In vivo evaluation of titanium implants coated with bioactive glass by pulsed laser deposition

During the past years, different techniques, like chemical treatment, plasma spraying, sputtering, enamelling or sol–gel; and materials, like metals, hydroxylapatite, calcium phosphates, among others, have been applied in different combinations to improve the performance of prostheses. Among the techniques, Pulsed Laser Deposition (PLD) is very promising to produce coatings of bioactive glass on any metal alloy used as implant. In this work the biocompatibility of PLD coatings deposited on titanium substrates was examined by implantation in vivo. Different coating compositions were checked to find the most bioactive that was then applied on titanium and implanted into paravertebral muscle of rabbit.     

Bioactive glass–ceramic coatings prepared by pulsed laser deposition from RKKP targets (sol–gel vs melt-processing route)

The deposition of innovative glass–ceramic composition (i.e. RKKP) coatings by Pulsed Lased Deposition (PLD) technique is reported. RKKP was synthesised following two methodologies: melt-processing and sol–gel, the latter being particularly suitable to tailor the compositional range. The PLD advantage with respect to other deposition techniques is the congruent transfer of the target composition to the coating. The physico-chemical properties of films were investigated by Scanning Electron and Atomic Force Microscopies, Fourier Transform Infrared Spectroscopy, Angular and Energy Dispersive X-ray Diffraction, and Vickers microhardness. The deposition performed at 12 J/cm² and 500 °C allows to prepare crystalline films with the composition that replicates rather well that of the initial targets. The 0.6 μm thin melt-processing RKKP films, possessing the hardness of 25 GPa, and the 4.3 μm thick sol–gel films with the hardness of 17 GPa were obtained.     

Biofunctionalization of porous titanium coatings through sol–gel impregnation with a bioactive glass–ceramic

In implant technology, open porous Ti coatings are applied as functional surface layers on prosthetic devices to improve osseointegration. Since a successful clinical performance strongly depends on the (initial) quality of bone ingrowth in the porous structure, surface functionalization of the porous Ti to incorporate an additional osteoconductive capacity is recommended. In this paper, a bioactive glass–ceramic coating is applied into the open porous network of Ti coatings with a pore throat size of 1–20 μm through a sol–gel process. Using an all-alkoxide precursor route, homogeneous amorphous powders of three- (SiO₂–CaO–P₂O₅) and four-component (SiO₂–CaO–Na₂O–P₂O₅) bioactive glass compositions are prepared. By sol impregnation followed by a heat treatment, it is possible to deposit a micrometer thin bioactive glass–ceramic layer on the walls of the internal pore surface, while the original porosity and the open pore structure of the Ti coatings are maintained. The tensile adhesion strength of the Ti/bioactive glass–ceramic composite coatings is 22 to 29 MPa, suggesting a good mechanical adhesion.     

Ceramic–metal and ceramic–polymer composites prepared by a biomimetic process

A biomimetic process was developed to prepare apatite–metal and apatite–polymer composites. A variety of metals and organic polymers incorporated surface functional groups such as Si–OH, Ti–OH or Ta–OH to induce formation of a biologically active bonelike apatite by chemical treatment or physical adsorption. Subsequent immersion in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma or 1.5 SBF led to the formation of a dense and uniform bonelike apatite layer on the surface. Apatite–metal and apatite–polymer composites prepared in this way are believed to be very useful as artificial bone substitutes.     

Nucleation and crystallization behaviors of nano-crystalline lithium–mica glass–ceramic prepared via sol–gel method

The paper investigates the effects of nucleation and crystallization treatments on nano-crystalline lithium–mica glass–ceramics, taking the composition LiMg₃AlSi_3(1+x)O_10+6xF₂ (x = 0.5) and 8 mass% MgF₂ synthesized by sol–gel technique. Here, X-ray diffraction, thermal analysis and transmission electron microscopy were used to assess the structural evolutions of as-synthesized nano-crystalline lithium–mica glass–ceramics. It was found that MgF₂ crystals perform as nuclei centers for the mica crystallization hence; a large quantity of mica crystallites obtained following the nucleation process at 400 °C for 12 h. For both the un-nucleated and nucleated samples, the crystallization activation energy was measured as 400.2 and 229.6 kJ mol^?1, respectively. Consequently, the calculated Avrami exponents demonstrated that the growth mechanism of mica crystallites, while applying appropriate nucleation treatment, changes from needle-like to three-dimensional growth.     

Nanostructured glass–ceramic coatings for orthopaedic applications

Glass–ceramics have attracted much attention in the biomedical field, as they provide great possibilities to manipulate their properties by post-treatments, including strength, degradation rate and coefficient of thermal expansion. In this work, hardystonite (HT; Ca₂ZnSi₂O₇) and sphene (SP; CaTiSiO₅) glass–ceramic coatings with nanostructures were prepared by a plasma spray technique using conventional powders. The bonding strength and Vickers hardness for HT and SP coatings are higher than the reported values for plasma-sprayed hydroxyapatite coatings. Both types of coatings release bioactive calcium (Ca) and silicon (Si) ions into the surrounding environment. Mineralization test in cell-free culture medium showed that many mushroom-like Ca and phosphorus compounds formed on the HT coatings after 5 h, suggesting its high acellular mineralization ability. Primary human osteoblasts attach, spread and proliferate well on both types of coatings. Higher proliferation rate was observed on the HT coatings compared with the SP coatings and uncoated Ti-6Al-4V alloy, probably due to the zinc ions released from the HT coatings. Higher expression levels of Runx2, osteopontin and type I collagen were observed on both types of coatings compared with Ti-6Al-4V alloy, possibly due to the Ca and Si released from the coatings. Results of this study point to the potential use of HT and SP coatings for orthopaedic applications.     

Biocompatible glass–ceramic materials for bone substitution

A new bioactive glass composition (CEL2) in the SiO₂–P₂O₅–CaO–MgO–K₂O–Na₂O system was tailored to control pH variations due to ion leaching phenomena when the glass is in contact with physiological fluids. CEL2 was prepared by a traditional melting-quenching process obtaining slices that were heat-treated to obtain a glass-ceramic material (CEL2GC) that was characterized thorough SEM analysis. Pre-treatment of CEL2GC with SBF was found to enhance its biocompatibility, as assessed by in vitro tests. CEL2 powder was then used to synthesize macroporous glass–ceramic scaffolds. To this end, CEL2 powders were mixed with polyethylene particles within the 300–600 μm size-range and then pressed to obtain crack-free compacted powders (green). This was heat-treated to remove the organic phase and to sinter the inorganic phase, leaving a porous structure. The biomaterial thus obtained was characterized by X-ray diffraction, SEM equipped with EDS, density measurement, image analysis, mechanical testing and in vitro evaluation, and found to be a glass–ceramic macroporous scaffold with uniformly distributed and highly interconnected porosity. The extent and size-range of the porosity can be tailored by varying the amount and size of the polyethylene particles.     

Highly porous 45S5 bioglass-derived glass–ceramic scaffolds by gelcasting of foams

Several types of alloplastic (artificial) grafts, known as scaffolds, have been developed for the treatment of bone defects caused by trauma and/or infection. Among the materials used to manufacture scaffolds, 45S5 Bioglass is a bioceramic that arouses significant interest due to ease preparation and excellent bioactive response. Among the various processing methods cited in the literature for the production of bioactive glass scaffolds, gelcasting is a method that produces macroporous structures, with interconnected and spherical pores and high mechanical strength. However, in the literature there are few reports about bioactive glass scaffolds produced by gelcasting method. In this work, 45S5-BG scaffolds were produced by gelcasting of foams varying the amount of foaming agent in order to optimize the desirable characteristics of the scaffold. The scaffolds show porosity between 70 and 86% and compressive strength of 1.22?±?0.7 and 0.78?±?0.4 MPa. In the biological studies, all 45S5-BG scaffolds showed cytocompatibility towards human osteoblastic cells and bioactive properties using SBF assay.     

Anion-exchange properties of nickel–aluminum layered double hydroxide prepared by liquid phase deposition

The optimum coordination structure of Ni–fluoro complexes for the preparation of Ni–Al LDH by LPD process and the diverse anion-exchange properties of as-deposited Ni–Al on α-alumina powder were quantitatively evaluated for the industrial application of new positive material for alkali secondary batteries. The [NiF_6−x−y(NH₃)_x(OH⁻)_y]ⁿ⁺ was more suitable than [NiF₆]⁴⁻ as the precursor of the deposition of Ni–Al LDH in the LPD reaction, and the improved LPD reaction achieved the synthesis of high purity and high crystallinity Ni–Al LDH. All anion-exchanged Ni–Al LDHs for OH⁻–, Cl⁻–, SO₄²⁻–, and CH₃COO⁻–forms kept the high crystallinity and showed the enlargement of interlayer distances. The tilting angle of the intercalated CH₃COO⁻ anions was about 15°. Anion-exchange capacity remained constant at a minimum of 0.8 meq g⁻¹ in pH >10, increased as pH decreased, and reached a maximum of 8 meq g⁻¹ at pH 2. Anion-exchange of OH⁻–form of Ni–Al LDH was accelerated by the neutralization of hydroxide ions in interlayers, in addition, the anion-exchange capacity and the crystallinity of Ni–Al LDH could be controlled by the amount of doped aluminum ions.     

Crystallization modifies osteoconductivity in an apatite–mullite glass–ceramic

The response to implantation of novel apatite glass–ceramics was evaluated using a weight bearing in vivo bone implant model. Five novel glasses with varying calcium to phosphate ratios were cast as short rods and heat-treated to crystallize principally apatite. One glass ceramic had an apatite stoichiometry (Ca : P=1.67); three were phosphate-rich and one calcium-rich. One of the phosphate-rich glasses was also tested in its glassy state to determine the effect of crystallization on the biological response. Rods were implanted into the midshaft of rat femurs and left for 28 days. The femurs were then harvested and processed for scanning electron microscopy, energy dispersive X-ray microanalysis and conventional histology as ground and polished sections. Four of the materials exhibited evidence of osseointegration and osteoconduction. However, there was a marked inflammatory response to one of the phosphate-rich glass–ceramics, and to the non-crystallized glass. Crystallization of the latter significantly improved the bone tissue response. The glass–ceramic with an apatite stoichiometry elicited the most favorable response and merited further study as an osteoconductive bone substitute in maxillofacial and orthopedic surgery.     

Fabrication of multi-walled carbon nanotube–carbon fiber hybrid material via electrophoretic deposition followed by pyrolysis process

An integrated multi-walled carbon nanotube (MWCNT)–carbon fiber (CF) hybrid material has been fabricated by electrophoretic deposition of acid-functionalized MWCNTs on CF surface followed by soaking in a 10% solution of petroleum pitch in toluene, followed by pyrolysis in a nitrogen atmosphere. It has been revealed that MWCNTs entirely covered the CF surface. Mechanical properties of composites reinforced by MWCNT–CF hybrids were considerably enhanced (up to 120% in tensile strength and 100% in elastic modulus) compared to composites reinforce by as-received CFs. According to fractography observations, robust interlocking occurred between epoxy matrix and MWCNT–CF hybrids.     

Dissolution behavior and bioactivity study of glass ceramic scaffolds in the system of CaO–P2O5–Na2O–ZnO prepared by sol–gel technique

Three-dimensional glass ceramic scaffolds from the system CaO–P₂O₅–Na₂O–ZnO have been prepared by coating polyurethane foams with sol–gel derived glass slurry. Main phase catena hexaphosphate (Ca₄P₆O₁₉), minor phases calcium pyrophosphate (β-Ca₂P₂O₇) and calcium metaphosphate (β-Ca(PO₃)₂) were detected in the prepared glass ceramics. In order to assess the potential use in hard tissue engineering, the dissolution and precipitation behavior of the glass ceramics was investigated in vitro after soaking in simulated body fluid (SBF) for different periods of time, and the bioactivity and biocompatibility studies were conducted using mouse MC3T3-E1. Ca₄P₆O₁₉ phase showed a good chemical durability in SBF solution over the period time of soaking. However, there were small quantities of apatite-like deposits formed on the surfaces after soaking 28 days, exhibiting a poor ability of inducing calcification in SBF. In vitro cell culture, a high degree of cell adhesion and spreading was achieved and large number of mineralized deposits composed of Ca, P and Zn were detected in these porous scaffolds. These results confirmed the biocompatibility and bioactivity of the glass ceramics and the positive effects on mouse MC3T3-E1 cell behavior although no continuous apatite layer was formed on scaffold surfaces after soaking in SBF, and also demonstrated that Zn doped this glass ceramics could strongly stimulate the formation of mineralized deposits in vitro culture of MC3T3-E1 cells.     

Study of glass-nanocomposite and glass–ceramic containing ferroelectric phase

Transparent glass nanocomposite in the pseudo binary system (100 − x) Li₂B₄O₇–xBaTiO₃ with x = 0 and 60 (in mol%) were prepared. Amorphous and glassy characteristics of the as-prepared samples were established via X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC) respectively. The precipitated BaTiO₃ nanocrystal phase embedded in the glass sample at x = 60 mol% was identified by transmission electron microscopic (TEM). The optical transmission bands at 598 and 660 nm were assigned to Ti³⁺ ions in tetragonal distorted octahedral sites. The precipitated Li₂B₄O₇, BaTi(BO₃)₂ and BaTiO₃ nanocrystallites phases with heat-treatment at 923 K for 6 h (HT923) in glass–ceramic were identified by XRD, TEM and infrared absorption spectroscopy. The as-prepared at x = 60 mol% and the HT923 samples exhibit broad dielectric anomalies in the vicinity of the ferroelectric-to-paraelectric transition temperature. The results demonstrate that the method presented may be an effective way to fabricate ferroelectric host and development of multifunctional ferroelectrics.     

Preparation of YAG gel coated ZrB2–SiC composite prepared by gelcasting and pressureless sintering

In this paper, gelcasting and pressureless sintering of YAG gel coated ZrB₂–SiC (YZS) composite were conducted. YAG gel coated ZrB₂–SiC (YZS) suspension was firstly prepared through sol–gel route. Poly (acrylic acid) was used as dispersant. YZS suspension had the lowest viscosity when using 0.6 wt.% PAA as dispersant. Gelcasting was conducted based on AM–MBAM system. The gelcast YZS sample was then pressureless sintered to about 97% density. During sintering, YAG promoted the densification process from solid state sintering to liquid phase sintering. The average grain sizes of ZrB₂ and SiC in the YZS composite were 3.8 and 1.3 μm, respectively. The flexural strength, fracture toughness and microhardness were 375 ± 37 MPa, 4.13 ± 0.45 MPa m^1/2 and 14.1 ± 0.5 GPa, respectively.     

Soft tissue attachment on sol–gel-treated titanium implants in vivo

This study was designed to examine the attachment and reactions of soft tissues to sol–gel-derived TiO₂ coatings. In the first experiment, TiO₂ coated and uncoated titanium cylinders were placed subcutaneously into the backs of rats for 3, 11 and 90 days. Tissue response and implant surfaces were characterized with routine light microscopy and scanning electron microscopic (SEM) analysis. In the second experiment, TiO₂-coated and uncoated discs were implanted subcutaneously into the backs of rats for 14 and 21 days. The discs were pulled out from the implantation sites with a mechanical testing device using a constant speed of 5 mm/min. Rupture force was registered, after which the discs were assigned for SEM and transmission electron microscopic (TEM) analysis. All the coated implants showed immediate contact with the surrounding soft tissues without a clear connective tissue capsule. Significantly better soft tissue response was measured for all the coated compared to the uncoated cylinders (p < 0.01). Higher rupture forces were measured for all coated discs, although the differences were not statistically significant. An immediate and tight connection between connective tissue fibroblasts and coatings was noticed in TEM analysis. Our study indicates that TiO₂ coatings improve soft tissue attachment on a titanium surface.     

Microstructure and stresses in a keatite solid–solution glass–ceramic

The microstructure of a translucent keatite solid–solution glass–ceramic (keatite s.s.) of the LAS-system (Li₂O–Al₂O₃–SiO₂) has been analyzed with SEM, AFM, XRF, XRD, and TEM. The glass–ceramic consists mainly of keatite s.s. with minor secondary phases such as zirconium titanate, gahnite and probably rutile. Furthermore the resistance to temperature differences (RTD) of this glass–ceramic was investigated. It is shown that, in spite of the relatively high coefficient of thermal expansion (CTE) of about 1 × 10⁻⁶ K⁻¹, an improved RTD can be achieved by special ceramization treatment. With this, compressive stresses in the first 100 μm to 150 μm are induced. These stresses can presumably be contributed to a difference in CTE between the surface-near zone and the bulk. Said CTE difference is caused by chemical gradients of CTE-relevant elements, such as Zn, K, and supposedly additional alkali elements such as Li. These stresses are useful to increase the strength and application range of glass–ceramics based on keatite s.s.

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Characteristics of glass ionomer cements composed of glass powders in CaO–SrO–ZnO–SiO2 system prepared by two different synthetic routes

Glass ionomer cements (GICs) are composed of an acid degradable glass, polyacrylic acid and water. Sol–gel processing to prepare the glass phase has certain advantages, such as the ability to employ lower synthesis temperatures than melt quenching and glasses that are reported to have higher purity. A previous study reported the effects of glass synthesis route on GIC fabrication. However, in that study, the sol–gel derived glass exhibited a reduced concentration of cations. This study investigates increasing the cation content of a sol–gel derived glass, 12CaO·4SrO·36ZnO·48SiO₂ (molar ratio) by heating before aging to reduce dissolution of cations. This glass was prepared by both sol–gel and melt-quenched routes. GICs were subsequently prepared using both glasses. The resultant cement based on the sol–gel derived glass had a shorter working time than the cement based on the melt-quenched one. Contrary to this, setting time was considerably longer for the cement based on the sol–gel derived glass than for the cement based on the melt-quenched one. The cements based on the sol–gel derived glass were stronger in both compression and biaxial flexure than the cements prepared from the melt-quenched glass. The differences in setting and mechanical properties were associated with both cation content in the glass phase and the different surface area of the resultant cements.     

Amorphous Ni–B alloy/ceramic composite membrane prepared by an improved electroless plating technique

A new amorphous Ni–B alloy/ceramic composite membrane was prepared by an improved electroless plating technique. The composite membrane exhibited not only high permeability, but also high permselectivity for hydrogen separation.