Chemical durability and microstructural analysis of glasses soaked in water and in biological fluids

A new glass, obtained from Bioglass^® BG45S5 original composition by substituting CaO with MgO, was produced and its chemical durability and microstructural characteristics were compared with that of Bioglass^®.The two glasses (labelled as BG45 and MG45) were soaked up to 4 weeks at physiological temperature in different solutions, i.e. bi-distilled water, Hank's Buffered Salt Solution 61200 (labelled as HBSS+), Hank's Buffered Salt Solution 14170 (labelled as HBSS−), and Kokubo's SBF. Moreover, the influence of either flat or flake surfaces was analysed for both glasses. Results showed that the chemical durability of a glass in saline at 37 °C, evaluated through pH and ICP-AES chemical analysis of the leached components, depended mainly on the chemical composition of the soaking solution. Moreover, the MG45 glass never exhibited hydroxyapatite crystal formation on its surface also after soaking in calcium-containing solutions. The apatite crystallisation and deposition mechanism, typical of a bioactive glass, was induced only if the glass itself contained calcium. The contemporaneous presence of calcium in the glass and in the soaking solution improved the reactivity of the glass, as apatite crystals nucleated in a shorter time and grew more quickly. As regards the morphology of the glass surface, rougher surfaces favoured the formation of hydroxyapatite crystals on glasses containing calcium.     

Dissolution properties of different compositions of biphasic calcium phosphate bimodal porous ceramics following immersion in simulated body fluid solution

Biphasic calcium phosphate (BCP) bimodal porous ceramics were prepared from a mixture of fine powders of hydroxyapatite (HAp) and beta-tricalcium phosphate (β-TCP) with varying HAp/β-TCP ratios. Two types of HAp powders and one type of β-TCP powder were used to produce porous BCP bioceramics with HAp/β-TCP weight ratios of 20/80, 40/60, and 80/20. Dissolution tests were performed to compare the dissolution properties of BCP-based bioceramics with different structural properties. Porous ceramic samples of approximately 0.5 g were individually soaked in 30 ml of simulated body fluid (SBF) solution at 36.5 °C for 1, 3, 7 and 10 days, respectively. The calcium content of the SBF solution was analyzed by ICP. The porous bodies were filtered, dried, and characterized using SEM, XRD, and FT-IR. The results indicate that the sample structural properties seem to have a greater effect than the storage environment on the dissolution properties.     

生理模拟液中的磷酸钙微晶玻璃的表面变化

应用玻璃结晶法制备了以磷酸钙为主体的多孔微晶玻璃载体材料。在一定的条件下对该药物载体材料进行了生理模拟液的浸泡实验,并用Fourier红外光谱和扫描电镜对其表面进行了表征分析。试验结果表明：经模拟液浸泡后,在材料的表面沉积了一定量的类骨磷灰石(碳酸羟基磷灰石),其形貌为球状颗粒,并证实了载体材料的粗糙表面有利于碳酸羟基磷灰石晶体的形成。研究结果有助于分析碳酸羟基磷灰石的形成机理及了解磷酸钙微晶玻璃载体材料在体内的骨诱导机理。     

Influence of the sintering temperature on the structural feature and bioactivity of sol–gel derived SiO2–CaO–P2O5 bioglass

A sol–gel method was utilized to synthesize the gel with the composition of 58 mol% SiO₂–38 mol% CaO–4 mol% P₂O₅. The thermal properties were studied using thermogravimetric and differential thermal analysis (TG/DTA). Then the gels were sintered at 700, 900, 1000 and 1200 °C. The structure features were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), in addition in vitro assays were carried out in simulated body fluid (SBF). The results revealed that at sintering temperature above 900 °C, crystallization occurred and glass-ceramics with pseudowollastonite and wollastonite were formed. Furthermore with the increase of sintering temperature, the amount of pseudowollastonite decreased while that of wollastonite increased. In vitro tests indicated that the crystallization did not inhibit the samples bioactivity. After soaking in SBF, the formation of apatite was confirmed on glass and glass-ceramics surface, and the bioactivity of the glass-ceramics was based on the formed pseudowollastonite and wollastonite.     

Apatite formation on titania–vaterite powders in simulated body fluid

Titania–hydroxyapatite composites were prepared by soaking compacts of a powder mixture consisting of crystalline titania and calcium carbonate (vaterite) to form apatite in simulated body fluid (SBF). The apatite crystal formed on compacts in SBF at 37 °C within 2 days. The apatite-forming ability of the mixtures was much higher than that of titania crystals such as anatase or rutile on their own. Calcium carbonate (vaterite), which has high solubility in the aqueous solution, plays an important role in the apatite formation; the dissolution is suggested to increase the supersaturation of the apatite in SBF. Formation of titanium hydroxide groups, which may induce the apatite formation, is drastically promoted on the powder-compacts by the soaking in SBF, independently of the structures of the titania crystals (anatase or rutile). The apatite formation on the compact of the titania–calcium carbonate (vaterite) powder mixture containing the anatase phase occurs in a shorter period than that on the one of titania (rutile)–calcium carbonate (vaterite). Crystalline titania (anatase phase) is suggested to be particularly effective in inducing the apatite nucleation.     

Polymer nanocomposites for bone tissue substitutes

Following the quest for new composite biomaterials for bone tissue engineering, this work presents the processing of new nanocomposite made of polycaprolactone matrix and wollastonite particles. Wollastonite nanopowder was obtained by thermal treatment of polymethyloxosilane resin mixed with silica and calcium hydroxide. Bioactive character of the ceramic nanopowder was verified in simulated body fluid (SBF). The apatite formation on wollastonite grain surface after immersion in SBF was observed. Basic mechanical properties of the samples containing various amount of ceramic nanoparticles have been examined. It was shown that the presence of small amount of wollastonite nanoparticles (0.5–1.0 wt%) improves significantly the Young's modulus, tensile strength, and work-of-fracture of polymer matrix composite. Increased content of ceramic nanoadditive (>2%) in nanocomposites resulted in degradation of their mechanical characteristics.     

Synthesis,characterization and bioactivity investigation of bioglass/hydroxyapatite composite

Bioactive glass of the type CaO–P₂O₅–SiO₂ was obtained by the sol–gel processing method. The obtained material was characterized by X-ray powder diffraction (XRD). Composite samples of hydroxyapatite with synthesized bioglass were prepared at 1000 °C and characterized by XRD, Fourier transform infrared spectroscopy (FTIR), and surface electron microscopy (SEM). The bioactivity was examined in vitro with respect to the ability of hydroxyapatite layer to form on the surface as a result of contact with simulated body fluid (SBF). XRD, FTIR and SEM studies were conducted before and after contact of the material with SBF. It could be detected that the bioglass was crystallized partly. Furthermore, silicated hydroxyapatite may have formed due to the diffusion of silicate groups to the apatite phase and these may have substituted for the phosphate groups. It can be concluded from SEM and FTIR results that apatite phase formed after 14 days in SBF.     

沉淀法制备硅酸钙及其体外生物活性的研究

采用沉淀法制备的硅酸钙粉体经成型,在1200℃下常压烧结,制备出高纯的硅酸钙陶瓷,通过模拟体液浸泡对其体外生物活性进行了研究。X射线衍射(XRD)和扫描电镜(SEM)的结果表明:在1200℃下烧结制得的硅酸钙陶瓷主晶相为β型硅酸钙(-βCS);在模拟体液中浸泡14d后其表面可见类骨羟基磷灰石生成,28d后生成大量羟基磷灰石。因此,沉淀法合成的硅酸钙具有良好的诱导类骨羟基磷灰石形成能力和体外生物活性。     

等离子喷涂硅灰石涂层结构和性能的研究

采用等离子喷涂技术，在Ti-6Al-4V基体上制备了硅灰石涂层，利用SEM和XRD分析技术对涂层的形貌，结构和相组成进行了研究，按ASTMC－633标准对涂层的结合强度也进行了测试，将涂层试样浸泡于模拟体液中以评估其生物活性，利用SEM及配备的能谱仪（EDS），XRD和IR对浸泡后涂层表面产物的形貌，结构和相组成等进行了分析，结果表明，等离子喷涂硅灰石涂层具有粗糙的表面和层状结构，涂层内部存在一些气孔和微裂纹，涂层的主晶相是三斜晶系硅灰口，也存在玻璃相，硅灰石涂层和Ti-6Al-4V基体热膨胀系数相近，因此涂层和T-6Al-4V基体具有较高的结合强度，其值可达约39MPa，模拟体液浸泡试验显示，硅灰石涂层表面能形成含有碳酸根的羟基磷灰石层，这表明硅灰石涂层会有良好的生物活性，可作为生物活性涂层的候选材料。     

电化学沉积制备多孔羟基磷灰石泡沫复合材料

以多孔聚氨酯泡沫为基体,经过预处理、电化学沉积等工艺制备了具有三维多孔网状结构的、高空隙率的羟基磷灰石泡沫复合材料,将羟基磷灰石涂层浸泡在模拟体液SBF中进行浸泡实验,通过扫描电子显微镜(SEM)、X射线衍射(XRD)和红外分析仪(FTIR)等技术对羟基磷灰石涂层进行了表征。实验结果表明:在合适的条件下可得到纯羟基磷灰石涂层;随着温度的升高,晶体端面边长和长度逐渐增大;涂层在模拟体液SBF中浸泡24h后,涂层表面生成了很多球状磷灰石颗粒相互堆积,磷灰石颗粒尺寸明显增大。     

In vitro apatite formation of calcium phosphate composite synthesized from fish bone

Calcium phosphate-based composite (CPC) is the main biomaterial substitute used for bone repair. Properties affecting bioactivity of this composite vary depending on the types of calcium phosphate crystalline phases. Hence, in this study, bioactivity behavior of novel CPC cement by the incorporation of calcium phosphate (CP), which was obtained from fish bones, dicalcium phosphate dehydrate, and chitosan solution, was monitored in simulated body fluid (SBF). In advance, the microstructure of CP produced by heat treatment (annealing) of fish bone was evaluated at two different temperatures 600 and 900°C. The X-ray diffraction (XRD) results showed that there was no secondary phase formation aside from natural hydroxyapatite (HA) in bones annealed; and the annealing process enhanced the crystallinity of CP phase in the bone matrix particularly when annealed at 900°C. After incubation of CPC cement in SBF, bone bonding ability and producing of biomimetic HA coat on the CPC cement surface were confirmed using XRD, fourier-transform infrared spectroscopy, and scanning electron microscopy. The analysis results show that needle-like and cauliflower apatite layer with the crystallite size about 100 nm was grown on the surface of CPC cement after 28 days incubation in SBF. Regardless of above findings, we conclude that varying the annealing temperature has tremendous effect on the production of natural HA from fish bone with required properties and the ultimate morphology of obtained CPC cements after soaking is directly depended on the degree of crystallinity of the prepared natural HA.     

Bioactivity evaluation of novel nanocomposite scaffolds for bone tissue engineering: The impact of hydroxyapatite

The objective of this study was to prepare scaffolds based on cellulose-graft-polyacrylamide composed of different contents of nano-hydroxyapatite (n-HAp). To this end, polyacrylamide was grafted onto cellulose in the presence of n-HAp through free radical polymerization. Then, the scaffolds of the dispersed grafted polymer nanocomposite powder were fabricated by the freeze-drying method. The grafted polymer nanocomposite scaffolds were tested and characterized using tensile test instrument, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analysis. Finally, bioactivity and apatite formation on the surface after immersion in a simulated body fluid (SBF) were determined by XRD and SEM analysis. According to the results, as the n-HAp content in the scaffold structure increased, the porosity, elastic modulus and compressive strength were increased. In addition, apatite was deposited very well on the interconnected irregular pores on the surface of the scaffolds after incubation in SBF, while the size of precipitated apatite was reduced by increasing the soaking time. The results indicated that the prepared grafted polymer nanocomposite scaffolds have a great potential as biocompatible materials for use in bone tissue engineering.     

Comparative analysis and antibacterial properties of thermally sintered apatites with varied processing conditions

Hydroxyapatite (HA) and biphasic hydroxyapatite/beta-tricalcium phosphate (biphasic HA/β-TCP) were synthesized using thermal sintering. The parameters- sintering temperature (600°C, 900°C, and 1200°C), biological source used (fish bone, egg shells, and fish scales), and soaking time (2, 6, and 10 hours) were permuted to study their effects on the properties of the resultant apatite. Morphological study revealed that the smallest (60 nm) spherical particle and the largest (470 nm) irregular shaped particle were obtained from the fish bone sample sintered at 600°C and at 1200°C respectively. FTIR and XRD results showed that as the sintering temperature is increased, the phase transformation from HA to β-TCP takes place. Only the final products from fishbone sample at 600°C are pure carbonated HA. The crystallinity of synthesized particles ranged from 79% to 98%. Soaking time has no effect on phase composition of the apatite but has significant effect on crystallite size; increase in soaking time increases crystallite size and particle shape becomes more spherical. Interestingly, the fish bone sample sintered at 900°C has higher crystallinity and crystallite size compared to the fish scale sample sintered at the same temperature. EDX confirmed that non-stoichiometric apatite with Ca/P ratio ranging from 1.47 to 1.91 can be obtained by varying the sintering conditions. The antibacterial test revealed that both calcium apatite obtained from fish bones and fish scales have inhibited bacterial growth; apatite from fish bone works faster than fish scales. The in vitro cytotoxicity test ensured that all the calcium apatite except for eggshell are non-cytotoxic. Thus, apatite with excellent microbial activity can be obtained by using fish wastes, and by tuning the sintering parameters, the apatite with desired types and properties can be synthesized for different biomedical applications.     

In-vitro formation and growth kinetics of apatite on a new light-cured composite calcium phosphate cement

Calcium phosphate cements are used as synthetic bone grafts with several advantages such as biocompatibility, osteoconductivity, and moldability. In this study, the synthesis of a biocement starting from calcium hydroxide (Ca(OH)₂) and Monocalcium Phosphate Monohydrate (MCPM) was investigated. A 6?wt% Na₂HPO₄ aqueous solution along with a modified polymeric resin (RIVA(SDI)^®) were adopted as the variable liquid phase in self- and light-cure cement groups. XRD analysis and FTIR spectroscopy were used to study the phase composition. The composite microstructure was characterized by scanning electron microscopy (SEM) and the degradation rates were measured by atomic absorption spectroscopy (AAS) analysis. In addition, the effect of soaking time of the cement in simulated body fluid (SBF) on the final phase and morphology was studied. The results showed that soaking the composite in SBF has a significant influence in phase transformation into hydroxyapatite, but following a slower kinetic in light-cured composite cements. Evidences of crosslinking reactions in light-cured cements were observable, which at the same time can legitimize slower apatite formation and faster biodegradation of these composite cements.     

Cytocompatibility,bioactivity and mechanical strength of calcium phosphate cement reinforced with multi-walled carbon nanotubes and bovine serum albumin

This paper reports on the in vitro cytotoxicity, bioactivity behaviour and mechanical properties of novel injectable calcium phosphate cement filled with hydroxylated multi-walled carbon nanotubes and bovine serum albumin (CPC/MWCNT-OH/BSA). To predict the in vitro bioactivity of the calcium phosphate composites, we investigated apatite formation on CPC/MWCNT-OH/BSA composites after soaking in simulated body fluid (SBF) for up to 28 days. Compressive strength tests, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and cell culture experiments with human CCD-18Co fibroblasts cell lines were performed to evaluate the effect of SBF pre-treatment on the mechanical, structural and biological properties of the CPC/MWCNT-OH/BSA composites. Although apatite formation increased significantly with SBF immersion period, the results showed that all soaked CPC/MWCNT-OH/BSA composites exhibited up to 2.5 times lower compressive strength (13–20 MPa), which were however higher than values reported for the strength of trabecular bone (2–12 MPa). Cell culture experiments showed that low concentrations (6.25 and 12.5 μg/ml) of bio-mineralised CPC/MWCNT-OH/BSA composites led to cell proliferative rather than cytotoxic effects on fibroblasts, evidenced by high cell viabilities (104–113%). The novel CPC/MWCNT-OH/BSA composites presented in this study showed favourable cytocompatible and bioactive behaviour along with high compressive strength (13–32 MPa) and are therefore considered as an attractive bone filling material.     

Synthesis and characterization of hydroxyapatite/β-tricalcium phosphate nanocomposites using microwave irradiation

Microwave assisted synthesis method is a relatively new approach employed to decrease synthesis time and form a more homogenous structure in biphasic calcium phosphate bioceramics. In this study, nanocrystalline HA/β-TCP composites were prepared by microwave assisted synthesis method and, for comparison reason, by conventional wet chemical methods. The chemical and phase composition, morphology and particle size of powders were characterized by FTIR, XRD and SEM, respectively. The use of microwave irradiation resulted in improved crystallinity. The amount of hydroxyapatite phase in BCP ranged from 5% to 17%. The assessment of bioactivity was done by soaking of powder compacts in simulated body fluid (SBF). The decreasing pH of the solution in the presence of β-TCP indicated its biodegradable behavior. Rod-like hydroxyapatite particles were newly formed during the treatment in SBF for microwave assisted substrate synthesis. In contrast, globular particles precipitate under same conditions if BCP substrates were synthesized using conventional wet chemical methods.     

Biomimetic apatite coating on P(EMA-co-HEA)/SiO2 hybrid nanocomposites

P(EMA-co-HEA)/SiO₂ nanocomposites with silica contents in the range of 0-30 wt% were prepared by co-polymerization of the organic monomers during the simultaneous sol-gel polymerization of the silica precursor. The ability of the hybrids to form hydroxyapatite (HAp) on their surfaces was tested in vitro by soaking the samples in a simulated body fluid (SBF) solution for different times up to 35 days. On the one hand, the composition and morphology of the HAp layer formed were characterized by SEM, EDS, FTIR and XRD; on the other, the exchange of soluble silicates and calcium and phosphate ions, and the structural changes taking place in the nanohybrids when immersed in SBF were analyzed by SEM/EDS. This is, up to our knowledge, the first time the HAp nucleation mechanism has been proposed for organic-silica nanohybrids and correlated with their respective nanostructures. The results revealed that the formation of a HAp coating was in all cases limited by the nucleation induction time, but the mechanism and rate of HAp nucleation were found to be different depending on the nanostructure of the samples, which differs, in turn, with the silica content as a consequence of the differing connectivity of the silica network. The nanohybrids with silica contents in the range of 10-20 wt% proved to be the most suitable for the development of bioactive synthetic scaffolds for bone or other mineralized tissues.     

In-vitro evaluation of wollastonite nanopowder produced by a facile process using cheap precursors for biomedical applications

Wollastonite nanopowder (β-CaSiO₃) is the most nanoceramic powder that is most frequently applied in biomedical applications due to its good bioactivity and biocompatibility. Although the preparation of wollastonite in a solid-state is distinguished as a simple and cheap method with large-scale production, it requires high temperatures (=1400 °C) and consumes quite a long time. The wet methods are considered the best when it comes to preparing the wollastonite nanopowders. However, it has some drawbacks such as its extravagant raw materials and its shorting in preparation which inhibits successful coverage for large-scale production. Herein facile, one-pot modified co-precipitation approach with an easy procedure, shorter reaction time, and in-expensive precursor sodium meta-silicate-pentahydrate and CaCO₃ has been utilized for large-scale production of wollastonite nano-powders (76–150 nm). The precipitated product was calcined at different temperatures (800, 900, 1000, and 1100 °C). The phase composition and microstructure of the calcined powders were investigated. They were analyzed by XRD, FTIR, FESEM, and HRTEM. The in-vitro bioactivities of the calcined powders at 1000 &1100 °C were investigated by analyzing their abilities to form apatite on their surface after 21 days in SBF. The apatite mineralization of the powder surfaces was examined through FESEM, EDX, and Raman spectra. The results show that a single-phase wollastonite got formed at all calcined temperatures with a unique silkworm texture. SBF in-vitro test states the formation of HA on the powder surface. Therefore, these powders are expected to be valuable and promising for biomedical applications such as coating and bio cement.     

Evaluation of ascorbic acid-loaded calcium phosphate bone cements: Physical properties and in vitro release behavior

In this study, different concentrations of ascorbic acid (50, 100 and 200 µg/mL) were added to the liquid phase of a calcium phosphate cement (CPC). The cements were immersed in simulated body fluid (SBF) for different intervals and physical, physicochemical and mechanical properties of them were evaluated. The release of added ascorbic acid from CPCs into the SBF solution was also studied. From the results, both setting time and injectability of CPC decreased by adding ascorbic acid, however the compressive strength was sharply increased before soaking in SBF solution. But, the compressive strength values of all cements (with or without ascorbic acid) soaked in SBF solution for more than 7 d duration were comparable. The X-ray diffractometry results showed that in vitro apatite formation ability of cement reactants did not change by adding ascorbic acid. The scanning electron microscopy images indicated that morphology of the formed apatite crystals was nano-needlelike and needle diameter was less than 100 nm. The loaded ascorbic acid was slowly released from CPC into the SBF solution so that about 10% and 20% of the loaded drug was released after 504 h for the cements containing 100 and 200 µg/mL ascorbic acid, respectively. The release rate was increased when the amount of added ascorbic acid decreased by 50 µg/mL.     

The role of strontium and potassium on crystallization and bioactivity of Na2O-CaO-P2O5-SiO2 glasses

The effect of SrO/CaO and K₂O/Na₂O replacements on the crystallization process of glasses based on Na₂O-CaO-P₂O₅-SiO₂ system was investigated. The glasses were thermally treated through controlled heat treatment regimes to obtain glass ceramic materials. Combeite Na₂Ca₂Si₃O₉, sodium calcium silicate Na₂Ca₃Si₆O₁₆, wollastonite solid solution, and whitlockite Ca₃(PO₄)₂ were identified as major crystalline phases in the prepared thermally treated glasses. No potassium and strontium-containing phases could be detected in the glass-ceramics; potassium seems to be accommodated in the wollastonite structure, while strontium might be incorporated in the sodium calcium silicate structure.The surface reactivity of the prepared glass-ceramic specimens was also studied in vitro in Kokobo's simulated body fluid (SBF). EDAX, SEM, inductively coupled plasma ICP, and FTIR were used to examine the formation of apatite layer's surface and characterize the glass ceramic surface and SBF compositional changes. A decrease in the bioactivity of the glass ceramic was observed as Na₂O was replaced by K₂O. Strontium together with calcium ions in the apatite layer formed was detected with SrO/CaO replacement.The role played by the glass oxide constituents in determining the crystallization and bioactivity behaviour of the prepared thermally treated glasses was discussed.