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.     

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.     

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.     

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.     

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.     

Direct Observation of Apatite Formation on Bioglass in Simulated Body Fluid by Atomic Force Microscopy

An in situ atomic force microscope (AFM) combined with surface potential measurement was used to observe the apatite formation on the 45S5 Bioglass-type glass in simulated body fluid (SBF). From the observation, it can be seen that small islands with 5-10 nm size are formed on the glass surface in the initial soaking period within 1 h.     

以滤纸为模板合成新型介孔生物活性玻璃微管材料

用快速滤纸为生物模板,通过先浸渍后焙烧的方法合成了介孔生物活性玻璃微管材料。快速滤纸的管状结构被完美复制,其管壁为生成的介孔生物玻璃材料。通过在合成过程中引入铁元素可以使材料具有一定的磁性。材料的形貌、结构和磁性通过扫描电镜、粉末X射线衍射、透射电镜、氮气吸附-脱附曲线,红外光谱和磁滞回线进行了表征。并且通过模拟体液浸泡方法考察了其矿化能力,以地塞米松为模型药物考察其释药能力和生物相容性。合成的介孔生物活性玻璃微管材料具有复杂的管状多级结构、快速的矿化能力和良好的生物相容性,并具备一定的磁性,是一种不可多得的药物缓释材料。     

以滤纸为模板合成新型介孔生物活性玻璃微管材料

用快速滤纸为生物模板,通过先浸渍后焙烧的方法合成了介孔生物活性玻璃微管材料。快速滤纸的管状结构被完美复制,其管壁为生成的介孔生物玻璃材料。通过在合成过程中引入铁元素可以使材料具有一定的磁性。材料的形貌、结构和磁性通过扫描电镜、粉末X射线衍射、透射电镜、氮气吸附-脱附曲线,红外光谱和磁滞回线进行了表征。并且通过模拟体液浸泡方法考察了其矿化能力,以地塞米松为模型药物考察其释药能力和生物相容性。合成的介孔生物活性玻璃微管材料具有复杂的管状多级结构、快速的矿化能力和良好的生物相容性,并具备一定的磁性,是一种不可多得的药物缓释材料。     

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.      

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.     

Bioactivity and Viscoelastic Characterization of Chitosan/Bioglass® Composite Membranes

Membranes of chitosan (CTS) and composite membranes of CTS with bioglass are prepared by solvent casting. The composite membranes are shown to induce the precipitation of apatite upon immersion in SBF. The biomineralization process is followed by measuring the variation of the viscoelastic properties of the membranes immersed in SBF, both online and offline. Non‐conventional DMA is used to measure the change in the storage modulus, E′, and the loss factor, tan δ, as a function of the immersion in SBF. A simple model is used to estimate the E′ of the apatite layer formed in vitro that is about 130 MPa. This work shows that innovate mechanical tests can be useful to characterize the mechanical performance of composites under physiological conditions.

     

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.     

Mechanical Properties and In Vitro Physico‐chemical Reactivity of Gel‐derived SiO2–Na2O–CaO–P2O5 Glass from Sand

In the present report, a bioactive glass was synthesized from silica sand as economic substitute to alkoxy silane reagents. Sodium metasilicate (Na₂SiO₃) obtained from the sand was hydrolyzed and gelled using appropriate reagents before sintering at 950 °C for 3 h to produce glass in the system SiO₂? Na₂O? CaO? P₂O₅. Compression test was conducted to investigate the mechanical strength of the glass, while immersion studies in simulated body fluid (SBF) was used to evaluate reactivity, bioactivity and degradability. Furthermore, the glass samples were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and energy dispersive X‐ray spectroscopy (EDX) to evaluate the microstructure and confirm apatite formation on the glass surface. The glass, dominated by bioactive sodium calcium silicate, Na₂Ca₂Si₃O₉ (combeite) crystals, had mechanical strength of 0.37 MPa and showed potentials for application as scaffold in bone repair.     

A study on biomineralization behavior of N-methylene phosphochitosan scaffolds

Biomimetic growth of calcium phosphate over natural polymer may be an effective approach to constituting an organic/inorganic composite scaffold for bone tissue engineering. In this work, N-methylene phosphochitosan (NMPCS) was prepared via formaldehyde addition and condensation with phosphoric acid in a step that allowed homogeneous modification without obvious deterioration in chitosan (CS) properties. The NMPCS obtained was characterized by using FT-IR and elemental analysis. The macroporous scaffolds were fabricated through a freeze-drying technique. A comparative study on NMPCS and CS scaffold biomimetic mineralization was carried out in different media, i.e, a simulated body fluid (SBF) or alternative CaCl(2) and Na(2)HPO(4) solutions respectively. Apatite formation within NMPCS and CS scaffolds was identified with FT-IR, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and X-ray diffractometery (XRD). The results revealed alternate soaking of the scaffolds in CaCl(2) and Na(2)HPO(4) solutions was better than soaking in SBF solution alone in relation to apatite deposition on the scaffold pore walls. Biomineralization provides an approach to improve nature derived materials, e.g., chitosan derivative NMPCS properties e.g., compressive modulus, etc. SEM image of a NMPCS/apatite composite scaffold.     

Mineralization of HA crystals regulated by terephthaloyl chloride-modified silk fibroin films

Terephthaloyl chloride(DB)-modified silk fibroin(SF) films were immersed into 1.5 times simulated body fluid(1.5 SBF) to regulate the mineralization of hydroxyapatite(HA) crystals at about 36.5℃for 24 h.UV was used to prove that the new bonds form between the DB and SF.The structure and morphology of the SF/HA were investigated by FTIR,ICP,XRD and SEM.The results showed that the apatite deposited on the matrix of SF mainly was HA.HA was self-assembled on the matrix of SF and formed three-dimensional framework when the weight ratio of DB/SF was 0.30.The content of DB affected the structure and morphology of the apatite composites deposited on the SF films.     

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。     

Bioactivity of a Bio-composite Fabricated from CoCrMo/Bioactive Glass by Powder Metallurgy Method for Biomedical Application

In present times, researchers are attracted towards studies on biocomposite as a potential biodegradable bone implant materials. Bioactivity of the composite in a simulated body fluid (SBF) was investigated. A porous Co-Cr-Mo based composite material with bio-glass 45S5 was produce by using powder metallurgy method (PM) technology. Prepared composite powders were cold pressed and sintered at 1000 °C for 2 h. X-ray diffraction (XRD), scanning electron microscopy were used for phase analysis and also for evaluation of particle distribution of composites. Bioactivity behaviour of the prepared nanocomposites was evaluated in simulated body fluid (SBF) for 1 up to 18 days. The results showed that the apatite layer were formed on the surface of sample with addition of bioactive glass. It was concluded that bioinert Co-Cr-Mo alloy could be successfully converted into bioactive composite by adding 6 wt% of BG particles.     

Recyclable hydrophilic-hydrophobic micropatterns on glass for microarray applications

A novel method for fabricating recyclable hydrophilic-hydrophobic micropatterns on glass chips is presented. TiOx patterns (100-2000 microm) were sputtered on glass chips via a through-hole mask. The patterned chips were then vapor-coated with fluoroalkylsilane, for example, (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (FTES) to form a hydrophobic coating layer. The fluoroalkyl chain of FTES film on TiOx patterns was photocleaved under UV irradiation, exposing the fresh hydrophilic TiOx patterns. The resulting chip could be used multiple times by repeating the coating and photocleaving processes with negligible deterioration of the hydrophobic FTES film coated on glass. If desired, bare glass patterns could also be generated by removing the TiOx patterns with KOH. The patterned glass chips have been successfully used for microarray fabrication.     

Negative dielectrophoretic patterning with colloidal particles and encapsulation into a hydrogel

Microparticle patterns have been fabricated on a nonconductive glass substrate and a conductive indium tin oxide (ITO) substrate using negative dielectrophoresis (n-DEP). The patterned microparticles on the substrate were immobilized by covalent bonding or embedded into polymer sheets or strings. The patterning device consisted of an ITO interdigitated microband array (IDA) electrode as the template, a glass or ITO substrate, and a polyester film (10-microm thickness) as the spacer. A suspension of 2-microm-diameter polystyrene particles was introduced into the device between the upper IDA and the bottom glass or ITO support. An ac electrical signal (typically 20 Vpp, 3 MHz) was then applied to the IDA, resulting in the formation of line patterns with low electric field gradient regions on the bottom support. When the glass substrate was used as the bottom support, the particles aligned under the microband electrodes of the IDA within 5 s because the aligned areas on the support were regions with the weakest electric field; however, for the ITO support, the particles were directed to the regions under the electrode gap and aligned on the support because these regions had the weakest electric field. The width of the particle lines could be roughly controlled by regulating the initial concentration of the suspended particles. The particles forming the line and grid patterns with single-particle widths were immobilized by using a cross-linking reaction between the amino groups on the aligned particles and N-hydroxysuccinimide-activated ester on the glass substrate activated by succinimidyl 4-(p-maleimidophenyl)-butyrate (SMPB). The patterned particles were also embedded in a photoreactive hydrogel polymer. A prepolymer solution of poly(ethylene glycol) diacrylate (PEG-DA) was used as the suspension medium to maintain the particle patterns in the polymerized hydrogel sheet and string following photopolymerization. The hydrogel sheets with particle patterns were fabricated by ultraviolet (UV) irradiation through the ITO-IDA template for 120 s. Hydrogel strings with the aligned particles were fabricated by using a conductive ITO support and a Pt-IDA template. Pt-IDA was used as a template as well as a photomask to block UV transmission. The present procedure affords extremely simple, rapid, and highly reproducible fabrication of particle arrays. The reusability of the template IDA electrode is also a substantial advantage over previous methods.