Chemical reaction of bioactive glass and glass-ceramics with a simulated body fluid

Glass-ceramic A-W containing crystalline apatite and wollastonite in an MgO-CaO-SiO₂ glassy matrix bonds to living bone through an apatite layer which is formed on its surface in the body. The parent glass G of glass-ceramic A-W and glass-ceramic A, which has the same composition as glass-ceramic A-W but contains only the apatite, also bond to living bone through the surface apatite layer, whereas glass-ceramic A-W(Al), which contains the apatite and wollastonite in an MgO-CaO-SiO₂-Al₂O₃ glassy matrix, neither forms the surface apatite layer nor bonds to living bone. In the present study, in order to reveal the mechanism of formation of the surface apatite layer, changes in ion concentrations of a simulated body fluid with immersion of these four kinds of glass and glass-ceramics were investigated. Bioactive glass G and glass-ceramics A and A-W all showed appreciable increases in Ca and Si concentrations, accompanied by an appreciable decrease in P concentration, whereas non-bioactive glass-ceramic A-W(Al) hardly showed any element concentration change. It was speculated from these results that dissolution of the Ca(II) and Si(IV) ions from bioactive glass and glass-ceramics plays an important role in forming the apatite layer on their surfaces in the body.     

Preparation and studies on surface modifications of calcium-silico-phosphate ferrimagnetic glass-ceramics in simulated body fluid

The structure and magnetic behaviour of 34SiO₂–(45 − x) CaO–16P₂O₅–4.5 MgO–0.5 CaF₂ − x Fe₂O₃ (where x = 5, 10, 15, 20 wt.%) glasses have been investigated. Ferrimagnetic glass-ceramics are prepared by melt quench followed by controlled crystallization. The surface modification and dissolution behaviour of these glass-ceramics in simulated body fluid (SBF) have also been studied. Phase formation and magnetic behaviour have been studied using XRD and SQUID magnetometer. The room temperature Mössbauer study has been done to monitor the local environment around Fe cations and valence state of Fe ions. X-ray photoelectron spectroscopy (XPS) was used to study the surface modification in glass-ceramics when immersed in simulated body fluid. Formation of bioactive layer in SBF has been ascertained using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The SBF solutions were analyzed using an absorption spectrophotometer. The magnetic measurements indicated that all these glasses possess paramagnetic character and the [Fe²⁺/Fe³⁺] ions ratio depends on the composition of glass and varied with Fe₂O₃ concentration in glass matrix. In glass-ceramics saturation magnetization increases with increase in amount of Fe₂O₃. The nanostructure of hematite and magnetite is formed in the glass-ceramics with 15 and 20 wt.% Fe₂O₃, which is responsible for the magnetic property of these glass-ceramics. Introduction of Fe₂O₃ induces several modifications at the glass-ceramics surface when immersed in SBF solution and thereby affecting the surface dissolution and the formation of the bioactive layer.     

在类仿生溶液中电沉积羟基磷灰石涂层的性能

在类仿牛溶液中用电沉积法在阳极氧化处理后的钛基体上电沉积均一的羟基磷灰石涂层,研究了阳极氧化处理后对HA涂层耐蚀性能、沉积效率和结合强度的影响.结果表明:用该方法沉积的HA涂层结构单元的排列与人骨类似,具有优良的生物诱导性能.经过阳极氧化后钛表面生成均匀的纳米孔洞结构,增强了与HA涂层的机械结合和涂层的阻抗值,提高了涂层的结合强度和耐腐蚀性能.同时,在类仿生溶液中二氧化钛吸附羟基,通过库仑力和氢键作用大大提高了沉积效率,并因其纳米孔洞结构促进HA的形核,形成更加细小、致密的针状HA晶体结构,提高了涂层的结合强度和耐腐蚀性能.     

Nucleation and growth of octacalcium phosphate on treated titanium by immersion in a simplified simulated body fluid

A simplified simulated body fluid solution (S-SBF) was used to study the kinetics and mechanism of nucleation and growth of octacalcium phosphate (OCP) on the surfaces of alkali and heat-treated titanium samples. After the alkali and heat treatments, the samples were soaked in S-SBF for periods varying up to 24 h. A thin layer of poorly crystallized calcium titanate was formed after 15 min of immersion, allowing for the deposition of another layer of amorphous calcium phosphate (ACP). After 2.5 h of immersion, OCP nuclei were observed on the surface of the ACP layer. After 5 h of immersion in S-SBF solution, the specimens were completely covered with a homogeneous plate-like layer of OCP. Analyses by transmission electron microscopy revealed that nucleation and growth of OCP occurred concomitantly to the crystallization of ACP in hydroxyapatite (HA). This transformation took place by solid-state diffusion, forming a needle-like HA structure underneath the OCP film.     

Bioactivity of calcium phosphate coatings prepared by electrodeposition in a modified simulated body fluid

The purpose of this study was to investigate bioactivity of calcium phosphate coatings prepared by electrodeposition in a modified simulated body fluid (SBF). Calcium phosphates were electrodeposited on commercially pure titanium substrates in the modified SBF at 60 °C for 1 h maintaining the cathodic potentials of − 1.5 V, − 2 V, and − 2.5 V (vs. SCE). Subsequently, the calcium phosphate coatings were transformed into apatites during immersion in the SBF at 36.5 °C for 5 days. The apatites consisted of needle-shaped crystallites distributed irregularly with different grain sizes. As the coatings were electrodeposited at higher cathodic potential, the crystallite of the apatites got denser and the grain sizes of the apatites became bigger during subsequent immersion in the SBF. However, as the coatings were electrodeposited at higher cathodic potential, the coatings were transformed into apatites with lower crystallinity and the Ca/P atomic ratio of the apatites got higher than 1.67, that of stoichiometric hydroxyapatite, after subsequent immersion in the SBF. In addition, CO₃²⁻ ions contained in the modified SBF were incorporated in the calcium phosphate coating during electrodeposition and had an influence on transforming the calcium phosphate into bonelike apatite during subsequent immersion in the SBF showing that CO₃²⁻ incorporated in the apatites disturbed crystallization of the apatites. These results revealed that the coating electrodeposited at − 2.0 V (vs. SCE) in the modified SBF containing CO₃²⁻ ions was the most bioactive showing transformation into carbonate apatite similar to bone apatite.     

Seeded growth of hydroxyapatite in simulated body fluid

The precipitation of calcium phosphates was investigated, in simulated body fluid (SBF), pH 7.40 and 37°C. The kinetics of the mineral phase forming in the SBF was measured using the constant supersaturation method. The approach provides a detailed investigation in the processes taking place in the SBF which is widely used for the study of biomineralization. The pH adjustment was done by a pH-stat instead of Tris-Buffer [Tris (hydroxymethyl) Aminomethane] to avoid the presence of organic soluble compounds. The stability of SBF was investigated and the stable supersaturated solutions were seeded. The technique of seeded precipitation was employed for the achievement of accurate and reproducible kinetics measurements. The crystal growth experiments in which SBF solutions of variable supersaturations were seeded with hydroxyapatite [Ca₅(PO₄)₃OH, HAP] crystals showed that the precipitation of calcium phosphates took place exclusively on specific active sites provided on the surface of the synthetic seed crystals. The crystal growth mechanism showed that the process was controlled by surface diffusion. The phase formed was HAP in the lattice of which CO₃²⁻ and Mg²⁺ ions were incorporated. SBF was the source of these ions. Moreover it was found that the less stable calcium phosphate dihydrate (CaHPO₄·2H₂O, DCPD) may form as a transient phase hydrolyzing rapidly into the more stable HAP. Morphological examination of the carbonated apatites formed in the SBF showed appreciable aggregation.     

超声化学法合成羟基磷灰石纳米棒

在37℃下的模拟体液中采用超声化学法制备羟基磷灰石(HA)纳米棒,研究了初始pH值和反应时间对合成磷酸钙产物晶相的影响.结果发现在初始pH＜7.5时产物为无水磷酸氢钙相和HA相的混合物,初始pH值≥7.5时产物为单一的HA相,延长超声波处理时间有利于羟基磷灰石晶相的生成,最佳的反应参数为初始pH≥7.5,反应时间在6h以上.利用TEM、FTIR对HA相产物进行表征发现,HA为含碳酸根羟基磷灰石,其形貌长度为200nm,直径为10～30nm的纳米棒,其在组成和形态上与生物体内的磷灰石相十分接近.     

镁基纳米复合材料在模拟体液中的腐蚀行为

以AZ80A市售镁合金为参照，研究了镁基纳米复合材料镁，即：碳纳米管（Mg／CNT）复合材料及氧化镁（Mg／MgO）纳米复合材料在模拟体液中的腐蚀行为．浸泡过程中测量溶液的pH值变化，在浸泡1、4、8、10、20和30d后计算其腐蚀速率，并通过XRD分析腐蚀产物成分．结果显示：Mg／MgO纳米复合材料比Mg／CNT复合材料耐腐蚀，Mg／CNT复合材料在4d时已经腐蚀完，AZSOA型镁舍金最耐腐蚀。三者的腐蚀产物成分基本相同，均为Mg2CI（0H）3-4H2O及少量的MgCl2.     

Corrosion process of pure magnesium in simulated body fluid

The chemical and physical processes of magnesium in simulated body fluid (SBF) were investigated. The corrosion rate of magnesium was measured after 3, 5, 7, 14 and 21 days of immersion, respectively. It was found that the corrosion rate decreased with increasing immersion time, while the pH of SBF changed inversely. Network-like cracks and pits were the main damages resulting from corrosion, and the localized buildup of chloride ions was the major cause of pit formation.     

Corrosion behavior of surface-modified titanium in a simulated body fluid

We investigate the influence of micro-sandblasting and electrochemical passivation on properties such as corrosion rate and surface roughness, which are important to the biocompatibility of titanium (Ti), using surface analysis techniques and electrochemical measurements. Results of microscopy and surface profilometry experiments reveal roughened but uniform surface topography with an average surface roughness in the 0.87–1.06 μm range, depending on the alternating current passivation voltage applied to the micro-sandblasted samples. Open circuit potential versus time measurements in Hank’s Balanced Salt Solution (HBSS, a simulated body fluid) allow determination of the corrosion potential (E _corr) and reveal a shift of E _corr toward higher values upon passivation, thus pointing to increased corrosion stability. Corrosion rates in HBSS range between 0.049 and 0.288 μm year⁻¹ for micro-sandblasted and passivated Ti, as compared to that for the micro-sandblasted and non-passivated surface that is 0.785 μm year⁻¹. Results from this study demonstrate that micro-sandblasting coupled with electrochemical passivation provides a roughened surface with increased corrosion stability and a low corrosion rate in HBSS. Application of this technique to Ti in medical and dental applications may be expected to result in an improvement of biocompatibility.     

Improve corrosion resistance of magnesium in simulated body fluid by dicalcium phosphate dihydrate coating

A dicalcium phosphate dihydrate (DCPD) coating composed of bar-shaped crystals was deposited on the surface of magnesium in order to slow down the corrosion rate of the substrate. The corrosion resistance of the DCPD-coated specimens was evaluated in a simulated body fluid (SBF) with uncoated specimens as a control. Time-dependent characteristics of specimens and the corresponding SBF were analyzed at 3, 5, 7, 14 and 21 days of immersion. Less weight loss and pH increase were observed for the coated group than the uncoated group. The coating was intact after 3 days of immersion although its dissolution was manifested by XRD examination. Noticeable DCPD dissolution occurred at the 5th day accompanied by a temporary increase in Ca and P concentrations in SBF which otherwise kept decreasing. Despite the dissolution of the coating, some DCPD particles were still observed on the surface of the substrate after 21 days of immersion. In contrast to the coated specimens, a porous layer of Mg(OH)₂ was formed on the surface of uncoated specimens at the 5th day of immersion. It was found that the corrosion rate of the coated group was substantially lower than that of the control.     

Calcium phosphate fibres synthesized from a simulated body fluid

The biomimetic coating method was used for fabricating calcium phosphate fibres for biomedical applications such as bone defect fillers. Natural cotton substrate was pre-treated with phosphorylation and a Ca(OH)₂ saturated solution. The pre-treated samples were then soaked in simulated body fluid (SBF) of two different concentrations, 1.5 times and 5.0 times the ion concentration of blood plasma. The cotton was then burnt out via sintering of the ceramic coating at 950^∘C, 1050^∘C, 1150^∘C, and 1250^∘C. The results demonstrated that osteoblastic cells were able to cover the entire surface cotton fibres, and the cell coverage appeared to be independent of surface roughness and Ca/P ratio of fibres.     

In vitro dissolution of calcium phosphate-mullite composite in simulated body fluid

In our recent research, we have developed novel CaP-mullite composites for bone implant applications. In order to realize such applications, the in vitro dissolution behaviour of these materials needs to be evaluated. In this perspective, the present paper reports the dissolution behavior of pure hydroxyapatite (HAp) and hydroxyapatite composites with 20–30 wt% mullite in simulated body fluid (SBF). The in vitro dissolution experiments were carried out for different time duration starting from 7 days up to 28 days. XRD and SEM results show almost no dissolution for pure HAp and HAp composite with 30 wt% mullite. However, HAp-20 wt% mullite composite exhibits considerable dissolution after 7 days. The α-TCP phase mainly contributes to the dissolution process. Based on the dynamic changes in pH, ionic conductivity, Ca and P ion concentration in SBF as well as microstructural observations of the bioceramic surfaces after various time frames of immersion in SBF, the differences in dissolution behaviour are discussed.     

Surface reaction of stoichiometric and calcium-deficient hydroxyapatite in simulated body fluid

In the present study, the immersion behavior of two kinds of sintered HA with different Ca/P ratios in two different extracellular simulated solutions (Tris buffer and Hank's solutions) was investigated and compared. Results indicated that an as-received Ca-deficient HA (FHA) had a lower Ca/P ratio, larger linear shrinkage and higher density than a stoichiometric HA (MHA). When FHA powder was calcined at 900 °C, its Ca-deficient apatite structure was unstable and a significant amount of -TCP phase was formed. When heated to 1250 °C in air, the highly crystalline apatite structure of MHA was still stable without any noticeable decomposition. The FTIR spectra indicated that both immersed MHA and FHA in Hank's solution were gradually covered with a layer of precipitated apatite during immersion. When immersed in Tris buffer solution, neither HA showed significant changes in their FTIR spectra. SEM observation indicated that the precipitation rate on immersed FHA surface was much higher than that on MHA surface when immersed in Hank's solution. The weight loss and pH data confirmed the higher dissolution rate of FHA than MHA in Hank's solution. © 2001 Kluwer Academic Publishers     

Study of yttrium containing bioactive glasses behaviour in simulated body fluid

The influence of yttrium oxide on the bioactivity of glasses in the system SiO₂-Na₂O-P₂O₅-CaO-B₂O₃-K₂O-MgO was studied in a simulated body fluid (SBF). Two series of glasses with different bioactivity were investigated. The reaction layers formed on the surface of the exposed glasses were evaluated by means of back scattered electron imaging of scanning electron microscopy equipped with energy dispersive X-ray analysis (BEI-SEM/EDXA). The concentration of Y, Ca and P released from the glasses into SBF, during 21 days was determined using inductively coupled plasma-emission spectroscopy ICP-AES and inductively coupled plasma-mass spectroscopy ICP-MS. Introducing yttrium in the selected bioactive glass tended to diminish the bioactivity of the glasses. The thickness of the calcium phosphate layer decreased with increasing yttrium oxide content. The same effect was also observed when yttrium oxide partially replaced only calcium, magnesium and phosphorous oxide in the precursor glass. The data show that we can produce bioactive glasses with yttrium oxide as a component. By suitable tailoring of the rest of the glasses the yttrium effect on the glass behavior in SBF should be possible to control and thus produce yttrium containing glasses with desired bioactivity.     

Biodegradable behaviors of AZ31 magnesium alloy in simulated body fluid

Magnesium alloys have unique advantages to act as biodegradable implants for clinical application. The biodegradable behaviors of AZ31 in simulated body fluid (SBF) for various immersion time intervals were investigated by electrochemical impedance spectroscopy (EIS) tests and scanning electron microscope (SEM) observation, and then the biodegradable mechanisms were discussed. It was found that a protective film layer was formed on the surface of AZ31 in SBF. With increasing of immersion time, the film layer became more compact. If the immersion time was more than 24 h, the film layer began to degenerate and emerge corrosion pits. In the meantime, there was hydroxyapatite particles deposited on the film layer. The hydroxyapatite is the essential component of human bone, which indicates the perfect biocompatibility of AZ31 magnesium alloy.     

TiO2纳米管阵列在模拟体液中诱导nHA沉积行为的研究

采用电化学阳极氧化法在钛金属表面制备了具有不同管径尺寸的TiO2纳米管阵列(TiO2nanotubearray,TNT)涂层。实验中通过模拟体液(simulatedbody fluid,SBF)浸泡法制备了纳米羟基磷灰石(nano-hydroxyapatite,nHA)/TNT复合涂层,并研究了nHA在纳米管表面生成的过程和机理。Ti—OH基团是HA在TNT表面成核的诱因,TiO2与HA晶体构成的晶格匹配结构能够促进HA的成核速率,锐钛矿和金红石混合相的TNT涂层诱导nHA生成的能力明显强于无定型的TNT涂层。涂层的润湿性受控于纳米管的管径尺寸,并能够影响nHA形成的速率,增强纳米管的亲水性有利于HA的沉积。     

Characterization and deposition behavior of silk hydrogels soaked in simulated body fluid

This paper reports the mineralization ability of semi-interpenetrating networks composed of regenerated silk fibroin and polyacrylamide hydrogels soaked in simulated body fluid (SBF1x). Hydrogels were prepared by polymerization of acrylamide and N,N′-methylenebisacrylamide in silk fibroin solution with a redox pair as initiator. The incorporation of the fibroin within the polyacrylamide matrix was proved by FTIR–ATR spectroscopy. Swelling measurements in saline solution were performed to evaluate the behavior of these hydrogels having various compositions. Mineralization assays in SBF1x solution revealed the presence of apatite-like crystals onto the surface of the silk fibroin/polyacrylamide hydrogels. Cytotoxicity test by extract method revealed that these hydrogels with various contents in silk fibroin have not developed cytotoxic effects on human fibroblast cultures which increases the possibility of their use in biomedical applications. Mechanical compressive tests revealed good strengths for silk fibroin/polyacrylamide hydrogels. In this way, organic–inorganic hybrids analogous to bone structure can be produced under biomimetic conditions and could be further used in biomedical applications.     

In vitro behavior of fluoridated hydroxyapatite coatings in organic-containing simulated body fluid

A dense and pure hydroxyapatite [HA, Ca₁₀(PO₄)₆(OH)₂] coating and a fluoridated HA [Ca₁₀(PO₄)₆(OH)_0.67F_1.33] are deposited on Ti6Al4V substrates by sol-gel dip coating method. Glucose and bovine serum albumin have been added in standard simulated body fluid (SBF) to form organic-containing SBF in simulation of the physiological blood plasma. The HA and the fluoridated HA coatings are immersed in the standard and modified SBF for time periods of 2, 4, 7, 14 and 28 days at 37 ± 0.1°C. After soaking, the coating surface is examined for nucleation and growth of apatite using SEM morphological observation. The post-soaking SBF solutions are analyzed via Inductively Coupled Plasma spectroscopy for calcium ion concentration. The results show that at concentration of 40 g/L, bovine serum albumin has significant retardation effect on apatite precipitation from SBF onto pure or fluoridated HA coatings; Fluorine-incorporation in HA has positive bio-activation effect in both standard SBF and organic-containing SBF. However, glucose addition in SBF does not generate significant influence on the bioactivity of HA and fluoridated HA.     

Initial formation of corrosion products on pure zinc in simulated body fluid

Zinc was recently suggested to be a potential candidate material for degradable coronary artery stent. The corrosion behavior of pure zinc exposed to r-SBF up to 336?h was investigated by electrochemical measurements and immersion tests. The morphology and chemical composites of the corrosion products were investigated by scanning electron microscope, grazing-incidence X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer. The results demonstrate that the initial corrosion products on the pure zinc mainly consist of zinc oxide/hydroxide and zinc/calcium phosphate compounds. The pure Zn encounters uniform corrosion with an estimated corrosion rate of 0.02–0.07?mm?y^?1 during the immersion, which suggests the suitability of pure Zn for biomedical applications.