Functional evaluation of mineral trioxide aggregate cement with choline dihydrogen phosphate

To improve the cytocompatibility of mineral trioxide aggregate (MTA) cement and its ability for reparative dentin formation, the effect of adding choline dihydrogen phosphate (CDHP), which is reported to be biocompatible, to MTA cement was investigated. The L929 cell proliferation showed that the addition of CDHP improved cell viability. The addition of CDHP shortened the setting time of MTA cement, with a significant decrease in consistency above 0.4 g/mL. Diametral tensile strength of the set cement was improved by the addition of 0.4 g/mL CDHP. Solubility was judged to be within the range of clinical application. The spontaneous precipitation of low crystalline hydroxyapatite was examined by immersing the set cement in phosphate buffer saline, and it was found that the ability of the cement with 0.4 g/mL of CDHP was significantly improved compared with that of the cement without CDHP.

Physical Properties and Antimicrobial Release Ability of Gentamicin-Loaded Apatite Cement/α-TCP Composites: An In Vitro Study

Apatite cement (AC), which has excellent osteoconductive ability, and alpha-tricalcium phosphate (α-TCP), which can be used for bone replacement, are useful bone substitute materials. The objective of this study was to clarify the physical properties and antimicrobial release ability of antibiotic-loaded AC/α-TCP composites in vitro. Gentamicin-loaded, rapid setting AC/α-TCP composites were prepared in 2 mixing ratios (10:3 and 10:6). The cement paste of AC/α-TCP composites was prepared in a plastic mold and dried in a thermostatic chamber at 37 °C and 100% relative humidity for 24 h. A diametral tensile strength test, powder X-ray diffraction analysis, and gentamicin release test were performed. The diametral tensile strengths of the AC/α-TCP composites were significantly less than that of AC alone. Powder X-ray diffraction patterns exhibited the characteristic peaks of hydroxyapatite in the AC/α-TCP composites and gentamicin-loaded AC/α-TCP composites. The concentration of the released gentamicin was maintained above the minimum inhibitory concentration of Staphylococcus aureus until Day 30 in both the gentamicin-loaded AC/α-TCP composites (10:3 and 10:6). Our results suggest that a gentamicin-loaded AC/α-TCP composite has potential as a drug delivery system. Further study is essential to investigate the antimicrobial activity and safety of the gentamicin-loaded AC/α-TCP composites in animal models.

Fabrication of bioresorbable hydroxyapatite bone grafts through the setting reaction of calcium phosphate cement

We prepared hydroxyapatite (HAp) bone grafts by the setting reaction of calcium phosphate cement, and investigated the effects of the porosity and crystallinity on the osteoconductivity and bioresorbability. We examined the effect of the water-mixing ratio, pressure, and post-heat treatment temperature during preparation on the crystallite size and porosity of the HAp blocks. The quantity of protein adsorption increased with increasing porosity and specific surface area (SSA) of the HAp blocks, whereas the initial cell attachment was similar despite the different porosities and crystallinities. In in vitro dissolution tests with a pH 5.5 buffer, which mimics an osteoclast-created Howship's lacuna, both the porosity and SSA of the HAp blocks affected the solubility; most likely due to the increased contact area with the buffer. Thus, HAp blocks prepared by the setting reaction of calcium phosphate cement could be applicable for bioresorbable HAp bone grafts because of the high porosity and SSA.

Deletion of epithelial cell-specific p130Cas impairs the maturation stage of amelogenesis

Amelogenesis consists of secretory, transition, maturation, and post-maturation stages, and the morphological changes of ameloblasts at each stage are closely related to their function. p130 Crk-associated substrate (Cas) is a scaffold protein that modulates essential cellular processes, including cell adhesion, cytoskeletal changes, and polarization. The expression of p130Cas was observed from the secretory stage to the maturation stage in ameloblasts. Epithelial cell-specific p130Cas-deficient (p130Cas^Δepi-) mice exhibited enamel hypomineralization with chalk-like white mandibular incisors in young mice and attrition in aged mouse molars. A micro-computed tomography analysis and Vickers micro-hardness testing showed thinner enamel, lower enamel mineral density and hardness in p130Cas^Δepi- mice in comparison to p130Cas^flox/flox mice. Scanning electron microscopy, and an energy dispersive X-ray spectroscopy analysis indicated the disturbance of the enamel rod structure and lower Ca and P contents in p130Cas^Δepi- mice, respectively. The disorganized arrangement of ameloblasts, especially in the maturation stage, was observed in p130Cas^Δepi- mice. Furthermore, expression levels of enamel matrix proteins, such as amelogenin and ameloblastin in the secretory stage, and functional markers, such as alkaline phosphatase and iron accumulation, and Na⁺/Ca²⁺+K⁺-exchanger in the maturation stage were reduced in p130Cas^Δepi- mice. These findings suggest that p130Cas plays important roles in amelogenesis (197 words).

In vitro investigation of the cell compatibility and antibacterial properties of titanium treated with calcium and ozone

The purpose of this study was to evaluate the surface modification of calcium ions on roughened titanium as a surface treatment of dental implants for cell attachment, growth, and initial bacterial adhesion. When a surface-roughened, pure titanium disk was immersed in a calcium chloride solution (100 mM) containing 20 ppm ozone for 24 h at 25ºC, calcium was detected on the surface by X-ray photoelectron spectroscopy. The calcium-modified, roughened titanium disk had a significantly greater concentration of the initially adhered cells as well as cells cultured over 7 days compared with titanium disks without surface modification. Furthermore, the initial bacterial adhesion on the calcium-ozone treated titanium disk was statistically less than on a pure titanium disk or titanium disk treated without ozone. Dissolved ozone was useful for modifying the surface of roughened titanium with calcium ions and the surface modification may be applicable for dental implants.

Enhanced Osseointegration Capability of Poly(ether ether ketone) via Combined Phosphate and Calcium Surface-Functionalization

Biomedical applications of poly(ether ether ketone) (PEEK) are hindered by its inherent bioinertness and lack of osseointegration capability. In the present study, to enhance osteogenic activity and, hence, the osseointegration capability of PEEK, we proposed a strategy of combined phosphate and calcium surface-functionalization, in which ozone-gas treatment and wet chemistry were used for introduction of hydroxyl groups and modification of phosphate and/or calcium, respectively. Surface functionalization significantly elevated the surface hydrophilicity without changing the surface roughness or topography. The cell study demonstrated that immobilization of phosphate or calcium increased the osteogenesis of rat mesenchymal stem cells compared with bare PEEK, including cell proliferation, alkaline phosphatase activity, and bone-like nodule formation. Interestingly, further enhancement was observed for samples co-immobilized with phosphate and calcium. Furthermore, in the animal study, phosphate and calcium co-functionalized PEEK demonstrated significantly enhanced osseointegration, as revealed by a greater direct bone-to-implant contact ratio and bond strength between the bone and implant than unfunctionalized and phosphate-functionalized PEEK, which paves the way for the orthopedic and dental application of PEEK.

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.

Characterization and thermal decomposition of synthetic carbonate apatite powders prepared using different alkali metal salts

Two types of synthetic carbonate apatite [potassium-containing carbonate apatite (CAK) and sodium-containing carbonate apatite (CANa)] were prepared and characterized by thermogravimetric analysis, X-ray diffraction analysis (XRD) and Fourier transform infrared spectroscopy. The chemical formulas of carbonate apatite were determined to be Ca_9.36K_0.12(PO₄)_5.12(CO₃)_0.88(OH)_1.73 and Ca_8.72Na_1.33(PO₄)_4.96(CO₃)_1.04(OH)_1.80, respectively. Thermogravimetric analysis showed that the final weight loss at 1,200°C reached about 11.2% for CAK and 13.9% for CANa. Carbonate loss gradually occurred above 150°C and continued to 1,200°C. The crystallinity of the apatite phase was found to be much improved between 800 and 850°C for CAK and 750 and 800°C for CANa, where rapid carbonate loss occurred. A small amount of CaO formed above 900°C. For CANa, NaCaPO₄ also formed above 700°C in both apatites. Although the lattice parameters of the carbonate apatites varied with temperature, the final a and c lattice parameters attained constant values of 0.9421 and 0.6881 nm.

Fabrication of carbonate apatite honeycomb and its tissue response

Carbonate apatite (CO₃ Ap) block can be used as a bone substitute because it can be remodeled to new natural bone in a manner conforming with the bone remodeling process. Among the many porous structures available, honeycomb (HC) structure is advantageous for rapid replacement of CO₃ Ap to bone. In this study, the feasibility to fabricate a CO₃ Ap HC was studied, along with its initial tissue response in rabbit femur bone defect. First, a mixture of Ca(OH)₂ and a wax-based binder was extruded from a HC mold. Then the fabricated HC was heated for binder removal and carbonation at 450°C in a mixed O₂ -CO₂ atmosphere, forming a CaCO₃ HC. When the CaCO₃ HC was immersed in 1 mol/L Na₃ PO₄ solution at 80°C for 7 days, its composition changed from CaCO₃ to CO₃ Ap, maintaining the structure of the original CaCO₃ HC. Compressive strengths of the CaCO₃ and CO₃ Ap HCs were 65.2 ± 7.4 MPa and 88.7 ± 4.7 MPa, respectively. When the rabbit femur bone defect was reconstructed with the CO₃ Ap HC, new bone penetrated the CO₃ Ap HC completely. Osteoclasts and osteoblasts were found on the surface of the newly formed bone and osteocytes were also found in the newly formed bone, indicating ongoing bone remodeling. Furthermore, blood vessels were formed inside the pores of CO₃ Ap HC. Therefore, CO₃ Ap HC has good potential as an ideal bone substitute. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1014-1020, 2019.

Synergistic effect of surface phosphorylation and micro-roughness on enhanced osseointegration ability of poly(ether ether ketone) in the rabbit tibia

This study was aimed to investigate the osseointegration ability of poly(ether ether ketone) (PEEK) implants with modified surface roughness and/or surface chemistry. The roughened surface was prepared by a sandblast method, and the phosphate groups on the substrates were modified by a two-step chemical reaction. The in vitro osteogenic activity of rat mesenchymal stem cells (MSCs) on the developed substrates was assessed by measuring cell proliferation, alkaline phosphatase activity, osteocalcin expression, and bone-like nodule formation. Surface roughening alone did not improve MSC responses. However, phosphorylation of smooth substrates increased cell responses, which were further elevated in combination with surface roughening. Moreover, in a rabbit tibia implantation model, this combined surface modification significantly enhanced the bone-to-implant contact ratio and corresponding bone-to-implant bonding strength at 4 and 8 weeks post-implantation, whereas modification of surface roughness or surface chemistry alone did not. This study demonstrates that combination of surface roughness and chemical modification on PEEK significantly promotes cell responses and osseointegration ability in a synergistic manner both in vitro and in vivo. Therefore, this is a simple and promising technique for improving the poor osseointegration ability of PEEK-based orthopedic/dental implants.

Fabrication of self-setting β-TCP granular cement using β-TCP granules and sodium hydrogen sulfate solution

Bridging beta-tricalcium phosphate (β-TCP) granules with dicalcium phosphate dihydrate (DCPD) creates a porous, interconnected β-TCP granular cement (GC) that is useful for reconstructing bone defects: the interconnected pores can accelerate new bone ingrowth and the set cement prevents the loss of granules from the bone defect area. However, the setting time of β-TCP GC in an acidic calcium phosphate solution is too short (<1 min) for handling in clinical applications, such as in orthopedic surgery. To address this issue, we sought to optimize the setting time of β-TCP GC using β-TCP granules and NaHSO₄ solution, as [Formula: see text] is a known inhibitor of DCPD formation. Both DCPD and calcium sulfate dihydrate (CSD) precipitated on the surface of β-TCP granules and bridged β-TCP granules to one another. Increasing NaHSO₄ concentration (from 0.5 mol/L to 5 mol/L) led to an increase in the amount of precipitant from 2.6 ± 0.2% to 21.6 ± 1.3% for DCPD and 1.3 ± 0.3% to 10.1 ± 0.5% for CSD. The diametral tensile strength was also increased from 0.03 ± 0.01 MPa to 2.0 ± 0.1 MPa with increasing NaHSO₄ concentration. When 2 mol/L NaHSO₄ solution was used as the liquid phase, setting time became 5.3 ± 0.2 min, which is suitable for handling in clinical applications to repair bone defects. In conclusion, β-TCP GC using NaHSO₄ solution as the liquid phase has good potential value as bone augmentation cement.

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.

Effect of setting atmosphere on apatite cement resorption: An in vitro and in vivo study

OBJECTIVES

The aim of this present study was to investigate the effect of setting atmosphere on replacement of apatite cement with new bone both in vitro and in vivo.

MATERIAL AND METHODS

Apatite cement consisting of an equimolar mixture of tetracalcium phosphate and anhydrous dicalcium phosphate was mixed with distilled water and allowed to set at 37 °C and 100% relative humidity under 0%_, 5%, and 100% CO₂ atmospheres. X-Ray diffraction and Fourier Transform Infrared Spectroscopy were employed to confirm the carbonate apatite formation. Micro-CT and histological evaluation was made at 1 and 6 month(s) using twelve 10-week-old specific-pathogen-free male Wistar rats.

RESULTS

B-type carbonate apatite was found when the apatite cement was set under 100% CO₂ and 5% CO₂. More carbonate apatite was formed in the case of 100% CO₂ when compared with 5% CO₂, and none was formed under 0% CO₂. Interestingly, unreacted tetracalcium phosphate was significant when apatite cement was set under 0% CO₂, indicating the formation of Ca-deficient hydroxyapatite. When a bone defect of rat tibia was reconstructed in these conditions of apatite cement and sintered hydroxyapatite, replacement of the apatite cement was confirmed 6 months after implantation, whereas no replacement was observed in the case of sintered hydroxyapatite. The amount of replacement of apatite cement with bone was greater, on the order of 100% CO₂ and 5% CO₂, followed by 0% CO₂.

CONCLUSION

The results obtained in the present study demonstrated that setting atmosphere clearly plays an important role in the replacement of set apatite cement with bone.

In vivo stability evaluation of Mg substituted low crystallinity ß-tricalcium phosphate granules fabricated through dissolution-precipitation reaction for bone regeneration

Although β-tricalcium phosphate (β-TCP) is widely used in clinical applications as a bone substitute owing to its positive tissue response and its ability to be replaced by new bone through a bone-remodeling process, it has the limitation of rapid resorption in vivo, which might become a reason for tissue atrophy and high crystallinity, which decrease biocompatibility. A reduction in the crystallinity might increase the biocompatibility of the bone substitute. To overcome the drawbacks of β-TCP, decrease in crystallinity and solubility, both are required. Therefore, in this study, the feasibility of fabricating Mg substituted low crystalline β-TCP (Mg-LC-β-TCP) granules formed in aqueous solution was evaluated in vivo focusing long-term adsorption and bone formation in bone defects formed in the rabbit femur using sintered β-TCP granules as a control. With Mg-LC-β-TCP, the resorption of the substitute was suppressed, and no tissue atrophy was observed even at 24 weeks post-implantation, whereas a few granules with surrounding tissue atrophy were observed at 12 weeks post-implantation. Tartrate-resistant acid phosphatase-staining indicated that the density of osteoclasts type cells with Mg-LC-β-TCP was significantly lower than that with β-TCP, and also the numbers of osteoblasts type cells with Mg-LC-β-TCP were significantly higher than that with β-TCP. It is suggested that Mg substitution to form low crystallinity β-TCP is a valuable way to overcome the limitations of β-TCP as a bone substitute.

Fabrication and evaluation of carbonate apatite-coated calcium carbonate bone substitutes for bone tissue engineering

Carbonate apatite-coated calcium carbonate (CO₃ Ap/CaCO₃ ) was fabricated through a dissolution-precipitation reaction using CaCO₃ granules as a precursor to accelerate bone replacement based on superior osteoconductivity of the CO₃ Ap shell, along with Ca²⁺ release from the CaCO₃ core and quicker resorption of the CaCO₃ core. In the present study, CaCO₃ , 10% CO₃ Ap/CaCO₃ , 30% CO₃ Ap/CaCO₃ , and CO₃ Ap granules were fabricated and examined histologically to evaluate their potential as bone substitutes. Larger contents of CaCO₃ in the granules resulted in higher Ca²⁺ release and promoted cell proliferation of murine preosteoblasts at 6 days compared with CO₃ Ap. Interestingly, in a rabbit femur defect model, 10% CO₃ Ap/CaCO₃ induced significantly higher new bone formation and higher material resorption compared with CO₃ Ap at 8 weeks. Nevertheless, CO₃ Ap showed a superior osteoconductive potential compared with 10% CO₃ Ap/CaCO₃ at 8 weeks. All tested granules were most likely resorbed by cell mediation including multinucleated giant cell functions. Therefore, we conclude that CO₃ Ap/CaCO₃ has a positive potential for bone tissue engineering based on well-controlled calcium release, bone formation, and material resorption.

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.

Compositional and histological comparison of carbonate apatite fabricated by dissolution-precipitation reaction and Bio-Oss®

Carbonate apatite (CO₃Ap) is an inorganic component of bone. This study aimed to compare the composition and tissue response to of CO₃Ap (CO₃Ap-DP) fabricated by the dissolution-precipitation reaction using calcite as a precursor and Bio-Oss®, which is widely used in orthopedic and dental fields as a synthetic bone substitute. X-ray diffraction and Fourier transform infrared results showed that CO₃Ap-DP and Bio-Oss® were both B-type carbonate apatite with low crystallinity. The average sizes of CO₃Ap-DP and Bio-Oss® granules were 450 ± 58 and 667 ± 168μ m, respectively, and their carbonate contents were 12.1 ± 0.6 and 5.6 ± 0.1 wt%, respectively. CO₃Ap-DP had a larger amount of CO₃ than Bio-Oss® but higher crystallinity than Bio-Oss®. When a bone defect made at the femur of rabbits was reconstructed with CO₃Ap-DP and Bio-Oss®, CO₃Ap-DP granules were partially replaced with bone, whereas Bio-Oss® remained at 8 weeks after implantation. CO₃Ap-DP granules elicited a significantly larger amount of new bone formation at the cortical bone portion than Bio-Oss® at 4 weeks after the implantation. The results obtained in the present study demonstrated that CO₃Ap-DP and Bio-Oss® showed different behavior even though they were both classified as CO₃Ap. The CO₃ content in CO₃Ap played a more important role than the crystallinity of CO₃Ap for replacement to bone and high osteoconductivity.

"Fabrication of arbitrarily shaped carbonate apatite foam based on the interlocking process of dicalcium hydrogen phosphate dihydrate"

Carbonate apatite (CO₃Ap) foam with an interconnected porous structure is highly attractive as a scaffold for bone replacement. In this study, arbitrarily shaped CO₃Ap foam was formed from α-tricalcium phosphate (α-TCP) foam granules via a two-step process involving treatment with acidic calcium phosphate solution followed by hydrothermal treatment with NaHCO₃. The treatment with acidic calcium phosphate solution, which is key to fabricating arbitrarily shaped CO₃Ap foam, enables dicalcium hydrogen phosphate dihydrate (DCPD) crystals to form on the α-TCP foam granules. The generated DCPD crystals cause the α-TCP granules to interlock with each other, inducing an α-TCP/DCPD foam. The interlocking structure containing DCPD crystals can survive hydrothermal treatment with NaHCO₃. The arbitrarily shaped CO₃Ap foam was fabricated from the α-TCP/DCPD foam via hydrothermal treatment at 200 °C for 24 h in the presence of a large amount of NaHCO₃.

Fabrication of dicalcium phosphate dihydrate-coated β-TCP granules and evaluation of their osteoconductivity using experimental rats

β-Tricalcium phosphate (β-TCP) has attracted much attention as an artificial bone substitute owing to its biocompatibility and osteoconductivity. In this study, osteoconductivity of β-TCP bone substitute was enhanced without using growth factors or cells. Dicalcium phosphate dihydrate (DCPD), which is known to possess the highest solubility among calcium phosphates, was coated on β-TCP granules by exposing their surface with acidic calcium phosphate solution. The amount of coated DCPD was regulated by changing the reaction time between β-TCP granules and acidic calcium phosphate solution. Histomorphometry analysis obtained from histological results revealed that the approximately 10mol% DCPD-coated β-TCP granules showed the largest new bone formation compared to DCPD-free β-TCP granules, approximately 2.5mol% DCPD-coated β-TCP granules, or approximately 27mol% DCPD-coated β-TCP granules after 2 and 4weeks of implantation. Based on this finding, we demonstrate that the osteoconductivity of β-TCP granules could be improved by coating their surface with an appropriate amount of DCPD.

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.

Fabrication of self-setting β-tricalcium phosphate granular cement

Bone defect reconstruction would be greatly improved if β-tricalcium phosphate (β-TCP) granules had the ability to self-set without sacrificing their osteoconductivity potential. This study aimed to identify a method to permit β-TCP self-setting whilst maintaining good osteoconductivity. When mixed with acidic calcium phosphate solution, β-TCP granules were found to readily set, forming a fully interconnected porous structure. On mixing, dicalcium phosphate dihydrate crystals formed on the surface of β-TCP granules, bridging the granules and resulting in the setting reaction. The setting time of the β-TCP granular cement (β-TCP GC) was approximately 1 min and its mechanical strength, in terms of diametral tensile strength, was approximately 0.8 MPa. The β-TCP GC and β-TCP granules both showed the same level of osteoconductivity within rat calvaria bone defects. At 2 and 4 weeks post-implantation, new bone formation was comparable between the two β-TCP based bone substitutes. We conclude that β-TCP GC has excellent potential for use as a cement in bone defect reconstruction. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 800-807, 2018.

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

Carbonate apatite (CO₃Ap) block, which is a bone replacement used to repair defects, was fabricated through a dissolution-precipitation reaction using a calcium hydrogen phosphate dihydrate (DCPD) block as a precursor. When the DCPD block was immersed in NaHCO₃ or Na₂CO₃ solution at 80 °C, DCPD converted to CO₃Ap within 3 days. β-Tricalcium phosphate was formed as an intermediate phase, and it was completely converted to CO₃Ap within 2 weeks when the DCPD block was immersed in Na₂CO₃ solution. Although the crystal structures of the DCPD and CO₃Ap blocks were different, the macroscopic structure was maintained during the compositional transformation through the dissolution-precipitation reaction. CO₃Ap block fabricated in NaHCO₃ or Na₂CO₃ solution contained 12.9 and 15.8 wt % carbonate, respectively. The diametral tensile strength of the CO₃Ap block was 2 MPa, and the porosity was approximately 57% regardless of the carbonate solution. DCPD is a useful precursor for the fabrication of CO₃Ap block.

Fabrication of calcite blocks from gypsum blocks by compositional transformation based on dissolution-precipitation reactions in sodium carbonate solution

Calcium carbonate (CaCO₃) has been used as a bone substitute, and is a precursor for carbonate apatite, which is also a promising bone substitute. However, limited studies have been reported on the fabrication of artificial calcite blocks. In the present study, cylindrical calcite blocks (ϕ6×3mm) were fabricated by compositional transformation based on dissolution-precipitation reactions using different calcium sulfate blocks as a precursor. In the dissolution-precipitation reactions, both CaSO₄·2H₂O and CaSO₄ transformed into calcite, a polymorph of CaCO₃, while maintaining their macroscopic structure when immersed in 1mol/L Na₂CO₃ solution at 80°C for 1week. The diametral tensile strengths of the calcite blocks formed using CaSO₄·2H₂O and CaSO₄ were 1.0±0.3 and 2.3±0.7MPa, respectively. The fabrication of calcite blocks using CaSO₄·2H₂O and CaSO₄ proposed in this investigation may be a useful method to produce calcite blocks because of the self-setting ability and high temperature stability of gypsum precursors.

A case of tophaceous pseudogout of the temporomandibular joint extending to the base of the skull

A case of tophaceous pseudogout (i.e., calcium pyrophosphate dihydrate (CPPD) crystal deposition disease) in the temporomandibular joint (TMJ), extending to the base of the skull, is reported. A 38-year-old man was referred to the hospital with mild pain in the right chin and tip of the tongue. Panoramic radiography showed a large calcified mass around the right TMJ. Computed tomography imaging revealed a large, granular, calcified mass surrounding the right condylar head and extending to the base of the skull. The mass was clinically and radiographically suspected to be a pseudogout lesion. A biopsy specimen was collected under general anaesthesia to confirm the diagnosis. On histology, the mass was found to contain deposits of numerous rod-shaped and rhomboid crystals, which suggested tophaceous pseudogout. The deposits were identified as CPPD crystal deposition, based on analysis by X-ray diffraction and Fourier transform infrared spectroscopy. These two crystallography methods were useful in confirming the diagnosis of CPPD crystal deposition disease in the TMJ.

Fabrication and Physical Evaluation of Gelatin-Coated Carbonate Apatite Foam

Carbonate apatite (CO₃Ap) foam has gained much attention in recent years because of its ability to rapidly replace bone. However, its mechanical strength is extremely low for clinical use. In this study, to understand the potential of gelatin-reinforced CO₃Ap foam for bone replacement, CO₃Ap foam was reinforced with gelatin and the resulting physical characteristics were evaluated. The mechanical strength increased significantly with the gelatin reinforcement. The compressive strength of gelatin-free CO₃Ap foam was 74 kPa whereas that of the gelatin-reinforced CO₃Ap foam, fabricated using 30 mass % gelatin solution, was approximately 3 MPa. Heat treatment for crosslinking gelatin had little effect on the mechanical strength of the foam. The gelatin-reinforced foam did not maintain its shape when immersed in a saline solution as this promoted swelling of the gelatin; however, in the same conditions, the heat-treated gelatin-reinforced foam proved to be stable. It is concluded, therefore, that heat treatment is the key to the fabrication of stable gelatin-reinforced CO₃Ap foam.

A superhydrophilic titanium implant functionalized by ozone gas modulates bone marrow cell and macrophage responses

Bone-forming cells and Mϕ play key roles in bone tissue repair. In this study, we prepared a superhydrophilic titanium implant functionalized by ozone gas to modulate osteoconductivity and inhibit inflammatory response towards titanium implants. After 24 h of ozone gas treatment, the water contact angle of the titanium surface became zero. XPS analysis revealed that hydroxyl groups were greatly increased, but carbon contaminants were largely decreased 24 h after ozone gas functionalization. Also, ozone gas functionalization did not alter titanium surface topography. Superhydrophilic titanium (O3-Ti) largely increased the aspect ratio, size and perimeter of cells when compared with untreated titanium (unTi). In addition, O3-Ti facilitated rat bone marrow derived MSCs differentiation and mineralization evidenced by greater ALP activity and bone-like nodule formation. Interestingly, O3-Ti did not affect RAW264.7 Mϕ proliferation. However, naive RAW264.7 Mϕ cultured on unTi produced a two-fold larger amount of TNFα than that on O3-Ti. Furthermore, O3-Ti greatly mitigated proinflammatory cytokine production, including TNFα and IL-6 from LSP-stimulated RAW264.7 Mϕ. These results demonstrated that a superhydrophilic titanium prepared by simple ozone gas functionalization successfully increased MSCs proliferation and differentiation, and mitigated proinflammatory cytokine production from both naive and LPS-stimulated Mϕ. This superhydrophilic surface would be useful as an endosseous implantable biomaterials and as a biomaterial for implantation into other tissues.

In vivo Performance of Biodegradable Calcium Phosphate Glass Ceramics using the Rabbit Model: Histological and SEM Observation

Two MK5 (45CaO-45P2O5-5MgO-5K2O, in mol%) and MT13 (45CaO-37P2O5-5MgO-13TiO2, in mol%) glasses are prepared in the meta- and pyrophosphate regions and crystallized to obtain MK5B and MT13B, respectively. MK5B was obtained by controlled crystallization, and MT13B by powder sintering. As a result of these heat treatment processes, the crystalline phases precipitated in the glassy matrix are KCa(PO3)3, β-Ca(PO3)2, β-Ca2P2O7and Ca4P6O19phases for MK5B and CaTi4(PO4)6, TiP2O7, α- and β-Ca2P2O7phases for MT13B. To assess the in vivo biological behavior of these glass ceramics, a mixed granulometry in the range 250-355 μm and 355-425 μm with a ratio of 1/1 was implanted for 2, 4, and 12 weeks in the tibiae of Japanese white rabbits. The results showed that the in vivo behavior was strongly affected by their solubility. All implanted materials, MK5B and MT13B, and β-tricalcium phosphate (β-TCP) as control material, showed signs of degradation in vivo. However, the levels of degradation were quite different throughout the implantation periods. The highest degradation was observed for MK5B glass ceramic and the lowest for MT13B with β-TCP in-between. All implanted materials allow for new bone formation in the bone defect area. At the longest implantation period (12 weeks), the MT13B and β-TCP materials were almost completely surrounded by new bone tissue, whereas MK5B showed some unfilled spaces. This behavior is discussed in terms of the high degradation observed in previous studies.

Effects of the method of apatite seed crystals addition on setting reaction of α-tricalcium phosphate based apatite cement

Appropriate setting time is an important parameter that determines the effectiveness of apatite cement (AC) for clinical application, given the issues of crystalline inflammatory response phenomena if AC fails to set. To this end, the present study analyzes the effects of the method of apatite seed crystals addition on the setting reaction of α-tricalcium phosphate (α-TCP) based AC. Two ACs, both consisting of α-TCP and calcium deficient hydroxyapatite (cdHAp), were analyzed in this study. In one AC, cdHAp was added externally to α-TCP and this AC was abbreviated as AC(EA). In the other AC, α-TCP was partially hydrolyzed to form cdHAp on the surface of α-TCP. This AC was referred to as AC(PH). Results indicate a decrease in the setting time of both ACs with the addition of cdHAp. Among them, for the given amount of added cdHAp, AC(PH) showed relatively shorter setting time than AC(EA). Besides, the mechanical strength of the set AC(PH) was also higher than that of set AC(EA). These properties of AC(PH) were attributed to the predominant crystal growth of cdHAp in the vicinity of the α-TCP particle surface. Accordingly, it can be concluded that the partial hydrolysis of α-TCP may be a better approach to add low crystalline cdHAp onto α-TCP based AC.

Fabrication of interconnected pore forming α-tricalcium phosphate foam granules cement

Interconnected pore forming calcium phosphate cement is useful for the reconstruction of bone defects as well as scaffold fabrication in tissue engineering. In this study, interconnected pore forming calcium phosphate cement was fabricated using α-tricalcium phosphate (α-TCP) foam granules. When α-TCP foam granules were mixed with acidic calcium phosphate solution prepared from monocalcium phosphate monohydrate (MCPM) and phosphoric acid solution, brushite crystals were precipitated. These crystals bridged the α-TCP foam granules immediately upon mixing. As a result of the brushite bridge between the α-TCP foam granules, fully interconnected macroporous α-TCP was obtained. The amount of brushite precipitate and the mechanical strength of the set cement increased with acidic calcium phosphate concentration.

Calcium phosphate crystallization on titania in a flowing Kokubo solution

Dry titania layers on air-oxidized titanium substrates have been found to be active enough to cause apatite to be deposited in Kokubo's simulated body fluid (SBF) in narrow confined spaces, such as those in narrow grooves and thin gaps. Such in vitro apatite deposition is the basis of the GRAPE(®) technique. The aim of the present study is to determine why GRAPE conditions favor apatite deposition when laminar SBF flow (at 0.01-0.3 ml/min) passes through a shallow channel (0.5 mm) between a pair of titanium substrates each with a dry layer of titania. Assessing the factors that control the heterogeneous nucleation process led to the proposal of the working hypothesis that there are nucleation pre-embryos, ion assemblies that can be stabilized to form embryos, on the titania layer but that they are removed by the SBF flow. Specimens were subjected to different combinations of processes. One combination was that titania layers were exposed to still or flowing SBF, and the other was that half of a specimen, the inlet or outlet side, was exposed to still or flowing SBF with the other half being covered. The surface morphologies of the specimens were then compared in detail. The conclusion was that exposure to still SBF for 2 days before exposure to flowing SBF was required for apatite to be deposited. Some complicated apatite deposition modes were observed, e.g., apatite was deposited even on areas unexposed to still SBF. All of the results were successfully interpreted using the working hypothesis. The conclusion was that the GRAPE(®) technique depends on the confined space holding pre-embryo and embryo assemblies.

Fabrication of strongly attached hydroxyapatite coating on titanium by hydrothermal treatment of Ti-Zn-PO4 coated titanium in CaCl 2 solution

Hydroxyapatite (HAp) coating was formed on zinc phosphate (Ti-Zn-PO4) coated Ti plates by hydrothermal treatment in CaCl2 solution at 200 °C for 12 h. Uniform surface coverage of the fabricated HAp coating was obtained by this method. SEM-EDX analysis of the adhesion test area showed that the presence of fractures only occurred in HAp crystals. On the other words cohesive fracture was seen in HAp coating layer formed on the Ti-Zn-PO4. The measured strength was around 42.3 ± 17 MPa. Rat bone marrow (RBM) mesenchymal stem cells were cultured and differentiation-induced on each sample (Ti plate, Ti-Zn-PO4 coated and HAp coated), and cell calcification properties were examined. Apparent differences in morphology and extension of the RBM cells were obtained, while the Ti-Zn-PO4 coated samples showed the highest cell number among all samples. After differentiation-induction, HAp coated samples showed the highest amount of alkaline phosphatase activity, and the highest level of cell calcification. Therefore, the hard tissue compatibility of Ti is improved by hydrothermally HAp coating of samples.

Effects of PLGA reinforcement methods on the mechanical property of carbonate apatite foam

The purpose of this study was to improve the mechanical property of brittle carbonate apatite (CO3Ap) foam aimed as bone substitute material by reinforcement with poly(DL-lactide-co-glycolide) (PLGA). The CO3Ap foam was reinforced with PLGA by immersion and vacuum infiltration methods. Compressive strength of CO3Ap foam (12.0±4.9 kPa) increased after PLGA reinforcement by immersion (187.6±57.6 kPa) or vacuum infiltration (407.0±111.4 kPa). Scanning electron microscopic (SEM) observation showed a gapless PLGA and CO3Ap foam interface and larger amount of PLGA inside the hollow space of the strut when vacuum infiltration method was employed. In contrast a gap was observed at the PLGA and CO3Ap foam interface and less amount of PLGA inside the hollow space of the strut when immersion method was employed. Strong PLGA-CO3Ap foam interface and larger amount of PLGA inside the hollow space of the strut is therefore the key to higher mechanical property obtained for CO3Ap foam when vacuum infiltration was employed for PLGA reinforcement.

Fabrication of bone cement that fully transforms to carbonate apatite

The objective of this study was to fabricate a type of bone cement that could fully transform to carbonate apatite (CO3Ap) in physiological conditions. A combination of calcium carbonate (CaCO3) and dicalcium phosphate anhydrous was chosen as the powder phase and mixed with one of three kinds of sodium phosphate solutions: NaH2PO4, Na2HPO4, or Na3PO4. The cement that fully transformed to CO3Ap was fabricated using vaterite, instead of calcite, as a CaCO3 source. Their stability in aqueous solutions was different, regardless of the type of sodium phosphate solution. Rate of transformation to CO3Ap in descending order was Na3PO4>Na2HPO4>NaH2PO4. Transformation rate could be affected by the pH of solution. Results of this study showed that it was advantageous to use vaterite to fabricate CO3Ap-forming cement.

Influence of PLGA concentrations on structural and mechanical properties of carbonate apatite foam

Reinforcement with bioresorbable polymer such as PLGA is one of the useful ways to improve the mechanical property of brittle carbonate apatite (CO3Ap) foam. In the present study, CO3Ap foam was reinforced with various concentrations of PLGA solution (5, 10, 15 and 20 wt%) using vacuum infiltration method and its influence on structure, porosity and mechanical property was investigated. It was found that the amount of PLGA inside the hollow space of the CO3Ap foam strut increased with the concentration of PLGA. Porosity likewise was significantly (p<0.05) reduced from 94% (CO3Ap foam without PLGA) down to 82% (CO3Ap foam reinforced with 20 wt% PLGA). Compressive strength of CO3Ap foam significantly (p<0.05) increased from 0.02 MPa (CO3Ap foam without PLGA) up to 1.5 MPa (CO3Ap foam reinforced with 20 wt% PLGA).

Fabrication of porous calcite using chopped nylon fiber and its evaluation using rats

Although porous calcite has attracted attention as bone substitutes, limited studies have been made so far. In the present study, porous calcite block was fabricated by introducing chopped nylon fiber as porogen. Ca(OH)2 powder containing 10 wt% chopped nylon fiber was compacted at 150 MPa, and sintered to burn out the fiber and to carbonate the Ca(OH)2 under stream of 1:2 O2-CO2. Sintering of Ca(OH)2 at 750 °C or lower temperature resulted in incomplete burning out of the fiber whereas sintering at 800 °C or higher temperature resulted in the formation of CaO due to the thermal decomposition of Ca(OH)2. However, sintering at 770 °C resulted in complete burning out of the fiber and complete carbonation of Ca(OH)2 to calcite without forming CaO. Macro- and micro-porosities of the porous calcite were approximately 23 and 16%, respectively. Diameter of the macropores was approximately 100 μm which is suitable for bone tissue penetration. Porous calcite block fabricated by this method exhibited good tissue response when implanted in the bone defect in femur of 12-weeks-old rat. Four weeks after implantation, bone bonded on the surface of calcite. Furthermore, bone tissue penetrated interior to the macropore at 8 weeks. These results demonstrated the good potential value of porous calcite as artificial bone substitutes.

Modulation of the osteoconductive property and immune response of poly(ether ether ketone) by modification with calcium ions

A Ca-modified PEEK facilitates osteoblastic cell proliferation and differentiation and shifts macrophage phenotype towards anti-inflammatory/wound healing type.

Fabrication of carbonate apatite blocks from set gypsum based on dissolution-precipitation reaction in phosphate-carbonate mixed solution

Carbonate apatite (CO3Ap), fabricated by dissolution-precipitation reaction based on an appropriate precursor, is expected to be replaced by bone according to bone remodeling cycle. One of the precursor candidates is gypsum because it shows self-setting ability, which then enables it to be shaped and molded. The aim of this study, therefore, was to fabricate CO3Ap blocks from set gypsum. Set gypsum was immersed in a mixed solution of 0.4 mol/L disodium hydrogen phosphate (Na2HPO4) and 0.4 mol/L sodium hydrogen carbonate (NaHCO3) at 80-200°C for 6-48 h. Powder X-ray diffraction patterns and Fourier transform infrared spectra showed that CO3Ap block was fabricated by dissolution-precipitation reaction in Na2HPO4-NaHCO3 solution using set gypsum in 48 h when the temperature was 100°C or higher. Conversion rate to CO3Ap increased with treatment temperature. CO3Ap block containing a larger amount of carbonate was obtained when treated at lower temperature.

Fabrication of solid and hollow carbonate apatite microspheres as bone substitutes using calcite microspheres as a precursor

Spherical carbonate apatite (CO3Ap) microspheres approximately 1 mm in diameter were fabricated by granulation of calcium hydroxide around a core followed by carbonation and phosphatization through dissolution-precipitation reaction. CO3Ap microspheres with high uniformity could not be achieved without using a core. Solid CO3Ap microspheres were obtained using a calcite core whereas hollow CO3Ap microspheres were obtained using a NaCl core. The obtained microsphere was identified as B-type CO3Ap by Fourier transform infrared analysis and the carbonate content was approximately 7-8 wt% regardless of the type of core used for sample preparation. The mechanical strength of both the solid and hollow CO3Ap microspheres was sufficient for practical use as a bone substitute.

Heterogeneous structure and in vitro degradation behavior of wet-chemically derived nanocrystalline silicon-containing hydroxyapatite particles

Nanocrystalline hydroxyapatite (HAp) and silicon-containing hydroxyapatite (SiHAp) particles were synthesized by a wet-chemical procedure and their heterogeneous structures involving a disordered phase were analyzed in detail by X-ray diffractometry (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and solid-state magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The effects of heterogeneous structure on in vitro biodegradability and the biologically active Ca(II)- and Si(IV)-releasing property of SiHAp particles were discussed. The (29)Si NMR analysis revealed that the Si(IV) was incorporated in the HAp lattice in the form of Q(0)(SiO(4)(4-)orHSiO(4)(3-)) species, accompanied by the formation of condensed silicate units outside the HAp lattice structure, where the fraction and amount of Q(0) species in the HAp lattice depends on the Si content. The (31)P and (1)H NMR results agreed well with the XRD, TEM and FTIR results. NMR quantitative analysis results were explained by using a core-shell model assuming a simplified hexagonal shape of HAp covered with a disordered layer, where Si(IV) in Q(0) was incorporated in the HAp lattice and a disordered phase consisted of hydrated calcium phosphates involving polymeric silicate species and carbonate anions. With the increase in the Si content in the HAp lattice, the in vitro degradation rate of the SiHAps increased, while their crystallite size stayed nearly unchanged. The biologically active Ca(II)- and Si(IV)-releasing ability of the SiHAps was remarkably enhanced at the initial stage of reactions by an increase in the amount of Si(IV) incorporated in the HAp lattice but also by an increase of the amount of polymeric silicate species incorporated in the disordered phase.

Hydrothermal calcium modification of 316L stainless steel and its apatite forming ability in simulated body fluid

To understand the feasibility of calcium (Ca) modification of type 316L stainless steel (316L SS) surface using hydrothermal treatment, 316L SS plates were treated hydrothermally in calcium chloride (CaCl(2)) solution. X-ray photoelectron spectroscopic analysis revealed that the surface of 316L SS plate was modified with Ca after hydrothermal treatment at 200°C. And the immobilized Ca increased with CaCl(2) concentration. However no Ca-modification was occurred for 316L SS plates treated at 100°C. When Ca-modified 316L SS plate was immersed in simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma, low crystalline apatite was precipitated on its surface whereas no precipitate was observed on non Ca-modified 316L SS. The results obtained in the present study indicated that hydrothermal treatment at 200°C in CaCl(2) solution is useful for Ca-modification of 316L SS, and Ca-modification plays important role for apatite precipitation in SBF.