Ultrafast bone-like apatite formation on bioactive tricalcium silicate cement using mussel-inspired polydopamine

The growing bone-like apatite layer at the tissue-implant interface is the essential condition for materials to bond robustly to surrounding bone and may provide a favorable environment for living bone formation. Inspired by versatility of mussel adhesive proteins, we developed an ultrafast and accessible route to accelerate effectively the formation of amorphous calcium phosphate (ACP), the precursor phase of bone-like apatite, on the surface of polydopamine (PDA)-coated tricalcium silicate (TCS) within 5?min in simulated body fluid (SBF). The key of the method lies in successful preparation of PDA coating on the surface of hydrated TCS by simple dip-coating of hydrated TCS in an aqueous solution of dopamine. A strong adsorption between PDA coating and surface of hydrated TCS could be formed via bidentate hydrogen and electrostatic bonds. After 7 d of soaking in SBF, the bone-like apatite layer on the surface of PDA-coated TCS disk, about 91.1?µm in height was thicker than that on the surface of pristine TCS disk, determining about 49.5?µm. The results indicate that PDA coating can facilitate the kinetic deposition of bone-like apatite on its surface. The abundant Ca²⁺ ions and the lower interface energy of ACP at the interface between ACP and surfaces of PDA-coated TCS disks are responsible for the ultrafast precipitation of ACP and formation of bone-like apatite layer which is carbonated hydroxyapatite (HA) confirmed by different analytical tools. The route can open avenues for development of PDA-coated TCS biomaterials for hard tissue repair and substitution.     

Bonelike Apatite Formation Induced on Zirconia Gel in a Simulated Body Fluid and Its Modified Solutions

Formation of bonelike apatite on zirconia gel in a simulated body fluid (SBF) with ion concentrations almost equal to those in human blood plasma, in modified SBF solutions to have increased pH values, and modified SBF solutions to have increased concentrations of calcium and phosphate ions has been investigated. The zirconia gel forms apatite on its surface in SBF, indicating that Zr-OH groups, abundant on the gel, act as effective apatite nucleation centers. Apatite formation is accelerated by increases in pH and in the concentration of calcium and phosphate ions, which is explained by an increase in the ionic activity product of the apatite in the SBF. These results suggest that zirconia ceramics may exhibit a bone-bonding ability by forming an apatite layer on their surfaces in the living body when they are modified to have many Zr-OH groups on their surfaces.     

Dependence of Apatite Formation on Silica Gel on Its Structure: Effect of Heat Treatment

The prerequisite for glasses and glass-ceramics to bond to living bone is the formation of biologically active bonelike apatite on their surfaces in the body. Our previous study showed that a silica gel prepared by hydrolysis and polycon- densation of tetraethoxysilane in aqueous solution containing poly(ethy1ene glycol) induces apatite nucleation on its surface in a simulated body fluid. In the present study, the effects of heat treatment of silica gel on its catalytic effects in apatite nucleation was investigated in a simulated body fluid. I t was found that apatite forms on the surfaces of silica gels heat-treated below 8OO°C, but not on those heat-treated above 900°C. The volume of nanometer-range pores in the gel remarkably decreased by heat treatment above 900°C. The concentration of silanol groups in the silica gels gradually decreased with increasing heat treatment temperature. The rate of silica dissolution from the gel into the simulated body fluid decreased remarkably by heat treatment above 900°C. This suggested that a special type of silanol group which is formed by soaking the gel treated below 800°C into the simulated body fluid is respon sible for apatite nucleation.     

Development of bioactive materials based on surface chemistry

All bioactive materials developed up to 1990 were based on calcium phosphate. It was later revealed that materials that form bonelike apatite on their surfaces in the living body bond to living bone through the apatite layer, and that apatite formation on a material is induced by various functional groups on its surface. Based on these findings, bioactive titanium was prepared by forming sodium titanates on its surface via NaOH and heat treatments, and applied to an artificial total hip joint. Porous titanium metal able to exhibit osteoconductivity as well as osteoinductivity was prepared by forming anatase on its surface via NaOH, HCl and heat treatments. Various bioactive materials with different physical properties are expected to be derived from ceramics, metals and organic polymers by modifying their surfaces with functional groups effective for apatite nucleation.     

Apatite-Forming Ability of Sodium-Containing Titania Gels in a Simulated Body Fluid

An essential condition for an artificial material to bond to living bone is the formation of bonelike apatite on its surface in the living body. The bonelike apatite can be reproduced on the bone-bonding material even in an acellular simulated body fluid (SBF) with ion concentrations almost equal to those of human blood plasma. In the present study, the dependence of the apatite-forming abilities of sodium-containing titania gels in a SBF on composition and structure is examined. The sodium-containing titania gels are model substances produced on the surface layer of bioactive titanium metal prepared by sodium hydroxide solution and heat treatments. When sodium-containing titania gels are immersed in the SBF, Na⁺ ions incorporated in the gels are exchanged with the H₃O⁺ ions in the SBF. This ion exchange causes an accompanying increase in the pH of the SBF and increases its ionic activity product, thus providing favorable conditions for apatite nucleation on the surfaces of the gels. Nevertheless, sodium-containing titania gels that do not contain anatase do not form apatite on their surfaces. Independent of the composition, the gels form apatite on their surfaces in the SBF, specifically when they contain anatase. These results imply that the Ti-OH groups on titania, which have been proposed to be responsible for the apatite formation, are effective for apatite nucleation when they are arranged in a specific structural unit based on the anatase structure.     

Structural evaluation,preliminary in vitro stability and electrochemical behavior of apatite coatings on Ti6Al4V substrates

Medical-grade alloys, such as Ti-6Al-4V, have been used for fixation of fractured bone and for the total replacement of defective bone. Their bioactivity could be improved by applying a bone-like apatite layer onto their surfaces. This, in turn, enhances their integration with the surrounding tissues upon implantation. In addition, the presence of a bioactive bone-like coating minimizes the likelihood of corrosion. Various methods are known for the formation of apatite coating onto Ti-6Al-4V, among which sputtering has shown its promise as a simple direct method. In the current work, a sputtering technique was used to develop a 300 nm-thick bone-like apatite layer onto Ti-6Al-4V. Structural composition, integrity and morphology of the as-coated and thermally treated coatings were investigated. Coated substrates were further evaluated after soaking them in a simulated body fluid (SBF) for up to 14 days. Results showed the formation of an amorphous apatite layer onto the alloy, that was further shown to partially crystallize upon heat treatment. As a result of SBF treatment, the apatite layer was found to remodel through a dissolution-precipitation mechanism due to its amorphous and non-stoichiometric nature, forming a smooth layer with better homogeneity and decreased surface roughness. Electrochemical analysis of the coated alloys showed the enhanced corrosion protection of the alloy surfaces by coating them with apatite. In addition, pre-grinding of the alloy surfaces before the formation of the coating was also found to improve the corrosion inhibition of the alloy surfaces in aqueous media.     

Relationship between valence of titania and apatite mineralization behavior in simulated body environment

Titania-based materials are attractive for hard tissue repair due to their bone-bonding ability induced by apatite formation in the body environment. Various surface treatments have therefore been developed to produce a hydrated titania layer on Ti and its alloys. Titania takes various valences, such as TiO (Ti²⁺) and Ti₂O₃ (Ti³⁺), as well as typical TiO₂ (Ti⁴⁺); however, there is no comprehensive study of structural effects on the apatite-forming ability of these titanias. In this study, we investigated apatite formation on titania powders with various valences in simulated body fluid. Anatase- and rutile-type TiO₂ formed apatite in simulated body fluid within 7 days, but TiO and Ti₂O₃ did not. In contrast, when the titania powders were treated with NaOH solution, the surface converted to tetravalent titania and all samples formed apatite. It is proposed that the surface electrical states of TiO and Ti₂O₃ are strongly affected by their bulk conductivity and that these behaved like pure Ti metal, which has poor apatite-forming ability. Apatite formation was favorable when the titania had a high absolute value and exhibited high fluctuations of zeta potential during initial stages in simulated body fluid, owing to adsorption of large amounts of Ca²⁺ and HPO₄²⁻.     

Bioactivity Characterization of Amorphous Silica Ceramics Derived from Rice Husk Ash

Rice husk ash has been used to prepare amorphous silica bioactive ceramics. Three varieties of silica powders, namely brown ash, white ash and silica gel containing 96.0, 99.8 and 99.9% silica respectively, were used to prepare silica ceramics. The bioactivity and biodegradability properties of these ceramics were evaluated. The formation of crystalline apatite was observed on all the specimens in simulated body fluid. The phase composition, morphology and calcium/phosphorous ratio of the apatite layer formed were evaluated by X-ray Diffraction, Scanning Electron Microscopy and Energy Dispersive Spectroscopy. Controlled biodegradability of amorphous silica in Tris buffer solution was found. These results suggest that the amorphous silica derived from rice husk ash is a promising and cost effective biomaterial.     

富含钙磷的多孔氧化钛膜及其生物活化机理

在不同电压下,钛经微弧氧化在表面形成富含钙磷的多孔氧化钛膜。通过模拟体液浸泡实验检测磷灰石的形成以确定样品的生物活性。实验结果表明：不同电压制备的微弧氧化样品在模拟体液浸泡后,只有400 V和450 V的样品表面生成磷灰石层,说明高电压制备的样品具有生物活性;而低电压制备的微弧氧化样品在模拟体液中浸泡长达50 d仍未见到任何物质沉积,表明其不具有生物活性。分析认为,粗糙多孔的表面虽有利于磷灰石的成核,但高电压下出现的CaTiO_3相及其水解吸引钙、磷沉积才是磷灰石形成的主要原因。     

In-vitro bioactivity of wollastonite materials derived from limestone and silica sand

This paper describes the behaviour of bioactive wollastonite materials containing Malaysian limestone and silica sand. Wollastonite, which is also known as calcium silicate (CaSiO₃), is an industrial mineral composed of calcium, silicon and oxygen. Pseudowollastonite, which is a primary crystal of wollastonite, was synthesised via a solid-state reaction at a temperature of 1450 °C. The in-vitro bioactivity of wollastonite was examined by soaking it in simulated body fluid (SBF) solution for 1–7 days at 36.5 °C. The soaked wollastonite samples were characterised using XRD, SEM-EDX, FTIR and ICP analyses. Apatite particles precipitated on the surface of the wollastonite sample after the sample was soaked in the SBF. The XRD analysis indicated the presence of an increasing amount of the hydroxyapatite phase as the soaking time increased. The SEM and EDX analyses indicated the formation of granules of agglomerated apatite particles on the surface of the soaked wollastonite sample. During the formation of apatite, phosphate ions from the SBF solution were consumed. This process was confirmed by ICP, which revealed a decrease in ion concentration after the soaking process. The FTIR analysis indicated that the peaks of the phosphate ions increase when the apatite layer forms on the surface of the wollastonite sample. After the soaking process, a calcium deficient hydroxyapatite layer was observed on the wollastonite sample. The study concludes that wollastonite produced from Malaysian limestone and silica sand is bioactive and may be used as an implantable biomaterial.     

Effect of Texture on the Rate of Hydroxyapatite Formation on Gel-Silica Surface

An apatite layer can be formed on pure gel-silica soaked in simulated body fluid. The rate of formation depends on solution parameters and sintering temperature of the gelsilica. In this study, the effect of the texture of the gel-silica on the rate of hydroxyapatite formation was investigated. The apatite formation was monitored by means of Fourier-transform infrared reflection spectroscopy as well as by the measurement of changes in the ion concentration of the fluid. The induction time for apatite nucleation on the gel silica decreased as pore size and pore volume increased. The substrate parameters that affect nucleation are discussed and a mechanism that assumes pores as nucleation sites for hydroxyapatite is proposed.     

The role of hexafluorozirconate in the formation of chromate conversion coatings on aluminum alloys

Aluminum based surfaces are routinely coated with a chromate based layer that provides unparalleled corrosion protection. Widely used conversion coating treatment formulations contain hexafluorozirconate as a major constituent besides chromate, ferricyanide, fluoride, and fluoborate. The function of hexafluorozirconate is the subject of this study as its function is still largely unknown. Hydrophobicity, surface morphology, and the chemistry of the surface, resulting from treatment with hexafluorozirconate, were studied using contact angle measurements, scanning electron microscopy, and energy dispersive spectroscopy, respectively. X-ray photoelectron spectroscopy was extensively utilized to determine the chemistry of the surface resulting from the hexafluorozirconate pretreatment. Our results indicate that fluoride ion containing hexafluorozirconate complex does not attack the oxide film in a manner that uncomplexed simple fluoride ion does. Hexafluorozirconate is involved in the formation of an Al-Zr-O-F based hydrated layer that increases the hydrophilicity of the surface, activates the surface, and lowers the corrosion resistance. These factors enhance the interaction of chromate with the alloy surface to result in the formation of a uniform conversion coating. Based on these results, a new model has been proposed for the formation of chromate conversion coatings.     

SiO2-CaO-P2O5体系生物活性材料的制备研究

化程度的提高会使生物活性有所下降.另外陈化时间应以2 d为宜.     

Maleated High Density Polyethylene Compatibilized High Density Polyethylene/Hydroxyapatite Composites for Biomedical Applications: Properties and Characterization

The study investigated the use of maleated high density polyethylene (mHDPE) as a compatibilizer in high density polyethylene/hydroxyapatite (HDPE/HA) composites for biomedical applications. The addition of HA increased the strength and stiffness of HDPE/HA composites while the use of mHDPE in HDPE/HA composites improved its elongation at break values. The SEM images revealed that the addition of mHDPE has induced the formation of HDPE fibrils in mHDPE/HA composites. The size of apatite layer increased with simulated body fluid (SBF) immersion time and the formation of apatite layers on the surface of composites indicates excellent biocompatibility properties.     

HA/TCP双相陶瓷的生物矿化研究

采用新型动态体外模拟系统对HA/TCP双相陶瓷进行了体外生物矿化性能研究,通过SEM、EDAX、FT-IR等测试手段研究并分析了模拟体液流速以及钙磷离子补充在矿化过程中对样品表面磷灰石晶体生长影响.研究发现,较低的模拟体液流速下样品表面形成针片状碳酸化羟基磷灰石晶体,而在较高的流速下,晶片交错生长,形成网状结构,将样品表面完全覆盖.同时,模拟体液Ca2+的及时补充也有助于矿化层的形成.     

In vitro properties of nano-hydroxyapatite/chitosan biocomposites

In vitro behavior of the composites was performed in simulated body fluid (SBF) to induce the formation of bone-like apatite layer onto their surfaces and its enhancement in the presence of citric acid (CA). The results proved the mineralization of calcium (Ca²⁺) and phosphorus (P) ions onto the composites which contain high chitosan concentration especially after longer time of immersion. The degradation data decreased with increase chitosan content especially C2 composites (containing 30% chitosan) and highly decreased in the presence of CA which increased binding strength through the composite. The swelling % increased with increase of chitosan content in HA composite but it decreased with CA addition as increase of interaction between three matrices. The Fourier Transformed Infrared Spectroscopy (FT-IR) and Scanning Electron Microscope (SEM-EDAX) confirmed the formation of bone-like apatite layer on the surface of the composites especially these containing CA. These biocomposites have unique in vitro properties for bone substitute's applications in the future.     

Structural discrepancies and in vitro nanoapatite formation ability of sol–gel derived glasses doped with different bone stimulator ions

In this study, sol–gel derived glasses were prepared based on the following general formula: 25CaO–5MO–70SiO₂ (M = Ca, Sr, Zn), and development of a calcium phosphate (CP) layer on their surfaces was studied by soaking them in a simulated body fluid (SBF) for different periods. The consequent formation of the CP layer and structural discrepancies of the formed layer of various glasses were studied by means of appropriate techniques such as X-ray diffractometry, Fourier transform infrared spectroscopy and scanning electron microscopy equipped with an energy dispersive system (EDS). The concentration of Ca, Si and M ions released from the samples into the SBF was measured by using inductively coupled plasma-atomic emission spectroscopy. The effect of compositional changes on proliferation and activity of osteoblastic cells was evaluated by employing rat calvaria-derived cells.According to the mechanism reported in the literature a SiO₂-rich layer was initially formed on the surfaces of all glasses exposed to SBF. The results showed that CP formation ability of the glasses was strongly dependent on its chemical compositions. It was observed that the ability of calcium phosphate formation on the glass surfaces was inhibited by ZnO substitution, whereas the ternary CaO–SrO–SiO₂ system exhibits progressively improved nanostructured carbonated apatite layer on the glass surfaces in comparison to binary CaO–SiO₂ glass. The results of cell culture tests revealed that both Zn and Sr had stimulatory effect on cell responses; the rate of cell proliferation was enhanced by the former and alkaline phosphatase activity was improved by the latter.     

氟磷灰石-氟金云母微晶玻璃的生物活性研究

通过模拟细胞外液浸泡及动物骨内种植的方法研究了氟磷灰石-氟金云母微晶玻璃的生物活性机理。借助于SEM/EDAX,薄膜XRD,IRRS及原子吸收光谱分析等技术,研究了该微晶玻璃在生理环境中表面羟墓碘灰石层的形成过程。根据微晶玻璃中主晶相种类、显微结构特点及溶液中各离子的浓度等讨沦了羟基碑灰石层的形成机理。认为微晶玻璃中残余玻璃相的Ca~(2+)溶出及溶液相对于羟基磷灰石的过饱和状态,对材料表面羟基碑灰石层的形成具有重要意义。形成的羟基磷灰石层具有较低的结晶度,它是由最初的无定形态含水富CaO,P_2O_5薄层晶化转变而成。     

Preparation of Bioglasses Developed from Bypass Cement Dust for Bone Regeneration and Comparing Their Radiation Damage Prediction with Natural Bone

Cement industry causes many respiratory diseases due to the formation of bypass cement dust (BCD) as by-product. For this purpose a new study to get ride BCD from the environment by prepared three selected bioglasses samples with composition Na₂O₍₁₀₎?+?P₂O_5(90-x)?+?BCD_(x) where x value?=?10, 20, 30 in mol%. BCD contains an appropriate amount of calcium ions that can contribute in bioglass formulation for bone regeneration. Cooperative characterization for the prepared glasses were carried out through FTIR and SEM analysis before and after immersion in simulated body fluid (SBF) solution for up to 23 days at 37 °C. Therefore, the three samples can only be directly compared in the range of BCD content between 10 and 30 wt.%. After immersion in SBF, porous apatite layer is formed on the glass surface after 13 days and become denser after 23 days. Our results showing that, the porous hydroxy apatite layer was formed faster in the BCD 30 sample than in the BCD10 and BCD 20 samples. Further, SEM analysis revealed the formation of highly porous apatite layer on the composite surfaces when immersed in SBF solution at 37 °C. These porous structures provide channels for bone in growth and improve the microscopic bioresorption. The predicting radiation damage and atomic displacements per atom in BCD-30 sample if it was implanted to a patient exposed to radiotherapy or x-rays has been calculated and compared with natural bone. The gamma shielding parameters, mass stopping power (MSP), range for both proton (H-ions) and alpha (He-ions) in bioglass-BCD-30 and human bone tissue have estimated.

     

预钙化加速类骨磷灰石在镍钛合金表面生长的电化学阻抗谱

通过酸碱处理活化NiTi合金表面,在模拟体液中仿生生长类骨磷灰石层以改善其生物相容性.采用电化学阻抗谱研究了预钙化对加速磷灰石沉积的影响,并基于双层模型建立了电子等效电路.结果表明:随着在模拟体液中浸泡时间的延长,化学处理的NiTi合金表面类骨磷灰石不断生长,并且添加预钙化试样浸泡3 d,即可在合金表面生长出均匀完整的类骨磷灰石层,而未预钙化试样表面沉积物稀少.对应电子等效电路中,预钙化试样电阻值明显大于未预钙化试样的,显示预钙化促进了活化NiTi合金表面类骨磷灰石的生长.