Surface modification of magnetron-sputtered hydroxyapatite thin films via silicon substitution for orthopaedic and dental applications

There have been a significant advances made in the field of bioceramics, particularly hydroxyapatite (HA) during the past 10 years. Emphasis has now shifted towards designing HA with enhanced bioactivity for bone tissue repair. The aim of this study was to assess whether surface wettability can be correlated with cellular interactions with silicon-substituted hydroxyapatite (SiHA)-coated titanium (Ti) substrates. SiHA thin coatings of varying Si compositions were deposited on Ti substrates via a magnetron co-sputtering technique. These coatings were then subjected to an in vitro study using primary human ostoeblast (HOB) cells, to evaluate their biological property. HOB cells showed initial poor adhesion and spreading on hydrophobic Ti surface. The application of HA or SiHA thin coatings on Ti substrates by magnetron co-sputtering technique renders the surface more hydrophilic, with water contact angles between 30 and 40°. HOB cells attached, spread and proliferated well on these coatings. Enhanced calcification (formation of calcium phosphate nodules across the collagenous matrices) was observed on SiHA coatings with increasing Si content. This interdisciplinary paper highlighted that enhanced bioactivity was associated with surface wettability. Producing a nanostructured HA coating on a Ti substrate by magnetron sputtering resulted in the promotion of cell proliferation and calcification, and the latter was further enhanced with Si substitution. Hence, SiHA thin coating holds great potential as an alternative dental material.     

Atomistic simulations of surface segregation of defects in solid oxide electrolytes

We performed atomistic simulations of yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (GDC) to study the segregation of point defects near (1 0 0) surfaces. A hybrid Monte Carlo–molecular dynamics algorithm was developed to sample the equilibrium distributions of dopant cations and oxygen vacancies. The simulations predict an increase of dopant concentration near the surface, which is consistent with experimental observations. Oxygen vacancies are also found to segregate in the first anion layer beneath the surface and to be depleted in the subsequent anion layers. While the ionic size mismatch between dopant and host cations has been considered as a driving force for dopant segregation to the surface, our simulations show that the correlation between individual point defects plays a dominant role in determining their equilibrium distributions. This correlation effect leads to more pronounced dopant segregation in GDC than in YSZ, even though the size mismatch between dopant and host cations is much greater in YSZ than in GDC.     

In situ AFM detection of pit onset location on a 304L stainless steel

A set-up combining an AFM and an electrochemical cell has been used to study in situ the local corrosion of a 304L stainless steel in an aqueous chloride-containing solution. The focus was made on the sites where pits were initiated under controlled potential in order to establish whether or not the pits were randomly distributed at the nanoscale. Grain boundaries and surface stoichiometric inhomogeneities appeared to concentrate pit onsets significantly. The influence of the mechanical history of the material, especially soft surface strain hardening, on the location of the first pits has been shown. The study revealed that 70% of the pits initiated at strain hardened areas resulting from mechanical polishing. A plausible model has been suggested to explain such a behaviour.     

退火温度及TiO_2结构对羟基磷灰石的沉积诱导作用

采用阳极氧化法在钛金属表面制备TiO2薄膜,将表面改性的钛金属在过饱和钙化溶液中浸泡,在其表面沉积羟基磷灰石,研究了退火处理温度对TiO2薄膜晶型转变的影响以及TiO2的晶型结构对羟基磷灰石的诱导沉积作用。研究表明,300℃退火处理,TiO2薄膜为板钛矿相,500℃退火处理转变为锐钛矿相,高于500℃退火处理,锐钛矿相开始向金红石相转变。其中锐钛矿相的TiO2对羟基磷灰石的沉积具有最好诱导作用,沉积物分布均匀,板钛矿相对羟基磷灰石的诱导作用最差,所形成的沉积层是由片状的羟基磷灰石围成的多孔结构。     

Characterization and Corrosion Behavior of Functional Gradient Hydroxyapatite Coating

The aim of the present work is to examine the characterization and corrosion behavior of functional gradient hydroxyapatite coating deposited on titanium-based alloy by plasma spray coating process. The functionally graded coating is designed to provide the crystalline hydroxyapatite at the interface with metallic substrate and the amorphous hydroxyapatite at the outer surface. It is considered that the top amorphous layer of hydroxyapatite has higher bioactivity, and its initial dissolution will lead to bone tissue growth enhancement and bonding, whereas the underneath crystalline hydroxyapatite coating after heat treatment is expected to enhance the long-term stability of coating at the interface with metal. The heat treatment of the underneath as-sprayed coating for crystallization was performed at 700 °C for 1 h. The characterization of the coatings was performed by various techniques such as scanning electron microscopy, energy-dispersive x-ray spectroscopy, x-ray diffraction analysis, surface roughness, and microhardness. It was observed from potentiodynamic scan that heat-treated coating exhibited better dissolution resistance as compared to the as-sprayed coating. Heat treatment of the hydroxyapatite coating resulted in improved crystallinity of the coating which may provide long-term stability to the coating.     

The effects of dopant on morphology formation in polyaniline graphite nanoplatelet composite

In this study, a nanocomposite (SELA-PANi/GNP) consisting of selenious acid (SELA) doped polyaniline (PANi) and graphite nanoplatelet (GNP) was prepared, and its structure and properties – in particular, morphology formation, as well as interaction between the two phases – were investigated using scanning electron microscopy (SEM), UV–vis spectroscopy, FTIR spectroscopy, X-ray diffraction, and electrical conductivity measurement. A PANi/GNP nanocomposite prepared in aqueous HCl solution (HCl-PANi/GNP) was also prepared for comparison with SELA-PANi/GNP. The results reveal that the dopant plays an important role in morphology formation in PANi/GNP nanocomposites. When HCl was used as the dopant, PANi coated GNPs were formed and no phase separation between PANi and GNP was seen. In contrast, when SELA was used as the dopant, the morphology of PANi remained unchanged in the composite, owing to the formation of rod or sphere micelle PANi structure during in situ polymerization; no interaction was observed between the two phases. The crystalline structure of PANi was not affected by the incorporation of GNP. The electrical conductivity of PANi/GNP increased with increasing GNP content, because of the electrical bridge effect of GNP in the PANi matrix.     

Structure and properties of selenious acid doped polyaniline with varied dopant content

In this study, the effects of dopant content on the structure, especially crystalline structure, and properties of selenious acid doped polyaniline (PAni) were investigated. The structure and properties of PAni were characterized by X-ray diffraction, FTIR spectroscopy, UV–vis spectroscopy, DSC, and TGA. By varying the dopant/monomer molar ratio (D/M), the morphology as well as the crystalline structure of PAni was significantly changed. The presence of water in the crystalline structure of PAni prepared with a low D/M ratio caused a change in the d-spacing of the PAni crystalline structure. The oxidation level and doping degree of PAni were also changed by varying the D/M ratio. The electrical conductivity of PAni increased with increasing D/M ratio, and the thermal stability of PAni in the doped state was about 200 °C for different D/M ratios.     

Layered nanostructures of polyaniline with graphene oxide as the dopant and template

Novel layered structures of polyaniline (PANI) doped with graphene oxide (GO) were directly prepared by adding GO aqueous solution into the emeraldine base form of PANI (PANI-EB) dissolved in a mixture solution of m-cresol and ethanol. The method is simple and inexpensive because of saving inorganic or organic acids as the dopant, opening a new way to prepare hybrid materials of PANI with GO. It was proposed that the π–π planar structure of GO and the carboxyl groups on the surface of GO are served as the template and dopant, respectively that results in the formation of the layered structures. The doping function of GO in the PANI-GO has been proved by structural characterizations and conductivity measured by a four-probe method.     

单相、双相及多相离子掺杂的羟基磷灰石研究进展

羟基磷灰石是天然骨组织成分中的重要组成部分,一直是生物医学领域关注和研究的重点。天然骨成分中的磷灰石,是一种结合着多种离子的羟基磷灰石,维持着生命系统的正常生长与发育。本研究阐述了羟基磷灰石的晶体结构;概述了研究者针对羟基磷灰石性能探究,其中包括生物相容性、生物活性、适宜的机械强度、优异的成骨性能和耐腐蚀性能。同时归纳了离子掺杂羟基磷灰石取代位点。在此基础上,重点阐述了近五年来单相、双相以及多相掺杂羟基磷灰石材料的研究,其中包括单相、双相以及多相离子掺杂对羟基磷灰石在结构性能、机械强度、抗菌性、降解性和成骨性等性能的影响,同时简单总结了离子掺杂对机械强度的影响规律。近年来虽然羟基磷灰石生物陶瓷材料在临床上作为植入物涂层、缓释药物的载体、骨移植物代替材料等被应用,但在临床方面广泛运用还面临着许多问题与挑战,所以本文同时展望了离子掺杂羟基磷灰石未来的的发展方向,有望在临床应用及发展方面有一定的指导意义。     

Preparation and bioactivity evaluation of bone-like hydroxyapatite nanopowder

Calcium phosphate ceramic such as hydroxyapatite (HA) is good candidate for bone substitutes due to their chemical and structural similarity to bone minerals. The bone mineral consists of tiny hydroxyapatite crystals in the nanoregime. Nanostructured hydroxyapatite is also expected to have better bioactivity than coarser crystals. This paper reports on the preparation and in vitro evaluation of bone-like hydroxyapatite nanopowder. The sol–gel prepared hydroxyapatite nanopowder was characterized for its phase purity, chemical homogeneity and bioactivity. Fourier transform infrared (FTIR) spectroscopy was used to identify the functional groups. X-ray diffraction (XRD) analysis was carried out to study the phase composition, crystallinity and the crystallite size of hydroxyapatite nanopowders that were sintered at different temperatures. The in vitro test was performed in a stimulated body fluid (SBF) medium. The changes of the pH of SBF medium were measured at pre-determined time intervals using a pH meter. The dissolution of calcium ions in SBF medium was determined by an atomic absorption spectrometer (AAS). FTIR result combined with the X-ray diffraction exhibited single phase of hydroxyapatite with carbonate peaks in the FTIR spectrum. The results indicate that increasing the sintering temperature increases the crystallinity and the crystallite size of hydroxyapatite nanopowders. Photomicrograph of transmission electron microscopy (TEM) showed that the obtained powder after sintering at 600 °C is composed of hydroxyapatite nanoparticles (20–30 nm). Dissolution rate of hydroxyapatite nanopowders was higher than conventional hydroxyapatite powders and closer to biological apatite due to its nanostructure dimensions. It was concluded that sol–gel prepared hydroxyapatite nanopowders had superior bioresorption and similar chemical and crystal structure to natural bone apatite.     

Preparation and cell-materials interactions of plasma sprayed strontium-containing hydroxyapatite coating

The use of strontium-containing hydroxyapatite (Sr-HA) as a biomaterial has been reported recently. In vitro and in vivo studies have shown that Sr-HA promotes osteoblast response and stimulates new bone formation. In order to extend its usage to major load-bearing applications, such as artificial hip replacement, it has been proposed that the material could be used in the form of a coating on implant surfaces. This paper reports a preliminary study of biocompatibility of plasma sprayed Sr-HA coatings on a metallic substrate. Coatings of Sr-HA containing 10 mol% Sr²⁺ was produced on titanium alloy substrates. The coating exhibited good bonding with the substrate. The bioactivity of Sr-HA coating was evaluated in vitro by immersion in simulated body fluid (SBF). After immersion in SBF, Sr-HA coating exhibited great ability to induce apatite precipitation on its surface. The possible effects of cell-materials interactions of Sr-HA coating were examined by culturing osteoprecursor cells (OPC1) on coating surfaces. The effect of Sr-HA was also compared to a hydroxyapatite (HA) coating, which is widely used in orthopedics and dentistry. The results indicated that Sr-HA coating had good biocompatibility with human osteoblasts. OPC1 cells survived and proliferated well on the surface of coating. Sr-HA coating promoted OPC1 cells attachment, and more local contacts were produced on the surface. The presence of Sr stimulated OPC1 cell differentiation and ALP expression. No deleterious effect on ECM formation and mineralization was found with Sr-HA coating. The results indicated that Sr-HA coating had good mechanical properties and bioactivity in vitro.     

Preparation and in vitro biocompatibility of hybrid oxide layer on titanium surface

A new technique combining microarc oxidation (MAO) and electrophoresis was introduced to develop a biocompatible oxide layer on pure titanium implant surface. Originally developed alkaline electrolyte containing nano-scale hydroxyapatite powder suspension was used in the new technique. In the electric field, nano-scale hydroxyapatite powder was electrophoretically moved and sintered into the gradually-formed oxide layer on titanium anode. Physio-chemical properties and in vitro biological performance of the newly-formed surface were examined and evaluated. A 8.5-μm thick oxide layer with high surface energy and roughness, which was composed of titanium dioxide and calcium phosphates as well as hydroxyapatite, was formed on titanium surface by the modified MAO technique. Osteoblasts cultured on the modified MAO titanium surface showed significantly increased alkaline phosphatase (ALP) activity comparing to machined and MAO titanium surface. Natural oxide surface of titanium could be transformed into a hybrid oxide layer by modified MAO treatment. The modified titanium surface, which is rough and porous, contains calcium phosphates and proved to be more biocompatible in vitro.     

A real time neutron diffraction study on the reaction of AsF5 with deuterated polyparaphenylene

The doping of deuterated polyparaphenylene [C₆D₄0]_n with AsF₅ has been investigated by real time neutron diffractometry at 100, 400 and 820 mbar AsF₅ pressure. The reaction appears to be diffusion controlled. Evidence for one doped phase with partial crystalline order was obtained. Structural considerations suggest two polymer chains plus one dopant “string” as the repetitive unit.     

Preparation of titanium oxide and hydroxyapatite on Ti–6Al–4V alloy surface and electrochemical behaviour in bio-simulated fluid solution

In order to improve the bonding strength between hydroxyapatite (HA) coating and Ti–6Al–4V substrate, a uniform titanium oxide film was obtained by controlled anodic oxidation. After that an alkaline treatment with NaOH solution was used to make them more bioactive. Finally hydroxyapatite coating has been prepared on Ti–6Al–4V substrate through electrochemical deposition. Comparative electrochemical behaviour of untreated and surface modified Ti–6Al–4V alloy, in bio-simulated fluid solution was investigated by electrochemical techniques. SEM was used to observe the morphology of modified surfaces and the thicknesses of the oxide films prepared were evaluated on the cross-sections of the samples using SEM–FIB.     

Carbonation of Mg powder to enhance the corrosion resistance of Mg-rich primers

This paper is a continuation of our investigation into the characteristic dichotomy of Mg-rich primers between accelerated salt-fog testing and natural weathering. Our earlier study suggested that magnesium powder reacted with atmospheric CO₂ to form a protective carbonate layer on its surface. In this study, magnesium powder was treated with aqueous carbonic acid to accelerate magnesium carbonate development. The treated magnesium powder was formulated into a Mg-rich primer and evaluated for its corrosion resistance. The Mg-rich primer formulated with the treated Mg powder performed better in the salt-fog test than the control primer based on untreated Mg powder.     

Effects of the electric conditions of AC-type microarc oxidation and hydrothermal treatment solution on the characteristics of hydroxyapatite formed on titanium

This study examined the effects of the conditions for AC-type microarc oxidation (MAO) and the type of hydrothermal treatment solution on the characteristics of hydroxyapatite(HAp)-containing oxide films deposited on commercially pure titanium (CP-Ti). The MAO treatments were carried out in an electrolyte containing 0.2 M calcium acetate monohydrate and 0.02 M β-glycerophosphoric acid disodium salt pentahydrate (β-GP) using AC-type rectangular electric pulses at different voltages and frequencies. HAp formation on the surface of the MAO-treated group was induced by a hydrothermal treatment in either an alkaline solution to form HT-treated groups or a 0.002 M β-GP solution (pH = 11.0) to produce HTP-treated groups. A mixed crystalline structure consisting of anatase TiO₂, rutile TiO₂ and CaTiO₃ was observed on the MAO-treated groups treated with a low frequency and voltage. When the AC frequency was increased, anatase TiO₂ became the dominant crystalline structure and there was an even distribution of pores. HAp particles were formed more densely on the HTP-treated groups than on the HT-treated groups. Among the HTP groups, the groups fabricated at higher frequencies contained more evenly distributed and crystallized HAp crystallites.     

Alternative technique for hydroxyapatite coatings

Flame Assisted Chemical Vapor Deposition (FACVD), a novel technique that shows an enormous potential in porous oxides deposition, was employed for the first time aiming to obtain hydroxyapatite (HA) coatings on 316 L stainless steel metallic substrates. Calcium acetate and ammonium phosphate diluted in ethanol were employed as precursor salts. A Ca/P molar ratio of 1.66 was employed in precursor solution, which is equivalent to stoichiometric hydroxyapatite. A porous coating, formed by an open and interconnected network, was observed by scanning electronic microscopy (SEM) and associated with homogenous reactions. Thickness of hydroxyapatite coating was 412 ± 3 μm. X-ray diffraction (XRD) analysis indicated the presence of crystalline coatings, mainly constituted by hydroxyapatite phase and traces of tricalcium phosphate (β-TCP). Carbonate in the hydroxyapatite coatings was identified by Fourier transform-infrared (FTIR) spectroscopy.     

The influence of the deposition parameters on the properties of an rf-magnetron-deposited nanostructured calcium phosphate coating and a possible growth mechanism

The deposition of a biocompatible calcium phosphate coating on the surface of materials for biomedical implants by rf-magnetron sputtering is reported. The deposition parameters to prepare either stoichiometric crystalline hydroxyapatite or amorphous calcium phosphate coating with a molar Ca/P ratio from 1.53 to 3.88 were established. Crystalline hydroxyapatite coating with a Ca/P ratio of 1.60 ± 0.07 can be deposited if the rf-power density is 0.49 W cm^­2 and if the samples are arranged within the area of the target erosion zone. A thorough investigation of the influence of rf-power, DC-bias on the substrate, deposition time on the properties of the calcium phosphate coating allowed to formulate a mechanism for the film growth.     

A-site-disorder-dependent magnetocaloric properties in the mono-valent-metal doped La0.7Ca0.3MnO3 manganites

The influence of mono-valence-metal (Li, Na, and K) doping effect on the structural, resistivity, magnetic and magnetocaloric properties of La_0.7Ca_0.3MnO₃ polycrystalline samples is studied for a fixed (5% at Ca site) dopant concentration. All the samples crystallize in orthorhombic structure and the lattice parameters increase continuously as the dopant atoms changes from Li to Na and then K. Paramagnetic-ferromagnetic phase transition at T_C and insulator-metal phase transition at T_p are observed for all studied samples. The transition temperature decreases as Ca atoms is replaced by Li, while the transition temperature shifts to higher values as Ca is substituted by Na or K. In addition, the maximum magnetic entropy change of the K-doped sample is much smaller than that of the free- and Na-doped samples. The results are discussed according to the change of A-site-disorder effect caused by the systematic variations of A-site average ionic radius 〈r_A〉 and A-site-cation mismatch σ².     

Conductive poly(α,ω-bis(3-pyrrolyl)alkanes)-coated wool fabrics

Cross-linked poly(α,ω-bis(3-pyrrolyl)alkanes) were directly applied to woven wool substrates by either chemical, vapour or mist polymerization methods. Choice of dopant could greatly improve the surface resistance. The optimum coating on textiles with the lowest surface resistance, highest colour-fastness and stability was achieved using a mist polymerization method with 1,8-bis(pyrrolyl)octane, iron(III) chloride (FeCl₃) as the oxidant and p-toluene sulfonic acid sodium salt (pTSA) as the dopant.