Calcium-binding phospholipids as a coating material for implant osteointegration.

Among the many biomolecules involved in the bone mineralization processes, anionic phospholipids play an important role because of their ability to bind calcium. In particular, phosphatidylserine is a natural component of the plasmalemma and of the matrix vesicles generated from the osteoblast membrane to create nucleation centres for calcium phosphate crystal precipitation. In the present work, we demonstrate that calcium-binding phospholipids can be used as biomimetic coating materials for improving the osteointegration of metal implants. Relatively thick phosphatidylserine-based coatings were deposited on titanium coupons by dip-coating. Upon dehydration in a simulated body fluid phospholipids were quickly crosslinked by calcium and re-arranged into a three-dimensional matrix able to induce rapid formation of a calcium phosphate mineral phase. The rate of mineralization was shown to be dependent on the adopted coating formulation. In the attempt to closely mimic the cell membrane composition, heterogeneous formulations based on the mixing of anionic phospholipids (either phosphatidylserine or phosphatidylinositol) with phosphatidylcholine and cholesterol were synthesized. However, surface plasmon resonance studies as well as scanning electron microscopy and elemental analysis demonstrated that the homogeneous phosphatidylserine coating was a more effective calcification environment than the heterogeneous formulations.     

Preparation of a fast photochromic ormosil matrix coating for smart windows

A novel photochromic dye (NPB)-doped ormosil matrix coating with fast spectrokinetics was studied as functional materials for smart windows. First, the NPB was modified into a reactive silylated dye (NPB-Si) by a silane coupling agent. Then, the NPB-Si was hydrolyzed and copolycondensed with methyl triethoxysilane to form the ormosil (NPB-PMS) via the sol–gel method. Finally, the photochromic ormosil matrix coating on the substrate was obtained by the following spin-coating process. Upon the activation by the UV irradiation, the ormosil coating displayed the characteristic dual absorption peaks at 504 and 628 nm, which indicated as a valuable neutral tone. The dual absorption is due to the existence of photoisomers. On the basis of the theoretical calculation, the trans–cis photoisomers displayed the longer wavelengths in visible region than those of trans–trans ones, which was due to the less coplanarity. The kinetics studies of coloration and decoloration of NPB-PMS indicated an accelerated conversion process than that of NPB-doped polystyrene coating. The improved spectrokinetics of NPB-PMS coating is ascribed to the nanoscaled cavities observed in their surfaces, which offered enough space for molecular rotation during the photochromism. Our results also demonstrated that the NPB-PMS coating had much better solvent wash-off resistance than the physically doped coating.     

Unified formulation for a family of advanced finite elements for smart multilayered plates

Abstract

Families of layer-wise and equivalent single-layer advanced finite elements for the analysis of smart multilayered plates are formulated in a unified framework. The proposed modeling strategy reduces the multifield problem to an effective mechanical plate by the condensation of the electromechanical state into the plate kinematics, which is assumed as a variable order expansion along the plate thickness. Carrera Unified Formulation is invoked to derive the elemental stiffness and mass matrices and the mechanical and magneto-electric equivalent forces. The obtained smart plate finite element equations involves kinematical variables only and this extends the tools developed for multilayered composite plates to smart laminates. Results for simply-supported magneto-electro-elastic multilayered square plates are presented to validate the proposed modeling approach and finite elements and to investigate their features.     

Fabrication of biomimetic apatite coating on porous titanium and their osteointegration in femurs of dogs

In the present study, porous titanium with three-dimensionally interconnected pores and a porosity of 74.3 ± 3.8% was made by a slurry foaming method. After being pretreated with acid–alkali or alkali–heat method and then immersed into a supersaturated calcium phosphate solution to form a biomimetic apatite coating on the surface, the porous titanium samples were hemi-transcortically implanted into the femurs of dogs for two months. The experimental results showed that the surface apatite coatings deposited on acid–alkali and alkali–heat treated porous titanium had different morphology and thickness. However, histological and histomorphometric analysis confirmed that both types of apatite-coated implants had excellent osteointegration with host bone, and their osteoconduction had also no significant difference. This study proved that both acid–alkali and alkali–heat treatments might have the same efficiency in activating porous titanium, and the apatite-coated porous titanium could be potential to be used in clinic.     

Cerium-based coating for enhancing the corrosion resistance of bio-degradable Mg implants

Recently there has been interest in employing degradable metallic implants for internal fixation in bone fracture healing. The major purpose of using degradable implants is to avoid a second surgery for implant removal when bone healing has completed. However, the corrosion rate of Mg in vivo is too high. Thus increasing the corrosion resistance of Mg is the key problem to address in the development of degradable Mg implants. One possible route is by way of surface treatment, which would lower the corrosion rate at the initial phase of bone healing, the period during which the implant provides mechanical support for the broken bone. In the present study cerium oxide coating was prepared on pure Mg by cathodic deposition in cerium nitrate solution followed by hydrothermal treatment. The coated samples were characterized by SEM, EDS and XRD. The corrosion resistance in Hanks’ solution (a simulated body fluid) was studied using polarization method and electrochemical impedance spectroscopy (EIS). The corrosion resistance of cerium oxide coated Mg in Hanks’ solution at 37 °C and pH 7.4 was higher than that of bare Mg by about two orders of magnitude.     

Nanoscale surface modification of a prosthetic material: case of Ti6Al4V into Ringer's solution

Nanoscale surface modification of Ti6Al4V prosthetic material was investigated at 37 degrees C into a physiological liquid named Ringer's solution. The root-mean-square surface roughness evolution of the material as a function of immersion time was evaluated by atomic force microscopy (AFM) and 3D reconstruction of scanning electron microscope images (SEM). The results obtained from both techniques clearly showed a decrease of the root-mean-square surface roughness during the first 6 hours of immersion in the physiological liquid that is followed by a stability of the roughness value at longer durations. Moreover, the study of the roughness parameters extracted from AFM measurements is used to explain the smoothing process occurring at the interface between the prosthetic material and the physiological liquid.     

A solution technique for indefinite systems of mixed finite elements

A solution technique for indefinite systems of symmetric linear, simultaneous equations, via the Hellinger–Reissner variational principle, is presented. The method utilizes symmetry of the global matrix and its expected real eigenvalues. Premultiplication of the global matrix with itself renders a positive definite matrix, hence enabling the use of any standard equation solver for a positive definite system and requiring only about twice the memory requirement for the original set of equations. Two subroutines, MULT and MULTIP, which are compatible with the sky-line technique, are also listed.     

Active anticorrosion and self-healing coatings: A review with focus on multi-action smart coating strategies

The development of smart coatings with potential for active anticorrosion and self-healing protection of metals is essential for long-term performance of metallic structures in aggressive chemical environments. Presently, emphasis has been placed on the development of advanced smart coatings for corrosion protection in different applications. Innovative multifunctional coatings with fascinating stimuliresponsive functionalities are considered “smart”. The stimuli-responsive functionalities of th...     

Influence of alloying elements on hot corrosion of superalloys and coatings: necessity of smart coatings for gas turbine engines

Abstract

Modern gas turbine engines require high performance materials and coatings to ensure high efficiency. The selection of high performance materials and coatings depends on the nature and concentration of alloying elements. The composition of materials and coatings, in particular, plays a major role in enhancing the life of gas turbine engines by exhibiting good resistance to oxidation and hot corrosion, which are major problems in gas turbine engines. The performances of several superalloys containing different alloying elements and MCrAlY type coatings containing a variety of major and minor alloying elements are described in detail. The effect of major and trace elements on the life of superalloys and coatings in the presence of pure Na₂SO₄, NaCl and vanadium containing environments is detailed. The relevant reaction mechanisms leading to the failure of superalloys and coatings are discussed. The major factors involved when selecting alloying elements for the preparation of superalloys to manufacture components intended for use under hot corrosion conditions and the selection of appropriate coatings are suggested. Finally, the necessity of innovation of 'smart coatings' to combat both oxidation and hot corrosion is discussed.     

Impedance spectroscopy monitoring of a polyurethane coating on mortar exposed to NaCl solution

Polyurethane coated OPC mortar specimens exposed to 1M NaCl solution were studied by impedance spectroscopy and SEM over a period of 4 years. Results showed a rapid reduction of the coating resistance over the first half year, followed by a slow decrease thereafter. The coating deteriorated starting from the surface in contact with the NaCl solution and the deterioration front reached the coating/substrate interface after around three years. Different stages of deterioration were clearly identified by impedance spectroscopy. The study demonstrates that impedance spectroscopy is a versatile and informative non-destructive method to assess and monitor the performance of surface treatments on concrete.     

Exact solution of shear problem for inclined cracked bending reinforced concrete elements

In spite of a wide experimental and theoretical data on shear that forms a basis for modern design approaches, exact solution of shear problem for inclined cracked bending reinforced concrete elements is still not found. It yields high dispersion in the bearing capacity of concrete according to the main compression stresses. A similar problem appears with the internal forces carried by shear reinforcement. The above mentioned problem is related to two parameters: the angle of the main compression stresses and that of the inclined links. Corresponding internal forces together with the force in the tensile reinforcement form a commonly used design model (truss model), therefore each force depends on the other. This fact is practically not considered in modern design provisions hence there are no tools to express the shear capacity accurately. The two angles should be considered simultaneously in every case, when the links section is taken according to the calculated value (but not to the minimum one). The present study is one of the first attempts, focused on considering the interaction between the internal forces in concrete and inks according to the design model. It allows calculation of an exact angle, defining the inclined cracks and forces in links within the known experimentally investigated limits of this angle.     

Bioactive glasses as carriers for bioactive molecules and therapeutic drugs: a review

Bioactive glasses (BG) show great promise for bone tissue engineering based on their key properties, e.g., biocompatibility, biodegradability, osteoconductivity as well as osteogenic and angiogenic potential, which make them excellent candidates for bone tissue scaffolds and bone substitute materials. Recent work has shown that dissolution products of bioactive glasses have the potential to induce angiogenesis in addition to their known effect of influencing gene expression and promoting osteoblastic differentiation. One of the most interesting features of BG is their ability to bond both to soft and hard tissues, depending on their composition. To intensify the positive impact of BG for medical applications, there are considerable research efforts on using bioactive glass based platforms as carriers for the encapsulation, delivery and controlled release of bioactive molecules and therapeutic drugs. Different types of bioactive glasses have been considered in combination with different therapeutic drugs, hormones, growth factors and peptides. Using bioactive glasses as drug delivery system combines thus the effectiveness of therapeutic drugs (or bioactive/signaling molecules) with the intrinsic advantages of this inorganic biomaterial. Considering research carried out in the last 15?years, this review presents the different chemical compositions and morphologies of bioactive glasses used as carrier for bioactive molecules and therapeutic drugs and discusses the expanding potential of BG with drug delivery capability focusing in the field of bone tissue engineering.     

Extraction of alkaline-earth elements from nitric acid with a solution of HDBP zirconium salt

Extraction of alkaline-earth metals with acidic zirconium salt of dibutyl hydrogen phosphate (HDBP AZS) increases in the order Ba < Sr < Ca. Magnesium is extracted substantially better than Ba, but by an order of magnitude worse than Ca. The maximal recovery of Sr is observed at Zr: HDBP ratio of 1: 9, similarly to extraction of TPE and REE. The recovery of Sr is possible from weakly acidic solutions (<0.5 M HNO₃); as the acidity increases, the Sr distribution coefficient decreases in proportion to [H⁺]^?3. The presence of TBP in the extractant slightly decreases the Sr extraction but simultaneously increases the extractant capacity. The latter effect is substantially less pronounced than for TPE and REE. In the experiment with model solutions on a bench of centrifugal extractors, the Sr decontamination factor from REE and TPE as high as 50–100 was attained.     

The role of nanocrystalline titania coating on nanostructured austenitic stainless steel in enhancing osteoblasts functions for regeneration of tissue

In the context of osseointegration of metallic implants, while nanostructuring the surface favorably modulates cellular response, the disinfective attributes required during the healing process are not available. Thus, in the present study, we demonstrate that nanocrystalline titania provides cumulative benefit of enhancing osteoblasts functions to promote the efficacy of metal implants together with the disinfective attributes. To this end, the primary objective here is to examine the select functions of bone forming cells (osteoblasts) on electrocrystallized nanonodular titania-coated nanograined/ultrafine grained (NG/UFG) austenitic stainless steel. The accompanying objective is to study the disinfective/antimicrobial activity. To the best of our understanding this is the first study of nanophase titania on a non-titanium substrate. The osteoblasts functions were investigated in terms of cell attachment, proliferation, and quantitative analysis of proteins, actin and vinculin. In comparison to the bare NG/UFG substrate, the nanophase titania-coated substrate exhibited higher degree of cell attachment and proliferation which are regulated via cellular and molecular interactions with proteins, actin and vinculin. The enhanced functions of osteoblasts suggest that nanophase titania adsorbs extracellular matrix proteins, fibronectin and vitronectin from serum enhancing protein, with subsequent binding of integrins and osteoblasts precursor to titania. The antimicrobial attributes assessed in terms of degradation of methyl orange and effectiveness in killing E. coli supports the viewpoint that large surface area of titania would be instrumental in reducing the detrimental effect of biologically reactive oxygen species produced by macrophages in the vicinity of the metal bone/implant interface. In summary, the study provides some new insights concerning nanostructuring of metallic substrates with specific physical and surface properties for medical devices with significantly improved cellular response.     

Quadrilateral elements for the solution of elasto‐plastic finite strain problems

In this paper two plane strain quadrilateral elements with two and four variables, are proposed. These elements are applied to the analysis of finite strain elasto‐plastic problems. The elements are based on the enhanced strain and B‐bar methodologies and possess a stabilizing term. The pressure and dilatation fields are assumed to be constant in each element's domain and the deformation gradient is enriched with additional variables, as in the enhanced strain methodology. The formulation is deduced from a four‐field functional, based on the imposition of two constraints: annulment of the enhanced part of the deformation gradient and the relation between the assumed dilatation and the deformation gradient determinant. The discretized form of equilibrium is presented, and the analytical linearization is deduced, to ensure the asymptotically quadratic rate of convergence in the Newton–Raphson method. The proposed formulation for the enhanced terms is carried out in the isoparametric domain and does not need the usually adopted procedure of evaluating the Jacobian matrix in the centre of the element. The elements are very effective for the particular class of problems analysed and do not present any locking or instability tendencies, as illustrated by various representative examples. Copyright © 2001 John Wiley & Sons, Ltd.     

Pore exclusion chromatography-inductively coupled plasma-mass spectrometry for monitoring elements in bacteria: a study on microbial removal of uranium from aqueous solution

The interstitial spaces between spherical particles in a packed column can act as a sieve that passes microorganisms below a certain size. If the bed is a perfusion-type material (containing a binary distribution of large and small pores), colloidal-size microorganisms are subject only to pore exclusion, while all molecules are subject to size exclusion among the various pores. Thus, microorganisms elute first, followed by macromolecules, and then small molecules. Coupling this separation method to an ICP magnetic sector mass spectrometer provides a sensitive, direct means to study the microbial uptake of heavy metals (i.e., uranium) from their surrounding environments. Multiple metal ions can be monitored in the microorganism and in the surrounding solution. In this way, definitive information can be provided for the remediation of radioactive waste sites. The effect of uranium on microbial growth is also discussed.     

Minimization of blast-induced dust emission using gene-expression programming and grasshopper optimization algorithm: a smart mining solution based on blasting plan optimization

In surface mining, blast-induced dust can be discharged to the atmosphere and impact the surrounding environment and nearby residential areas, especially if a large volume of rock is blasted under inappropriate meteorological conditions such as high wind speed. Many attempts have been done to predict the blast-induced dust emission distance but the literature of the dust reduction is limited to change stemming materials based on water capsules. This study develops a methodology using gene expression programming and grasshopper optimization algorithm to find an optimal blasting plan with minimum blast-induced dust in a mine close to sensitive ecosystem and residential areas. The best gene expression programming model, which indicates relationship between dependent and independent variables, was first determined based on 100 blasting data collected from the mine. The model with the R² of 0.9559 and 0.9145, respectively, for training and validating parts was chosen as the best model. The model, as an objective function, was considered in grasshopper optimization algorithm to find the optimal blasting plan with minimum dust emission level. Compared to the old blasting plans of the mine, the optimal plan resulted in a reduction of 76.82% in the emission distance of the blast-induced under constant meteorological conditions. Sensitivity analysis on the system parameters revealed the high sensitivity of the output to wind speed, air temperature, air humidity, powder factor, and stemming.

Graphical abstract