Influence of Si substitution on the reactivity of α-tricalcium phosphate

α-TCP-based Calcium Phosphate Cements: a critical review

Calcium phosphates are promising materials for applications in bone repair and substitution, particularly for their bioactivity and ability to form self-setting cements. Among them, α-tricalcium phosphate (α-TCP) stands out due to its high solubility, its hydration reaction and bioresorbability. The synthesis of α-TCP is particularly complex and the interactions between some of the synthesis parameters are still not completely understood. The variety of methods available to synthesize α-TCP has provided a substantial variance in the properties of α-TCP-based cements and the decision about which method, parameters and starting reagents will be used for the powder's synthesis is determinant of the properties of the resulting material. Therefore, this review paper focuses on α-TCP's synthesis and properties, presenting the synthesis methods currently in use as well as a discussion of how the synthesis parameters and the cement preparation affect the reactivity and mechanical properties of the material, providing a guide for the selection of the most suitable process for each α-TCP application. STATEMENT OF SIGNIFICANCE: α-TCP is a calcium phosphate and it is currently one of the most investigated bioceramics for applications that explore its bioresorbability and the hydration reaction of α-TCP-based cements. Despite the increasing number of publications on the topic, there are still aspects not well understood. This review article aims at contributing to this fascinating subject by offering an update on the state of the art of α-TCP's synthesis methods, while also addressing topics that are not often discussed about this material, such as the preparation of α-TCP-based cements and how its parameters affect the properties of the resulting cements.

Silicon-substituted calcium phosphate promotes osteogenic-angiogenic coupling by activating the TLR4/PI3K/AKT signaling axis

Silicon-substituted calcium phosphate (Si-CaP) is a promising bioactive material for bone tissue engineering. The mechanism of Si-CaP regulates osteogenic-angiogenic coupling during bone regeneration has not been fully elucidated. In this study, we screened the targets of Si-CaP and osteogenic-angiogenic coupling. 83 common genes were regarded as key targets for Si-CaP regulation of the osteogenic-angiogenic coupling. Then, we performed protein-protein interaction analysis, GO and KEGG enrichment analysis of these 83 targets to further predict their molecular mechanism. Our results showed that Si-CaP treatment could regulate the osteogenic-angiogenic coupling by up-regulating the expression of Toll-like receptor 4 (TLR4), and the phosphorylation of AKT which in turn activating the PI3K/AKT signaling pathway, promoting the expression of RUNX2, OPN, VEGF. In addition, we also found that TLR4 siRNA treatment could block the PI3K/AKT signaling pathway, while inhibiting the promoting effect of Si-CaP. However, although LY294002 can achieve the same inhibitory effect as TLR4 siRNA by blocking the PI3K/AKT signaling pathway, it could not affect the expression of TLR4. This indicates that TLR4 is an upstream activator of PI3K/AKT signaling pathway. These results are highly consistent with the prediction of bioinformatics. In conclusion, we have elucidated the role of TLR4/PI3K/AKT signaling axis in Si-CaP mediated osteogenic-angiogenic coupling for the first time. This study provides new data onto the regulatory role and molecular mechanism of Si-CaP in the process of osteogenic-angiogenic coupling, which strongly supports its wide application for bone tissue engineering.

Ferric oxide: A favorable additive to balance mechanical strength and biological activity of silicocarnotite bioceramic

Ideal materials for bone regeneration should have not only a good bioactivity, but also a good mechanical strength to provide an initial support for new bone formation. How to get a balance between high mechanical property and good bioactivity is a challenging issue for bone regeneration materials. In the present work, a biocompatible additive Fe₂O₃ was selected to optimize the comprehensive properties of a novel calcium phosphate silicate (CPS) ceramic using a mechanical mixing method. The effects of Fe₂O₃ content on microstructure, bending strength, apatite formation ability and cytocompatibility of Fe-CPS bioceramics were investigated and the related mechanism was also discussed. The obtained Fe-CPS bioceramics showed enhanced mechanical and favorable bioactivity performances. Especially, the Fe-CPS bioceramic with 1.5 wt% Fe₂O₃ sintered at 1250 °C presented the highest bending strength of 91.9 MPa. While, Fe-CPS bioceramics still exhibited a good ability on apatite formation in simulated body fluid (SBF), and cytocompatibility test revealed that Fe-CPS bioceramics were favorable for cell adhesion and proliferation. All the results indicated that Fe-CPS bioceramics are promising candidate materials for bone regeneration at load bearing applications.

Osteoblastic and anti-osteoclastic activities of strontium-substituted silicocarnotite ceramics: In vitro and in vivo studies

Osteoporosis bone defect is a refractory orthopaedic disease which characterized by impaired bone quality and bone regeneration capacity. Current therapies, including antiosteoporosis drugs and artificial bone grafts, are not always satisfactory. Herein, a strontium-substituted calcium phosphate silicate bioactive ceramic (Sr-CPS) was fabricated. In the present study, the extracts of Sr-CPS were prepared for in vitro study and Sr-CPS scaffolds were used for in vivo study. The cytocompatibility, osteogenic and osteoclastogenic properties of Sr-CPS extracts were characterized in comparison to CPS. Molecular mechanisms were also evaluated by Western blot. Sr-CPS extracts were found to promote osteogenesis by upregulating Wnt/β-catenin signal pathways and inhibit osteoclastogenesis through downregulating NF-κB signal pathway. In vivo, micro-CT, histological and histomorphometric observation were conducted after 8 weeks of implantation to evaluate the bone formation using calvarial defects model in ovariectomized rats. Compared with CPS, Sr-CPS significantly promoted critical sized ovariectomy (OVX) calvarial defects healing. Among all the samples, Sr-10 showed the best performance due to a perfect match of bone formation and scaffold degradation rates. Overall, the present study demonstrated that Sr-CPS ceramic can dually modulate both bone formation and resorption, which might be a promising candidate for the reconstruction of osteoporotic bone defect.

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Easy-to-perform and cost-effective fabrication of Sr-CPS scaffold.

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Dual modulation of bone formation and resorption.

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Outstanding performances in the osteoporotic bone defect healing process.

Ionic Substitutions in Non-Apatitic Calcium Phosphates

Calcium phosphate materials (CaPs) are similar to inorganic part of human mineralized tissues (i.e., bone, enamel, and dentin). Owing to their high biocompatibility, CaPs, mainly hydroxyapatite (HA), have been investigated for their use in various medical applications. One of the most widely used ways to improve the biological and physicochemical properties of HA is ionic substitution with trace ions. Recent developments in bioceramics have already demonstrated that introducing foreign ions is also possible in other CaPs, such as tricalcium phosphates (amorphous as well as α and β crystalline forms) and brushite. The purpose of this paper is to review recent achievements in the field of non-apatitic CaPs substituted with various ions. Particular attention will be focused on tricalcium phosphates (TCP) and "additives" such as magnesium, zinc, strontium, and silicate ions, all of which have been widely investigated thanks to their important biological role. This review also highlights some of the potential biomedical applications of non-apatitic substituted CaPs.

Addition of Wollastonite Fibers to Calcium Phosphate Cement Increases Cell Viability and Stimulates Differentiation of Osteoblast-Like Cells

Calcium phosphate cement (CPC) that is based on α-tricalcium phosphate (α-TCP) is considered desirable for bone tissue engineering because of its relatively rapid degradation properties. However, such cement is relatively weak, restricting its use to areas of low mechanical stress. Wollastonite fibers (WF) have been used to improve the mechanical strength of biomaterials. However, the biological properties of WF remain poorly understood. Here, we tested the response of osteoblast-like cells to being cultured on CPC reinforced with 5% of WF (CPC-WF). We found that both types of cement studied achieved an ion balance for calcium and phosphate after 3 days of immersion in culture medium and this allowed subsequent long-term cell culture. CPC-WF increased cell viability and stimulated cell differentiation, compared to nonreinforced CPC. We hypothesize that late silicon release by CPC-WF induces increased cell proliferation and differentiation. Based on our findings, we propose that CPC-WF is a promising material for bone tissue engineering applications.