Preparation and applications of a variety of fluoroalkyl end-capped oligomer/hydroxyapatite composites

A variety of fluoroalkyl end-capped oligomers were applied to the preparation of fluorinated oligomer/hydroxyapatite (HAp) composites (particle size: 38-356 nm), which exhibit a good dispersibility in water and traditional organic solvents. These fluoroalkyl end-capped oligomer/HAp composites were easily prepared by the reactions of disodium hydrogen phosphate and calcium chloride in the presence of self-assembled molecular aggregates formed by fluoroalkyl end-capped oligomers in aqueous solutions. In these fluorinated HAp composites thus obtained, fluoroalkyl end-capped acrylic acid oligomers and 2-methacryloyloxyethanesulfonic acid oligomer/HAp nanocomposites afforded transparent colorless solutions toward water; however, fluoroalkyl end-capped N,N-dimethylacrylamide oligomer and acryloylmorpholine oligomer were found to afford transparent colorless solutions with trace amounts of white-colored HAp precipitants under similar conditions. HAp could be encapsulated more effectively into fluorinated 2-methacryloyloxyethanesulfonic acid oligomeric aggregate cores to afford colloidal stable fluorinated oligomer/HAp composites, compared to that of fluorinated acrylic acid oligomers. These fluorinated oligomer/HAp composites were applied to the surface modification of glass and PVA to exhibit a good oleophobicity imparted by fluorine. HAp formation was newly observed on the modified polyethylene terephthalate film surface treated with fluorinated 2-methacryloyloxyethanesulfonic acid oligomers and acrylic acid oligomer/HAp composites by soaking these films into the simulated body fluid.     

DNA/羟基磷灰石杂化膜修饰电极用于研究DNA与量子点的相互作用

首次利用溶胶-凝胶一步法制备了纳米多孔羟基磷灰石(HAp)-DNA杂化膜修饰玻碳电极,HAp优良的生物相容性和独特的吸附性可以将DNA固定在HAp多孔薄膜上,而DNA的大分子结构对HAp膜起到稳定剂的作用.采用循环伏安法和交流阻抗法系统地研究了电极表面固定DNA的稳定性以及固定的DNA与非电活性核壳型量子点CdTe/C...     

Effect of preparative conditions on crystallinity of apatite particles obtained from simulated body fluids

Preparation of colloidal hydroxyapatite (HAp) particles under body fluid conditions was investigated with focusing on the effect of preparative conditions on crystallinity of the resulting particles. Tris(hydroxymethyl)aminomethane was added to 1.5SBF (a solution having 1.5 times higher ion concentrations than those of a simulated body fluid, SBF) to increase the solution pH, which resulted in induction of homogeneous nucleation of HAp in the solution. Colloidal HAp particles having diameters about 300 nm were obtained. When the reaction was proceeded at 70°C and the sample was dried by heating, it was effective to obtain HAp particles having high crystallinity. Experimental results support that remaining water in the sample contributed to increase HAp crystallinity.     

Preparation and applications of novel fluoroalkyl end‐capped vinyltrimethoxysilane oligomer/hydroxyapatite nanocomposites

Novel fluoroalkyl end‐capped vinyltrimethoxysilane oligomer/hydroxyapatite (HAp) nanocomposites were prepared by the reaction of calcium nitrate tetrahydrate and phosphoric acid in the presence of the corresponding oligomer. These fluorinated oligomer/HAp composites thus obtained are nanometer size‐controlled fine particles (83–173 nm), and were found to exhibit good dispersibility in methanol, ethanol, and isopropyl alcohol. These fluorinated HAp nanocomposites were applied to the surface modification of glass and poly(methyl methacrylate) (PMMA) to exhibit good hydro‐ and oleophobic characteristics imparted by fluorine on their surface. In addition, the surface structural changes of the modified polyethylene terephtalate and PMMA films treated with these fluorinated nanocomposites before and after soaking in a simulated body fluid (SBF) were analyzed by using SEM, XRD, and EDX to observe the formation of spherical HAp deposits on the surface. Copyright © 2009 John Wiley & Sons, Ltd.     

In situ monitoring by DSC and modeling of curing of vinyl polysiloxanes in layered silicate nanocomposites

The study of curing mechanism and the related kinetics in montmorillonite/vinyl-terminated polysiloxane nanocomposites was carried out. Commercially unmodified montmorillonite, as well as two different types of organically modified products, under the trade names: Nanofil 116, Cloisite 20A and Cloisite 30B, respectively, was used as the reinforcing nanofillers. The vulcanization reaction was followed by isothermal and non-isothermal differential scanning calorimetry analysis. The Cloisite 20A/PDMS systems showed increased reaction rate at the early stages of cross-linking, followed by a retardation of the rate and extension of curing time, with respect to the pure PDMS. On the other hand, Cloisite 30B decreases the curing rate of PDMS during the whole process, whereas a significant increase in this parameter was recorded in the case of unmodified clay/PDMS nanocomposites. This diversity of the effect of various types of fillers was attributed to physicochemical interactions between the cross-linking system and organoclay particles mainly due to their surface chemistry. In an attempt to further evaluate the obtained results, it was found that the autocatalytic model shows good fitting with the experimental data.     

Alkoxysilane functionalized polycaprolactone/polysiloxane modified epoxy resin through sol-gel process

Incorporating elastic polysiloxane and/or an inorganic silica network in epoxy resin could result in the enhancement of physico-chemical properties due to the existence of Si-O bonds. To improve the compatibility between polysiloxane and epoxy matrices and intensively strengthen the properties of the modified system, here polysiloxane was introduced into epoxy resin through compatibilizing epoxy-immiscible polysiloxane with epoxy-miscible polycaprolactone segments via a sol-gel process. To fulfill the process, a blend containing alkoxysilane-functionalized polycaprolactone/polydimethylsiloxane (PCS-2Si) was firstly synthesized using direct nucleophilic addition between -OH groups of polydiol and -NCO of a silane. And then a series of modified epoxy resins were prepared in different epoxy/PCS-2Si weight ratios. All the modified composites were characterized by conventional methods, and their morphological, thermal degradation and surface properties were studied. The results showed that increasing the PCS-2Si content caused the changes of miscibility between epoxy and polysiloxane. Also, the thermal stability of the modified composites was greatly improved. As for the temperature value at 5% weight loss, it reached to 308.5 °C for the composite containing 50-60% (wt%) PCS-2Si, over 150 °C higher than that for neat amine-cured epoxy resin. Similarly, the modified composites showed good hydrophobicity. The improvement of these properties came from the improved interaction between PCS-2Si and epoxy, the forming of Si-O-Si network and the enrichment of siloxane chains on the surface of films. Therefore, it is believed that this modified epoxy appears promising as new high performance and highly functional materials.     

Systematic evolution of a porous hydroxyapatite-poly(vinylalcohol)-gelatin composite

Hydroxyapatite (HAp)-poly(vinylalcohol) (PVA)-gelatin nanocomposite was biomimetically synthesized and characterized. Fourier transform infrared spectroscopy (FT-IR) analysis of hydroxyapatite, hydroxyapatite-poly(vinylalcohol) and hydroxyapatite-poly(vinylalcohol)-gelatin composites show modification of hydroxyl, amide and phosphate bands as a result of chemical interaction of hydroxyapatite with the above composite matrices. Transmission electron microscopy (TEM) confirmed the time-dependent development of a porous structure of hydroxyapatite-poly(vinylalcohol)-gelatin as a consequence of nucleation at the HAp aggregate-matrix interface. A literature survey holds great promise for the above as scaffolds in terms of increased mechanical properties and bioactivity.     

Electrophoretic Deposition of Hydroxyapatite Coatings on Metal Substrates: A Nanoparticulate Dual-Coating Approach

Hydroxyapatite coatings can be readily deposited on metal substrates by electrophoretic deposition. However, subsequent sintering is highly problematic owing to the fact that temperatures in excess of 1100°C are required for commercial hydroxyapatite powders to achieve high density. Such temperatures damage the metal and induce metal-catalysed decomposition of the hydroxyapatite. Furthermore, the firing shrinkage of the hydroxyapatite coating on a constraining metal substrate leads to severe cracking. The present study has overcome these problems using a novel approach: the use of aged nanoparticulate hydroxyapatite sols (lower sintering temperature) and a dual coating strategy that overcomes the cracking problem. Dual layers of uncalcined hydroxyapatite (HAp) powder were electrophoretically coated on Ti, Ti6Al4V and 316L stainless steel metal substrates, sintered at 875–1000°C, and characterised by SEM and XRD, and interfacial shear strength measurement. Dual coatings on stainless steel had an average high bond strength (about 23 MPa), and dual coatings on titanium and titanium alloy had moderate strengths (about 14 and 11 MPa, respectively), in comparison with the measured shear strength of bone (35 MPa). SEM and XRD demonstrated that the second layer blended seamlessly with the first and filled the cracks in the first. The superior result on stainless steel is attributed to a more appropriate thermal expansion match with hydroxyapatite, the thinner oxide layer, or a combination of these factors.     

Poly(dimethylsiloxane)/palygorskite composites: preparation,characterization, and properties

Poly(dimethylsiloxane) (PDMS) composites were prepared by simple blending process using palygorskite (PG) or modified palygorskite (MP). This study has been designed to determine the influences of PG or MP on the thermal stability and the mechanical properties of PDMS composites. The thermal stability of PG and MP were also studied by thermogravimetric analysis (TGA). The results showed that MP had the similar thermal stability to PG, and PG or MP not only increased the thermal stability but also improved the mechanical properties of PDMS composites. Meanwhile, compared with PG/PDMS composites, MP/PDMS composites had better thermal stability and mechanical properties owing to the better dispersion of MP into the matrix, the stronger chemical interfacial interaction between MP and the matrix. Copyright © 2010 John Wiley & Sons, Ltd.     

Composites of kaolin and polydimethylsiloxane

Kaolin particles were surface-treated with isobutyltrimethoxysilane (IBTMS), hydrogenated tallow (HT), and a polyisobutyl chain-based stabilizer (SAP) to make composites with polydimethylsiloxane (PDMS). IBTMS did not cover the strong acid sites on the kaolin surface and as a result a cross-linking reaction occurred for silanol-terminated PDMS. The polyisobutyl chain of SAP was found to be incompatible with PDMS and this caused aggregation of the kaolin particles. HT was the most effective at dispersing the particles into silanol-terminated PDMS. The aggregation state of the composites was characterized using rheology and microscopy. Both showed the HT-treated particles were well-dispersed in low molecular weight silanol-terminated PDMS, and they were weakly flocculated in higher molecular weight silanol-terminated PDMS. However, the same particles aggregated when dispersed in methyl-terminated PDMS. It appears the silanol-terminated PDMS acted as costabilizer through interaction with the kaolin surface. Transverse relaxation NMR was used to probe mobility of the PDMS chains in the composites. This showed little dependence on surface treatment, aggregation state, or polymer end groups. For all samples, chain mobility decreased with increasing kaolin concentration.     

Stability of cross-linked acetic acid lignin-containing polyurethane

The thermo-oxidative stability of acetic acid lignin-containing polyurethane (LPU) that contains cross-linking agents, such as 1-aminopropyltriethoxy-silane (APTS) and/or trimethylolpropane (TMP) was investigated based on the thermogravimetric analysis (TGA) method, their kinetic parameters in the thermo-oxidative process was determined. FT-IR certified the occurrence of interaction between lignin and polyurethane (PU). It was found that continuous membrane can be formed when lignin concentration was 43.3%, but rupture took place when it increased to 50%. When the degradation was performed in nitrogen, TG and dynamic differential thermogravimetry (DTG) results demonstrated that the PU underwent three stages of degradation while the LPU involved one main degradation stage with a shoulder, and the degradation stability increased with the increase in the lignin concentration and PEG length. It was also found that the addition of a cross-linking agent is beneficial to the improvement of thermal stability and, in particular, APTS gave the best thermal stability for the LPU produced, among the cross-linking agents tested. Furthermore, LPU exhibited multistage degradation process in air and displayed higher thermo-oxidative stability than PU. At the same time, the kinetic study showed that LPU modified with APTS exhibited higher activation energy than LPU modified with TMP. And the maximum activation energy was found for the sample modified with the simultaneous addition of APTS and TMP.     

羟基磷灰石/胶原矿化机理的研究进展

仿生合成的羟基磷灰石(HAp)/胶原复合材料的结构和成分与天然骨相似,具有很好的生物相容性、生物活性和生物可降解性,有望成为新一代的骨替代材料。羟基磷灰石/胶原矿化过程其实质是晶体在自组装的胶原纤维上形成的过程,但这一过程在体内是如何进行的至今仍然不清楚。对胶原矿化机理的研究能为制备具有更优越结构和功能的新型骨替代材料提供理论参考。本文概述了羟基磷灰石/胶原矿化机理的研究进展。     

Electrically polarized biphasic calcium phosphates: adsorption and release of bovine serum albumin

In this study, we applied electrical polarization technique to increase adsorption and control protein release from biphasic calcium phosphate (BCP). Three different biphasic calcium phosphate (BCP) composites, with hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP), were processed and electrically polarized. Our study showed that stored charge was increased in the composites with the increase in HAp percentage. Adsorption of bovine serum albumin (BSA), as a model protein, on the poled as well as unpoled surfaces of the composites was studied. The highest amount of BSA adsorption was obtained on positively poled surfaces of each composite. Adsorption isotherm study suggested a multilayer adsorption of BSA on the BCP composites. The effect of electrical polarization on BSA release kinetics from positively charged BCP surfaces was studied. A gradual increase in percent BSA release from positively charged BCP surfaces with decreasing stored charge was observed. Our study showed that the BCP based composites have the potential to be used as a drug or growth factor delivery vehicle.     

The Surface Structure of Hydroxyapatite Single Crystal and the Accumulation of Arachidic Acid

Single crystals of hydroxyapatite (HAp) were grown by a flux method using beta-tricalcium phosphate and Ca(OH)(2) under hot isostatic pressure. After chemical etching by 0.05 N HCl aqueous solution, the HAp crystal surfaces were observed by an atomic force microscope (AFM) and shown dominantly to consist of steps with heights corresponding to a lattice distance d(100) or its 2/3. Arachidic acid films were accumulated on the etched HAp crystal by a Langmuir-Blodgett method. From section analyses by AFM, a distance between the carboxyl groups of arachidic acid and the HAp surface was estimated to be approximately 0.04 nm, sufficiently adjacent for a chemical interaction to take place. Copyright 2000 Academic Press.     

DNA-纳米多孔羟基磷灰石修饰电极用于研究DNA与亚甲基蓝的相互作用

利用溶胶-凝胶法将具有优良生物相容性和独特吸附性的羟基磷灰石(HAp)修饰在玻碳电极上形成纳米多孔薄膜. 电化学实验结果证明该纳米多孔羟基磷灰石薄膜能有效地将双链DNA吸附于其表面. 采用循环伏安法系统研究了固定在HAp薄膜上的DNA与亚甲基蓝(MB)之间的相互作用. 实验结果表明, 在20～200 mV•s^－1扫描速度范围内该电极反应过程系表面反应控制; 在pH 6.0～7.4范围内, MB在DNA修饰电极上的峰电位随pH的增加而向负方向移动; 当磷酸盐缓冲溶液中的离子强度小于59 mmol•L^－1时, MB与DNA之间为静电作用, 当离子强度大于59 mmol•L^－1时, 二者之间既有静电作用, 也有部分嵌入作用. 根据Langmuir吸附公式, 得出MB与DNA之间的结合常数为4.2×10⁴ mol^－1•L.     

Modification of a hydrophilic linear polyurethane by crosslinking with a polydimethylsiloxane. Influence of the crosslink density and of the hydrophobic/hydrophilic balance on the water transport properties

A hydrophilic thermoplastic polyurethane (TPU) was modified by reactive extrusion to obtain in a first step a grafted and soluble material and to finally form by a hydrolysis condensation process a weakly crosslinked network. Different isocyanates were used as grafting agents and a α,ω‐dihydroxypoly(dimethylsiloxane) (PDMS) was used to modify the hydrophilic/hydrophobic balance of the material and the chain length between the crosslinks. The influence of the isocyanate functionality and of the PDMS content were studied on the network formation and on the thermomechanical and water sorption properties. The networks properties were also compared with those of a TPU/PDMS blend. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 48–61, 2006     

Facile synthesis and applications of polypropylene/polydimethylsiloxane graft copolymer

It is of great significance to synthesize polyolefin/polysiloxane hybrid materials due to their unique combination of crystalline polyolefin segments and semiorganic polysiloxane segments. Herein, we report the syntheses of a novel polypropylene/polydimethylsiloxane (PP‐g‐PDMS) graft copolymer via the coupling reactions between maleic anhydride‐grafted PP and monoaminopropyl‐terminated PDMS. The chemical structures of PP‐g‐PDMS have been characterized by Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR), and gel permeation chromatography (GPC). The correlation between reaction conditions and the structural parameters of PP‐g‐PDMS has been established. Consequently, the potential applications of resultant PP‐g‐PDMS were investigated, and the results showed that PP‐g‐PDMS can serve as an efficient compatibilizer in heterogeneous PP/PDMS blend system and also as an ideal processing aid for high‐viscosity PP.     

Biomimetic approach towards the preparation of hydroxyapatite and hydroxyapatite/chitosan/β-cyclodextrin nanoparticles: application to controlled drug release

Hydroxyapatite (HAp) and hydroxyapatite/chitosan/β-cyclodextrin (HAp/CS/β-CD) nanoparticles were successfully prepared in the modified simulated body fluid (SBF) solution at the physiological conditions (pH 7.4, temperature?=?37 °C). CS/β-CD nanoparticles acted as templates for the synthesis of HAp/CS/β-CD nanoparticles to improve the nanoarchitecture of HAp and its crystallinity.The nanoparticles were characterized by FT-IR spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD). Kneading and coprecipitation methods were applied to prepare the inclusion complex involving β-CD and p-THPP (5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin), a photosensitizer for anti-cancer drugs. The 1:1 stoichiometric ratio of the formed inclusion complex was characterized by a formation constant of 7.216?×?10² mol^?1 dm³ and analyzed by ¹H NMR, FTIR, and UV–Vis. The p-THPP delivery release in vitro was in this order: HAp/CS/β-CD?<?CS/β-CD?<?<?HAp/β-CD?<?β-CD, hinting at a better controlled release by HAp/CS/β-CD nanoparticles.     

Nanocrystalline hydroxyapatite: micelle templated synthesis and characterization

Nanocrystalline calcium phosphate based inorganic, hydroxyapatite (HAp), was synthesized using the dodecyl phosphate micelle system. The surfactant concentration during synthesis played an important role on the final properties of these HAp nanoparticles. A surfactant concentration close to the critical micelle concentration produced the nanoparticles with the highest surface area, with porous less agglomerated morphology. Compacts made of these nanopowders showed between 97 and 98% theoretical density of phase-pure HAp and promoted cell-material interaction when cytotoxicity tests were performed.     

A study on the melting and crystallization of polyoxymethylene‐copolymer/hydroxyapatite nanocomposites

In this work, isothermal crystallization kinetics of polyoxymethylene copolymer (POM) in POM/hydroxyapatite (HAp) nanocomposites has been investigated. Melting behavior and crystalline structure formation were studied using TOPEM DSC, positron lifetime spectroscopy (PALS), atomic force microscopy (AFM) and ¹³C and ³¹P solid‐state NMR. The highest degree of crystallinity was found for POM/0.5% HAp nanocomposite and the lowest for POM/2.5% HAp. Isothermal crystallization analysis showed that an introduction of HAp nanoparticles led to effective heterogeneous nucleation and formation of crystals with higher Avrami exponent. Besides, changes in overall crystallization rate were observed – the highest overall crystallization rate was found for POM/0.5% HAp sample, while the lowest for POM/2.5% HAp was observed. Generally, for POM in POM/HAp nanocomposites, a significant decrease in nucleation activation energy (K_g), and the fold surface free energy (σ_e) was found. For nanocomposite containing 2.5% HAp, heterogeneous nucleation takes place as well, but too high concentration of nanoparticles hinders POM crystallization and enhances formation of more defected crystals as confirmed by AFM data. The presence of HAp nanoparticles in the POM matrix was confirmed by ³¹P MAS‐NMR, but their influence on the crystallization process was not observed in the ¹³C CP‐MAS‐NMR spectra. Copyright © 2012 John Wiley & Sons, Ltd.