Fabrication of Carbonate Apatite Block through a Dissolution-Precipitation Reaction Using Calcium Hydrogen Phosphate Dihydrate Block as a Precursor

Injectable Self-Harden Antibiofilm Bioceramic Cement for Minimally Invasive Surgery

There is an urgent demand for antibacterial bone grafts in clinics. Worryingly, the misuse and overuse of antibiotics accelerate the emergence of drug-resistant bacteria. Therefore, this study prepared a novel injectable bioceramic cement without antibiotics (FS-BCS), which showed good antibacterial properties by loading iron and strontium onto a matrix composed of brushite and calcium sulfate. The setting time, injectability, microstructure, antibacterial properties, anti-biofilm properties, and cytocompatibility of the novel bioceramic cement were evaluated thoroughly. The results showed that the material was highly injectable and antiwashout. The antibacterial tests revealed that FS-BCS inhibited the growth of 99.9% E. coli and S. aureus separately in the broth due to the synergistic effect of strontium and iron. Simultaneously, crystal violet and fluorescent staining tests revealed that the material could significantly inhibit the formation of E. coli and S. aureus biofilms. In addition, the co-incorporation of iron and strontium promoted the proliferation and migration of osteoblasts. Therefore, FS-BCS has good application potential in antibiotic-free anti-infection bone grafting using minimally invasive surgery.

Bioactive Carbonate Apatite Cement with Enhanced Compressive Strength via Incorporation of Silica Calcium Phosphate Composites and Calcium Hydroxide

Carbonate apatite (CO₃Ap) is a bioceramic material with excellent properties for bone and dentin regeneration. To enhance its mechanical strength and bioactivity, silica calcium phosphate composites (Si-CaP) and calcium hydroxide (Ca(OH)₂) were added to CO₃Ap cement. The aim of this study was to investigate the effect of Si-CaP and Ca(OH)₂ on the mechanical properties in terms of the compressive strength and biological characteristics of CO₃Ap cement, specifically the formation of an apatite layer and the exchange of Ca, P, and Si elements. Five groups were prepared by mixing CO₃Ap powder consisting of dicalcium phosphate anhydrous and vaterite powder added by varying ratios of Si-CaP and Ca(OH)₂ and 0.2 mol/L Na₂HPO₄ as a liquid. All groups underwent compressive strength testing, and the group with the highest strength was evaluated for bioactivity by soaking it in simulated body fluid (SBF) for one, seven, 14, and 21 days. The group that added 3% Si-CaP and 7% Ca(OH)₂ had the highest compressive strength among the groups. SEM analysis revealed the formation of needle-like apatite crystals from the first day of SBF soaking, and EDS analysis indicated an increase in Ca, P, and Si elements. XRD and FTIR analyses confirmed the presence of apatite. This combination of additives improved the compressive strength and showed the good bioactivity performance of CO₃Ap cement, making it a potential biomaterial for bone and dental engineering applications.

Fast and Efficient Removal of Uranium onto a Magnetic Hydroxyapatite Composite: Mechanism and Process Evaluation

The exploration and rational design of easily separable and highly efficient sorbents with satisfactory capability of extracting radioactive uranium (U)-containing compound(s) are of paramount significance. In this study, a novel magnetic hydroxyapatite (HAP) composite (HAP@ CoFe2O4), which was coupled with cobalt ferrite (CoFe2O4), was rationally designed for uranium(VI) removal through a facile hydrothermal process. The U(VI) ions were rapidly removed using HAP@ CoFe2O4 within a short time (i.e., 10 min), and a maximum U(VI) removal efficiency of 93.7% was achieved. The maximum adsorption capacity (Qmax) of the HAP@CoFe2O4 was 338 mg/g, which demonstrated the potential of as-prepared HAP@CoFe2O4 in the purification of U(VI) ions from nuclear effluents. Autunite [Ca(UO2)2(PO4)2(H2O)6] was the main crystalline phase to retain uranium, wherein U(VI) was effectively extracted and immobilized in terms of a relatively stable mineral. Furthermore, the reacted HAP@CoFe2O4 can be magnetically recycled. The results of this study reveal that the suggested process using HAP@CoFe2O4 is a promising approach for the removal and immobilization of U(VI) released from nuclear effluents.

Carbonate apatite artificial bone

Bone apatite is not hydroxyapatite (HAp), it is carbonate apatite (CO3Ap), which contains 6-9 mass% carbonate in an apatitic structure. The CO3Ap block cannot be fabricated by sintering because of its thermal decomposition at the sintering temperature. Chemically pure (100%) CO3Ap artificial bone was recently fabricated through a dissolution-precipitation reaction in an aqueous solution using a precursor, such as a calcium carbonate block. In this paper, methods of fabricating CO3Ap artificial bone are reviewed along with their clinical and animal results. CO3Ap artificial bone is resorbed by osteoclasts and upregulates the differentiation of osteoblasts. As a result, CO3Ap demonstrates much higher osteoconductivity than HAp and is replaced by new bone via bone remodeling. Granular-type CO3Ap artificial bone was approved for clinical use in Japan in 2017. Honeycomb-type CO3Ap artificial bone is fabricated using an extruder and a CaCO3 honeycomb block as a precursor. Honeycomb CO3Ap artificial bone allows vertical bone augmentation. A CO3Ap-coated titanium plate has also been fabricated using a CaCO3-coated titanium plate as a precursor. The adhesive strength is as high as 76.8 MPa, with excellent tissue response and high osteoconductivity.

Inorganic process for wet silica-doping of calcium phosphate

Silica is not only a biocompatible trace element but also an essential element for bone formation and metabolism. Therefore, it is often doped into bioceramics such as calcium phosphate and calcium carbonate for enhancing biomaterial ability. Heretofore, organic silica materials are employed as silica sources, but the residual organic matter is a significant drawback in biomaterial applications. Therefore, in this study, we introduce a one-pot inorganic synthesis method for the formation of silica-doped octacalcium phosphate (OCP) using Na₂SiO₃ as the silica source. Silica was intercalated into the OCP unit lattice, replacing its hydrous layer structure, and then a layer-by-layer structure of apatite and silica was formed. Furthermore, by immersing the fabricated silica-doped OCP into suitable solutions, both silica-doped hydroxyapatite and carbonate apatite were fabricated through a one-step inorganic processes.

We introduced a one-pot synthesis method for silica doping of calcium phosphate. Silica easily incorporated into OCP interlayer optimizing Na₂SiO₃ concentrations.

Hydrothermal synthesis of perfectly shaped micro- and nanosized carbonated apatite

Herein we present a Ca[EDTA]-based synthesis and comparative study of perfectly shaped plate-like, rod–like, and prism-like carbonated apatites.

Calcium phosphate enriched synthetic tyrosine-derived polycarbonate - dicalcium phosphate dihydrate polymer scaffolds for enhanced bone regeneration

Optimal repair of large craniomaxillofacial (CMF) defects caused by trauma or disease requires the development of new, synthetic osteoconductive materials in combination with cell-based therapies, to overcome the limitations of traditionally used bone graft substitutes. In this study, tyrosine-derived polycarbonate, E1001(1k) scaffolds were fabricated to incorporate the osteoinductive coating, Dicalcium phosphate dihydrate (DCPD). The biocompatibility of E1001(1k)-DCPD, E1001(1k)-βTCP and E1001(1k) scaffolds was compared using in vitro culture with human dental pulp stem cells (hDPSCs). We found that the DCPD coating was converted to carbonated hydroxyapatite over time in in vitro culture in Osteogenic Media, while the βTCP did not. hDPSCs exhibited slow initial attachment and proliferation on DCPD E1001(1k) scaffolds, but subsequently improved over time in culture, and promoted osteogenic differentiation. To the best of our knowledge, this study highlights for the first time the effects of Osteogenic Media on phase changes of DCPD, and on DCPD scaffold cytocompatibility with hDPSCs. DCPD showed similar hDPSC biocompatibility and osteoconductivity as compared to βTCP, and osteogenic differentiation of seeded hDPSCs. These studies suggest that E1001(1k)-DCPD scaffolds are a superior tool for craniofacial bone regeneration and provide the foundation for future in vivo testing.

Effect of CaSO₄Dissolution-Precipitation Time on Formation of Porous Carbonate Apatite as Bone Replacement Material

Introduction: Carbonate apatite type B (C-Ap) has been used as a bone replacement material because of its osteoconductive properties. Clinically, the pores formed in bone replacement material aid in cell mobility and nutrient supply, thereby increasing the bone regeneration ability. CO32- ions found in this material are useful for maintaining a stable physiological environment in the bone in order for it to be easily absorbed by osteoclasts. Porous C-Ap type B is formed using the dissolution–precipitation method by immersing porous anhydrous CaSO4 in a mixture of carbonate and phosphate solutions. Purpose: The present study aimed to evaluate the effect of immersion ofCaSO4using the dissolution–precipitation method on the formation of porous C-Ap type B with calcium sulfate precursor hemihydrate. Method: Porous C-Ap type B was produced usinga mixture of calcium sulfate hemihydrate precursors with 50 wt% polymethylmethacrylate (PMMA) porogen and distilled water. After hardening, the calcium sulfate dihydrate containing PMMA was burned in an oven at 700°C for 4 h to remove the PMMA. The specimen was immersed in a mixture of sodium phosphate (Na3PO4) and sodium carbonate (Na2CO3) for 6, 12, and 24 h. Phase testing through X-ray diffraction (XRD) using CuKα radiation at 40 kV and 40 mA was performed. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR, Thermo Fisher Scientific, Waltham, Massachusetts, USA) was used for detecting the functional groups of CO32- and PO42-. Results: XRD results showed the formation of C-Ap at 6 and 12 h, but the anhydrous CaSO4 phase remained; alternatively, this phase was absent after 24 h of immersion phase andFTIR showed the presence of the functional groups of CO32- compounds. Conclusion: Porous C-Ap type B can be formed from CaSO4 precursors after 24 h of immersion using the dissolution–precipitation method.

Fabrication of porous carbonate apatite granules using microfiber and its histological evaluations in rabbit calvarial bone defects

Carbonate apatite (CO₃ Ap) granules are known to show good osteoconductivity and replaced to new bone. On the other hand, it is well known that a porous structure allows bone tissue to penetrate its pores, and the optimal pore size for bone ingrowth is dependent on the composition and structure of the scaffold material. Therefore, the aim of this study was to fabricate various porous CO₃ Ap granules through a two-step dissolution-precipitation reaction using CaSO₄ as a precursor and 30-, 50-, 120-, and 205-μm diameter microfibers as porogen and to find the optimal pore size of CO₃ Ap. Porous CO₃ Ap granules were successfully fabricated with pore size 8.2-18.7% smaller than the size of the original fiber porogen. Two weeks after the reconstruction of rabbit calvarial bone defects using porous CO₃ Ap granules, the largest amount of mature bone was seen to be formed inside the pores of CO₃ Ap (120) [porous CO₃ Ap granules made using 120-μm microfiber] followed by CO₃ Ap (50) and CO₃ Ap (30). At 4 and 8 weeks, no statistically significant difference was observed based on the pore size, even though largest amount of mature bone was formed in case of CO₃ Ap (120). It is concluded, therefore, that the optimal pore size of the CO₃ Ap is that of CO₃ Ap (120), which is 85 μm.

Fabrication and Histological Evaluation of Porous Carbonate Apatite Block from Gypsum Block Containing Spherical Phenol Resin as a Porogen

The utility of carbonate apatite (CO₃Ap) as a bone substitute has been demonstrated. The feasibility of fabricating macroporous CO₃Ap was evaluated through a two-step dissolution–precipitation reaction using gypsum as the precursor and spherical phenol resin as the porogen. Porogen-containing gypsum was heated to burn out the porogen and to fabricate macroporous structures. Gypsum transformed into CaCO₃ upon immersion in a sodium carbonate solution, while maintaining its macroporous structure. Next, CaCO₃ transformed into CO₃Ap upon immersion in a Na₂HPO₄ solution while maintaining its macroporous structure. The utility of the macroporous CO₃Ap for histologically reconstructing bone defects was evaluated in rabbit femurs. After 4 weeks, a much larger bone was formed inside the macroporous CO₃Ap than that inside non-macroporous CO₃Ap and macroporous hydroxyapatite (HAp). A larger amount of bone was observed inside non-macroporous CO₃Ap than inside macroporous HAp. The bone defects were completely reconstructed within 12 weeks using macroporous CO₃Ap. In conclusion, macroporous CO₃Ap has good potential as an ideal bone substitute.

Rapid and effective removal of uranium (VI) from aqueous solution by facile synthesized hierarchical hollow hydroxyapatite microspheres

Rapidly increasing development of nuclear power stimulates the exploration of low-cost and highly efficient materials to selectively remove uranium (VI) from contaminated wastewater streams. Herein, we successfully developed a novel hydroxyapatite (HAP) adsorbent by using a facile and template-free hydrothermal method. The XRD results demonstrated that the HAP was crystallized in hexagonal structure (space group P63/m(176)), and the images of SEM and TEM indicated that the HAP possessed hollow and hierarchical nanostructure. A large BET specific surface area (182.6 m²/g) and average pore size of 10.5 nm, suggested that the hierarchical hollow HAP microspheres could provide sufficient active sites for highly efficient removal of uranium from aqueous solutions, indicated the HAP might be a prompt emergency material for the remediation of nuclear leakage accident. Freundlich isotherm and pseudo-second-order kinetics model fitted well to sorption experimental data. The study was further advanced by FT-IR and XPS. The sorption mechanism was mainly attributed to surface chemisorption between U(VI) and HAP, forming a new U-containing compound, viz., autunite (Ca(UO₂)₂(PO₄)₂·3H₂O).

Physical and Histological Comparison of Hydroxyapatite, Carbonate Apatite, and β-Tricalcium Phosphate Bone Substitutes

Three commercially available artificial bone substitutes with different compositions, hydroxyapatite (HAp; Neobone^®), carbonate apatite (CO₃Ap; Cytrans^®), and β-tricalcium phosphate (β-TCP; Cerasorb^®), were compared with respect to their physical properties and tissue response to bone, using hybrid dogs. Both Neobone^® (HAp) and Cerasorb^® (β-TCP) were porous, whereas Cytrans^® (CO₃Ap) was dense. Crystallite size and specific surface area (SSA) of Neobone^® (HAp), Cytrans^® (CO₃Ap), and Cerasorb^® (β-TCP) were 75.4 ± 0.9 nm, 30.8 ± 0.8 nm, and 78.5 ± 7.5 nm, and 0.06 m²/g, 18.2 m²/g, and 1.0 m²/g, respectively. These values are consistent with the fact that both Neobone^® (HAp) and Cerasorb^® (β-TCP) are sintered ceramics, whereas Cytrans^® (CO₃Ap) is fabricated in aqueous solution. Dissolution in pH 5.3 solution mimicking Howship's lacunae was fastest in CO₃Ap (Cytrans^®), whereas dissolution in pH 7.3 physiological solution was fastest in β-TCP (Cerasorb^®). These results indicated that CO₃Ap is stable under physiological conditions and is resorbed at Howship's lacunae. Histological evaluation using hybrid dog mandible bone defect model revealed that new bone was formed from existing bone to the center of the bone defect when reconstructed with CO₃Ap (Cytrans^®) at week 4. The amount of bone increased at week 12, and resorption of the CO₃Ap (Cytrans^®) was confirmed. β-TCP (Cerasorb^®) showed limited bone formation at week 4. However, a larger amount of bone was observed at week 12. Among these three bone substitutes, CO₃Ap (Cytrans^®) demonstrated the highest level of new bone formation. These results indicate the possibility that bone substitutes with compositions similar to that of bone may have properties similar to those of bone.

Feasibility evaluation of low-crystallinity β-tricalcium phosphate blocks as a bone substitute fabricated by a dissolution-precipitation reaction from α-tricalcium phosphate blocks

Although sintered β-tricalcium phosphate blocks have been used clinically as artificial bone substitutes, the crystallinity of β-tricalcium phosphate, which might dominate biocompatibility, is extremely high. The objective of this study is to evaluate the feasibility of fabricating low-crystallinity β-tricalcium phosphate blocks, which are expected to exhibit good biocompatibility via a dissolution-precipitation reaction of α-tricalcium phosphate blocks as a precursor under hydrothermal conditions at 200°C for 24 h. Although β-tricalcium phosphate is a metastable phase, the presence of Mg²⁺ in the reaction solution inhibits the formation of its corresponding stable phase and induces β-tricalcium phosphate formation under acidic conditions. It was found that low-crystallinity β-tricalcium phosphate blocks could be fabricated from α-tricalcium phosphate blocks immersed in 1.0 mol/L MgCl₂ + 0.1 mol/L NaH₂PO₄ solution while maintaining the shape of the α-tricalcium phosphate blocks. The crystallite size of the fabricated β-tricalcium phosphate blocks was 42 nm, which was substantially smaller than that of the sintered β-tricalcium phosphate blocks. When the fabricated β-tricalcium phosphate blocks were implanted into bone defects in rabbit femurs, they exhibited excellent tissue responses. In particular, the initial osteoconductivity (two and four weeks) was substantially greater than that of sintered β-tricalcium phosphate blocks.

Co-existence effect of tricalcium phosphate and bioactive glass on biological and biodegradation characteristic of Poly L-Lactic Acid (PLLA) in trinary composite scaffold form

The purpose of this study is to analyze the co-existence effect of 30 wt.% TCP-BG phases on degradation and precipitation behaviors of PLLA based composite scaffold in biological media. First, phase separation method was used to synthesize of the pure PLLA and the trinary composite scaffolds, and second they were immersed in SBF solution for 45 days. Subsequently, the degradation and precipitation characteristic were investigated by analyzing of pH value and weight changes of the immersed samples, the ability of biological products formation and the change of relative molecular weight of PLLA matrix as function of the degradation time. Finally, the experimental data of relative molecular weight change were verified by Han and Pan model and comparisons were made between them. Results have represented precipitation of huge amount of carbonate apatite on surface of the composite scaffold, and also the acidity of SBF media changes moderately which is prove better bioactivity properties compare to the pure PLLA scaffold. The results of comparison with the model point to quiet good agreement between them in early stage of degradation. So, the consequences suggest that the TCP-BG/PLLA composite scaffold have great potential to be applied in bone replacements or repairs.

Evaluation of carbonate apatite blocks fabricated from dicalcium phosphate dihydrate blocks for reconstruction of rabbit femoral and tibial defects

This study aimed to evaluate in vivo behavior of a carbonate apatite (CO₃Ap) block fabricated by compositional transformation via a dissolution-precipitation reaction using a calcium hydrogen phosphate dihydrate [DCPD: CaHPO₄·2H₂O] block as a precursor. These blocks were used to reconstruct defects in the femur and tibia of rabbits, using sintered dense hydroxyapatite (HAp) blocks as the control. Both the CO₃Ap and HAp blocks showed excellent tissue response and good osteoconductivity. HAp block maintained its structure even after 24 weeks of implantation, so no bone replacement of the implant was observed throughout the post-implantation period in either femoral or tibial bone defects. In contrast, CO₃Ap was resorbed with increasing time after implantation and replaced with new bone. The CO₃Ap block was resorbed approximately twice as fast at the metaphysis of the proximal tibia than at the epiphysis of the distal femur. The CO₃Ap block was resorbed at an approximately linear change over time, with complete resorption was estimated by extrapolation of data at approximately 1-1.5 years. Hence, the CO₃Ap block fabricated in this study has potential value as an ideal artificial bone substitute because of its resorption and subsequent replacement by bone.