Influence of saline solution on hydration behavior of β-dicalcium silicate in comparison with biphasic calcium phosphate/hydroxyapatite bio-ceramics

Regulation of the antibiotic elution profile from tricalcium phosphate bone cement by addition of bioactive glass

This work aimed at tailoring of different properties of antibacterial drug delivery Ca-phosphate cements by incorporation of bioactive glass (BG). The cements were prepared from beta-tricalcium phosphate cement (β-TCP) and BG based on 50 SiO2-20 CaO-15 Na2O-7 B2O3-4 P2O5-4 Al2O3 wt% with different percentages of BG [5, 10, 15, and 20% (w/w)]. The composite cements were characterized by XRD, FTIR, and TEM. Moreover, in vitro bioactivity and biodegradation were evaluated in the simulated body fluid (SBF) at 37 °C. In addition, physical properties and mechanical strength were determined. Also, the effect of glass addition on the drug release profile was examined using gentamicin. Finally, the antimicrobial activity was studied against Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumonia bacteria, one unicellular fungal strain (Candida albicans), and one multicellular fungal strain (Mucor racemosus). The results showed that after soaking in SBF, the compression strength values ranged from 14 to 36 MPa, the bulk densities and porosities were within 1.35 to 1.49 g/cm3 and 51.3 to 44.71%, respectively. Furthermore, gentamicin was released in a sustained manner, and BG decreased the released drug amount from ~ 80% (in pure β-TCP) to 47-53% in the composite cements. A drug release profile that is sustained by all samples was achieved. The antimicrobial test showed good activity of gentamicin-conjugated cements against bacteria and fungi used in this study. Additionally, cytotoxicity results proved that all samples were safe on MG-63 cells up to 50 µg/mL with no more than 7-12% dead cells. From the view of the physico-mechanical properties, bioactivity, biodegradation, and drug release rate, 20BG/β-TCP sample was nominated for practical bone grafting material, where it showed appropriate setting time and a relatively high mechanical strength suitable for cancellous bone.

The mTOR/ULK1 signaling pathway mediates the autophagy-promoting and osteogenic effects of dicalcium silicate nanoparticles

A novel bioactive inorganic material containing silicon, calcium and oxygen, calcium silicate (Ca₂SiO₄, C₂S) with a CaO-SiO₂ ingredient, has been identified as a potential candidate for artificial bone. Autophagy has an essential function in adult tissue homoeostasis and tumorigenesis. However, little is known about whether silicate nanoparticles (C₂S NPs) promote osteoblastic differentiation by inducing autophagy. Here we investigated the effects of C₂S NPs on bone marrow mesenchymal stem cell differentiation (BMSCs) in osteoblasts. Furthermore, we identified the osteogenic gene and protein expression in BMSCs treated with C₂S NPs. We found that autophagy is important for the ability of C₂S NPs to induce osteoblastic differentiation of BMSCs. Our results showed that treatment with C₂S NPs upregulated the expression of BMP2, UNX2, and OSX in BMSCs, and significantly promoted the expression of LC3 and Beclin, while P62 (an autophagy substrate) was downregulated. C₂S NP treatment could also enhance Alizarin red S dye (ARS), although alkaline phosphatase (ALP) activity was not significantly changed. However, all these effects could be partially reversed by 3-MA. We then detected potential signaling pathways involved in this biological effect and found that C₂S NPs could activate autophagy by suppressing mTOR and facilitating ULK1 expression. Autophagy further activated β-catenin expression and promoted osteogenic differentiation. In conclusion, C₂S NPs promote bone formation and osteogenic differentiation in BMSCs by activating autophagy. They achieve this effect by activating mTOR/ULK1, inducing autophagy, and subsequently triggering the WNT/β-catenin pathway to boost the differentiation and biomineralization of osteoblasts.

Dicalcium Silicate Induced Proinflammatory Responses through TLR2-Mediated NF-κB and JNK Pathways in the Murine RAW 264.7 Macrophage Cell Line

Proinflammatory responses are important aspects of the immune response to biomaterials, which may cause peri-implantitis and implant shedding. The purpose of this study was to test the cytotoxicity and proinflammatory effects of dicalcium silicate particles on RAW 264.7 macrophages and to investigate the proinflammatory response mechanism induced by C₂S and tricalcium phosphate (TCP). C₂S and TCP particles were characterized using scanning electron microscopy (SEM), energy spectrum analysis (EDS) and X-ray diffraction (XRD). Cytotoxicity and apoptosis assays with C₂S and TCP in the murine RAW 264.7 cell line were tested using the cell counting kit-8 (CCK-8) assay and flow cytometry (FCM). The detection results showed that C₂S and TCP particles had no obvious toxicity in RAW 264.7 cells and did not cause obvious apoptosis, although they both caused an oxidative stress response by producing ROS when the concentrations were at 100 μg/mL. C₂S particles are likely to induce a proinflammatory response by inducing high TLR2, TNF-α mRNA, TNF-α proinflammatory cytokine, p-IκB, and p-JNK1 + JNK2 + JNK3 expression levels. When we added siRNA-TLR2-1, a significant reduction was observed. These findings support the theory that C₂S particles induce proinflammatory responses through the TLR2-mediated NF-κB and JNK pathways in the murine RAW 264.7 macrophage cell line.

β-Dicalcium Silicate Cement Modified with β-Tricalcium Phosphate: In Vitro Bioactivity and Mechanical Strength

Calcium-silicate cement mainly based on dicalcium-silicate (C2S) was synthesized by the mean of solid state reaction. Beta-C3P was added to C2S to obtain C2S-C3P. Zinc oxide and bismuth oxide was incorporated to prepare radioc cement. In this work, the bioactivity and the mechanical strength of the synthesized cement were investigated. The in vitro test was carried out by immersion of cement pastilles in the artificial saliva in different periods from 4 hours to 30 days. Whereas the mechanical strength of some samples was operated at 28 and 72 days. The specimens are characterized by X-ray diffraction , Infrared spectroscopy and scanning electron microscopy. The finding results indicated that hydroxyapatite may appear after 24 hours of soaking; it was also shown that the presence of C3P with a small amount of the cement can enhance the bioactivity and develop more resistance strength of cement. Moreover, the addition of zinc oxide and bismuth oxide increase the radiopacity of the cement. However, the mechanical strength enhances with the incorporation of the zinc oxide while decrease with bismuth oxide. It was concluded then that there is possibility of combining addition of C3P (10%) and an agent radiopacifiers ZnO/Bi2O3(15%) with small amounts on C2S to obtain a cement with excellent bioactivity, good mechanical strength and significante radiopacity that makes this material a great candidate as a biomaterial for biomedical use.

Acid transformation of bauxite residue: Conversion of its alkaline characteristics

Bauxite residue (BR) is a highly alkaline solid hazardous waste produced from bauxite processing for alumina production. Alkaline transformation appears to reduce the environmental risk of bauxite residue disposal areas (BRDAs) whilst potentially providing opportunities for the sustainable reuse and on-going management of BR. Mineral acids, a novel citric acid and a hybrid combination of acid-gypsum treatments were investigated for their potential to reduce residue pH and total alkalinity and transform the alkaline mineral phase. XRD results revealed that with the exception of andradite, the primary alkaline solid phases of cancrinite, grossular and calcite were transformed into discriminative products based on the transformation used. Supernatants separated from BR and transformed bauxite residue (TBR) displayed distinct changes in soluble Na, Ca and Al, and a reduction in pH and total alkalinity. SEM images suggest that mineral acid transformations promote macro-aggregate formation, and the positive promotion of citric acid, confirming the removal or reduction in soluble and exchangeable Na. NEXAFS analysis of Na K-edge revealed that the chemical speciation of Na in TBRs was consistent with BR. Three acid treatments and gypsum combination had no effect on Na speciation, which affects the distribution of Na revealed by sodium STXM imaging.