Controlling apatite microparticles formation by calcining electrospun sol–gel derived ultrafine silica fibers

Electrospun ultrafine silica fibers were calcined at 150–800 °C. The relation of calcination temperature to the ability to form biomimetic apatite in a simulated body fluid solution (SBF) was evaluated. The largest apatite particles, formed on non-calcined fibers after 1 week of soaking in SBF, were 10 μm in diameter, had a narrow size distribution (coefficient of variation 9%), and were similar to pearls on string. The particles size decreased with increasing calcination temperature below 250 °C and the particles formed on the fibers calcined at 250 °C were 4.5 μm in diameter. No particles were found on those calcined above 500 °C. By using a concentrated SBF at 1.5-times higher ionic concentrations than SBF, the size of apatite microparticles increased about 50%. The fibrous substrate covered with apatite particles was effective for osteoblastic differentiation of pre-osteoblastic cells.     

Micropatterning of bioactive glass nanoparticles on chitosan membranes for spatial controlled biomineralization

Bioactive glass nanoparticles (BG-NPs) capable of inducing apatite precipitation upon immersion in simulated body fluid (SBF) were patterned on free-standing chitosan membranes by microcontact printing using a poly(dimethylsiloxane) (PDMS) stamp inked in a BG-NPs pad. Formation of the patterns was characterized by scanning electron microscopy (SEM). Mineralization of the bioactive glass patterns was induced in vitro by soaking the samples in SBF over different time points up to 7 days. The confined apatite deposition in the patterned regions with diameters of 50 μm was confirmed by Fourier-transformed infrared spectroscopy (FTIR), energy-dispersive X-ray (EDX) analysis, and SEM. In vitro tests confirmed the preferential attachment and proliferation of L929 cells to the areas printed with BG-NPs of the membranes. This approach permits one to spatially control the properties of biomaterials at the microlevel and could be potentially used in guided tissue regeneration for skin, vascular, articular, and bone tissue engineering and in cellular cocultures or to develop substrates able to confine cells in regions with controlled geometry at the cell's length scale.     

Induction and Acceleration of Bonelike Apatite Formation on Tantalum Oxide Gel in Simulated Body Fluid

Untreated tantalum metal forms bonelike apatite layer on its surface in a simulated body fluid (SBF) after a long period. The apatite formation on the tantalum metal is significantly accelerated, when the metal was previously subjected to NaOH and heat treatments to form an amorphous sodium tantalate on its surface. The fast formation of the apatite on the NaOH- and heat-treated tantalum metal was explained as follows. The sodium tantalate on the surface of the metal releases the Na⁺ ion via exchange with H₃O⁺ ion in SBF to form a lot of Ta-OH groups on its surface. Thus formed Ta-OH groups induce the apatite nucleation and the released Na⁺ ion accelerates the apatite nucleation by increasing ionic activity product of the apatite in SBF due to increase in OH^– ion concentration. In the present study, in order to confirm this explanation, apatite formations on sodium tantalate gels with different Na/Ta atomic ratios, which were prepared by a sol-gel method were investigated. It was found that even Na₂O-free tantalum oxide gel forms the apatite on its surface in SBF. This proves that the Ta-OH groups abundant on the gel can induce the apatite nucleation. The apatite-forming ability of the gels increased with increasing Na/Ta atomic ratios of the gels. The sodium-containing tantalum oxide gels released the Na⁺ ion, the amount of which increased with increasing Na/Ta atomic ratios of the gels. The released Na⁺ ion gave an increase in pH of SBF. These results prove that the apatite nucleation induced by the Ta-OH groups is accelerated with the released Na⁺ ion by increasing ionic activity product of the apatite in SBF.     

In vitro surface biocompatibility of high-content silicon-substituted calcium phosphate ceramics

The present work investigates surface biocompatibility of silicon-substituted calcium phosphate ceramics. Different silicon-substituted calcium phosphate ceramic bodies were prepared from co-precipitated powders by sintering at 1300°C. The in vitro bioactivity of the ceramics was assessed in simulated body fluid (SBF) at 37°C for periods up to 4 weeks. The changes in the surface morphology and composition were determined by scanning electron microscopy (SEM) coupled with electron probe microanalysis and energy dispersive spectrometer (EDX). Inductively coupled plasma optical emission spectroscopy (ICP-OES) was used to observe the change in ionic concentration of SBF after removal of the samples. The bioactivity of the ceramics increased with an increasing silicate ion substitution in a systematic way. The surface of ceramics with 2.23% silicon substitution was partially covered with apatite layer after one week, while ceramics with 8.1% silicon substitution were completely covered with apatite in the first week. The porous microstructure of high-concentration Si-substituted ceramics helps the dissolution of surface ions and the leaching process. This allows SBF to reach supersaturation in a short time and accelerate the deposition of apatite layer.      

Growth of calcium hydroxyapatite (Ca-HAp) on cholesterol and cholestanol crystals from a simulated body fluid: A possible insight into the pathological calcifications associated with atherosclerosis

An experimental study into calcium phosphate (CP) nucleation and growth on cholesterol and cholestanol surfaces from a supersaturated simulated body fluid (SBF) is presented with the overall aim of gaining some fundamental insights into the pathological calcifications associated with atherosclerosis. Soaking of pressed cholesterol disks at physiological temperature in SBF solutions was found to lead to CP nucleation and growth if the disks were surface roughened and if an SBF with concentrations of the calcium and hydrogen phosphate ions at 2.25x physiological concentrations was used. The CP phase deposited was shown via SEM micrographs to possess a florette type morphology akin to that observed in earlier reported studies. The use of recrystallised cholesterol and cholestanol microcrystals as substrates for soaking in SBF facilitated the observation of CP deposition. In general, cholesterol recrystallised from polar solvents like 95% ethanol as a cholesterol monohydrate phase which was a better substrate for CP growth than cholesterol recrystallised from more non-polar solvents (e.g., benzene) which produced anhydrous cholesterol phases. CP was also observed to form on recrystallised cholestanol microcrystals, a molecule closely related to cholesterol. Inductively coupled plasma optical emission spectrometry (ICP-OES) data gave confirmation that Ca:P mole ratios of the grown CP were 1.3-1.5 suggesting a mixed phase of octacalcium phosphate (OCP) and Ca-deficient HAp and that the CP coating grows (with time of soaking) on the substrates after nucleation in the SBF growth medium. Infrared (IR) spectra of the extracted coatings from the cholesterol substrates confirmed that the CP phase deposited is a semi crystalline HAp with either carbonate substituted into its structure or else co-deposited as calcium carbonate. Soaking experiments involving modified cholesterol substrates in which the OH group in the molecule was replaced with the oleiyl or phosphonate group showed no CP nucleation and growth. This observation illustrates the importance of the known epitaxial relationship between cholesterol and HAp (which theoretically predicts favourable deposition of one phase upon the other) and the consequences of its destruction (by chemical modification of the cholesterol). In the case of the phosphorylated cholesterol, failure of this substrate to nucleate CP phases may have also been caused by the reduction in concentration of free solution Ca2+ in the SBF medium by complexation with the phosphonate groups on the phosphorylated cholesterol. This would have reduced the ion product of Ca2+ and inorganic phosphate and lowered the degree of supersaturation in the SBF medium.     

Biomimetic Apatite Deposition on Calcium Silicate Gel Glasses

In order to understand the Biomimetic apatite formation mechanism on gel glasses, a glass (in mol-%) SiO₂ 80%—CaO 20% (80S20C) was prepared by the sol-gel method and its behaviour in a simulated body fluid (SBF) was studied. To study the role of phosphorous in the in vitro apatite formation, a gel glass (in mol-%) SiO₂ 80%—CaO 17%—P₂O₅ 3% (80S17C3P) was prepared comparing its behaviour in SBF with that of 80S20C. In both studies, a protocol without renovation of SBF (static) was used. To mimic the conditions in the living organisms, an in vitro protocol with continuous renovation of solution (dynamic) was proposed. To check the feasibility of dynamic protocol, 80S20C and 80S17C3P were studied in dynamic and results compared with obtained in static. Static studies of 80S20C allowed us to verify that phosphorus is not essential for bioactivity because the apatite-like layer was formed from the phosphorous in SBF. However, a 3 mol-% of P₂O₅ in 80S17C3P gel glass favoured apatite crystallization. In dynamic, complete assays were performed with ionic concentrations and pH in solution almost equal to human plasma. After 7 days in dynamic, apatite crystals and crystalline aggregates were larger than in static. Besides, compositional variations were observed in the newly formed layer as a function of the protocol. In static, the layer formed in both glasses contained calcium and phosphorous, (Ca/P molar ratio = 1.6) and silicon. In dynamic, the layer did not contain silicon and the Ca/P molar ratio was 1.2. Differences in composition and pH of assay solution, 8 in static and 7.3 in dynamic could explain these variations. In static, an apatite close to stoichiometric could be formed. In dynamic, a mixture of calcium deficient apatite and other calcium phosphates could constitute the layer.     

不同磺化及碱处理聚醚醚酮的表面化学组成及体外生物活性评价

提出一种酸碱结合改性聚醚醚酮（PEEK）方法,并评价其对PEEK表面类骨磷灰石形成的影响.结果表明,通过磺化处理引入-SO₃H,显著改善了样品的亲水性,且磺化程度与H₂SO₄浓度和磺化反应时间成正比,并影响样品的表面形貌.质量分数为85% H₂SO₄处理30 min的PEEK-S具有较好的改性效果.将PEEK-S进一步用NaOH处理,可继续引入Na元素并提高样品的亲水性,但会受处理时间的影响.模拟体液（SBF）浸泡的生物活性评价结果表明,磺化后碱处理24 h的PEEK-Na具有快速的类骨磷灰石沉积能力,浸泡3 d的样品表面即可完全被沉积的类骨磷灰石覆盖,表现出较佳的生物活性.此酸碱双重改性方法操作简单,可大幅度提升PEEK的生物活性,具有较好的应用前景.     

Control of surface topography in biomimetic calcium phosphate coatings

The behavior of cells responsible for bone formation, osseointegration, and bone bonding in vivo are governed by both the surface chemistry and topography of scaffold matrices. Bone-like apatite coatings represent a promising method to improve the osteoconductivity and bonding of synthetic scaffold materials to mineralized tissues for regenerative procedures in orthopedics and dentistry. Polycaprolactone (PCL) films were coated with calcium phosphates (CaP) by incubation in simulated body fluid (SBF). We investigated the effect of SBF ion concentration and soaking time on the surface properties of the resulting apatite coatings. CaP coatings were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), and energy dispersive X-ray spectrometry (EDX). Young's modulus (E(s)) was determined by nanoindentation, and surface roughness was assessed by atomic force microscopy (AFM) and mechanical stylus profilometry. CaP such as carbonate-substituted apatite were deposited onto PCL films. SEM and AFM images of the apatite coatings revealed an increase in topographical complexity and surface roughness with increasing ion concentration of SBF solutions. Young's moduli (E(s)) of various CaP coatings were not significantly different, regardless of the CaP phase or surface roughness. Thus, SBF with high ion concentrations may be used to coat synthetic polymers with CaP layers of different surface topography and roughness to improve the osteoconductivity and bone-bonding ability of the scaffold.     

Adsorption and bioactivity studies of albumin onto hydroxyapatite surface

Bovine serum albumin (BSA) may have an inhibitory or promoter effect on hydroxyapatite (HA) nucleation when apatite is precipitated in a medium containing the protein. In this study we evaluated the influence of BSA on the precipitation of calcium phosphate phases (CP) from simulated body fluid (SBF) when the protein was previously bounded to HA surface. The kinetics of BSA immobilization onto hydroxyapatite surface was performed in different buffers and protein concentrations in order to adjust experimental conditions in which BSA was tightly linked to HA surface for long periods in SBF solution. It was shown that for BSA concentration higher than 0.1mg/mL the adsorption to HA surface followed Langmuir-Freundlich mechanisms, which confirmed the existence of cooperative protein-protein interactions on HA surface. Fourier Transformed Infrared Attenuated Total Reflectance Microscopy (FTIRM-ATR) evidenced changes in BSA conformational state in favor of less-ordered structure. Analyses from high resolution grazing incident X-ray diffraction using synchrotron radiation (GIXRD), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) showed that a poorly crystalline calcium phosphate was precipitated on the surface of HA discs coated with BSA, after the immersion in SBF for 4 days. The new bioactive layer had morphological characteristics similar to the one formed on the HA surface without protein. It was identified as a carbonated apatite with preferential crystal growth along apatite 002 direction. The GIXRD results also revealed that BSA layer bound to the surface inhibited the HA dissolution leading to a reduction on the formation of new calcium phosphate phase.     

A comparative study of the in vitro degradation of poly(l-lactic acid)/β-tricalcium phosphate scaffold in static and dynamic simulated body fluid

Porous poly(l-lactic acid)/β-tricalcium phosphate (PLLA/β-TCP) composite is a new promising scaffold for bone tissue engineering. Porous scaffolds fabricated by liquid anti-solvent precipitation principle were subjected to degradation in dynamic simulated body fluid (DSBF) and in static simulated body fluid (SSBF) at 37 °C for 24 weeks, respectively. Results indicated that a large number of apatite layer were formed on the scaffolds. The results further indicated that SBF flow decreased the degradation rate of molecular weight and compressive strength significantly. The porosity and mass changes were related to the apatite formation and SBF flow. All the results might be owed to the mutual effects of the flow of SBF and the addition of β-TCP. The degradation rate of scaffolds could be adjusted by the additional fraction of β-TCP to meet the requirements of application in vivo.     

含10mol%氧化硅的钙磷酸盐玻璃陶瓷的合成及其体外生物活性

采用高分子网络凝胶法合成出SiO2-CaO-P2O5生物玻璃陶瓷,该材料具有较低含硅量和高钙磷比(nCa/nP=1.57)的特点,更接近人体硬组织的成分。将材料在SBF溶液浸泡研究材料的体外生物活性,通过TG/DTA,XRD,FTIR和SEM等方法对粉体和浸泡后的样品表面进行表征,ICP-AES对SBF溶液中钙、磷、硅离子的浓度进行检测。结果表明,氧化硅的添加有利于玻璃陶瓷表面磷灰石晶相的形成;随着浸泡时间的延长,沉积在样品表面的碳酸羟基磷灰石层逐渐由球型突起变为叶片状,溶液中钙、磷离子浓度降低,而硅离子浓度增加,说明材料具有良好的生物活性,适宜作为牙齿和骨骼的替代或修复材料。     

PHBV/Sol-gel Bioglass多孔材料在模拟生理溶液中的化学反应研究

3-羟基丁酸-co-3-羟基戊酸共聚物(PHBV)/生物活性玻璃(SGBG)是一种用于骨和软骨组织工程支架的新型多孔复合材料,本文探讨了PHBV/SGBG在模拟生理溶液中的一系列化学反应,以及多孔材料在模拟生理溶液中浸泡后的成分和结构变化.研究结果表明,在SBF溶液中浸泡后,SGBG与SBF溶液的离子交换反应和PHBV的降解反应使SBF溶液的离子浓度发生变化,并在PHBV/SGBG表面形成了结晶态类骨碳酸羟基磷灰石.     

Synthesis and characterization of ZnO nanowires by thermal oxidation of Zn thin films at various temperatures

In this research high-quality zinc oxide (ZnO) nanowires have been synthesized by thermal oxidation of metallic Zn thin films. Metallic Zn films with thicknesses of 250 nm have been deposited on a glass substrate by the PVD technique. The deposited zinc thin films were oxidized in air at various temperatures ranging between 450 °C to 650 °C. Surface morphology, structural and optical properties of the ZnO nanowires were examined by scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) and photoluminescence (PL) measurements. XRD analysis demonstrated that the ZnO nanowires has a wurtzite structure with orientation of (002), and the nanowires prepared at 600 °C has a better crystalline quality than samples prepared at other temperatures. SEM results indicate that by increasing the oxidation temperature, the dimensions of the ZnO nanowires increase. The optimum temperature for synthesizing high density, ZnO nanowires was determined to be 600 °C. EDX results revealed that only Zn and O are present in the samples, indicating a pure ZnO composition. The PL spectra of as-synthesized nanowires exhibited a strong UV emission and a relatively weak green emission.     

Formation mechanism of carbogenic nanoparticles with dual photoluminescence emission

We present a systematic investigation of the formation mechanism of carbogenic nanoparticles (CNPs), otherwise referred to as C-dots, by following the pyrolysis of citric acid (CA)-ethanolamine (EA) precursor at different temperatures. Pyrolysis at 180 °C leads to a CNP molecular precursor with a strongly intense photoluminescence (PL) spectrum and high quantum yield formed by dehydration of CA-EA. At higher temperatures (230 °C) a carbogenic core starts forming and the PL is due to the presence of both molecular fluorophores and the carbogenic core. CNPs that exhibit mostly or exclusively PL arising from carbogenic cores are obtained at even higher temperatures (300 and 400 °C, respectively). Since the molecular fluorophores predominate at low pyrolysis temperatures while the carbogenic core starts forming at higher temperatures, the PL behavior of CNPs strongly depends on the conditions used for their synthesis.     

Apatite-forming ability of bioactive poly(l-lactic acid)/grafted silica nanocomposites in simulated body fluid

Bioactive PLLA/surface-grafted silica (g-SiO?) nanocomposite scaffolds were fabricated by solid-liquid phase separation method. And solid PLLA/g-SiO? nanocomposite films were prepared by solution casting method. A series of parallel tube-like morphology and internal ladder-like structure of PLLA/g-SiO? nanocomposite scaffolds were observed by SEM. The formation of bone-like apatite in the simulated body fluid (SBF) was characterized by XRD, IR, SEM, EDS and weight measurement. The silica incorporation favors the formation of apatite. The growth of apatite with immersion time is found on the surfaces of both the PLLA/g-SiO? nanocomposite scaffolds and the films. The potential mechanism is that silanol groups of g-SiO? in the nanocomposites serve as nucleation sites for the formation of bone-like apatite crystals.     

Biomimetic apatite formation and biocompatibility on chemically treated Ti‐6Al‐7Nb alloy

Alkali treatment of the Ti‐6Al‐7Nb alloys with subsequent heat treatment has been adopted as an important surface treatment procedure for apatite formation in dental implants. This study examined the effects of alkali treatment on the precipitation of apatite on a Ti‐6Al‐7Nb alloy. All samples were immersed in a Hanks' Balanced Salts Solution [simulated body fluid (SBF)] at pH 7.4 and 36.5 °C for 15 days. The surface structural changes of samples due to the alkali treatment and immersing in SBF were analyzed by XRD, SEM and XPS. The cell toxicity was evaluated based on the optical density of the surviving cells. The samples were implanted into the abdominal connective tissue of mice for 4 weeks. A sodium titanate hydrogel layer was formed after immersion in an NaOH solution. A dense and uniform bone‐like apatite layer precipitated on the alkali and heat‐treated Ti‐6Al‐7Nb alloy in the SBF. There was a significant difference in cell toxicity between the treated and untreated Ti‐6Al‐7Nb (P < 0.05). The thickness of the fibrous capsule formed around the implant body was decreased significantly by the alkali and heat treatment (P < 0.05). The alkali treatment samples showed a better biocompatibility than the commercial metal samples. Copyright © 2008 John Wiley & Sons, Ltd.     

不同表面官能团和化学组成共聚物微球的表面生物矿化研究

采用具有不同共聚物组成和端基官能团的聚己内酯-b-聚乙二醇共聚物(PCL-b-PEG),通过双乳液溶剂挥发法制备了一系列具有不同表面性质的生物降解高分子微球.采用生物模拟矿化的方法以磷灰石修饰微球表面.进一步通过扫描电镜、热重分析仪、X-射线衍射仪和光电子能谱仪对微球表面磷灰石的形貌、含量、结构和组成进行了分析.研究了微球表面亲水性、粗糙度、官能团以及矿化时间对于磷灰石形成的影响.最终实验结果表明,随着共聚物中PEG含量增加,微球表面粗糙度和亲水性增加,因此微球表面磷灰石含量增加.同时微球表面官能团以及矿化时间的不同也会对磷灰石的形成和分布产生明显影响.     

Order and disorder effects in nano-ZrO(2) investigated by micro-Raman and spectrally and temporarily resolved photoluminescence

Pure and europium (Eu(3+)) doped ZrO(2) synthesized by an oil-in-water microemulsion reaction method were investigated by in situ and ex situ X-ray diffraction (XRD), ex situ Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), steady state and time-resolved photoluminescence (PL) spectroscopies. Based on the Raman spectra excited at three different wavelengths i.e. 488, 514 and 633 nm and measured in the spectral range of 150-4000 cm(-1) the correlation between the phonon spectra of ZrO(2) and luminescence of europium is clearly evidenced. The PL investigations span a variety of steady-state and time resolved measurements recorded either after direct excitation of the Eu(3+) f-f transitions or indirect excitation into UV charge-transfer bands. After annealing at 500 °C, the overall Eu(3+) emission is dominated by Eu(3+) located in tetragonal symmetry lattice sites with a crystal-field splitting of the (5)D(0)-(7)F(1) emission of 20 cm(-1). Annealing of ZrO(2) at 1000 °C leads to a superposition of Eu(3+) emissions from tetragonal and monoclinic lattice sites with monoclinic crystal-field splitting of 200 cm(-1) for the (5)D(0)-(7)F(1) transition. At all temperatures, a non-negligible amorphous/disordered content is also measured and determined to be of monoclinic nature. It was found that the evolutions with calcination temperature of the average PL lifetimes corresponding to europium emission in the tetragonal and monoclinic sites and the monoclinic phase content of the Eu(3+) doped ZrO(2) samples follow a similar trend. By use of specific excitation conditions, the distribution of europium on the amorphous/disordered surface or ordered/crystalline sites can be identified and related to the phase content of zirconia. The role of zirconia host as a sensitizer for the europium PL is also discussed in both tetragonal and monoclinic phases.     

Fabrication of Bioactive Polyoxymethylene Nanocomposites for Bone Tissue Replacement

Summary: Stearic acid modified nano hydroxyapatite (n-SHA) filled polyoxymethylene (POM) nanocomposites were prepared by melt mixing method for bone tissue replacement and regeneration applications. Contact angle measurements of POM nanocomposites were carried out to understand the effect of n-SHA addition on the hydrophobicity of nanocomposites. The mechanical properties like tensile strength, Young's modulus and elongation at break were found to be increased significantly by the incorporation of n-SHA into the POM matrix. The bone-bonding ability of the nanocomposites was evaluated by examining the apatite formation on their surface after soaking in simulated body fluid (SBF) and apatite formation was studied by atomic force microscopy (AFM). The protein adhesion studies revealed the enhanced biocompatibility of the nanocomposites due to the presence of n-SHA nanofillers on the surface and it provides favorable binding sites for protein adsorption. The significant improvement in the biocompatibility as well as mechanical, thermal and hydrophobic properties of the POM nanocomposites makes it a potential future material for bone implantation.     

医用钛表面组织结构和形貌特征与表面生物活性的研究

通过物理、化学或者电化学表面改性的方法改变钛表面氧化钛膜的结构、化学成份等可赋予钛金属及其合金生物活性,从而在体内实现材料与硬组织间的生物活性结合。本文探讨钛表面氧化钛膜的结构、化学成份、表面形貌和微观结构对其生物活性的影响。