Deposition behavior and properties of silk fibroin scaffolds soaked in simulated body fluid

Porous 3D silk fibroin (SF) scaffolds were prepared directly from the SF solution with the addition of methanol and glutaraldehyde by a freeze-drying method. The scaffolds were then soaked in the simulated body fluid (SBF) for the deposition of hydroxyapatite (HA) crystals. The XRD and FTIR results showed that the SF were in β-sheet structure, resulting in the high thermal stability and mechanical properties of scaffolds. The XRD and AAS data revealed that the SF scaffolds could induce the continuous growth and enrichment of HA crystals onto the scaffolds with the extension of soaking time. The mechanical properties of scaffolds increased first with the HA-deposition within 3 d of soaking, then it declined. During the full soaking period, no significant change was observed on the porosity and water-binding ability, which were kept at about 84% and 800%, respectively. The cell cultivation results showed that the scaffolds have the satisfied cell biocompatibility, which was promoted after the HA-deposition. This work suggests that the porous 3D SF scaffolds may be a potential candidate in the bone engineering.     

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。     

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.     

纳米细菌纤维素/聚乙烯醇复合水凝胶在模拟体液中的疲劳行为

聚乙烯醇(PVA)复合水凝胶作为半月板及软骨等长期承重植入体,在生理环境中的疲劳行为关系到植入体的持久性和稳定性。采用弥散增强的方法将纳米细菌纤维素(BC)均匀分散在PVA水凝胶基体中,制备了纳米BC/PVA复合水凝胶。在模拟体液(SBF)环境中,采用压缩疲劳过程分析、疲劳前后刚度变化分析及疲劳前后尺寸稳定性分析3种方法,测试和评价了复合水凝胶的抗疲劳性能和力学稳定性。结果表明:纳米BC/PVA复合水凝胶在模拟人体环境中具有良好的抗疲劳性能,能够满足体内植入物的抗疲劳性能需求;纳米BC的加入可以有效提升复合水凝胶的力学稳定性和抗疲劳性能,但随着纳米BC含量的进一步升高,复合水凝胶的抗疲劳性能有所减弱,当PVA与纳米BC质量比为30∶1时,纳米BC/PVA复合水凝胶疲劳前期与后期最大位移变化量最小(0.002mm),疲劳前后刚度变化最小(5.41%),且疲劳前后尺寸稳定性最强,变形量仅为0.427mm,抗疲劳性能达到最佳。     

In-vitro study of the spontaneous calcification of PHEMA-based hydrogels in simulated body fluid

In-vitro calcification of poly(2-hydroxyethyl methacrylate) (PHEMA)-based hydrogels in simulated body fluid (SBF) under a steady/batch system without agitation or stirring the solutions has been investigated. It was noted that the formation of calcium phosphate (CaP) deposits primarily proceeded through spontaneous precipitation. The CaP deposits were found both on the surface and inside the hydrogels. It appears that the effect of chemical structure or reducing the relative number of oxygen atoms in the copolymers on the degree of calcification was only important at the early stage of calcification. The morphology of the CaP deposits was observed to be spherical aggregates with a thickness of the CaP layer less than 0.5 μ m. Additionally, the CaP deposits were found to be poorly crystalline or to have nano-size crystals, or to exist mostly as an amorphous phase. Characterization of the CaP phases in the deposits revealed that the deposits were comprised mainly of whitlockite [Ca₉MgH(PO₄)₇] type apatite and DCPD (CaHPO₄⋅2H₂O) as the precursors of hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂]. The presence of carbonate in the deposits was also detected during the calcification of PHEMA based hydrogels in SBF solution.     

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.     

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.     

Electrochemical behavior of biocompatible AZ31 magnesium alloy in simulated body fluid

Dense oxidation coatings have been successfully developed on biocompatible AZ31 magnesium alloy, using microarc oxidation technique, to improve the corrosion resistance. Three different deposition voltages of 250, 300, and 350 V have been employed. The effect of voltage on the coating corrosion resistance has been evaluated through electrochemical experiments in a simulated body fluid (SBF) up to 7 days. Potentiodynamic polarization and electrochemical impedance spectroscopy scans were performed in the SBF solution, followed by optical microscopy surface inspection. The results indicate that the corrosion rates of the coatings are in the order of 250 < 300 < 350 V after immersion for 7 days, and the charge transfer resistance (R _ct) of the three samples is in the order of 250 > 300 > 350 V. Both the electrochemical tests and the surface inspection suggest that the 250 V coating has the highest corrosion resistance, with lowest corrosion current density, highest R _ct, and the best surface quality.     

Influence of Tris in simulated body fluid on degradation behavior of pure magnesium

In current paper, influence of tris-hydroxymethyl-aminomethane (tris) in simulated body fluid (SBF) on degradation behavior of pure magnesium is investigated using electrochemical tests as well as degradation measurement. Our results shows that tris mainly affects earlier degradation behavior of pure magnesium alloy. Tris and HCl used in preparation of SBF will form Tris–HCl which only lowers corrosion potential of magnesium slightly but accelerates degradation rates of pure magnesium by teens times. Consumption of OH^? generated during magnesium dissolution by Tris–HCl progressively promotes transformation from Mg to Mg²⁺, which is the main reason for quite high degradation rate of pure magnesium in SBF. Pure magnesium is also more sensitive to pitting corrosion due to inclusion of Tris–HCl in SBF. This study deepens the understanding on degradation mechanism of biomedical magnesium alloys.     

Fretting wear behavior of calcium phosphate-mullite composites in dry and albumin-containing simulated body fluid conditions

In a recent work, it has been shown that it is possible to achieve a better combination of compressive strength, flexural strength and toughness properties in calcium phosphate (CaP) composites containing 20 and 30 wt% mullite (3Al₂O₃·2SiO₂). In view of their potential application as load bearing implants, the present work reports the friction and wear properties of the newly developed composites against zirconia under dry ambient as well as in simulated body fluid (SBF) containing bovine serum albumin (BSA) protein. For comparison, experiments were also conducted on monolithic hydroxyapatite (HAp, Ca₁₀(PO₄)₆(OH)₂) and mullite under identical conditions. Under the investigated fretting conditions, the mullite-containing composites exhibited higher coefficient of friction (COF) of 0.4–0.6, compared to pure HAp (COF ~ 0.25–0.3). Although the wear resistance of the composites containing 20 or 30 wt% mullite was better in dry conditions, higher wear rate was measured in SBF conditions. The difference in tribological properties has been analyzed in reference to the difference in phase assemblage and mechanical properties. A comparison with some competing biomaterials reveals good potential of the investigated CaP-mullite composites for application as wear resistant implants.     

激光表面改性对NiTi形状记忆合金腐蚀行为的影响

采用连续波Nd：YAG固体激光,在NiTi形状记忆合金表面制备出表面致密、无7L洞和裂纹的氮化层,测试了这种激光改性层在37℃模拟人体体液Hank’s溶液中的电化学阳极极化曲线和交流阻抗谱,研究了改性层的腐蚀行为．结果表明,NiTi合金氮化层的腐蚀电位和击穿电位正移,反应转移电阻明显提高,而腐蚀电流及界面电容下降．这说明激光气体氮化有效地改善了NiTi形状记忆合金在模拟人体体液中的电化学抗腐蚀性能．     

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.     

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.     

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.     

Effect of D-fructose on the in-vitro corrosion behavior of AZ31 magnesium alloy in simulated body fluid

The effect of addingd-fructose to simulated body fluid(SBF) on the corrosion behavior of AZ31 magnesium(Mg) alloy at 37.C and at a pH of 7.4 was studied by potentiodynamic polarization(PDP), electrochemical impedance spectroscopy(EIS), potentiostatic polarization and hydrogen(H2) collecting techniques,Raman spectroscopy technique, scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), X-ray photoelectron spectroscopy analysis(XPS) and Fourier transformed infrared(FTIR). The results demonstrated that the addition of fructose enhanced the deposition of phosphates forming thick and compact corrosion products, which inhibited the transmission of aggressive ions into the Mg substrate. As a result, both the anodic dissolution of Mg and negative difference effect(NDE) were suppressed. Thus, the corrosion resistance of AZ31 Mgalloy in SBF was significantly improved.     

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     

In vitro degradation behavior of M1A magnesium alloy in protein-containing simulated body fluid

Magnesium alloys possess unique advantages to be used as biodegradable implants for clinical applications. In this study, in vitro cells responses and degradation behaviors of magnesium alloy M1A in simulated body fluid (SBF) and albumin-containing SBF (A-SBF) were systematically investigated. Cell responses, in terms of Cell morphology and cell proliferation, imply that M1A possesses good viability for MG63 cells. The corrosion behaviors of M1A are strongly affected by the addition of albumin through the combined effects of adsorption and chelation. Electrochemical testing indicates that such an absorbed albumin layer makes M1A to be more noble with a smaller corrosion current. Corrosion rate monitored by hydrogen evolution rate suggests that the quickly adsorbed albumin serves as an effective protective layer, resulting in a much slower hydrogen release rate at initial stage. With increasing immersion time, a higher corrosion rate is observed since the chelation effect exerts more significant acceleration effects on the removal of the passivation layer. The corrosion mode evaluated by surface morphology of the samples changes from a nonuniform-anisotropic mode for M1A in SBF to a uniform-isotropic mode for M1A in A-SBF.     

Effects of microstructural mechanisms on the localized oxidation behavior of NiTi shape memory alloys in simulated body fluid

Localized oxidation and corrosion behavior of a nickel–titanium (NiTi) shape memory alloy (SMA) was investigated via static immersion experiments in a simulated body fluid solution. Detailed electron microscopy examinations on the sample surfaces revealed preferential formation of local oxide particles around dislocation networks, which constitute high-energy zones. Moreover, various intermediate phases were detected in addition to the parent NiTi phase around dislocation networks. These are also areas with enhanced diffusion, which promotes Ni release. These findings emphasize the significant role of fine microstructural features, such as dislocation networks, on the oxidation and Ni release, and thus, the biocompatibility of the NiTi SMAs.     

Characterization of 17-4 PH stainless steel foam for biomedical applications in simulated body fluid and artificial saliva environments

Highly porous 17-4 PH stainless steel foam for biomedical applications was produced by space holder technique. Metal release and weight loss from 17–4 PH stainless steel foams was investigated in simulated body fluid and artificial saliva environments by static immersion tests. Inductively coupled plasma-mass spectrometer was employed to measure the concentrations of various metal ions released from the 17-4 PH stainless steel foams into simulated body fluids and artificial saliva. Effect of immersion time and pH value on metal release and weight loss in simulated body fluid and artificial saliva were determined. Pore morphology, pore size and mechanical properties of the 17-4 PH stainless steel foams were close to human cancellous bone.     

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.