

Establishment of drug delivery system (DDS) in bone substitute materials for local treatment of bone defects still requires ambitious solutions for a retarded drug release. We present two novel DDS, a weakly cationic dendritic glycopolymer and a cationic polyelectrolyte complex, composed of dendritic glycopolymer and cellulose sulfate, for the proteasome inhibitor bortezomib. Both DDS are able to induce short-term retarded release of bortezomib from calcium phosphate bone cement in comparison to a burst-release of the drug from bone cement alone. Different release parameters have been evaluated to get a first insight into the release mechanism from bone cements. In addition, biocompatibility of the calcium phosphate cement, modified with the new DDS was investigated using human mesenchymal stromal cells.

Design and evaluation of a nanoenhanced anti-infective calcium phosphate bone cements

Post-operative complications due to infections are the most common problems that occur following dental and orthopedic implant surgeries and bone repair procedures. Preventing post-surgical infections is therefore a critical need that current polymethylmethacrylate (PMMA) bone cement fail to address. Calcium phosphate cements (CPCs) are unique in their ability to crystallize calcium and phosphate salts into hydroxyapatite (HA) and hence is naturally osteoconductive. Due to its low mechanical strength its use in implant fixation and bone repair is limited to non-load bearing applications. The present work describes a new and novel antibiotic-doped clay nanotube CPC composite with enhanced mechanical properties as well as sustained release properties.

Strontium modified calcium phosphate cements – approaches towards targeted stimulation of bone turnover

Strontium modified calcium phosphate cements can target local bone turnover by stimulating osteoblast proliferation and differentiation (1) as well as bone mineralisation (2), reducing osteoclastogenesis (3) and resorption activity, increase osteoclast apoptosis (4) and affect osteoblast/osteoclast paracrine signalling (5).

Spine-Ghost: A New Bioactive Cement for Vertebroplasty

An innovative, resorbable and injectable composite cement (Spine-Ghost) to be used for augmentation and restoration of fractured vertebrae was developed. Type III α-calcium sulfate hemihydrate (CSH) was selected as the bioresorbable matrix, while spray-dried mesoporous bioactive particles (SD-MBP, composition 80/20% mol SiO2/CaO), were added to impart high bioactive properties to the cement; a glass-ceramic containing zirconia was chosen as a second dispersed phase, in order to increase the radiopacity of the material. After mixing with water, an injectable paste was obtained. The developed cement proved to be mechanically compatible with healthy cancellous bone, resorbable and bioactive by soaking in simulated body fluid (SBF), cytocompatible through in-vitro cell cultures and it could be injected in ex-vivo sheep vertebra. Comparisons with a commercial control were carried out.

Development of a novel calcium phosphate cement composed mainly of calcium sodium phosphate with high osteoconductivity

Two novel calcium phosphate cements (CPC) have been developed using calcium sodium phosphate (CSP) as the main ingredient. The first of these cements, labeled CAC, contained CSP, α-tricalcium phosphate (TCP), and anhydrous citric acid, whereas the second, labeled CABC, contained CSP, α-TCP, β-TCP, and anhydrous citric acid. Biopex(®)-R (PENTAX, Tokyo, Japan), which is a commercially available CPC (Com-CPC), and OSferion(®) (Olympus Terumo Biomaterials Corp., Tokyo, Japan), which is a commercially available porous β-TCP, were used as reference controls for analysis. In vitro analysis showed that CABC set in 5.7 ± 0.3 min at 22 °C and had a compressive strength of 86.0 ± 9.7 MPa after 5 days. Furthermore, this material had a compressive strength of 26.7 ± 3.7 MPa after 2 h in physiologic saline. CAC showed a statistically significantly lower compressive strength in the presence of physiologic saline and statistically significantly longer setting times than those of CABC. CABC and CAC exhibited apatite-forming abilities in simulated body fluid that were faster than that of Com-CPC. Samples of the materials were implanted into the femoral condyles of rabbits for in vivo analysis, and subsequent histological examinations revealed that CABC exhibited superior osteoconductivity and equivalent bioresorbability compared with Com-CPC, as well as superior osteoconductivity and bioresorbability compared with CAC. CABC could therefore be used as an alternative bone substitute material.

Calcium phosphate cements for bone substitution: chemistry, handling and mechanical properties

Since their initial formulation in the 1980s, calcium phosphate cements (CPCs) have been increasingly used as bone substitutes. This article provides an overview on the chemistry, kinetics of setting and handling properties (setting time, cohesion and injectability) of CPCs for bone substitution, with a focus on their mechanical properties. Many processing parameters, such as particle size, composition of cement reactants and additives, can be adjusted to control the setting process of CPCs, concomitantly influencing their handling and mechanical performance. Moreover, this review shows that, although the mechanical strength of CPCs is generally low, it is not a critical issue for their application for bone repair--an observation not often realized by researchers and clinicians. CPCs with compressive strengths comparable to those of cortical bones can be produced through densification and/or homogenization of the cement matrix. The real limitation for CPCs appears to be their low fracture toughness and poor mechanical reliability (Weibull modulus), which have so far been only rarely studied.

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.

Bioactive calcium sulfate/magnesium phosphate cement for bone substitute applications

A novel calcium sulfate/magnesium phosphate cement (CSMPC) composite was prepared and studied in the present work. The physical properties including the phases, the microstructures, the setting properties and the compressive strengths of the CSMPCs were studied. The bio-performances of the CSMPCs were comprehensively evaluated using in vitro simulated body fluid (SBF) method and in vitro cell culture. The dependence of the physical and chemical properties of the CSMPC on its composition and microstructure was studied in detail. It is found that the CSMPC composites exhibited mediate setting times (6-12 min) compared to the calcium sulfate (CS) and the magnesium phosphate cement (MPC). They showed an encapsulation structure in which the unconverted hexagonal prism CSH particles were embedded in the xerogel-like MPC matrix. The phase compositions and the mechanical properties of the CSMPCs were closely related to the content of MPC and the hardening process. The CSMPCs exhibited excellent bioactivity and good biocompatibility to support the cells to attach and proliferate on the surface. The CSMPC composite has the potential to serve as bone grafts for the bone regeneration.

A novel and easy-to-prepare strontium(II) modified calcium phosphate bone cement with enhanced mechanical properties

The aim of this study was to evaluate two different approaches to obtaining strontium-modified calcium phosphate bone cements (SrCPCs) without elaborate synthesis of Sr-containing calcium phosphate species as cement precursors that could release biologically effective doses of Sr(2+) and thus could improve the healing of osteoporotic bone defects. Using strontium carbonate as a strontium(II) source, it was introduced into a hydroxyapatite-forming cement either by the addition of SrCO3 to an α-tricalcium phosphate-based cement precursor mixture (A-type) or by substitution of CaCO3 by SrCO3 during precursor composition (S-type). The cements, obtained after setting in a water-saturated atmosphere, contained up to 2.2at.% strontium in different distribution patterns as determined by time-of-flight secondary ion mass spectrometry and energy-dispersive X-ray spectroscopy. The setting time of CPC and A-type cements was in the range of 6.5-7.5min and increased for substitution-type cements (12.5-13.0min). Set cements had an open porosity between 26 and 42%. Compressive strength was found to increase from 29MPa up to 90% in substituted S-type cements (58MPa). SrCPC samples released between 0.45 and 1.53mgg(-1) Sr(2+) within 21days and showed increased radiopacity. Based on these findings, the SrCPC developed in this study could be beneficial for the treatment of defects of systemically impaired (e.g. osteoporotic) bone.

Synthesis of spherical calcium phosphate particles for dental and orthopedic applications

Calcium phosphate materials have been used increasingly in the past 40 years as bone graft substitutes in the dental and orthopedic fields. Accordingly, numerous fabrication methods have been proposed and used. However, the controlled production of spherical calcium phosphate particles remains a challenge. Since such particles are essential for the synthesis of pastes and cements delivered into the host bone by minimally-invasive approaches, the aim of the present document is to review their synthesis and applications. For that purpose, production methods were classified according to the used reagents (solutions, slurries, pastes, powders), dispersion media (gas, liquid, solid), dispersion tools (nozzle, propeller, sieve, mold), particle diameters of the end product (from 10 nm to 10 mm), and calcium phosphate phases. Low-temperature calcium phosphates such as monetite, brushite or octacalcium phosphate, as well as high-temperature calcium phosphates, such as hydroxyapatite, β-tricalcium phosphate or tetracalcium phosphate, were considered. More than a dozen production methods and over hundred scientific publications were discussed.

Relevance of the setting reaction to the injectability of tricalcium phosphate pastes

The aim of the present work was to analyze the influence of the setting reaction on the injectability of tricalcium phosphate (TCP) pastes. Even if the injection was performed early after mixing powder and liquid, powder reactivity was shown to play a significant role in the injectability of TCP pastes. Significant differences were observed between the injection behavior of non-hardening β-TCP pastes and that of self-hardening α-TCP pastes. The differences were more marked at low liquid-to-powder ratios, using fine powders and injecting through thin needles. α-TCP was, in general, less injectable than β-TCP and required higher injection loads. Moreover, clogging was identified as a mechanism hindering or even preventing injectability, different and clearly distinguishable from the filter-pressing phenomenon. α-TCP pastes presented transient clogging episodes, which were not observed in β-TCP pastes with equivalent particle size distribution. Different parameters affecting powder reactivity were also shown to affect paste injectability. Thus, whereas powder calcination resulted in an increased injectability due to lower particle reactivity, the addition of setting accelerants, such as hydroxyapatite nanoparticles, tended to reduce the injectability of the TCP pastes, especially if adjoined simultaneously with a Na2HPO4 solution. Although, as a general trend, faster-setting pastes were less injectable, some exceptions to this rule were found. For example, whereas in the absence of setting accelerants fine TCP powders were more injectable than the coarse ones, in spite of their shorter setting times, this trend was inverted when setting accelerants were added, and coarse powders were more injectable than the fine ones.

Setting Time Comparison of Four Antimicrobial Laden Calcium Sulfate Plasters

Background

The surgeon may implant calcium sulfate pellets (aka gypsum) as a resorbable antimicrobial vehicle at the surgical site in severe cases of osteomyelitis. Gypsum setting times with or without antibiotic additives are found scattered throughout the literature, but often factors known to alter setting time are either not disclosed or not held constant between experiments. To our knowledge, no prior study compares the setting time of calcium sulfate plaster mixed with the four commonly used antibiotics under constant conditions as presented here.

Purpose

To compare the setting times of calcium sulfate hemihydrate mixtures containing vancomycin, cefazolin, tobramycin, or amphotericin B.

Materials and methods

Groups consisted of samples comprised of 6.3 gm calcium sulfate hemihydrate (CSH) mixed with approximately 1/4th a vial of lyophilized antimicrobial (vancomycin, cefazolin, tobramycin or amphotericin B) with CSH powder to normal saline ratio of 1.7 gm/ml and mixed for 30 seconds at controlled speed and humidity. Each sample initial setting time (Ti) and final setting time (Tf) were established by Gillmore needles method according to ASTM standard C266- 08 apparatus specifications.

Results

Kruskal-Wallis one-way analysis of variance by ranks revealed that antibiotic type affected the initial and final setting times of gypsum (p < 0.05). Post hoc analysis using Dunn's multiple comparisons indicated that there was no difference between control Ti (7.2 ± 1.1 min) and that of vancomycin or cefazolin group (9.8 ± 1.7 or 14.2 ± 1.3 min, respectively, p > 0.05), but the Ti of the tobramycin and amphotericin B groups (31.8 ± 5.7 and 140.4 ± 18.0 min) differed from the control Ti (p < 0.05). Likewise, there was no difference of control Tf (p > 0.05, 12.2 ± 1.1 min) when compared to vancomycin or cefazolin groups (22.2 ± 6.9 or 25.7 ± 4.1 min), but that the Tf of tobramycin and amphotericin B groups (76.3 ± 5.9 and 200.0 ± 21.1 min) each differed from the control group (p < 0.05).

Conclusion

This experiment is aimed to help surgeons plan when they should begin preparing their calcium sulfate antibiotic beads during surgery. As a general guideline, allow 15 minutes to set when adding a 1 gm vial of vancomycin or cefazolin, 30 minutes for adding a 1.2 gm vial tobramycin, and 2.5 hours for adding a 50 mg vial of amphotericin B.

Kroger J, Beaufond P, Inceoglu S, Maskiewicz V, Cheng W, Brier-Jones JE. Setting Time Comparison of Four Antimicrobial Laden Calcium Sulfate Plasters. The Duke Orthop J 2013;3(1):36-40.

Calcium phosphate cements as drug delivery materials

Calcium phosphate cements are used as synthetic bone grafts, with several advantages, such as their osteoconductivity and injectability. Moreover, their low-temperature setting reaction and intrinsic porosity allow for the incorporation of drugs and active principles in the material. It is the aim of the present work to: a) provide an overview of the different approaches taken in the application of calcium phosphate cements for drug delivery in the skeletal system, and b) identify the most significant achievements. The drugs or active principles associated to calcium phosphate cements are classified in three groups, i) low molecular weight drugs; ii) high molecular weight biomolecules; and iii) ions.

Polymeric additives to enhance the functional properties of calcium phosphate cements

The vast majority of materials used in bone tissue engineering and regenerative medicine are based on calcium phosphates due to their similarity with the mineral phase of natural bone. Among them, calcium phosphate cements, which are composed of a powder and a liquid that are mixed to obtain a moldable paste, are widely used. These calcium phosphate cement pastes can be injected using minimally invasive surgery and adapt to the shape of the defect, resulting in an entangled network of calcium phosphate crystals. Adding an organic phase to the calcium phosphate cement formulation is a very powerful strategy to enhance some of the properties of these materials. Adding some water-soluble biocompatible polymers in the calcium phosphate cement liquid or powder phase improves physicochemical and mechanical properties, such as injectability, cohesion, and toughness. Moreover, adding specific polymers can enhance the biological response and the resorption rate of the material. The goal of this study is to overview the most relevant advances in this field, focusing on the different types of polymers that have been used to enhance specific calcium phosphate cement properties.

Calcium orthophosphates: occurrence, properties, biomineralization, pathological calcification and biomimetic applications

The present overview is intended to point the readers' attention to the important subject of calcium orthophosphates. This type of materials is of special significance for human beings, because they represent the inorganic part of major normal (bones, teeth and antlers) and pathological (i.e., those appearing due to various diseases) calcified tissues of mammals. For example, atherosclerosis results in blood vessel blockage caused by a solid composite of cholesterol with calcium orthophosphates, while dental caries and osteoporosis mean a partial decalcification of teeth and bones, respectively, that results in replacement of a less soluble and harder biological apatite by more soluble and softer calcium hydrogenphosphates. Therefore, the processes of both normal and pathological calcifications are just an in vivo crystallization of calcium orthophosphates. Similarly, dental caries and osteoporosis might be considered an in vivo dissolution of calcium orthophosphates. Thus, calcium orthophosphates hold a great significance for humankind, and in this paper, an overview on the current knowledge on this subject is provided.

α-Tricalcium phosphate: synthesis, properties and biomedical applications

Nowadays, α-tricalcium phosphate (α-TCP, α-Ca(3)(PO(4))(2)) is receiving growing attention as a raw material for several injectable hydraulic bone cements, biodegradable bioceramics and composites for bone repair. In the phase equilibrium diagram of the CaO-P(2)O(5) system, three polymorphs corresponding to the composition Ca(3)(PO(4))(2) are recognized: β-TCP, α-TCP and α'-TCP. α-TCP is formed by heating the low-temperature polymorph β-TCP or by thermal crystallization of amorphous precursors with the proper composition above the transformation temperature. The α-TCP phase may be retained at room temperature in a metastable state, and its range of stability is strongly influenced by ionic substitutions. It is as biocompatible as β-TCP, but more soluble, and hydrolyses rapidly to calcium-deficient hydroxyapatite, which makes α-TCP a useful component for preparing self-setting osteotransductive bone cements and biodegradable bioceramics and composites for bone repairing. The literature published on the synthesis and properties of α-TCP is sometimes contradictory, and therefore this article focuses on reviewing and critically discussing the synthetic methods and physicochemical and biological properties of α-TCP-based biomaterials (excluding α-TCP-based bone cements).

Novel magnesium phosphate cements with high early strength and antibacterial properties

Magnesium phosphate cements (MPCs) have been extensively used as fast setting repair cements in civil engineering. They have properties that are also relevant to biomedical applications, such as fast setting, early strength acquisition and adhesive properties. However, there are some aspects that should be improved before they can be used in the human body, namely their highly exothermic setting reaction and the release of potentially harmful ammonia or ammonium ions. In this paper a new family of MPCs was explored as candidate biomaterials for hard tissue applications. The cements were prepared by mixing magnesium oxide (MgO) with either sodium dihydrogen phosphate (NaH(2)PO(4)) or ammonium dihydrogen phosphate (NH(4)H(2)PO(4)), or an equimolar mixture of both. The exothermia and setting kinetics of the new cement formulations were tailored to comply with clinical requirements by adjusting the granularity of the phosphate salt and by using sodium borate as a retardant. The ammonium-containing MPC resulted in struvite (MgNH(4)PO(4)·6H(2)O) as the major reaction product, whereas the MPC prepared with sodium dihydrogen phosphate resulted in an amorphous product. Unreacted magnesium oxide was found in all the formulations. The MPCs studied showed early compressive strengths substantially higher than that of apatitic calcium phosphate cements. The Na-containing MPCs were shown to have antibacterial activity against Streptococcus sanguinis, which was attributed to the alkaline pH developed during the setting reaction.